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FXUS62 KRAH 182043
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
345 PM EST FRI JAN 18 2008

.SYNOPSIS...
WEAK HIGH PRESSURE WILL EXTEND INTO CENTRAL NC FROM THE CENTRAL
APPALACHIANS TONIGHT. LOW PRESSURE WILL DEVELOP OVER THE GULF OF
MEXICO TONIGHT AND MOVE NORTHEAST ALONG THE GEORGIA AND SOUTH
CAROLINA COAST SATURDAY. WIDESPREAD RAIN AND SNOW IS EXPECTED
ACROSS THE AREA SATURDAY. ARCTIC HIGH PRESSURE WILL EXPAND INTO
THE REGION FROM THE WEST BY SUNDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 200 PM FRI...
FOLLOWING A WEAK TROUGH ACROSS THE AREA THIS EVENING...WEAK HIGH 
PRESSURE BUILDS ACROSS THE CENTRAL APPALACHIANS TO THE MID ATLC 
COAST OVERNIGHT.  LIGHT SW WIND CALMS THIS EVENING THEN BECOMES 
LIGHT NE TOWARD DAYBREAK.  WITH THE LAST OF THE LOW STRATUS CLOUD 
COVER ERODING ACROSS THE SRN TIER THIS AFTERNOON...SKIES WILL BE 
MOSTLY CLEAR THIS EVENING EXCEPT FOR CIRRUS STREAKING NE FROM A 
DISTURBANCE IN THE GULF AND STRONG JET LEVEL WINDS ALOFT.  SKIES 
BECOME INCREASINGLY CLOUDY AFTER MIDNIGHT...WITH MODELS SHOWING DEEP 
SATURATION JUST PRIOR TO DAYBREAK SAT.  CHANCES OF RAIN APPEAR 
NEGLIGIBLE UNTIL INCREASING SLIGHT CHANCE OVER THE SOUTHERN HALF 
TOWARD DAYBREAK.  LOW TEMPERATURES IN THE LOWER TO MID 30S FOLLOW 
CONSENSUS GUIDANCE.  -RFG

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY/...

AS OF 300 PM THIS EVENING...
STRONGLY DYNAMIC SYSTEM CONTINUES TO DIG INTO THE WESTERN GULF OF 
MEXICO ...IMPRESSIVE WATER VAPOR LOOP... WITH DEEP SOUTHWEST FLOW 
DEVELOPING ACROSS THE SOUTHEASTERN CONUS. PRECIP WILL SPREAD VERY 
RAPIDLY UP THE ATLANTIC COAST OVERNIGHT AS THE GULF SYSTEM INTERACTS 
WITH A NORTHERN STREAM TROF...INDUCING CYCLOGENESIS. THE ENSUING LOW 
WILL MOVE UP THE COAST...PASSING OFF THE NC COAST TOMORROW 
AFTERNOON.

EXPECT TO SEE RAIN INTO THE SOUTHERN TIER OF THE CWFA BY SUNRISE... 
SPREADING ALL THE WAY TO THE VA BORDER BY LATE MORNING. INITIALLY... 
THERMAL PROFILES WILL SUPPORT SNOW...PERHAPS MIXED WITH SOME 
RAIN...IN THE FAR NORTHWEST (TRIAD AREA)... AND RAIN ELSEWHERE.

COLD AIR WILL BE EDGING IN FROM THE NORTHWEST AS THE DAY 
PROGRESSES...AIDED BY EVAP COOLING. WILL SEE A CHANGEOVER FROM RAIN 
TO A MIX OF RAIN AND SNOW ...THEN FINALLY TO ALL SNOW...EASTWARD IN 
THE AFTERNOON OVER THE PIEDMONT. ALONG INTERSTATE 95 AND 
EASTWARD...CHANGEOVER WILL BE IN THE MID TO LATE AFTERNOON.

PRECIPITATION AXIS LOOKS TO LIE GENERALLY ALONG AND EAST OF 
INTERSTATE 95...BUT THIS IS SUBJECT TO ERRORS IN THE TRACK AND 
STRENGTH OF THE LOW...WHICH HAS YET TO GEN UP. STRONG DYNAMICS AND 
UPPER DIFFLUENCE IN THE ENTRANCE OF A 170KT JET WOULD POINT TOWARDS 
ERRORS BEING ON THE LOW SIDE...WITH STRONGER CYCLOGENESIS AND MORE 
PRECIPITATION. AT THIS TIME...EXPECT 1 TO 3 INCHES IN THE NORTHWEST 
WHICH WILL HAVE PREDOMINANT SNOW...BUT LESSER AMOUNTS DUE TO 
DISTANCE FROM THE STORM. SNOW ACROSS THE REMAINDER OF THE PIEDMONT 
WILL RANGE FROM 2 TO 4 INCHES IN THE TRIANGLE AREA...WHERE THE SNOW 
WILL TAPER OFF AFTER MIDNIGHT. THREE TO FIVE INCHES ARE FORECAST 
FOR THE NORTHERN COASTAL PLAIN...ROCKY MOUNT...TARBORO...ROANOKE 
RAPIDS AREAS...WHERE SNOW WILL LINGER THROUGHOUT THE NIGHT...ALBEIT 
LIGHTER TOWARDS MORNING. 

THE CENTRAL AND SOUTHERN COASTAL PLAIN ARE MORE PROBLEMATIC...AS 
THEY WILL BE INITIALLY WARMER AND THE RAIN CHANGEOVER TO SNOW WILL 
OCCUR LATER IN THE DAY. AT THIS TIME WILL ISSUE A WINTER STORM WATCH 
FROM 4 PM THROUGH TOMORROW NIGHT...THERE IS UNCERTAINTY AS TO 
EXACTLY WHEN THE CHANGEOVER WILL OCCUR AND HOW MUCH PRECIPITATION 
CAN BE EXPECTED AFTERWARD.

WILL ISSUE A WINTER STORM WARNING FOR SNOWFALL OF 3 TO 5 INCHES FROM 
ALAMANCE COUNTY AND AREAS  EAST...ACROSS THE NORTHERN 
TIER...INCLUDING THE CENTRAL AND NORTHERN PIEDMONT AND NORTHERN 
COASTAL PLAIN COUNTIES. 

ELSEWHERE ACROSS THE FORECAST AREA...A WINTER STORM ADVISORY WILL BE 
ISSUED FOR SNOWFALL ACCUMULATIONS OF 1 TO 3 INCHES...BEGINNING AS 
EARLY AS THE MORNING HOURS IN THE TRIAD...AND AS LATE AS THE EVENING 
HOURS IN THE SOUTHERN COASTAL PLAIN AND SANDHILLS. SEE RDUWSWRAH FOR 
FULL DETAILS. 

SLOWER TIMING OF THE NAM WITH NEGATIVELY TILTING VORTMAX SWINGING 
ACROSS THE AREA COMBINED WITH STRONG COLD HORIZONTAL AND VERTICAL 
THERMAL ADVECTION...RESULTS IN RE-GENERATION OF MOISTURE IN 
DENDRITIC GROWTH ZONE...BELOW 700 MB. ADDITIONALLY THE NAM SHOWS 
STRONG MID FRONTOGENETIC FORCING...WITH THE POTENTIAL FOR SLANTWISE 
CONVECTIVE BURSTS OF SNOW OR FLURRIES AS SYSTEM EXITS THE AREA. THUS 
WILL WILL INTRODUCE A SLIGHT CHANCE OF SNOW OR FLURRIES SUNDAY 
MORNING ACROSS THE NORTHERN COASTAL PLAIN THROUGH 15Z. 

HIGH TEMPERATURES SUNDAY WILL GREATLY DEPEND ON PENDING SNOW 
COVER...AS FULL SUN THICKNESSES WOULD SUPPORT HIGHS IN THE LOWER 30S 
NORTH TO MID 30S SOUTH.   

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
AS OF 300 PM THURSDAY...
SUNDAY NIGHT...LOOK FOR COLDEST NIGHT DURING THIS ARCTIC OUTBREAK TO 
OCCUR SUNDAY NIGHT/MONDAY MORNING...WITH MODEL CONSENSUS INDICATING 
OPTIMAL RADIATIONAL CONDITIONS AS THE STRONG 1039 TO 1042 MB SURFACE 
HIGH BUILDS DIRECTLY OVER THE AREA......BEFORE PUSHING OFFSHORE 
DURING THE DAY ON MONDAY. MINS SUNDAY NIGHT WILL PLUNGE EASILY INTO 
THE LOWER TO MID TEENS...OR EVEN COLDER...WITH THE POTENTIAL FOR  
RESIDUAL SNOW COVER. OBVIOUSLY...BLACK ICE WILL ONCE AGAIN POSE A 
MAJOR THREAT ACROSS ALL OF CENTRAL NC AS ANY SNOW MELT OR RESIDUAL 
MOISTURE ON ROADS WILL FORM A THIN GLAZE OF ICE. WILL HIGHLIGHT THE 
THREAT IN THE HAZARDOUS WEATHER OUTLOOK. 

THEN THE MODERATION OF THE FRIGID CONDITIONS BEGIN DURING THE DAY ON 
MONDAY AS SWLY LOW-LEVEL WAA DEVELOPS IN RESPONSE TO HIGH PRESSURE  
MOVING OFFSHORE AND RISING HEIGHTS ALOFT. HIGHS IN THE UPPER 30S 
NW TO MID 40S SE.   

TUESDAY THROUGH FRIDAY...LOW PREDICTABILITY INVOLVING SHORTWAVE WAVE 
IMPULSES IN A PROGRESSIVE ZONAL FLOW RESULTS IN LOW CONFIDENCE 
FORECAST OF RAIN CHANCES AND MOISTURE AVAILABILITY THROUGH THE 
PERIOD. WILL KEEP SLIGHT CHANCE POPS IN FOR TUESDAY THROUGH 
WEDNESDAY WITH NORTHERN STREAM CLIPPER PASSES THROUGH THE GREAT 
LAKES. BEST CHANCE FOR RAIN LOOKS TO BE TOWARDS THE END OF THE WEEK 
WITH APPROACHING SOUTHERN STREAM INVERTED SURFACE TROUGH.  

&&

.AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
AS OF 1245 PM FRIDAY...LOW STRATUS CLOUD DECK IS ERODING FROM THE 
NE ACROSS CENTRAL NC WITH KINT AND KFAY LIKELY TO BE LAST TO IMPROVE 
TO VFR 19Z-20Z.  VFR CONDITIONS ARE EXPECTED LATER THIS AFTERNOON 
THROUGH EARLY TONIGHT.  OVERNIGHT...A WEAK PRESSURE PATTERN AND 
NEARLY CALM WIND WILL FAVOR AREAS OF LIGHT FOG.  INCREASING HIGHER 
CLOUDINESS SHOULD LIMIT STRONG RADIATIONAL COOLING AND LIMIT FOG 
DENSITY TO MVFR VSBY...MAINLY AFTER MIDNIGHT.

TOWARD DAYBREAK SAT...DEVELOPING STRONG LOW PRESSURE OVER THE GULF 
OF MEXICO IS EXPECTED TO TRACK NORTHEAST.  THE AIR SHOULD BECOME 
DEEPLY SATURATED TO THE NORTH OF THE LOW INTO CENTRAL NC AROUND 
DAYBREAK AND STRONG UPPER LEVEL DYNAMICS ARE EXPECTED TO GENERATE 
LARGE SCALE LIFT TO PRODUCE PCPN OVER THE AREA. MODELS DEPICT A 
THERMAL STRUCTURE THAT FAVORS PCPN STARTING AS A RAIN-SNOW MIX NW 
AND RAIN SE SHORTLY AFTER DAYBREAK...AND GRADUALLY TURN TO MORE SNOW 
DURING THE COURSE OF THE EVENT SATURDAY.  VFR AND MVFR CONDITIONS 
EARLY SHOULD DETERIORATE TO IFR AND LIFR SAT MORNING AND CONTINUE 
INTO SAT EVENING.

HIGH PRESSURE WITH AN ARCTIC AIRMASS WILL ARRIVE LATE SAT NIGHT TO 
IMPROVE CONDITIONS TO VFR BY DAYBREAK SUN. VERY COLD AIR IS EXPECTED 
FOR LATE SAT NIGHT-MON NIGHT.  OTHERWISE THE DRY AIRMASS SHOULD 
MAINTAIN VFR CONDITIONS.  

FOR TUE...MOIST SWLY FLOW AND INCREASING MOISTURE MAY LEAD TO 
LOWERING STRATOCUMULUS CLOUD BASES AND POSSIBLE MVFR CONDITIONS WITH 
SCATTERED SHOWERS. 

ANOTHER AREA OF HIGH PRESSURE SHOULD PRODUCE MAINLY VFR WEATHER TUE 
NIGHT AND WED.  -RFG

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY FROM 4 PM SATURDAY TO 6 AM EST SUNDAY FOR 
NCZ077-078-085-086-088-089.
WINTER WEATHER ADVISORY FROM 12 PM SATURDAY TO MIDNIGHT EST 
SATURDAY NIGHT FOR NCZ073>075-083-084.
WINTER STORM WARNING FROM 12 PM SATURDAY TO MIDNIGHT EST 
SATURDAY NIGHT FOR NCZ007>010-023>026-040-041-076.
WINTER WEATHER ADVISORY FROM 6 AM TO 9 PM EST SATURDAY FOR 
NCZ021-022-038-039.
WINTER STORM WARNING FROM 4 PM SATURDAY TO 6 AM EST SUNDAY FOR 
NCZ011-027-028-042-043.

&&

$$
SYNOPSIS...RFG
NEAR TERM...RFG
SHORT TERM...MLM
LONG TERM...CBL
AVIATION...RFG