WFO RAH Text Data |
FXUS62 KRAH 311039 CCA AFDRAH AREA FORECAST DISCUSSION...CORRECTED TYPO NATIONAL WEATHER SERVICE RALEIGH NC 300 AM EST WED JAN 31 2007 SPECIAL RELEASES...GSO UA 06Z THURSDAY. MORE THAN LIKELY WILL HAVE A 18Z THURSDAY ALSO. .SHORT TERM /TODAY THROUGH THURSDAY NIGHT/... TODAY AND TONIGHT... COLD FRONT HAS PUSHED EAST OF CWA EARLY THIS MORNING. ON ITS HEEL IS A COLD AND VERY AIR MASS. THIS COLD AND VERY DRY AIR WILL FILTER INTO CWA AS HIGH PRESSURE BUILDS IN FROM THE WEST TODAY AND SETTLES OVER THE AREA TONIGHT. PLENTY OF SUNSHINE EXPECTED TODAY BUT CAA WILL RESULT IN TEMPERATURES ACROSS MUCH OF THE CWA STRUGGLING TO GET OUT OF THE 30S. EXPECT A RANGE OF UPPER 30S TO LOWER 40S. ADDITIONALLY AIR MASS QUITE DRY WITH DEWPOINTS IN THE SINGLE DIGITS WITH SOME SUB-ZERO DEWPOINTS BY AFTERNOON. WILL SEE MID AND HIGH LEVEL CLOUDS OVERSPREAD THE AREA TONIGHT. LOWS IN THE MID 20S. HOWEVER THE EXTENT AND ARRIVAL OF CLOUDS TONIGHT COULD AFFECT OVERNIGHT MINS. THIS COLD DRY AIR MASS IN PLACE OVER CENTRAL NORTH CAROLINA WILL BE SETTING THE STAGE FOR A ROUND OF WINTRY WEATHER ON THURSDAY. THURSDAY AND THURSDAY NIGHT... CLASSIC IN SITU COLD AIR DAMMING EVENT WILL UNFOLD DURING THIS TIME... WHERE DIABATIC COOLING VIA EVAPORATION WILL BE THE IMPETUS FOR THE DEVELOPMENT OF THE DAMMING WEDGE. TYPICALLY IN SITU DAMMING CASES CANNOT SUSTAIN THEMSELVES FOR LONG DURATIONS... SINCE THEY LACK A CONTINUAL SUPPLY OF COLD DRY AIR ADVECTION IN THE LOW LEVELS... COURTESY OF A PARENT SURFACE HIGH TO OUR NORTH. THE LATENT HEAT OF FUSION AND RESULTING WARMING DURING FREEZING RAIN ULTIMATELY MAKES IT SELF LIMITING. AS HAS BEEN ADVERTISED BY PREVIOUS SHIFTS... THE SURFACE HIGH WILL BE WEAK... TRANSIENT... AND LOCATED TOO FAR SOUTH TO SUPPORT A *CLASSIC* WINTER WEATHER EVENT ACROSS CENTRAL NORTH CAROLINA. HOWEVER... VERY COLD... DRY AIR WILL BE IN PLACE ACROSS THE REGION FROM THE ARCTIC AIRMASS CURRENTLY SETTLING OVERHEAD. THIS AIRMASS... AT 06Z 31 JANUARY... WAS CHARACTERIZED BY SURFACE DEWPOINTS IN THE SINGLE DIGITS UPSTREAM OVER THE TENNESSEE VALLEY AND BELOW ZERO WESTWARD INTO THE UPPER MIDWEST. THIS EVENT MAY BE ONE OF THOSE RARE CASES THAT BECAUSE THE AIR IS SO COLD AND DRY TO START THE EVENT... POTENTIALLY SIGNIFICANT ICING COULD RESULT BEFORE A GRADUAL WARMING AND CHANGEOVER TO LIQUID. FRICTIONAL CONVERGENCE ALONG THE SOUTHEAST US COAST AS A RESULT OF THE RETURN FLOW AROUND THE DEPARTING SURFACE HIGH... WILL AID IN THE DEVELOPMENT OF A COASTAL FRONT BY THURSDAY MORNING. MEANWHILE A DEVELOPING WARM FRONT ALONG THE NORTHERN GULF OF MEXICO WILL LIFT NORTH AND MERGE WITH THE COASTAL FRONT DURING THE DAY THURSDAY. THE COMBINATION OF THESE FEATURES WILL PROVIDE THE BAROCLINIC ZONE THAT SEVERAL WAVES OF SURFACE LOW PRESSURE WILL ULTIMATELY TRACK NORTHEAST ALONG. THE IN SITU WEDGE SHOULD HOLD THIS BAROCLINIC ZONE AND EXPECTED LOW TRACK SOUTHEAST OF OUR CWA... THEREBY MINIMIZING SIGNIFICANT SURFACE WARMING THROUGHOUT THE EVENT. THE EXIT REGION OF A STRONG SOUTHWESTERLY 170 KNOT UPPER JET NOSING ACROSS THE LOWER MISSISSIPPI AND TENNESSEE VALLEYS LATE WEDNESDAY NIGHT/EARLY THURSDAY WILL PROMOTE THE DEVELOPMENT OF DEEP ISENTROPIC LIFT/WARM AIR ADVECTION IN THE THERMALLY INDIRECT LOW LEVEL RETURN BRANCH OF THE UPPER JET. THIS WILL RESULT IN RAPID MOISTENING OF THE ATMOSPHERE JUST AFTER DAYBREAK THURSDAY. PRECIPITATION SHOULD BEGIN REACHING THE GROUND FROM SOUTH TO NORTH SHORTLY THEREAFTER. THE TRENDS NOMOGRAM AND MODEL FORECAST SOUNDINGS BOTH INDICATE THAT PRECIPITATION AT THE ONSET WOULD LIKELY FALL IN THE FORM OF SNOW... WITH SLEET MIXED IN AS THE DAY WEARS ON. THIS PERIOD OF FROZEN PRECIPITATION WOULD BE VERY SHORT LIVED... AN HOUR OR SO AT MOST... ACROSS THE SANDHILLS AND COASTAL PLAIN... BEFORE RAPIDLY TRANSITIONING TO A COLD RAIN BY MIDDAY. THE PIEDMONT... ESPECIALLY THE WESTERN HALF... COULD SEE A PERIOD OF SEVERAL HOURS OF SNOW/SLEET BEFORE TRANSITIONING TO FREEZING RAIN DURING THE AFTERNOON... AS THE STRONG LOW LEVEL JET CREATES A PRONOUNCED WARM NOSE ALOFT. ONCE THE SNOW/SLEET TRANSITIONS TO FREEZING RAIN... THE FREEZING RAIN COULD CONTINUE THROUGH SUNSET ON EITHER SIDE OF A LINE FROM ALBEMARLE TO SANFORD TO RALEIGH TO HENDERSON... INCLUDING THE TRIANGLE. THE TEMPERATURE STRUCTURE IN THE LOWER TROPE WOULD BE SUPPORTIVE OF FREEZING RAIN AFTER SUNSET AND THROUGHOUT THE EVENING HOURS ACROSS THE CLIMATOLOGICALLY FAVORED AREAS APPROXIMATELY ALONG AND WEST OF A LINE FROM ASHEBORO TO HILLSBOROUGH TO ROXBORO... INCLUDING THE TRIAD. ITS INTERESTING THAT THE MODELS ARE KEYING ON TWO BOUTS OF DEEP LIFT AND PRECIPITATION DURING THE EVENT... ONE DURING THE MIDDAY TO EARLY AFTERNOON HOURS THURSDAY... THEN ANOTHER DURING THE EVENING HOURS. THE FIRST WOULD BE ASSOCIATED WITH THE INITIAL SURGE OF WARM ADVECTION AND CONVERGENCE ON THE NOSE OF THE LOW LEVEL JET... AND THE SECOND ASSOCIATED WITH THE DIFFERENTIAL CYCLONIC VORTICITY ADVECTION AHEAD OF THE UPPER LOW CURRENTLY SPINNING OFF THE BAJA OF CALIFORNIA. THE SECOND OF THE TWO AREAS OF MAXIMUM LIFT APPEARS AT THIS TIME THAT IT WOULD BE FOCUSED FROM SOUTHERN GEORGIA TO SOUTHEASTERN NORTH CAROLINA... AFFECTING PRIMARILY THE SOUTHEAST HALF OF OUR CWA. IF THAT WERE THE CASE... THE SECOND ROUND WOULD BE PREDOMINATELY LIQUID... SINCE THE BULK OF IT WOULD LIKELY NOT EXTEND FAR ENOUGH NORTHWEST INTO THE SUBFREEZING SURFACE AIR. THE ORIENTATION AND MAGNITUDE OF THE MODEL QPF FOR THE SECOND ROUND OF PRECIPITATION... FROM BOTH THE NAM AND GFS FOR THE PAST SEVERAL RUNS... SUGGEST THAT THE MODELS ARE GENERATING DEEP MOIST CONVECTION IN THE AFOREMENTIONED AREAS FROM SOUTHERN GA TO SOUTHEASTERN NC. ACCORDINGLY... INSTABILITY PARAMETERS FROM THE MODELS REVEAL THAT LIKELIHOOD.. AND SPC HAS THOSE AREA HIGHLIGHTED IN THE SWODY2. THUS... LATER SHIFTS WILL NEED TO MONITOR THE POTENTIAL FOR THIS UPSTREAM CONVECTION TO ALTER THE CURRENT THINKING REGARDING ROUND TWO BEING A BIT TOO FAR EAST TO CAUSE ADDITIONAL SIGNIFICANT ICING CONCERNS. WITH ALL OF THIS IN MIND... A WINTER STORM WATCH WILL BE ISSUED FOR LOCATIONS ALONG AND WEST OF A LINE FROM APPROXIMATELY ROCKINGHAM TO CARTHAGE TO RALEIGH TO LOUISBURG TO WARRENTON. IT IS STILL TOO EARLY TO GET SPECIFIC WITH PRECIPITATION AMOUNTS... BUT IT APPEARS THAT AROUND AN INCH OF SNOW/SLEET WOULD BE POSSIBLE IN THE WATCH AREA THROUGH MIDDAY THURSDAY... WITH ICE ACCRUAL OF ONE QUARTER INCH OR MORE THURSDAY AFTERNOON/EVENING... ESPECIALLY ACROSS THE WESTERN PIEDMONT. -MWS && .LONG TERM /FRIDAY THROUGH TUESDAY/... FRIDAY... SOME LIGHT RAIN AND/OR DRIZZLE WILL LINGER DURING THE MORNING HOURS AS STORM SYSTEM LIFTS OFF TO THE NORTHEAST. MODEL TRENDS ARE INDICATING CLEARING FAIRLY QUICKLY BUT THINK CLOUDS WILL BE SLOW TO CLEAR. WILL TWEAK CURRENT FORECAST MAXES TO ACCOUNT FOR SLOWER CLEARING. FRIDAY NIGHT THROUGH TUESDAY... NO CHANGES TO CURRENT FORECAST TRENDS. LATEST OPS GFS KEEPS PRECIP IN SOUTHERN STREAM SUPPRESSED SOUTH OF AREA FOR LATE IN THE WEEKEND. BUT TRENDS ARE SHOWING PRECIP SHIELD NUDGING A BIT FURTHER NORTH EACH RUN. LOOKS LIKE ANOTHER ROUND OF BITTER COLD EARLY NEXT WEEK. && .AVIATION /07Z-06Z/... VFR CONDS EXPECTED THROUGHOUT THE TAF PERIOD. CAA ASSOC/W FROPA WILL BRING NW WINDS AT 10-15 KTS THROUGH 10Z... THEN DECREASE TO LESS THAN 10 KT AROUND SUNRISE. THE WINDS PICK UP AGAIN TO 8-12 KT FROM THE NW AROUND 14Z AND CONTINUE THROUGH THE DAY. NW WINDS DIMINISH TO LIGHT WIND BY MID TO LATE AFTERNOON. EXPECT AN INCREASE IN HIGH CLOUDINESS IN THE AFTERNOON. & && .RAH WATCHES/WARNINGS/ADVISORIES... WINTER STORM WATCH FROM 6AM THURSDAY MORNING THROUGH MIDNIGHT THURSDAY NIGHT FOR NCZ007>010-021>026-038>041-073>076-083-084. && $$ SHORT TERM...RA/MWS LONG TERM...RA AVIATION...VINCENT FXUS62 KRAH 311503 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 1000 AM EST WED JAN 31 2007 .UPDATE... && .SHORT TERM /REST OF TODAY/... WV IMAGERY SHOWS IMPRESSIVE VORT MAX CURRENTLY MOVING OFFSHORE...THE BRUNT OF CAA OCCURRED IMMEDIATELY WITH AND BEHIND THE SHARP SHORT WAVE TROUGH WITH H5 HEIGHT FALLS OF 120 METERS OFFSHORE AND HEIGHT RISES OF 120 METERS UPSTREAM OVER THE OHIO VALLEY. EMPIRICAL PROOF OF THE WELL ADVERTISED ARCTIC AIRMASS THAT HAS SETTLED OVER CENTRAL NC OVER THE PAST 6 HOURS IS THE -14C 850 TEMPERATURE AND 30C DEWPOINT DEPRESSION ANALYZED AT KGSO IN THE 850 AND 700MB UPPER AIR CHARTS. TEMPERATURES ARE STRUGGLING TO WARM INTO THE MID TO UPPER 20S ACROSS THE WESTERN AND CENTRAL PIEDMONT UNDER FULL SUN WITH LOWER 30S IN THE SOUTHERN COASTAL PLAIN. CURRENTLY...DEWPOINTS ARE SOLIDLY IN THE SINGLE DIGITS...WITH THE FORECAST FOR DEWPOINTS TO DROP TO NEAR OR BELOW ZERO THIS AFTERNOON STILL ON TRACK AS SHORT-TERM MODEL SOUNDINGS INDICATE A DRY ADIABTIC PROFILE TO 900MB WITH DRIER AIR THROUGH THE MIXING LAYER JUST ABOVE THE SURFACE. THE DRY ADIABATIC IN-HOUSE THICKNESS SCHEME...SUPPORTS HIGHS IN THE MID 30S WEST...UPPER 30S CENTRAL...TO AROUND 40 EAST AND SOUTH. THIS WILL REQUIRE ONLY MINOR MODIFICATIONS TO FORECAST HIGHS. OTHERWISE NO OTHER CHANGES FOR THE CENTRAL NC FORECAST IN THE QUIET BEFORE THE STORM PHASE. WINTER STORM WATCH CONTINUES FOR THURSDAY MORNING THROUGH THURS EVENING FOR AREAS SURROUNDING AND WEST AND NORTH OF THE US 1 CORRIDOR. && .PREV DISCUSSION... /ISSUED 300 AM EST WED JAN 31 2007/ SHORT TERM /TODAY THROUGH THURSDAY NIGHT/... TODAY AND TONIGHT... COLD FRONT HAS PUSHED EAST OF CWA EARLY THIS MORNING. ON ITS HEEL IS A COLD AND VERY AIR MASS. THIS COLD AND VERY DRY AIR WILL FILTER INTO CWA AS HIGH PRESSURE BUILDS IN FROM THE WEST TODAY AND SETTLES OVER THE AREA TONIGHT. PLENTY OF SUNSHINE EXPECTED TODAY BUT CAA WILL RESULT IN TEMPERATURES ACROSS MUCH OF THE CWA STRUGGLING TO GET OUT OF THE 30S. EXPECT A RANGE OF UPPER 30S TO LOWER 40S. ADDITIONALLY AIR MASS QUITE DRY WITH DEWPOINTS IN THE SINGLE DIGITS WITH SOME SUB-ZERO DEWPOINTS BY AFTERNOON. WILL SEE MID AND HIGH LEVEL CLOUDS OVERSPREAD THE AREA TONIGHT. LOWS IN THE MID 20S. HOWEVER THE EXTENT AND ARRIVAL OF CLOUDS TONIGHT COULD AFFECT OVERNIGHT MINS. THIS COLD DRY AIR MASS IN PLACE OVER CENTRAL NORTH CAROLINA WILL BE SETTING THE STAGE FOR A ROUND OF WINTRY WEATHER ON THURSDAY. THURSDAY AND THURSDAY NIGHT... CLASSIC IN SITU COLD AIR DAMMING EVENT WILL UNFOLD DURING THIS TIME... WHERE DIABATIC COOLING VIA EVAPORATION WILL BE THE IMPETUS FOR THE DEVELOPMENT OF THE DAMMING WEDGE. TYPICALLY IN SITU DAMMING CASES CANNOT SUSTAIN THEMSELVES FOR LONG DURATIONS... SINCE THEY LACK A CONTINUAL SUPPLY OF COLD DRY AIR ADVECTION IN THE LOW LEVELS... COURTESY OF A PARENT SURFACE HIGH TO OUR NORTH. THE LATENT HEAT OF FUSION AND RESULTING WARMING DURING FREEZING RAIN ULTIMATELY MAKES IT SELF LIMITING. AS HAS BEEN ADVERTISED BY PREVIOUS SHIFTS... THE SURFACE HIGH WILL BE WEAK... TRANSIENT... AND LOCATED TOO FAR SOUTH TO SUPPORT A *CLASSIC* WINTER WEATHER EVENT ACROSS CENTRAL NORTH CAROLINA. HOWEVER... VERY COLD... DRY AIR WILL BE IN PLACE ACROSS THE REGION FROM THE ARCTIC AIRMASS CURRENTLY SETTLING OVERHEAD. THIS AIRMASS... AT 06Z 31 JANUARY... WAS CHARACTERIZED BY SURFACE DEWPOINTS IN THE SINGLE DIGITS UPSTREAM OVER THE TENNESSEE VALLEY AND BELOW ZERO WESTWARD INTO THE UPPER MIDWEST. THIS EVENT MAY BE ONE OF THOSE RARE CASES THAT BECAUSE THE AIR IS SO COLD AND DRY TO START THE EVENT... POTENTIALLY SIGNIFICANT ICING COULD RESULT BEFORE A GRADUAL WARMING AND CHANGEOVER TO LIQUID. FRICTIONAL CONVERGENCE ALONG THE SOUTHEAST US COAST AS A RESULT OF THE RETURN FLOW AROUND THE DEPARTING SURFACE HIGH... WILL AID IN THE DEVELOPMENT OF A COASTAL FRONT BY THURSDAY MORNING. MEANWHILE A DEVELOPING WARM FRONT ALONG THE NORTHERN GULF OF MEXICO WILL LIFT NORTH AND MERGE WITH THE COASTAL FRONT DURING THE DAY THURSDAY. THE COMBINATION OF THESE FEATURES WILL PROVIDE THE BAROCLINIC ZONE THAT SEVERAL WAVES OF SURFACE LOW PRESSURE WILL ULTIMATELY TRACK NORTHEAST ALONG. THE IN SITU WEDGE SHOULD HOLD THIS BAROCLINIC ZONE AND EXPECTED LOW TRACK SOUTHEAST OF OUR CWA... THEREBY MINIMIZING SIGNIFICANT SURFACE WARMING THROUGHOUT THE EVENT. THE EXIT REGION OF A STRONG SOUTHWESTERLY 170 KNOT UPPER JET NOSING ACROSS THE LOWER MISSISSIPPI AND TENNESSEE VALLEYS LATE WEDNESDAY NIGHT/EARLY THURSDAY WILL PROMOTE THE DEVELOPMENT OF DEEP ISENTROPIC LIFT/WARM AIR ADVECTION IN THE THERMALLY INDIRECT LOW LEVEL RETURN BRANCH OF THE UPPER JET. THIS WILL RESULT IN RAPID MOISTENING OF THE ATMOSPHERE JUST AFTER DAYBREAK THURSDAY. PRECIPITATION SHOULD BEGIN REACHING THE GROUND FROM SOUTH TO NORTH SHORTLY THEREAFTER. THE TRENDS NOMOGRAM AND MODEL FORECAST SOUNDINGS BOTH INDICATE THAT PRECIPITATION AT THE ONSET WOULD LIKELY FALL IN THE FORM OF SNOW... WITH SLEET MIXED IN AS THE DAY WEARS ON. THIS PERIOD OF FROZEN PRECIPITATION WOULD BE VERY SHORT LIVED... AN HOUR OR SO AT MOST... ACROSS THE SANDHILLS AND COASTAL PLAIN... BEFORE RAPIDLY TRANSITIONING TO A COLD RAIN BY MIDDAY. THE PIEDMONT... ESPECIALLY THE WESTERN HALF... COULD SEE A PERIOD OF SEVERAL HOURS OF SNOW/SLEET BEFORE TRANSITIONING TO FREEZING RAIN DURING THE AFTERNOON... AS THE STRONG LOW LEVEL JET CREATES A PRONOUNCED WARM NOSE ALOFT. ONCE THE SNOW/SLEET TRANSITIONS TO FREEZING RAIN... THE FREEZING RAIN COULD CONTINUE THROUGH SUNSET ON EITHER SIDE OF A LINE FROM ALBEMARLE TO SANFORD TO RALEIGH TO HENDERSON... INCLUDING THE TRIANGLE. THE TEMPERATURE STRUCTURE IN THE LOWER TROPE WOULD BE SUPPORTIVE OF FREEZING RAIN AFTER SUNSET AND THROUGHOUT THE EVENING HOURS ACROSS THE CLIMATOLOGICALLY FAVORED AREAS APPROXIMATELY ALONG AND WEST OF A LINE FROM ASHEBORO TO HILLSBOROUGH TO ROXBORO... INCLUDING THE TRIAD. ITS INTERESTING THAT THE MODELS ARE KEYING ON TWO BOUTS OF DEEP LIFT AND PRECIPITATION DURING THE EVENT... ONE DURING THE MIDDAY TO EARLY AFTERNOON HOURS THURSDAY... THEN ANOTHER DURING THE EVENING HOURS. THE FIRST WOULD BE ASSOCIATED WITH THE INITIAL SURGE OF WARM ADVECTION AND CONVERGENCE ON THE NOSE OF THE LOW LEVEL JET... AND THE SECOND ASSOCIATED WITH THE DIFFERENTIAL CYCLONIC VORTICITY ADVECTION AHEAD OF THE UPPER LOW CURRENTLY SPINNING OFF THE BAJA OF CALIFORNIA. THE SECOND OF THE TWO AREAS OF MAXIMUM LIFT APPEARS AT THIS TIME THAT IT WOULD BE FOCUSED FROM SOUTHERN GEORGIA TO SOUTHEASTERN NORTH CAROLINA... AFFECTING PRIMARILY THE SOUTHEAST HALF OF OUR CWA. IF THAT WERE THE CASE... THE SECOND ROUND WOULD BE PREDOMINATELY LIQUID... SINCE THE BULK OF IT WOULD LIKELY NOT EXTEND FAR ENOUGH NORTHWEST INTO THE SUBFREEZING SURFACE AIR. THE ORIENTATION AND MAGNITUDE OF THE MODEL QPF FOR THE SECOND ROUND OF PRECIPITATION... FROM BOTH THE NAM AND GFS FOR THE PAST SEVERAL RUNS... SUGGEST THAT THE MODELS ARE GENERATING DEEP MOIST CONVECTION IN THE AFOREMENTIONED AREAS FROM SOUTHERN GA TO SOUTHEASTERN NC. ACCORDINGLY... INSTABILITY PARAMETERS FROM THE MODELS REVEAL THAT LIKELIHOOD.. AND SPC HAS THOSE AREA HIGHLIGHTED IN THE SWODY2. THUS... LATER SHIFTS WILL NEED TO MONITOR THE POTENTIAL FOR THIS UPSTREAM CONVECTION TO ALTER THE CURRENT THINKING REGARDING ROUND TWO BEING A BIT TOO FAR EAST TO CAUSE ADDITIONAL SIGNIFICANT ICING CONCERNS. WITH ALL OF THIS IN MIND... A WINTER STORM WATCH WILL BE ISSUED FOR LOCATIONS ALONG AND WEST OF A LINE FROM APPROXIMATELY ROCKINGHAM TO CARTHAGE TO RALEIGH TO LOUISBURG TO WARRENTON. IT IS STILL TOO EARLY TO GET SPECIFIC WITH PRECIPITATION AMOUNTS... BUT IT APPEARS THAT AROUND AN INCH OF SNOW/SLEET WOULD BE POSSIBLE IN THE WATCH AREA THROUGH MIDDAY THURSDAY... WITH ICE ACCRUAL OF ONE QUARTER INCH OR MORE THURSDAY AFTERNOON/EVENING... ESPECIALLY ACROSS THE WESTERN PIEDMONT. -MWS LONG TERM /FRIDAY THROUGH TUESDAY/... FRIDAY... SOME LIGHT RAIN AND/OR DRIZZLE WILL LINGER DURING THE MORNING HOURS AS STORM SYSTEM LIFTS OFF TO THE NORTHEAST. MODEL TRENDS ARE INDICATING CLEARING FAIRLY QUICKLY BUT THINK CLOUDS WILL BE SLOW TO CLEAR. WILL TWEAK CURRENT FORECAST MAXES TO ACCOUNT FOR SLOWER CLEARING. FRIDAY NIGHT THROUGH TUESDAY... NO CHANGES TO CURRENT FORECAST TRENDS. LATEST OPS GFS KEEPS PRECIP IN SOUTHERN STREAM SUPPRESSED SOUTH OF AREA FOR LATE IN THE WEEKEND. BUT TRENDS ARE SHOWING PRECIP SHIELD NUDGING A BIT FURTHER NORTH EACH RUN. LOOKS LIKE ANOTHER ROUND OF BITTER COLD EARLY NEXT WEEK. AVIATION /07Z-06Z/... VFR CONDS EXPECTED THROUGHOUT THE TAF PERIOD. CAA ASSOC/W FROPA WILL BRING NW WINDS AT 10-15 KTS THROUGH 10Z... THEN DECREASE TO LESS THAN 10 KT AROUND SUNRISE. THE WINDS PICK UP AGAIN TO 8-12 KT FROM THE NW AROUND 14Z AND CONTINUE THROUGH THE DAY. NW WINDS DIMINISH TO LIGHT WIND BY MID TO LATE AFTERNOON. EXPECT AN INCREASE IN HIGH CLOUDINESS IN THE AFTERNOON. & && .RAH WATCHES/WARNINGS/ADVISORIES... WINTER STORM WATCH FROM THURSDAY MORNING THROUGH THURSDAY EVENING FOR NCZ007>010-021>026-038>041-073>076-083-084. && $$ SHORT TERM...CBL FXUS62 KRAH 311524 AAA AFDRAH AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE RALEIGH NC 1024 AM EST WED JAN 31 2007 .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... A BROAD LONG WAVE TROUGH WITH A TAP TO THE ARCTIC DOMINATES THE FLOW ACROSS THE EASTERN 2/3RDS OF THE CONUS DURING THE PERIOD, THIS SHOULD RESULT IN BELOW TO MUCH BELOW NORMAL TEMPERATURES OVER CENTRAL NC. MODEL AND ENSEMBLE OUTPUT SHOWS ONE ARCTIC HIGH EXTENDING INTO THE AREA FROM THE NORTHERN PLAINS OVER THE WEEKEND REPLACED BY ANOTHER ARCTIC AIRMASS ON TUE AND WED. THESE AIRMASSES ARE SEPARATED BY A RELATIVELY DRY COLD FRONT TRAILING A CLIPPER LOW OVER THE GREAT LAKES LATE MONDAY. GIVEN THE DOMINANT FLOW ALOFT FROM THE NW AND NO SIGNIFICANT PERTURBATIONS IN THE SOUTHERN STREAM... CONDITIONS SHOULD REMAIN DRY THROUGH THE PERIOD WITH ONLY PASSING HIGH CLOUDINESS WITH THE COLD FRONT LATE MONDAY. -RFG && .PREV DISCUSSION... /ISSUED 1000 AM EST WED JAN 31 2007/ UPDATE... SHORT TERM /REST OF TODAY/... WV IMAGERY SHOWS IMPRESSIVE VORT MAX CURRENTLY MOVING OFFSHORE...THE BRUNT OF CAA OCCURRED IMMEDIATELY WITH AND BEHIND THE SHARP SHORT WAVE TROUGH WITH H5 HEIGHT FALLS OF 120 METERS OFFSHORE AND HEIGHT RISES OF 120 METERS UPSTREAM OVER THE OHIO VALLEY. EMPIRICAL PROOF OF THE WELL ADVERTISED ARCTIC AIRMASS THAT HAS SETTLED OVER CENTRAL NC OVER THE PAST 6 HOURS IS THE -14C 850 TEMPERATURE AND 30C DEWPOINT DEPRESSION ANALYZED AT KGSO IN THE 850 AND 700MB UPPER AIR CHARTS. TEMPERATURES ARE STRUGGLING TO WARM INTO THE MID TO UPPER 20S ACROSS THE WESTERN AND CENTRAL PIEDMONT UNDER FULL SUN WITH LOWER 30S IN THE SOUTHERN COASTAL PLAIN. CURRENTLY...DEWPOINTS ARE SOLIDLY IN THE SINGLE DIGITS...WITH THE FORECAST FOR DEWPOINTS TO DROP TO NEAR OR BELOW ZERO THIS AFTERNOON STILL ON TRACK AS SHORT-TERM MODEL SOUNDINGS INDICATE A DRY ADIABTIC PROFILE TO 900MB WITH DRIER AIR THROUGH THE MIXING LAYER JUST ABOVE THE SURFACE. THE DRY ADIABATIC IN-HOUSE THICKNESS SCHEME...SUPPORTS HIGHS IN THE MID 30S WEST...UPPER 30S CENTRAL...TO AROUND 40 EAST AND SOUTH. THIS WILL REQUIRE ONLY MINOR MODIFICATIONS TO FORECAST HIGHS. OTHERWISE NO OTHER CHANGES FOR THE CENTRAL NC FORECAST IN THE QUIET BEFORE THE STORM PHASE. WINTER STORM WATCH CONTINUES FOR THURSDAY MORNING THROUGH THURS EVENING FOR AREAS SURROUNDING AND WEST AND NORTH OF THE US 1 CORRIDOR. PREV DISCUSSION... /ISSUED 300 AM EST WED JAN 31 2007/ SHORT TERM /TODAY THROUGH THURSDAY NIGHT/... TODAY AND TONIGHT... COLD FRONT HAS PUSHED EAST OF CWA EARLY THIS MORNING. ON ITS HEEL IS A COLD AND VERY AIR MASS. THIS COLD AND VERY DRY AIR WILL FILTER INTO CWA AS HIGH PRESSURE BUILDS IN FROM THE WEST TODAY AND SETTLES OVER THE AREA TONIGHT. PLENTY OF SUNSHINE EXPECTED TODAY BUT CAA WILL RESULT IN TEMPERATURES ACROSS MUCH OF THE CWA STRUGGLING TO GET OUT OF THE 30S. EXPECT A RANGE OF UPPER 30S TO LOWER 40S. ADDITIONALLY AIR MASS QUITE DRY WITH DEWPOINTS IN THE SINGLE DIGITS WITH SOME SUB-ZERO DEWPOINTS BY AFTERNOON. WILL SEE MID AND HIGH LEVEL CLOUDS OVERSPREAD THE AREA TONIGHT. LOWS IN THE MID 20S. HOWEVER THE EXTENT AND ARRIVAL OF CLOUDS TONIGHT COULD AFFECT OVERNIGHT MINS. THIS COLD DRY AIR MASS IN PLACE OVER CENTRAL NORTH CAROLINA WILL BE SETTING THE STAGE FOR A ROUND OF WINTRY WEATHER ON THURSDAY. THURSDAY AND THURSDAY NIGHT... CLASSIC IN SITU COLD AIR DAMMING EVENT WILL UNFOLD DURING THIS TIME... WHERE DIABATIC COOLING VIA EVAPORATION WILL BE THE IMPETUS FOR THE DEVELOPMENT OF THE DAMMING WEDGE. TYPICALLY IN SITU DAMMING CASES CANNOT SUSTAIN THEMSELVES FOR LONG DURATIONS... SINCE THEY LACK A CONTINUAL SUPPLY OF COLD DRY AIR ADVECTION IN THE LOW LEVELS... COURTESY OF A PARENT SURFACE HIGH TO OUR NORTH. THE LATENT HEAT OF FUSION AND RESULTING WARMING DURING FREEZING RAIN ULTIMATELY MAKES IT SELF LIMITING. AS HAS BEEN ADVERTISED BY PREVIOUS SHIFTS... THE SURFACE HIGH WILL BE WEAK... TRANSIENT... AND LOCATED TOO FAR SOUTH TO SUPPORT A *CLASSIC* WINTER WEATHER EVENT ACROSS CENTRAL NORTH CAROLINA. HOWEVER... VERY COLD... DRY AIR WILL BE IN PLACE ACROSS THE REGION FROM THE ARCTIC AIRMASS CURRENTLY SETTLING OVERHEAD. THIS AIRMASS... AT 06Z 31 JANUARY... WAS CHARACTERIZED BY SURFACE DEWPOINTS IN THE SINGLE DIGITS UPSTREAM OVER THE TENNESSEE VALLEY AND BELOW ZERO WESTWARD INTO THE UPPER MIDWEST. THIS EVENT MAY BE ONE OF THOSE RARE CASES THAT BECAUSE THE AIR IS SO COLD AND DRY TO START THE EVENT... POTENTIALLY SIGNIFICANT ICING COULD RESULT BEFORE A GRADUAL WARMING AND CHANGEOVER TO LIQUID. FRICTIONAL CONVERGENCE ALONG THE SOUTHEAST US COAST AS A RESULT OF THE RETURN FLOW AROUND THE DEPARTING SURFACE HIGH... WILL AID IN THE DEVELOPMENT OF A COASTAL FRONT BY THURSDAY MORNING. MEANWHILE A DEVELOPING WARM FRONT ALONG THE NORTHERN GULF OF MEXICO WILL LIFT NORTH AND MERGE WITH THE COASTAL FRONT DURING THE DAY THURSDAY. THE COMBINATION OF THESE FEATURES WILL PROVIDE THE BAROCLINIC ZONE THAT SEVERAL WAVES OF SURFACE LOW PRESSURE WILL ULTIMATELY TRACK NORTHEAST ALONG. THE IN SITU WEDGE SHOULD HOLD THIS BAROCLINIC ZONE AND EXPECTED LOW TRACK SOUTHEAST OF OUR CWA... THEREBY MINIMIZING SIGNIFICANT SURFACE WARMING THROUGHOUT THE EVENT. THE EXIT REGION OF A STRONG SOUTHWESTERLY 170 KNOT UPPER JET NOSING ACROSS THE LOWER MISSISSIPPI AND TENNESSEE VALLEYS LATE WEDNESDAY NIGHT/EARLY THURSDAY WILL PROMOTE THE DEVELOPMENT OF DEEP ISENTROPIC LIFT/WARM AIR ADVECTION IN THE THERMALLY INDIRECT LOW LEVEL RETURN BRANCH OF THE UPPER JET. THIS WILL RESULT IN RAPID MOISTENING OF THE ATMOSPHERE JUST AFTER DAYBREAK THURSDAY. PRECIPITATION SHOULD BEGIN REACHING THE GROUND FROM SOUTH TO NORTH SHORTLY THEREAFTER. THE TRENDS NOMOGRAM AND MODEL FORECAST SOUNDINGS BOTH INDICATE THAT PRECIPITATION AT THE ONSET WOULD LIKELY FALL IN THE FORM OF SNOW... WITH SLEET MIXED IN AS THE DAY WEARS ON. THIS PERIOD OF FROZEN PRECIPITATION WOULD BE VERY SHORT LIVED... AN HOUR OR SO AT MOST... ACROSS THE SANDHILLS AND COASTAL PLAIN... BEFORE RAPIDLY TRANSITIONING TO A COLD RAIN BY MIDDAY. THE PIEDMONT... ESPECIALLY THE WESTERN HALF... COULD SEE A PERIOD OF SEVERAL HOURS OF SNOW/SLEET BEFORE TRANSITIONING TO FREEZING RAIN DURING THE AFTERNOON... AS THE STRONG LOW LEVEL JET CREATES A PRONOUNCED WARM NOSE ALOFT. ONCE THE SNOW/SLEET TRANSITIONS TO FREEZING RAIN... THE FREEZING RAIN COULD CONTINUE THROUGH SUNSET ON EITHER SIDE OF A LINE FROM ALBEMARLE TO SANFORD TO RALEIGH TO HENDERSON... INCLUDING THE TRIANGLE. THE TEMPERATURE STRUCTURE IN THE LOWER TROPE WOULD BE SUPPORTIVE OF FREEZING RAIN AFTER SUNSET AND THROUGHOUT THE EVENING HOURS ACROSS THE CLIMATOLOGICALLY FAVORED AREAS APPROXIMATELY ALONG AND WEST OF A LINE FROM ASHEBORO TO HILLSBOROUGH TO ROXBORO... INCLUDING THE TRIAD. ITS INTERESTING THAT THE MODELS ARE KEYING ON TWO BOUTS OF DEEP LIFT AND PRECIPITATION DURING THE EVENT... ONE DURING THE MIDDAY TO EARLY AFTERNOON HOURS THURSDAY... THEN ANOTHER DURING THE EVENING HOURS. THE FIRST WOULD BE ASSOCIATED WITH THE INITIAL SURGE OF WARM ADVECTION AND CONVERGENCE ON THE NOSE OF THE LOW LEVEL JET... AND THE SECOND ASSOCIATED WITH THE DIFFERENTIAL CYCLONIC VORTICITY ADVECTION AHEAD OF THE UPPER LOW CURRENTLY SPINNING OFF THE BAJA OF CALIFORNIA. THE SECOND OF THE TWO AREAS OF MAXIMUM LIFT APPEARS AT THIS TIME THAT IT WOULD BE FOCUSED FROM SOUTHERN GEORGIA TO SOUTHEASTERN NORTH CAROLINA... AFFECTING PRIMARILY THE SOUTHEAST HALF OF OUR CWA. IF THAT WERE THE CASE... THE SECOND ROUND WOULD BE PREDOMINATELY LIQUID... SINCE THE BULK OF IT WOULD LIKELY NOT EXTEND FAR ENOUGH NORTHWEST INTO THE SUBFREEZING SURFACE AIR. THE ORIENTATION AND MAGNITUDE OF THE MODEL QPF FOR THE SECOND ROUND OF PRECIPITATION... FROM BOTH THE NAM AND GFS FOR THE PAST SEVERAL RUNS... SUGGEST THAT THE MODELS ARE GENERATING DEEP MOIST CONVECTION IN THE AFOREMENTIONED AREAS FROM SOUTHERN GA TO SOUTHEASTERN NC. ACCORDINGLY... INSTABILITY PARAMETERS FROM THE MODELS REVEAL THAT LIKELIHOOD.. AND SPC HAS THOSE AREA HIGHLIGHTED IN THE SWODY2. THUS... LATER SHIFTS WILL NEED TO MONITOR THE POTENTIAL FOR THIS UPSTREAM CONVECTION TO ALTER THE CURRENT THINKING REGARDING ROUND TWO BEING A BIT TOO FAR EAST TO CAUSE ADDITIONAL SIGNIFICANT ICING CONCERNS. WITH ALL OF THIS IN MIND... A WINTER STORM WATCH WILL BE ISSUED FOR LOCATIONS ALONG AND WEST OF A LINE FROM APPROXIMATELY ROCKINGHAM TO CARTHAGE TO RALEIGH TO LOUISBURG TO WARRENTON. IT IS STILL TOO EARLY TO GET SPECIFIC WITH PRECIPITATION AMOUNTS... BUT IT APPEARS THAT AROUND AN INCH OF SNOW/SLEET WOULD BE POSSIBLE IN THE WATCH AREA THROUGH MIDDAY THURSDAY... WITH ICE ACCRUAL OF ONE QUARTER INCH OR MORE THURSDAY AFTERNOON/EVENING... ESPECIALLY ACROSS THE WESTERN PIEDMONT. -MWS LONG TERM /FRIDAY THROUGH TUESDAY/... FRIDAY... SOME LIGHT RAIN AND/OR DRIZZLE WILL LINGER DURING THE MORNING HOURS AS STORM SYSTEM LIFTS OFF TO THE NORTHEAST. MODEL TRENDS ARE INDICATING CLEARING FAIRLY QUICKLY BUT THINK CLOUDS WILL BE SLOW TO CLEAR. WILL TWEAK CURRENT FORECAST MAXES TO ACCOUNT FOR SLOWER CLEARING. FRIDAY NIGHT THROUGH TUESDAY... NO CHANGES TO CURRENT FORECAST TRENDS. LATEST OPS GFS KEEPS PRECIP IN SOUTHERN STREAM SUPPRESSED SOUTH OF AREA FOR LATE IN THE WEEKEND. BUT TRENDS ARE SHOWING PRECIP SHIELD NUDGING A BIT FURTHER NORTH EACH RUN. LOOKS LIKE ANOTHER ROUND OF BITTER COLD EARLY NEXT WEEK. AVIATION /07Z-06Z/... VFR CONDS EXPECTED THROUGHOUT THE TAF PERIOD. CAA ASSOC/W FROPA WILL BRING NW WINDS AT 10-15 KTS THROUGH 10Z... THEN DECREASE TO LESS THAN 10 KT AROUND SUNRISE. THE WINDS PICK UP AGAIN TO 8-12 KT FROM THE NW AROUND 14Z AND CONTINUE THROUGH THE DAY. NW WINDS DIMINISH TO LIGHT WIND BY MID TO LATE AFTERNOON. EXPECT AN INCREASE IN HIGH CLOUDINESS IN THE AFTERNOON. & && .RAH WATCHES/WARNINGS/ADVISORIES... WINTER STORM WATCH FROM THURSDAY MORNING THROUGH THURSDAY EVENING FOR NCZ007>010-021>026-038>041-073>076-083-084. && $$ LONG TERM...RFG FXUS62 KRAH 311950 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 245 PM EST WED JAN 31 2007 .SHORT TERM /TONIGHT THROUGH FRIDAY/... NON-CLASSICAL DAMMING WINTER EVENT TO UNFOLD ACROSS CENTRAL NC THURSDAY MORNING...AS TRANSITORY PARENT HIGH CURRENTLY CENTERED OVER WV/VA/KY MOVES QUICKLY WELL OFF THE CAROLINA COAST. TEMPERATURES WILL QUICKLY DROP OFF THIS EVENING...THEN LEVEL OFF OR RISE A DEGREE OR TWO AS HIGH-LEVEL CLOUD DECK SPREADS WEST TO EAST INTO THE AREA. THUS EXPECT MINS TO BE ACHIEVED BY MIDNIGHT WITH A NON-DIURNAL TEMPERATURE TREND. WITH THE PARENT HIGH IN AN UNFAVORED/ATYPICAL LOCATION TO PROVIDE A CONTINUOUS SOURCE OF CAA...MIN TEMPERATURES TONIGHT/THURSDAY MORNING ARE HIGHLY CRITICAL IN DETERMINING THE AMOUNT OF FROZEN AND FREEZING PRECIP THAT WILL BE REALIZED THROUGH 00Z FRIDAY. THE DIFFERENCE OF OVERNIGHT LOWS IN THE MID 20S VERSES UPPER 20S WILL BE ONE FACTOR IN DETERMINING WHETHER WARNING CRITERIA OF ICE ACCRUAL IS ACHIEVED. THE OTHER SIGNIFICANT PLAYER DUE TO THE ATYPICAL SET UP IS TIMING AND QPF AMOUNTS...WHICH IS A MUST TO LOCK IN IN-SITU DAMMING HIGH...WITH DIABATIC COOLING MAXIMIZED WITH SFC DEWPOINTS IN THE SINGLE TO LOWER TEENS AT THE START OF PRECIP. AGAIN...I CANNOT STRESS THESE TWO CRITICAL COMPONENTS ENOUGH...THE PRE-EXISTING COLD AIR AND THE TIMING AND QPF AMOUNTS ARE KEY IN REALIZING ADVISORY (LESS THAN 0.10") OR WARNING (0.25" OR MORE)ICE CRITERIA. THERE ARE NO MAJOR CHANGES TO CHANGEOVER TIMING OR DOMINANT PRECIP TYPE...WITH THE WARM NOSE QUICKLY WARMING THE MID-LEVELS AND THEN THE LOW-LEVELS IN THE COASTAL PLAIN AOA 15Z...MORE GRADUAL IN THE CENTRAL PIEDMONT AND NORTHERN COASTAL PLAIN AOA 17Z...WITH THE WARMING MUCH DELAYED IN THE WESTERN PIEDMONT AND NORTHERN CENTRAL PIEDMONT UNTIL AROUND 00Z PER FORECAST SURFACE TW. ONE TO TWO INCHES OF SNOW IS POSSIBLE INITIALLY THROUGH 21Z WITH AN ADDITIONAL 0.25" OF ICE FROM 21Z TO 00Z ALONG AND WEST OF A LINE EXTENDING FROM ALBEMARLE...TO SILER CITY...TO DURHAM...THROUGH WARRENTON. WILL UPGRADE THE WINTER STORM WATCH TO A WINTER STORM WARNING FOR THIS AREA. JUST EAST OF THAT AREA...INCLUDING ROCKINGHAM...SANFORD... RALEIGH...ROCKY MOUNT AND ROANOKE RAPIDS...A WINTER STORM ADVISORY WILL BE ISSUED FOR ICE ACCRUAL OF A TRACE TO 0.10" WITH SNOWFALL OF LESS THAN INCH AT ONSET. A SPECIAL WEATHER STATEMENT WILL BE ISSUED FOR THE REMAINDER OF THE FORECAST AREA HIGHLIGHTING A BRIEF PERIOD OF SNOW/RAIN BEFORE QUICKLY CHANGING OVER TO RAIN. THERE ARE NOTABLE LIQUID QPF DIFFERENCES BETWEEN THE NAM AND GFS WITH THE GFS STILL SLIGHTLY FASTER AT ONSET. THE NAM QUICKLY CATCHES UP THOUGH WITH THE HEAVIEST QPF AXIS MUCH FARTHER NORTH AND WEST OF THE GFS FROM 18Z TO 00Z. THE GFS QPF IS PREFERRED KEEPING THE HEAVIEST QPF ALONG THE SE CWA WITH THE BAROCLINIC ZONE ALONG THE COASTAL TROUGH AND STRONGEST WAA. ANOTHER IMPORTANT FEATURE IS A LULL IN PRECIP LATE THURSDAY AFTERNOON ACROSS THE WEST WITH A SECONDARY WAVE OF PRECIP DEVELOPING IN THE WEST FROM 00 TO 06Z AS VORTICITY ADVECTION ALOFT APPROACHES FROM THE WEST. AT THIS POINT EXPECT TEMPERATURES IN THE EXTREME NW PIEDMONT TO BE RIGHT AT OR JUST ABOVE FREEZING...RESULTING IN LITTLE TO NO ADDITIONAL ICE ACCRUAL. WILL END PRECIP AS DRIZZLE OR FREEZING DRIZZLE IN THE FAR NW FRIDAY MORNING...ENDING AS RAIN EVERYWHERE ELSE. LIQUID QPF TOTALS OF A HALF INCH IN THE WEST TO JUST OVER AN INCH IN THE SOUTHEAST. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... FRI NGT-SAT NGT...A SOUTHERN STREAM WAVE PASSES TO OUR SOUTH...KEEPING MAINLY HIGH CLOUDINESS OVER CENTRAL NC AND NARROWING THE DIURNAL TEMPERATURE RANGE SOMEWHAT FROM THE PREVIOUS CYCLE FOR FRI NIGHT THROUGH SAT NGT. SUN-WED...A BROAD LONG WAVE TROUGH WITH A TAP TO THE ARCTIC DOMINATES THE FLOW ACROSS THE EASTERN 2/3RDS OF THE CONUS DURING THE PERIOD. THIS SHOULD RESULT IN BELOW TO MUCH BELOW NORMAL TEMPERATURES OVER CENTRAL NC. MODEL AND ENSEMBLE OUTPUT SHOWS ONE ARCTIC HIGH EXTENDING INTO THE AREA FROM THE NORTHERN PLAINS OVER THE WEEKEND REPLACED BY ANOTHER ARCTIC AIRMASS ON TUE AND WED. THESE AIRMASSES ARE SEPARATED BY A RELATIVELY DRY COLD FRONT TRAILING A CLIPPER LOW OVER THE GREAT LAKES LATE MONDAY. GIVEN THE DOMINANT FLOW ALOFT FROM THE NW AND NO SIGNIFICANT PERTURBATIONS IN THE SOUTHERN STREAM... CONDITIONS SHOULD REMAIN DRY THROUGH THE PERIOD WITH ONLY PASSING HIGH CLOUDINESS WITH THE COLD FRONT LATE MONDAY. && .AVIATION /18Z-18Z/... VFR CONDITIONS PREVAIL OVER CENTRAL NC THROUGH DAYBREAK THU BUT WITH INCREASING HIGH CLOUDINESS LOWERING BASES TO AROUND 9 THSD FT AROUND 06Z AND TO AROUND 5 THSD FT AROUND 12Z. SHORTLY AFTER 12Z SNOW AND SLEET IS EXPECTED TO OVERSPREAD THE AREA FROM THE WEST LOWERING CONDITIONS TO IFR BY 15Z WITH VSBY BELOW 3 MILES AND CIGS BELOW 1 THSD FT. BY 18Z...PRECIPITATION IS EXPECTED TO TURN TO RAIN AT KFAY AND KRWI AND TO FREEZING RAIN AT KRDU...KGSO...AND KINT. && .RAH WATCHES/WARNINGS/ADVISORIES... WINTER STORM WARNING FROM 6 AM THURSDAY TO MIDNIGHT EST THURSDAY NIGHT FOR NCZ007>010-021>025-038>040-073-074. WINTER WEATHER ADVISORY FROM 6 AM THURSDAY TO MIDNIGHT EST THURSDAY NIGHT FOR NCZ011-026>028-041-043-075-076-083-084. && $$ SHORT TERM...CBL LONG TERM...RFG AVIATION...RFG FXUS62 KRAH 010256 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 956 PM EST WED JAN 31 2007 .SHORT TERM /REST OF TONIGHT THROUGH THURSDAY/... PRECIPITATION MOVING QUICKLY EAST ACROSS THE DEEP SOUTH THIS EVENING. TEMPS ACROSS THE OUR AREA HAVE LOWERED INTO THE UPPER 20S TO AROUND 30. IF TEMPS HOLD STEADY AT CURRENT LEVELS...UPCOMING EVENT MAY NOT BE AS DIRE AS FORECAST. HOWEVER STILL APPEARS THAT WE ARE STILL 3-4 HOURS FROM OVERCAST SKIES SO TEMPS MAY STILL FALL A FEW MORE DEGREES BEFORE LEVELING OFF. 12Z/18Z RUN OF GFS DID A DECENT JOB WITH EASTWARD PROGRESSION OF PRECIP OVER THE DEEP SOUTH THIS AFTERNOON. BASED ON THIS TREND WENT AHEAD AND MENTIONED A CHANCE POP ALONG THE SOUTHERN BORDER COUNTIES AFTER 08Z. STILL APPEARS THAT PRECIP WILL EXPAND ACROSS CENTRAL NC THU MORNING. WITH SUB CLOUD LAYER BONE DRY...EVAPORATIVE COOLING WILL CAUSE PRECIP TO START OUT AS SNOW MIXED WITH SLEET THEN TRANSITION TO FREEZING RAIN AS WARMER AIR ALOFT OVERSPREADS CENTRAL NC IN STRENGTHEN LOW LEVEL SLY FLOW. DID NOTE ON 00Z ANALYSIS THAT THE 850MB 0 DEGREE ISOTHERM EXTENDED FROM ATLANTA TO MOREHEAD CITY SO THE WARMER AIR ALOFT DOES NOT HAVE FAR TO GO. BIG UNCERTAINTY REMAINS ON EXPECTED PRECIP AMOUNTS. IF PRECIP AMOUNTS HEAVIER THAN EXPECTED (AND A FEW SHORT RANGE MODELS ARE DEPICTING AMOUNTS AROUND 0.75 THU IN THE TRIAD REGION), MAY BE LOOKING AT A SIGNIFICANT ICING EVENT OVER THE NW PIEDMONT. ALSO...BASED ON THE SURFACE WET BULB TEMPERATURES NOT WARMING TO NEAR FREEZING UNTIL THU EVENING...FREEZING RAIN EVENT IN THE NW PIEDMONT MAY LAST A FEW HOURS LONGER THAN EARLIER ANTICIPATED. THUS...HAVE SEGMENTED THE WARNING TO INDICATE THE POTENTIAL FOR A BIT MORE ICING IN THE FAR NE AND NW PIEDMONT VERSUS THE REMAINDER OF THE WARNING AREA. MADE MENTION OF SCATTERED POWER OUTAGES AND A FEW DOWN TREES IN THIS REGION. ALSO ADDED HARNETT AND JOHNSTON TO THE ADVISORY AREA AS THEY MAY EXPERIENCE ENOUGH FREEZING RAIN TO RESULT IN A LIGHT GLAZE ON EXPOSED OBJECTS. THE PARAMETERS TO WATCH THE NEXT FEW HOURS WILL BE HOW LOW THE TEMPS GET IN THE REGION BEFORE THE THICKER CLOUDS ARRIVE...AND HOW FAST THE PRECIP EXPANDS TO OUR SW. IF PRECIP ARRIVES A COUPLE OF HOURS EARLIER THAN ANTICIPATED...SNOW AMOUNTS MAY BE A BIT GREATER. && .PREV DISCUSSION... /ISSUED 245 PM EST WED JAN 31 2007/ SHORT TERM /TONIGHT THROUGH FRIDAY/... NON-CLASSICAL DAMMING WINTER EVENT TO UNFOLD ACROSS CENTRAL NC THURSDAY MORNING...AS TRANSITORY PARENT HIGH CURRENTLY CENTERED OVER WV/VA/KY MOVES QUICKLY WELL OFF THE CAROLINA COAST. TEMPERATURES WILL QUICKLY DROP OFF THIS EVENING...THEN LEVEL OFF OR RISE A DEGREE OR TWO AS HIGH-LEVEL CLOUD DECK SPREADS WEST TO EAST INTO THE AREA. THUS EXPECT MINS TO BE ACHIEVED BY MIDNIGHT WITH A NON-DIURNAL TEMPERATURE TREND. WITH THE PARENT HIGH IN AN UNFAVORED/ATYPICAL LOCATION TO PROVIDE A CONTINUOUS SOURCE OF CAA...MIN TEMPERATURES TONIGHT/THURSDAY MORNING ARE HIGHLY CRITICAL IN DETERMINING THE AMOUNT OF FROZEN AND FREEZING PRECIP THAT WILL BE REALIZED THROUGH 00Z FRIDAY. THE DIFFERENCE OF OVERNIGHT LOWS IN THE MID 20S VERSES UPPER 20S WILL BE ONE FACTOR IN DETERMINING WHETHER WARNING CRITERIA OF ICE ACCRUAL IS ACHIEVED. THE OTHER SIGNIFICANT PLAYER DUE TO THE ATYPICAL SET UP IS TIMING AND QPF AMOUNTS...WHICH IS A MUST TO LOCK IN IN-SITU DAMMING HIGH...WITH DIABATIC COOLING MAXIMIZED WITH SFC DEWPOINTS IN THE SINGLE TO LOWER TEENS AT THE START OF PRECIP. AGAIN...I CANNOT STRESS THESE TWO CRITICAL COMPONENTS ENOUGH...THE PRE-EXISTING COLD AIR AND THE TIMING AND QPF AMOUNTS ARE KEY IN REALIZING ADVISORY (LESS THAN 0.10") OR WARNING (0.25" OR MORE)ICE CRITERIA. THERE ARE NO MAJOR CHANGES TO CHANGEOVER TIMING OR DOMINANT PRECIP TYPE...WITH THE WARM NOSE QUICKLY WARMING THE MID-LEVELS AND THEN THE LOW-LEVELS IN THE COASTAL PLAIN AOA 15Z...MORE GRADUAL IN THE CENTRAL PIEDMONT AND NORTHERN COASTAL PLAIN AOA 17Z...WITH THE WARMING MUCH DELAYED IN THE WESTERN PIEDMONT AND NORTHERN CENTRAL PIEDMONT UNTIL AROUND 00Z PER FORECAST SURFACE TW. ONE TO TWO INCHES OF SNOW IS POSSIBLE INITIALLY THROUGH 21Z WITH AN ADDITIONAL 0.25" OF ICE FROM 21Z TO 00Z ALONG AND WEST OF A LINE EXTENDING FROM ALBEMARLE...TO SILER CITY...TO DURHAM...THROUGH WARRENTON. WILL UPGRADE THE WINTER STORM WATCH TO A WINTER STORM WARNING FOR THIS AREA. JUST EAST OF THAT AREA...INCLUDING ROCKINGHAM...SANFORD... RALEIGH...ROCKY MOUNT AND ROANOKE RAPIDS...A WINTER STORM ADVISORY WILL BE ISSUED FOR ICE ACCRUAL OF A TRACE TO 0.10" WITH SNOWFALL OF LESS THAN INCH AT ONSET. A SPECIAL WEATHER STATEMENT WILL BE ISSUED FOR THE REMAINDER OF THE FORECAST AREA HIGHLIGHTING A BRIEF PERIOD OF SNOW/RAIN BEFORE QUICKLY CHANGING OVER TO RAIN. THERE ARE NOTABLE LIQUID QPF DIFFERENCES BETWEEN THE NAM AND GFS WITH THE GFS STILL SLIGHTLY FASTER AT ONSET. THE NAM QUICKLY CATCHES UP THOUGH WITH THE HEAVIEST QPF AXIS MUCH FARTHER NORTH AND WEST OF THE GFS FROM 18Z TO 00Z. THE GFS QPF IS PREFERRED KEEPING THE HEAVIEST QPF ALONG THE SE CWA WITH THE BAROCLINIC ZONE ALONG THE COASTAL TROUGH AND STRONGEST WAA. ANOTHER IMPORTANT FEATURE IS A LULL IN PRECIP LATE THURSDAY AFTERNOON ACROSS THE WEST WITH A SECONDARY WAVE OF PRECIP DEVELOPING IN THE WEST FROM 00 TO 06Z AS VORTICITY ADVECTION ALOFT APPROACHES FROM THE WEST. AT THIS POINT EXPECT TEMPERATURES IN THE EXTREME NW PIEDMONT TO BE RIGHT AT OR JUST ABOVE FREEZING...RESULTING IN LITTLE TO NO ADDITIONAL ICE ACCRUAL. WILL END PRECIP AS DRIZZLE OR FREEZING DRIZZLE IN THE FAR NW FRIDAY MORNING...ENDING AS RAIN EVERYWHERE ELSE. LIQUID QPF TOTALS OF A HALF INCH IN THE WEST TO JUST OVER AN INCH IN THE SOUTHEAST. LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... FRI NGT-SAT NGT...A SOUTHERN STREAM WAVE PASSES TO OUR SOUTH...KEEPING MAINLY HIGH CLOUDINESS OVER CENTRAL NC AND NARROWING THE DIURNAL TEMPERATURE RANGE SOMEWHAT FROM THE PREVIOUS CYCLE FOR FRI NIGHT THROUGH SAT NGT. SUN-WED...A BROAD LONG WAVE TROUGH WITH A TAP TO THE ARCTIC DOMINATES THE FLOW ACROSS THE EASTERN 2/3RDS OF THE CONUS DURING THE PERIOD. THIS SHOULD RESULT IN BELOW TO MUCH BELOW NORMAL TEMPERATURES OVER CENTRAL NC. MODEL AND ENSEMBLE OUTPUT SHOWS ONE ARCTIC HIGH EXTENDING INTO THE AREA FROM THE NORTHERN PLAINS OVER THE WEEKEND REPLACED BY ANOTHER ARCTIC AIRMASS ON TUE AND WED. THESE AIRMASSES ARE SEPARATED BY A RELATIVELY DRY COLD FRONT TRAILING A CLIPPER LOW OVER THE GREAT LAKES LATE MONDAY. GIVEN THE DOMINANT FLOW ALOFT FROM THE NW AND NO SIGNIFICANT PERTURBATIONS IN THE SOUTHERN STREAM... CONDITIONS SHOULD REMAIN DRY THROUGH THE PERIOD WITH ONLY PASSING HIGH CLOUDINESS WITH THE COLD FRONT LATE MONDAY. AVIATION /18Z-18Z/... VFR CONDITIONS PREVAIL OVER CENTRAL NC THROUGH DAYBREAK THU BUT WITH INCREASING HIGH CLOUDINESS LOWERING BASES TO AROUND 9 THSD FT AROUND 06Z AND TO AROUND 5 THSD FT AROUND 12Z. SHORTLY AFTER 12Z SNOW AND SLEET IS EXPECTED TO OVERSPREAD THE AREA FROM THE WEST LOWERING CONDITIONS TO IFR BY 15Z WITH VSBY BELOW 3 MILES AND CIGS BELOW 1 THSD FT. BY 18Z...PRECIPITATION IS EXPECTED TO TURN TO RAIN AT KFAY AND KRWI AND TO FREEZING RAIN AT KRDU...KGSO...AND KINT. && .RAH WATCHES/WARNINGS/ADVISORIES... WINTER STORM WARNING FROM 6 AM THURSDAY TO MIDNIGHT EST THURSDAY NIGHT FOR NCZ007>010-021>025-038>040-073-074. WINTER WEATHER ADVISORY FROM 6 AM THURSDAY TO MIDNIGHT EST THURSDAY NIGHT FOR NCZ011-026>028-041>043-075>077-083-084. && $$ SHORT TERM...RLH/WSS FXUS62 KRAH 010814 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 312 AM EST THU FEB 1 2007 SPECIAL GSO UA IN FOR 06Z AND 18Z SCHEDULED. .SHORT TERM /TODAY THROUGH SATURDAY NIGHT/... TODAY THROUGH FRIDAY... INTERESTING AND SOMEWHAT TRICKY FORECAST FOR THE NEXT 24 HOURS OVER A LARGE PORTION OF CENTRAL NORTH CAROLINA. MID/HIGH LEVEL CLOUDS SPREADING INTO AREA RESULTING IN TEMPERATURES BOUNCING AROUND SHOWING RISES WHICH MAKES FORECAST ALL THE MORE TRICKY. BUT DEWPOINTS ARE QUITE LOW...STILL SINGLE DIGITS IN NORTHWEST BUT A SLIGHT RISE OVER SOUTH/SOUTHWEST SECTIONS. HOWEVER EXPECT TEMPERATURES TO FALL ONCE PRECIP STARTS. ONSET TIMING AND QPF AMOUNTS ARE THE KEY FACTORS. PRECIPITATION CURRENTLY OVER DEEP SOUTH HANDLED QUITE WELL BY GFS. LATEST RADAR TRENDS SHOW AREA ADVANCING NORTHEAST/EAST FAIRLY QUICKLY. HEAVIER MIX PRECIP CURRENTLY INTO NORTH AND NORTH CENTRAL GEORGIA WITH SOME LIGHTER ECHOES ALOFT NOW OVER CENTRAL CWA. SOME DIFFERENCES EXIST BETWEEN NAM/GFS WHILE THERE ARE SIMILARITIES. NAM IS THE COLDEST AND WETTEST. NAM BRINGS CORE OF HIGHEST PRECIP ACROSS THE CWA WHILE GFS MOVES ACROSS MAINLY SOUTHERN SECTIONS. ALSO NAM HAS MORE PRONOUNCED INSITU WEDGE AND PROFILES FOR GSO/RDU BELOW FREEZING THROUGH 18Z INDICATING A LONGER PERIOD OF SNOW. GFS WEAKER ON INSITU WEDGE AND PROFILES INDICATE PRECIP TRANSITIONING OVER SLEET/FREEZING RAIN BY THE AFTERNOON. TOUGH CALL AS GFS HAS BEEN FAIRLY CONSISTENT AND PERFORMANCE GOOD SO FAR THIS WINTER. GFS PARTIALS ARE MORE IN LINE WITH LATEST GSO RAOB (06Z). 06Z GSO SOUNDING SHOWING QUITE A BIT OF MID LEVEL DRY AIR. PER GFS GOOD ISENTROPIC LIFT COMMENCES OVER CWA AT 12Z WHILE NAM FURTHER SOUTH AND SOUTHWEST. BOTH NAM/GFS SHOWING TWO ROUNDS OF PRECIP MOVING ACROSS THE AREA...ONE DURING THE DAY...THEN ANOTHER WITH SECOND WAVE 00Z-06Z. OVERALL WILL LEAN TOWARD GFS WITH MODIFICATION. WILL HOLD ON TO ALL SNOW LONGER IN NORTHWEST PIEDMONT. ALSO SLOWER TREND ON TRANSITION OF PRECIP IN EASTERN PIEDMONT TO ALL RAIN. ADDITIONALLY WILL ADJUST TEMPERATURE TRENDS TO KEEP COLDER THROUGH 00Z. FOR FRIDAY WILL KEEP DRIZZLE MENTIONED THROUGH MID MORNING. --RA FRIDAY NIGHT THROUGH SATURDAY NIGHT... AT THIS POINT WILL CONTINUE CURRENT FORECAST TREND. DRY AND COLD. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... BROAD UPPER LEVEL TROUGH REMAIN ANCHORED OVER THE AREA THROUGH THE PERIOD TO REINFORCE COLD AIR OVER THE AREA. AT THE SURFACE HIGH PRESSURE BUILDS OVER THE AREA SUNDAY. SUNDAY NIGHT...A BOUNDARY DEVELOPS ALONG THE VIRGINIA/NORTH CAROLINA BORDER AND EXTENDS WEST AND SOUTHWEST TO TENNESSEE...THEN TO A LOW OVER EASTERN TEXAS. THERE IS SOME MOISTURE AND WEAK UPPER SUPPORT ASSOCIATED WITH THIS FEATURE ...HOWEVER WILL LEAVE FORECAST DRY AT THE PRESENT TIME. THIS SYSTEM WILL BE PUSHED TO THE SOUTHEAST LATE MONDAY AND EARLY TUESDAY AS ARCTIC HIGH PRESSURE BUILDS OVER THE AREA...AND REMAINS OVER THE REGION THROUGH WEDNESDAY. THE RESULT OF THIS ARCTIC AIRMASS WILL BE BELOW TO MUCH BELOW NORMAL TEMPERATURES. -RHJ && .AVIATION /07Z-06Z/... ALTOCUMULUS BEGINNING TO MOVE INTO THE FOOTHILLS AT THIS TIME. CLOUDS WILL LOWER OVERNIGHT AND LIKELY DROP BELOW VFR A COUPLE OF HOURS AFTER SUNRISE AT THE TAF LOCATIONS. CEILINGS BELOW 1000 FEET ONCE PRECIPITATION BEGINS WITH MVFR VISIBILITIES IN GENERAL. CEILINGS BELOW 600 FEET MOST OF THE AFTERNOON AND INTO THE NIGHT. ALL TAF SITES EXPECTING SOME NON-LIQUID PRECIPITATION THURSDAY WITH FAYETTEVILLE HAVING THE LEAST IMPACT AND SHORTEST DURATION...AND GREENSBORO AND WINSTON-SALEM MOST IMPACTED BY WINTER WEATHER. ACCUMULATING SNOW THURSDAY MORNING WILL MIX WITH SLEET AND CHANGE TO FREEZING RAIN IN THE AFTERNOON. LESSER AMOUNTS OF SNOW AND SLEET AS ONE MOVES EAST BUT FREEZING RAIN WILL BE A CONCERN. -RLH/VINCENT && .RAH WATCHES/WARNINGS/ADVISORIES... WINTER STORM WARNING FROM 6 AM THIS MORNING TO MIDNIGHT EST TONIGHT FOR NCZ007>010-021>025-038>040-073-074. WINTER WEATHER ADVISORY FROM 6 AM THIS MORNING TO MIDNIGHT EST TONIGHT FOR NCZ011-026>028-041>043-075>077-083-084. && $$ SHORT TERM...RA/RHJ/VINCENT LONG TERM...RHJ AVIATION...VINCENT FXUS62 KRAH 011547 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 1045 AM EST THU FEB 1 2007 .UPDATE... && .SHORT TERM /REST OF TODAY/... THE INITIAL HEAVY BURST OF SNOW HAS RESULTED IN HEAVIEST SNOWFALL TOTALS ACROSS THE SOUTHERN HALF OF CWA...SEEN CLEARLY EARLIER ON THE KRAX RADAR IMAGERY WITH THE BRIGHT BAND REFLECTIVITY EXTENDING OVER THE SOUTHERN SECTOR. REPORTS INDICATE THE HIGHEST AMOUNTS ACROSS THE SOUTHWEST PIEDMONT...STANLY...ANSON...AND MONTGOMERY AND MOORE COUNTIES. 1 TO 1.5 INCHES WAS REPORTED IN THE SANDHILLS AND SOUTHERN COASTAL PLAIN...WHICH PROMPTED RAISING A WINTER WX ADVISORY THROUGH NOON. MEANWHILE ACROSS THE NORTHERN HALF...SNOW AMOUNTS ARE LESS THAN AN INCH WITH THE TRIAD AND COUNTIES ALONG THE VA BORDER REPORTING ONLY A TRACE. CURRENTLY... REAL TIME REPORTS...AIRCRAFT(AMDAR)SOUNDINGS...AND THE MRR-VERTICALLY POINTING RADAR...ARE ALL SHOWING THE ADVERTISED WARMING NOSE ALOFT ADVANCING NORTH WITH THE MELTING LAYER STARTING TO DESCEND DOWN TO THE SURFACE. REPORTS EXTENDING FROM ALBEMARLE...MOORE... FAYETTEVILLE HAVE CHANGED OVER TO SLEET OR FREEZING RAIN. THE LATEST RUC IS MODELING THE THERMAL PROFILE FAIRLY WELL WHEN COMPARED TO THE LATEST AMDAR SOUNDING FROM GSO...WITH IT A LITTLE TOO COOL ALOFT AND SLIGHTLY TOO WARM NEAR THE SURFACE SURFACE. WITH THE MAIN WARM/MOIST AIR CONVEYOR BELT DIRECTED IN A MORE SW TO NE FASHION AND TRANSLATING IN A MORE EASTERLY DIRECTION...RADARS RETURNS HAVE BEEN HARD TO COME BY ACROSS THE TRIAD. IT APPEARS THAT THE PREDICTED SNOWFALL OF 1 TO 2 INCHES WILL NOT BE REALIZED. HOWEVER...PRECIP WILL SPREAD BACK NORTH THIS AFTERNOON AS THE WELL-DEFINED WAVE OVER ALABAMA TRANSLATES NE TOWARDS CENTRAL NC. BY THAT TIME...THE THERMAL PROFILE WILL BE WARMING TO SUPPORT A TRANSITION TO SLEET AND THE ANTICIPATED FREEZING RAIN. THERE IS STILL YET ANOTHER WAVE OVER THE TEXAS AND OKLAHOMA THIS IS PROGGED TO APPROACH THE AREA BETWEEN 00Z TO 06Z. SO BY NO MEANS IS THE TRIAD OUT OF THE WOODS...WITH A QUARTER OF AN INCH ICE STILL VERY POSSIBLE. WILL BE KEEPING ALL WARNINGS AND ADVISORIES UP...BUT LOWER THE SNOWFALL AMOUNTS AND POPS. OTHERWISE...MINOR ADJUSTMENTS TO FORECAST OF P-TYPE AND TIMING OF CHANGEOVER. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... THE FLOW ALOFT IS DOMINATED BY A BROAD LARGE SCALE TROUGH OVER THE EASTERN TWO-THIRDS OF THE CONUS WITH A TROUGH AXIS THAT STEEPENS OVER THE APPALACHIANS AROUND TUE NIGHT...THEN FLATTENS AS THE TROUGH LOSES AMPLITUDE BY THU. SURFACE FEATURES SHOW WEAK HIGH PRESSURE DRIFTING ACROSS THE AREA SUN NGT AND MON AHEAD OF A COLD FRONT MON NIGHT THAT USHERS ANOTHER ARCTIC AIRMASS SOUTHEASTWARD OUT OF THE NORTHERN PLAINS. THE OVERNIGHT GFS SHOWS A WEAK LOW FORMATION IN THE LEE OF THE APPALACHIANS WITH THE COLD FRONT LATE MON... SUGGESTING SOME MOISTURE CONVERGENCE IN LOWER TO MID LEVELS. OTHER MODELS DO NOT RESOLVE THIS FEATURE. THE SURFACE LAYER IS EXPECTED TO BE VERY DRY WITH DEW POINTS OF 10-15 DEGREES AND CHANCES OF PRECIPITATION HITTING THE GROUND REMAIN LESS THAN 15 PERCENT IN THE RAH CWA. TEMPERATURES DROP TO BETWEEN 10 AND 20 DEGREES BELOW NORMAL FOLLOWING THE ARCTIC COLD FRONT FOR TUE AND WED MODERATING BUT STILL BELOW NORMAL ON THU. && .PREV DISCUSSION... /ISSUED 312 AM EST THU FEB 1 2007/ SHORT TERM /TODAY THROUGH SATURDAY NIGHT/... TODAY THROUGH FRIDAY... INTERESTING AND SOMEWHAT TRICKY FORECAST FOR THE NEXT 24 HOURS OVER A LARGE PORTION OF CENTRAL NORTH CAROLINA. MID/HIGH LEVEL CLOUDS SPREADING INTO AREA RESULTING IN TEMPERATURES BOUNCING AROUND SHOWING RISES WHICH MAKES FORECAST ALL THE MORE TRICKY. BUT DEWPOINTS ARE QUITE LOW...STILL SINGLE DIGITS IN NORTHWEST BUT A SLIGHT RISE OVER SOUTH/SOUTHWEST SECTIONS. HOWEVER EXPECT TEMPERATURES TO FALL ONCE PRECIP STARTS. ONSET TIMING AND QPF AMOUNTS ARE THE KEY FACTORS. PRECIPITATION CURRENTLY OVER DEEP SOUTH HANDLED QUITE WELL BY GFS. LATEST RADAR TRENDS SHOW AREA ADVANCING NORTHEAST/EAST FAIRLY QUICKLY. HEAVIER MIX PRECIP CURRENTLY INTO NORTH AND NORTH CENTRAL GEORGIA WITH SOME LIGHTER ECHOES ALOFT NOW OVER CENTRAL CWA. SOME DIFFERENCES EXIST BETWEEN NAM/GFS WHILE THERE ARE SIMILARITIES. NAM IS THE COLDEST AND WETTEST. NAM BRINGS CORE OF HIGHEST PRECIP ACROSS THE CWA WHILE GFS MOVES ACROSS MAINLY SOUTHERN SECTIONS. ALSO NAM HAS MORE PRONOUNCED INSITU WEDGE AND PROFILES FOR GSO/RDU BELOW FREEZING THROUGH 18Z INDICATING A LONGER PERIOD OF SNOW. GFS WEAKER ON INSITU WEDGE AND PROFILES INDICATE PRECIP TRANSITIONING OVER SLEET/FREEZING RAIN BY THE AFTERNOON. TOUGH CALL AS GFS HAS BEEN FAIRLY CONSISTENT AND PERFORMANCE GOOD SO FAR THIS WINTER. GFS PARTIALS ARE MORE IN LINE WITH LATEST GSO RAOB (06Z). 06Z GSO SOUNDING SHOWING QUITE A BIT OF MID LEVEL DRY AIR. PER GFS GOOD ISENTROPIC LIFT COMMENCES OVER CWA AT 12Z WHILE NAM FURTHER SOUTH AND SOUTHWEST. BOTH NAM/GFS SHOWING TWO ROUNDS OF PRECIP MOVING ACROSS THE AREA...ONE DURING THE DAY...THEN ANOTHER WITH SECOND WAVE 00Z-06Z. OVERALL WILL LEAN TOWARD GFS WITH MODIFICATION. WILL HOLD ON TO ALL SNOW LONGER IN NORTHWEST PIEDMONT. ALSO SLOWER TREND ON TRANSITION OF PRECIP IN EASTERN PIEDMONT TO ALL RAIN. ADDITIONALLY WILL ADJUST TEMPERATURE TRENDS TO KEEP COLDER THROUGH 00Z. FOR FRIDAY WILL KEEP DRIZZLE MENTIONED THROUGH MID MORNING. --RA FRIDAY NIGHT THROUGH SATURDAY NIGHT... AT THIS POINT WILL CONTINUE CURRENT FORECAST TREND. DRY AND COLD. LONG TERM /SUNDAY THROUGH WEDNESDAY/... BROAD UPPER LEVEL TROUGH REMAIN ANCHORED OVER THE AREA THROUGH THE PERIOD TO REINFORCE COLD AIR OVER THE AREA. AT THE SURFACE HIGH PRESSURE BUILDS OVER THE AREA SUNDAY. SUNDAY NIGHT...A BOUNDARY DEVELOPS ALONG THE VIRGINIA/NORTH CAROLINA BORDER AND EXTENDS WEST AND SOUTHWEST TO TENNESSEE...THEN TO A LOW OVER EASTERN TEXAS. THERE IS SOME MOISTURE AND WEAK UPPER SUPPORT ASSOCIATED WITH THIS FEATURE ..HOWEVER WILL LEAVE FORECAST DRY AT THE PRESENT TIME. THIS SYSTEM WILL BE PUSHED TO THE SOUTHEAST LATE MONDAY AND EARLY TUESDAY AS ARCTIC HIGH PRESSURE BUILDS OVER THE AREA...AND REMAINS OVER THE REGION THROUGH WEDNESDAY. THE RESULT OF THIS ARCTIC AIRMASS WILL BE BELOW TO MUCH BELOW NORMAL TEMPERATURES. -RHJ AVIATION /07Z-06Z/... ALTOCUMULUS BEGINNING TO MOVE INTO THE FOOTHILLS AT THIS TIME. CLOUDS WILL LOWER OVERNIGHT AND LIKELY DROP BELOW VFR A COUPLE OF HOURS AFTER SUNRISE AT THE TAF LOCATIONS. CEILINGS BELOW 1000 FEET ONCE PRECIPITATION BEGINS WITH MVFR VISIBILITIES IN GENERAL. CEILINGS BELOW 600 FEET MOST OF THE AFTERNOON AND INTO THE NIGHT. ALL TAF SITES EXPECTING SOME NON-LIQUID PRECIPITATION THURSDAY WITH FAYETTEVILLE HAVING THE LEAST IMPACT AND SHORTEST DURATION...AND GREENSBORO AND WINSTON-SALEM MOST IMPACTED BY WINTER WEATHER. ACCUMULATING SNOW THURSDAY MORNING WILL MIX WITH SLEET AND CHANGE TO FREEZING RAIN IN THE AFTERNOON. LESSER AMOUNTS OF SNOW AND SLEET AS ONE MOVES EAST BUT FREEZING RAIN WILL BE A CONCERN. -RLH/VINCENT && .RAH WATCHES/WARNINGS/ADVISORIES... WINTER WEATHER ADVISORY UNTIL NOON EST TODAY FOR NCZ078-085- 086-088-089. WINTER STORM WARNING UNTIL MIDNIGHT EST TONIGHT FOR NCZ007>010- 021>025-038>040-073-074. WINTER WEATHER ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR NCZ011- 026>028-041>043-075>077-083-084. && $$ SHORT TERM...CBL FXUS62 KRAH 011822 AAA AFDRAH AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE RALEIGH NC 122 PM EST THU FEB 1 2007 .SHORT TERM /REST OF TODAY/... ...DROPPING ADVISORIES AND CUTTING WARNINGS BACK... STRONG SOUTHWEST FLOW OFF THE SURFACE HAS ALLOWED THE SNOW TO END ACROSS ALL OF CENTRAL NC. SURFACE WET BULBS HAVE WARMED TO FREEZING AND ABOVE FROM US1 EAST. WITH TEMPERATURES HOVERING AROUND FREEZING AND GIVEN THE LACK OF A COLD REINFORCING SHOT OF COLD AIR SIGNIFICANT FREEZING RAIN IS NOT EXPECTED. ONLY RAIN IS EXPECTED OVER MOST OF CENTRAL NC FROM US1 EAST WITH SOME LIGHT FREEZING RAIN POSSIBLE FROM DURHAM WEST AND NORTH. A SECOND SURGE OF MOISTURE WILL MOVE IN FROM THE SE OVERNIGHT...HOWEVER...TEMPERATUERS OVERNIGHT WILL REMAIN JUST ABOVE FREEZING ALLOWING THE PRECIP TO FALL AS RAIN. GFS AND NAM THICKNESSES FOR BOTH GSO AND RDU SUPPORT ALL RAIN AND NO FREEZING RAIN BY 06Z. WILL GO WITH AN ADVISORY FOR THE POSSIBILITY OF LIGHT FREEZING RAIN FROM DURHAM WEST ALONG AND NORTH OF HIGHWAY 64. && .AVIATION... A COOL SATURATED AIRMASS IN THE WAKE OF LOW PRESSURE ALONG THE NC COAST WILL MAINTAIN IFR AND LIFR CONDITIONS ACROSS CENTRAL NC THROUGH TONIGHT AND FRI MORNING. WIDESPREAD RAIN...WITH SOME FREEZING RAIN POSSIBLE AT KINT AND KGSO EARLY THIS AFTERNOON...WILL TAPER TO DRIZZLE EARLY THIS EVENING. MORE AREAS OF RAIN WILL LIKELY CROSS CENTRAL NC IN THE PREDAWN HOURS FRI MORNING...ENDING SHORTLY AFTERNOON DAYBREAK. CONDITIONS WILL GRADUALLY IMPROVE TO ABOVE IFR FRI AFTERNOON AS A SURGE OF DRIER AIR PUSHES IN FROM THE WEST. && .RAH WATCHES/WARNINGS/ADVISORIES... WINTER WEATHER ADVISORY UNTIL 6 PM EST THIS AFTERNOON FOR NCZ007-008-021>025-038>040. && $$ FXUS62 KRAH 011917 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 215 PM EST THU FEB 1 2007 .SHORT TERM /TONIGHT THROUGH FRIDAY/... TONIGHT...SATELLITE IMAGERY SHOWS A SERIES OF WAVES EMBEDDED IN THE LONG EXTENSION OF THE 150KT SUBTROPICAL JET...EXTENDING FROM THE MEXICAN PLATEAU INTO THE MID-ATLANTIC REGION. THE FIRST S/W DISTURBANCE IS CURRENTLY MOVING THROUGH THE FORECAST AREA...AS THE HEAVIEST PRECIPITATION SHIFTS TO THE EASTERN CWA. THERE WILL BE A LULL IN PRECIPITATION ACROSS CENTRAL NC THIS AFTERNOON AND EARLY EVENING...UNTIL THE SECOND MORE ROBUST UPPER WAVE(CURRENTLY ROUNDING BASE OF THE LONG WAVE TROUGH OVER TEXAS)APPROACHES THE AREA BETWEEN 06Z TO 12Z. PRECIP WILL FILL BACK INTO THE AREA AS FORCING ALOFT FROM LF EXIT REGION AND POSITIVE VORTICITY ADVECTION SPREADS FROM SW TO NE OVER THE AREA. THE LATEST RUC AND MESONAM SOUNDINGS AND SFC TW SUPPORT ALL RAIN ACROSS THE ADVISORY AREA BY 00Z...WITH FURTHER SUPPORT FROM PARTIAL THICKNESS NOMOGRAM AND CONSENSUS OF THE VARIOUS P-TYPE ALGORITHMS(RAMER...BOURGOUIN...REVISED NCEP). AS A RESULT CONFIDENCE IS HIGH THAT THE THREAT OF FREEZING RAIN WILL BE OVER BY 6PM(IF NOT EARLIER)...AND THUS WILL NOT BE EXTENDED. WILL ADJUST GRIDS TO SHOW RAIN INCREASING LATE IN THE EVENING... AND THEN GRADUALLY TAPERING OFF INTO DRIZZLE AS MID-LEVELS BEGIN TO DRY OUT BY AROUND DAYBREAK. TEMPERATURES OVERNIGHT WILL BE STEADY OR SLIGHTLY RISING WITH ABSENCE OF CAA AND AS THE RAIN FALLS INTO THE 3 TO 5C WARM NOSE. TEMPERATURES OVERNIGHT IN THE LOWER TO MID 30S. FRIDAY...A CHANCE OF RAIN IN THE MORNING...THEN RAIN ENDING WEST TO EAST. CENTRAL NC REMAINS IN WARM SECTOR AND LOW-LEVELS REMAIN SATURATED UNTIL FROPA WHICH OCCURRS AROUND 00Z. HIGHS 45 TO 50. && .LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/... FRIDAY NIGHT THROUGH SUNDAY..DRY SURGE COMMENCES FRIDAY NIGHT WITH CLEARING SKIES. NAM/GFS REMAIN A BIT AT ODDS CONCERNING THE DEEPENING TROF OVER THE SOUTHWESTERN CONUS...WITH THE NAM BEING CLOSER TO CONSENSUS WITH THE UKMET/ECMWF...HAVING A MORE AMPLIFIED UPPER TROF AND DELAYING THE COLD AIR PUSH INTO THE EASTERN CONUS. THE RESULTING MOS MAX TEMPS ARE THUS A BIT IN QUESTION...BUT WILL TOP OUT MAINLY IN THE MID AND UPPER 40S REGARDLESS. THE SURFACE HIGH AND THE UPPER TROF EDGE EAST ON SUNDAY. NAM IS SLOWER WITH THIS PROGRESSION AS IT DRIVES ARTIC AIR DEEPER INTO THE MIDWEST...CONTINUING TO AMPLIFY THE UPPER TROF AND DELAY THE COLDEST AIR. WILL CONTINUE MOSTLY CLEAR SKIES WITH HIGHS STRUGGLING INTO THE 40 TO 45 DEGREE RANGE. THE FLOW ALOFT IS DOMINATED BY A BROAD LARGE SCALE TROUGH OVER THE EASTERN TWO-THIRDS OF THE CONUS WITH A TROUGH AXIS THAT STEEPENS OVER THE APPALACHIANS AROUND TUE NIGHT...THEN FLATTENS AS THE TROUGH LOSES AMPLITUDE BY THU. SURFACE FEATURES SHOW WEAK HIGH PRESSURE DRIFTING ACROSS THE AREA SUN NGT AND MON AHEAD OF A COLD FRONT MON NIGHT THAT USHERS ANOTHER ARCTIC AIRMASS SOUTHEASTWARD OUT OF THE NORTHERN PLAINS. THE OVERNIGHT GFS SHOWS A WEAK LOW FORMATION IN THE LEE OF THE APPALACHIANS WITH THE COLD FRONT LATE MON... SUGGESTING SOME MOISTURE CONVERGENCE IN LOWER TO MID LEVELS. OTHER MODELS DO NOT RESOLVE THIS FEATURE. THE SURFACE LAYER IS EXPECTED TO BE VERY DRY WITH DEW POINTS OF 10-15 DEGREES AND CHANCES OF PRECIPITATION HITTING THE GROUND REMAIN LESS THAN 15 PERCENT IN THE RAH CWA. TEMPERATURES DROP TO BETWEEN 10 AND 20 DEGREES BELOW NORMAL FOLLOWING THE ARCTIC COLD FRONT FOR TUE AND WED MODERATING BUT STILL BELOW NORMAL ON THU. && .AVIATION /18Z-18Z/... A COOL SATURATED AIRMASS IN THE WAKE OF LOW PRESSURE ALONG THE NC COAST WILL MAINTAIN IFR AND LIFR CONDITIONS ACROSS CENTRAL NC THROUGH TONIGHT AND FRI MORNING. WIDESPREAD RAIN...WITH SOME FREEZING RAIN POSSIBLE AT KINT AND KGSO EARLY THIS AFTERNOON...WILL TAPER TO DRIZZLE EARLY THIS EVENING. MORE AREAS OF RAIN WILL LIKELY CROSS CENTRAL NC IN THE PREDAWN HOURS FRI MORNING...ENDING SHORTLY AFTERNOON DAYBREAK. CONDITIONS WILL GRADUALLY IMPROVE TO ABOVE IFR FRI AFTERNOON AS A SURGE OF DRIER AIR PUSHES IN FROM THE WEST. && .RAH WATCHES/WARNINGS/ADVISORIES... WINTER WEATHER ADVISORY UNTIL 6 PM EST THIS AFTERNOON FOR NCZ007-008-021>025-038>040. && $$ SHORT TERM...CBL LONG TERM...RFG/MLM AVIATION...RFG