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FXUS62 KRAH 192023
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
320 PM EST SAT JAN 19 2008

.SYNOPSIS...
LOW PRESSURE OVER THE GULF OF MEXICO WILL SHIFT RAPIDLY NORTHEAST 
OFF OF THE NORTH CAROLINA COAST THIS EVENING...MOVING RAPIDLY AWAY 
INTO THE ATLANTIC OVERNIGHT.  COLD HIGH PRESSURE WILL BUILD IN 
TONIGHT AND PROVIDE FOR CHILLY TEMPERATURES SUNDAY INTO MONDAY.  THE 
HIGH MOVES QUICKLY TO THE EAST TUESDAY AHEAD OF A COLD FRONT...WHICH 
SWEEPS THROUGH THE AREA TUESDAY NIGHT.

&&

.NEAR TERM /UNTIL MIDNIGHT TONIGHT/...

AS OF 200 PM...PRECIPITATION RAPIDLY BRAKING OUT ACROSS THE PIEDMONT 
OF NC. THIS PRECIPITATION IS IN RESPONSE TO MID LEVEL 
FRONTOGENETICAL FORCING AND LIFT IN THE RIGHT REAR OF THE UPPER JET. 
COOLING AT THE LOW LEVELS ALONG WITH COOLING FROM MELTING SNOW ALOFT 
WILL ALLOW PRECIPITATION TO CHANGE OVER TO SNOW THIS AFTN AND EVE. 

SNOW HAS BEEN FALLING IN THE TRIAD AREA FOR AROUND AN HOUR TO 90 
MINUTES AGO. TEMPERATURES HAVE FALLEN DRAMATICALLY SINCE THE PRECIP 
STARTED WITH GSO FALLING 7 DEGREES OR SO IN THE HOUR SINCE THE SNOW 
STARTED. TEMPS SHOULD FALL TO AROUND FREEZING BY AROUND 400 PM 
ACROSS MOST OF THE TRIAD. THE 18Z RAOB FROM GSO WAS DRY IN THE LOWER 
LEVELS BUT BECOMING COLD AND SUFFICIENT FOR SNOW. THE WARM AIR 
TEMPERATURES AND THE SHORT DURATION OF SNOW SHOULD KEEP 
ACCUMULATIONS IN THE TRIAD AREA DOWN...GENERALLY RANGING AROUND AN 
INCH WITH UP TO 2 INCHES IN LOCATIONS EAST OF GSO AND HBI.

GETTING REPORTS OF SNOW MIXING WITH THE RAIN IN WESTERN PARTS OF THE 
NORTHEAST PIEDMONT AND TRIANGLE AREA (SANFORD...CARY AND DURHAM). 
LATEST AMDAR AIRCRAFT SOUNDING AT RDU FROM 1724Z HAD THE FREEZING 
LEVEL AT AROUND 2600 FEET. SHOULD SEE THE CHANGE OVER BEGIN IN THE 
TRIANGLE AREA OCCUR BETWEEN 200 AND 300 PM. LOOKS LIKE THE PRECIP IN 
THE TRIANGLE AREA WILL BE SUFFICIENT TO COOL TEMPS TO THE LOWER 30S 
BY AROUND 500 OR 600 PM. ACCUMULATIONS WILL BE DIFFICULT TO PINPOINT 
BUT THEY SHOULD RANGE BETWEEN 1 TO 2 INCHES ON GRASSY SURFACES WITH 
SOME SPOTS POTENTIALLY GETTING UP TO 3 INCHES MAINLY IN THE SWEET 
SPOT WHERE THE COLD AIR ARRIVES EARLY ENOUGH AND THE QPF WILL BE 
SUFFICIENT. THE SWEET SPOT SHOULD SETUP EAST OF TTA...RDU AND LHZ. 

ACROSS THE COASTAL PLAIN AND SANDHILLS IT WILL STILL BE ANOTHER FEW 
HOURS FOR THE CHANGEOVER TO ARRIVE BUT FOR SNOW LOVERS THE PRECIP 
WILL PERSIST THE LONGEST SO THESE LOCATIONS COULD BE THE BIG WINNERS 
IN THE RAH CWA. WILL NOT MAKE MAJOR CHANGES TO FORECAST IN THIS 
AREA WHILE MONITORING THE LARGE AREA OF LIGHT TO MODERATE PRECIP 
UPSTREAM ACROSS SC. ACCUMULATION TOTALS SHOULD RANGE IN THE 1 TO 2 
INCH RANGE WITH THE HIGHER END OF THOSE AMOUNTS NORTH AND WEST OF 
FAY AND GSB. NOTE THAT SNOW IS STILL FALLING IN ATLANTA WITH VSBYS 
AROUND 1 MILE AFTER HAVING SEVERAL INCHES OF SNOW...A POTENTIALLY 
TROUBLING SIGN FOR OUR SE COUNTIES. 

PRECIP WILL TAPER OFF QUICKLY FROM WEST TO EAST THIS EVENING. SNOW 
SHOULD END IN THE TRIAD BETWEEN 5 AND 7 PM IN THE TRIANGLE BETWEEN 6 
AND 9 PM AND IN THE COASTAL PLAIN TOWARD MIDNIGHT. 

WILL KEEP ADVISORIES AS THEY ARE. SEE LITTLE VALUE IN POTENTIALLY 
ALTERING THEIR STRUCTURE WITH UNCERTAINTY REMAINING IN THE FORECAST. 
ACCUMULATION AMOUNTS WILL 

KEEP IN MIND THAT MOST ACCUMULATION WILL OCCUR ON GRASSY SURFACES... 
CARS... AND ROOFTOPS GIVEN THE ABOVE FREEZING NEAR SURFACE 
TEMPERATURES AND ALREADY WET GROUND. THUS ROADWAYS.. SHOULD MAINLY 
BE WET OR SLUSHY THROUGH SUNSET... WITH A HARD FREEZE OVER WHEN 
TEMPERATURES DROP INTO THE 20S AFTER SUNSET. -BLAES

&&

.SHORT TERM /MIDNIGHT TONIGHT THROUGH TUESDAY NIGHT/...

AS OF 200 PM SATURDAY... LOW LEVEL DOWNSLOPE FLOW BEGINS IN EARNEST 
OVERNIGHT... ALTHOUGH THE ARRIVAL OF THE SURFACE COLD FRONT... NOW 
STRETCHING FROM THE EASTERN GREAT LAKES THROUGH TN... WILL LAG THE 
850 MB FRONT AND SHOULD LEAD TO LINGERING LOW CLOUDS IN THE EAST 
OVERNIGHT. OTHERWISE SKIES SHOULD CLEAR SWIFTLY BY MORNING WITH 
STRONG SUBSIDENCE AND DRYING THROUGH THE COLUMN AS THE MID LEVEL 
SHORTWAVE TROUGH AXIS SWINGS THROUGH. LOWS OF 19-27 TONIGHT ARE A 
SHADE BELOW MOS GUIDANCE NUMBERS IN THE WEST BUT MATCH WELL WITH 
UPSTREAM LOWS LAST NIGHT.

THE POLAR HIGH NOW CENTERED OVER EAST KS IS STILL EXPECTED TO BRING 
FRIGID TEMPERATURES FOR SUNDAY... WITH FORECAST 850 MB TEMPERATURES 
DOWN TO -12 TO -13C AND ANOMALOUSLY LOW 1000-850 MB THICKNESSES IN 
THE 1240S. AS THE SURFACE FRONT WILL HOLD OFF PASSING THROUGH 
CENTRAL NC UNTIL LATE TONIGHT... THE INCREASE IN WINDS WILL 
FORTUNATELY NOT OCCUR UNTIL NEAR OR SHORTLY AFTER DAYBREAK... BUT 
NEVERTHELESS THE WIND CHILL VALUES ARE LIKELY TO DROP WELL DOWN INTO 
THE TEENS THROUGH SUNDAY MORNING AND EARLY AFTERNOON. CLEAR SKIES 
ARE STILL ANTICIPATED WITH FORECAST SOUNDINGS INDICATING A DRY 
COLUMN. LOCAL HIGH TEMPERATURE TECHNIQUE WITH A NEARLY DRY ADIABATIC 
PROFILE FROM 900 MB DOWN INDICATES HIGHS OF 30-37... A SLIGHT 
DOWNWARD BUMP FROM THE PREVIOUS FORECAST. THE 1040 MB HIGH DRIFTS 
OVERHEAD SUNDAY NIGHT AND WILL HAVE LOWS OF 10-18 DEGREES UNDER 
CLEAR SKIES. THIS WILL BE THE COLDEST NIGHT OF THIS WINTER SEASON... 
AND BASED ON UPSTREAM LOWS LAST NIGHT... EVEN A FEW SINGLE DIGIT 
READINGS ARE LIKELY. 

FOR MONDAY THROUGH TUESDAY NIGHT... DRY AND STABLE CONDITIONS 
PERSIST THROUGH MONDAY. THICKNESSES REBOUND SLIGHTLY BUT THE AIR 
MASS CHARACTER AND COLD START TO THE DAY STILL FAVOR MUCH BELOW 
NORMAL HIGHS OF 37-44. THE SURFACE HIGH SHIFTS OFF TO THE ENE MONDAY 
NIGHT INTO TUESDAY... PROPELLED BY A POSITIVELY TILTED MID LEVEL 
TROUGH DROPPING FROM CENTRAL CANADA INTO THE UPPER MIDWEST... AND 
ITS ATTENDANT COLD FRONT ALONG WHICH A SURFACE LOW TRACKS ACROSS THE 
PLAINS INTO THE GREAT LAKES. LOW LEVEL RETURN FLOW AROUND THE 
SURFACE HIGH SHOULD BRING AN INCREASE IN CLOUDS MONDAY NIGHT... 
PRIMARILY IN WESTERN NC WHERE ISENTROPIC UPGLIDE BEGINS EARLY 
TUESDAY AND IN COASTAL SECTIONS ALONG A MODEL-INDICATED INVERTED 
TROUGH. THIS UPGLIDE STRENGTHENS TUESDAY... AND WHILE THE MID LEVEL 
FLOW REMAINS QUITE FLAT WITH MINOR PERTURBATIONS KICKING OUT OF THE 
DESERT SOUTHWEST DISSIPATING BEFORE REACHING NC... THE STRENGTHENING 
UPPER JET TO OUR WEST MAY PROVIDE LARGE SCALE SUPPORT FOR LIFT AND 
ENHANCE THE EFFECTS OF THE ISENTROPIC UPGLIDE. WILL BRING IN CHANCE 
POPS TUESDAY THROUGH TUESDAY NIGHT... UNTIL THE COLD FRONT DROPS 
THROUGH CENTRAL NC IN THE PREDAWN HOURS WEDNESDAY. THE DIFFUSE 
NATURE OF THE FORCING AND THE LACK OF A DISCERNABLE FOCUS SHOULD 
LEAD TO MODEST PRECIP AMOUNTS. FORECAST SOUNDINGS AND MSLP PROGS 
DEPICT AN IN SITU COOL POOL OVER THE NORTHWEST CWA... WHICH MAY 
SUPPORT A LITTLE FREEZING RAIN AT THE ONSET IN THE TRIAD AREA EARLY 
TUESDAY... BUT WHILE SUCH A RESIDUAL COOL STABLE POCKET IS NOT OUT 
OF THE QUESTION GIVEN THE VERY DRY NATURE OF THE EXITING AIR MASS... 
IT IS FAR TO EARLY TO BE ABLE TO PIN THIS DOWN. WILL MENTION LIQUID 
PRECIP ONLY FOR NOW. WILL HAVE LOWS OF 24-29 MONDAY NIGHT... AND 
HIGHS OF 43-50 TUESDAY. -GIH

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...

AS OF 300 PM SATURDAY... PRECIP SHOULD QUICKLY EXIT THE COASTAL 
PLAIN AROUND DAYBREAK WEDNESDAY AS THE COLD FRONT SHOULD BE TRACKING 
OFF THE COAST. HIGH PRESSURE BUILDS IN WEAKLY FROM THE WEST AT THE 
SURFACE AND THE ECMWF INDICATES DOWNSLOPE LOW LEVEL FLOW AT 12Z 
WEDNESDAY FAVORING A MORE RAPID CLEARING TREND THAN THE 12Z OP GFS 
INDICATES... AND WHILE THIS CLEARER SOLUTION IS PREFERRED... THE 
STRENGTHENING 250 MB JET SHOULD BRING A WIDESPREAD SHIELD OF HIGH 
CLOUDS WEDNESDAY WITH OROGRAPHIC ENHANCEMENT POSSIBLE. 1000-850 MB 
THICKNESSES DROP BACK DOWN INTO THE 1290S ALTHOUGH THIS LAYER IS 
CAPTURING A PART OF THE STABLE LAYER ALOFT... AND BASED ON FORECAST 
SOUNDINGS... HIGHS MAY STRUGGLE TO GET PAST THE LOWER 40S IN THE 
PIEDMONT ESPECIALLY IF THE SHROUD OF HIGH CLOUDINESS IS THICK. 

ANOTHER POTENTIAL SYSTEM OF CONCERN ARRIVES THURSDAY AS ANOTHER 
SHORTWAVE TROUGH DROPS THROUGH THE MIDATLANTIC AND NORTHEAST... BUT 
THE ECMWF AND GFS BEGIN TO DIFFER SIGNIFICANTLY. THE ECMWF IS MORE 
AMPLIFIED WITH THIS WAVE AND THUS SUPPRESSES THE SURFACE HIGH 
SOUTHWARD OVER THE CAROLINAS AND SOUTHEAST AND HOLDS A DEVELOPING 
SURFACE LOW WELL DOWN OVER THE GULF... WHEREAS THE GFS IS LESS 
AMPLIFIED WITH A MORE NORTHERLY SURFACE HIGH AND LOW CLOSER TO THE 
GULF COAST... BRINGING MORE PRECIP INTO THE SOUTHEAST STATES. THE 
GFS HAS WAVERED IN THE LAST FEW RUNS AND THE MORE STABLE AND DRIER 
ECMWF IS PREFERRED. CONSIDERABLE CLOUD COVER IS STILL EXPECTED 
HOWEVER AS THE WAVE THAT DROPS THROUGH IS RATHER POTENT BUT SHOULD 
BE OPERATING ON A LOW-PW COLUMN. HIGHS THURSDAY SHOULD REMAIN WELL 
BELOW NORMAL... AROUND 40 TO 46. 

ANOTHER SURFACE HIGH PASSES OVERHEAD THROUGH FRIDAY WITH BRIEF LOW 
AMPLITUDE RIDGING IN THE MID LEVELS... AND CONTINUED COOL CONDITIONS 
ARE EXPECTED. THE GFS/ECMWF BRING IN ANOTHER CHANCE OF PRECIPITATION 
OVER THE WEEKEND AS BROAD TROUGHING KICKS INTO THE PLAINS... HOWEVER 
THEY DO NOT AGREE ON TIMING OR THERMAL STRUCTURE... AND PREFER TO 
KEEP ANY POPS ON THE LOW SIDE WITH BELOW NORMAL TEMPERATURES LIKELY 
TO PERSIST UNDER CONSIDERABLE CLOUD COVER. -GIH

&&

.AVIATION /19Z SATURDAY THROUGH THURSDAY/...

AS OF 1255 PM SATURDAY... PRECIPITATION RAPIDLY BRAKING OUT ACROSS 
THE PIEDMONT OF NC. THIS PRECIPITATION IS IN REPSONSE TO MID LEVEL 
FRONTOGENETICAL FORCING AND LIFT IN THE RIGHT REAR OF THE UPPER JET. 
HAD A FEW REPORTS OF SNOW AND GRAUPEL IN THE TRIAD AREA. 

COLD AND ESPECIALLY DRY AIR IS MAKING ITS WAY INTO THE AREA WITH 
DEWPOINTS DOWN TO NEAR 20 IN THE TRIAD AND LOW 30S ACROSS THE 
SOUTHERN AND NORTHAST PIEDMONT. SFC TEMPS ARE STILL MILD...BUT 
EVAPORATIONAL COOLING SHOULD INITIALLY DROP TEMPS SEVERAL DEGREES 
AND THEN MELTING SHOULD COOL THE REAMINDER OF THE COLUMN TO NEAR 
FREEZING. THIS WILL ALLOW THE ADVERTISED TRANSITION FROM RAIN TO 
SNOW TO OCCUR THIS AFTERNOON. PRECIP SHOULD START OUT AS SNOW IN THE 
TRIAD (INT AND GSO). RAIN AT RDU SHOULD CHANGEOVER BETWEEN 18 AND 
20Z WITH THE CHANGEOVER OCCURING AT RWI AND FAY BETWEEN 20 AND 22Z.

CURRENTLY VFR CONDITIONS ARE REPORTED IN THE PIEDMONT (RDU...GSO AND 
INT) BUT THIS SHOULD BE SHORT LIVED AS PRECIP WILL BRING VSBYS AND 
CIGS DOWN TO MVFR TEMPO IFR FOR MUCH OF THIS AFTERNOON AND EARLY 
EVE. ACROSS THE COASTAL PLAIN LIGHT RAIN HAS REDUCED VSBYS TO 3 TO 4 
MILES AT FAY AND RWI WITH VFR CIGS. AS PRECIP BECOMES STEADIER 
SHOULD SEE BOTH CIGS AND VSBYS DROP TO MVFR AND THEN IFR CONDITIONS 
THIS AFTERNOON. 

ALL OF THE PRECIP SHOULD TAPER OFF CLOSE TO SUNSET IN THE TRIAD... 
AROUND 9PM NEAR RDU AND TOWARD MIDNIGHT IN FAY. RAPID DRYING WILL 
MOVE OVERNIGHT AND SUNDAY SHOULD FEATURE VFR CONDITIONS WITH A NW 
FLOW. 

AS THE HIGH PRESSURE AREA MOVES OFF THE NORTHEAST COAST TUESDAY... A 
MOIST SOUTHWEST FLOW WILL LEAD TO INCREASING MOISTURE AND A LOWERING 
OF CLOUD BASES. MVFR CONDITIONS WITH SCATTERED SHOWERS WILL BE 
POSSIBLE TUESDAY AND TUESDAY NIGHT. HIGH PRESSURE WILL BUILD BACK 
OVER THE AREA WEDNESDAY. -BLAES

&&

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

&&

$$
SYNOPSIS...DJF/MWS
NEAR TERM...BLAES/MWS
SHORT TERM...HARTFIELD
LONG TERM...HARTFIELD
AVIATION...BLAES