-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 092003
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
300 PM EST MON DEC 9 2013

.SYNOPSIS... A SLOW-MOVING FRONTAL SYSTEM WEST OF THE APPALACHIANS
WILL DRIFT ACROSS OUR REGION TONIGHT AND TUESDAY. CHILLY HIGH
PRESSURE WILL BUILD INTO OUR REGION TUESDAY NIGHT AND WEDNESDAY.

&&

.NEAR TERM /THROUGH TUESDAY/...
AS OF 250 PM MONDAY...

CENTRAL NC REMAINS WELL ENTRENCHED WITHIN THE RESIDUAL COLD AIR
DAMMING AIRMASS TODAY...WITH THE WEDGE FRONT STILL WELL TO OUR SOUTH
NEAR THE SAVANNAH RIVER VALLEY.  WHILE THE DEPTH OF THE RESIDUAL
COLD POOL IS DECREASING...PER 12Z KGSO RAOB AND AIRCRAFT
SOUNDINGS...THERE IS STILL A 30-40KT FLOW AT 850MB AND ENOUGH WARM
ADVECTION TO KEEP STATIC STABILITY STRONG AND THE CAD LOCKED IN.
TEMPS HAVE RISEN VERY SLOWLY TODAY AND STILL RANGE FROM THE UPPER
30S TO NEAR 50.  WINDS JUST ABOVE THE SURFACE ARE FORECAST TO WEAKEN
A LITTLE THIS EVENING BEFORE A SHORTWAVE AND SURFACE LOW IMPACT THE
AREA LATER TONIGHT AND TUESDAY. AS SUCH... THE CURRENT BAND OF
PRECIP OVER THE WESTERN PIEDMONT SHOULD WEAKEN A BIT THIS
EVENING...AND IF IT DOES SO...FOG MAY REDEVELOP AFTER SUNSET.  A FEW
SITES ARE CURRENTLY REPORTING 1/2SM AND 1/4SM AROUND THE SOUTHERN
PIEDMONT...AND WE PLAN TO ISSUE AN SPS FOR THE EARLY EVENING HOURS.

TONIGHT...
A SHORTWAVE OVER THE SOUTHERN PLAINS WILL SHEAR OUT AS IT
LIFTS TOWARD THE OHIO VALLEY TONIGHT...BUT WILL RE-ENERGIZE THE
SOUTHWESTERLY FLOW LEVEL FLOW OVER THE SOUTHEAST US AND CAUSE A WEAK
AREA OF LOW PRESSURE TO DEVELOP AND ADVANCE ALONG THE SLOWLY
RETREATING WEDGE FRONT.  MEANWHILE... THE PRIMARY COLD FRONT WEST OF
THE MOUNTAINS TODAY WILL BEGIN TO CROSS THE MOUNTAINS AND BEND SOUTH
INTO THE NC FROM THE NORTH-NORTHWEST LATE TONIGHT. WHILE THE
STRONGEST FORCING FROM MID-LEVEL FGEN AND UPPER DIVERGENCE
ASSOCIATED WITH THE RIGHT ENTRANCE REGION OF THE MAIN UPPER JET WILL
PASS TO OUR NORTHWEST ACROSS THE CENTRAL APPALACHIANS...A 50KT LOW
LEVEL JET... ISENTROPIC LIFT... LOW-LEVEL FRONTOGENESIS ASSOCIATED
WITH THE COLD FRONT SHOULD BE SUFFICIENT TO PRODUCE RAIN AREAWIDE.
DETERMINISTIC MODEL QPF AMOUNTS RANGE FROM 0.25" TO 0.50" AND THE
SREF MEAN IS AROUND 0.50".  MODELS SHOW SOME WEAK INSTABILITY OVER
EASTERN NC WITH THE PASSAGE OF THE SURFACE LOW LATE TONIGHT...BUT
ITS UNCLEAR WHETHER OR NOT ISENTROPIC LIFT AND LOW-LEVEL THETA
ADVECTION WILL BE ENOUGH TO OVERCOME THE LOW-LEVEL STABILITY NORTH
OF THE WEDGE FRONT FOR ANY THUNDER.  AFTER A LULL THIS
EVENING...WILL SHOW POPS RAMPING UP TO CATEGORICAL AGAIN AFTER
MIDNIGHT AND CONTINUING INTO TUESDAY...HIGHEST IN THE WEST.  TEMPS
WILL HOLD RELATIVELY STEADY IN THE UPPER 30S AND 40S
TONIGHT...POSSIBLY RISING SLIGHTLY IN THE SOUTH WITH THE APPROACH OF
THE SURFACE LOW.

TUESDAY... THE PASSAGE OF THE AFOREMENTIONED SHORTWAVE TO OUR NORTH
WILL SWEEP THE SURFACE COLD FRONT ACROSS THE AREA...WITH PRECIP
COMING TO AN END BETWEEN 18Z AND 00Z WITH THE ARRIVAL A DRIER AND
GUSTY NORTHWESTERLY WIND.  THICKNESSES BEGIN TO CRASH AFTER
18Z...BUT FORECAST SOUNDINGS ARE DRY ABOVE 0C AND PRECIP SHOULD END
AS JUST RAIN.  HIGHS 43 TO 60 NORTHWEST TO SOUTHEAST.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/...
-- Changed Discussion --
AS OF 250 PM MONDAY...

FOR TUESDAY NIGHT: BOTH THE MID LEVEL TROUGH AXIS AND THE RIGHT REAR
QUAD OF THE UPPER JET WILL BE MOVING QUICKLY OFF THE NORTHEAST COAST
EARLY TUE EVENING... AS THE SURFACE FRONT PUSHES OFFSHORE. SURFACE
HIGH PRESSURE NOW CENTERED JUST EAST OF THE CENTRAL ROCKIES WILL
BEGIN TO BUILD IN FROM THE WEST... WITH THICKNESSES CONTINUING TO
DROP... DOWN INTO THE 1290S BY DAYBREAK. DRY AIR PUNCHING IN ALOFT
ON FLAT WESTERLY MID LEVEL FLOW ALONG WITH DIFFLUENT AND DOWNSLOPE
WNW FLOW 850 MB SHOULD YIELD RAPID CLEARING WITH A VERY STABLE AND
DRY COLUMN. THE COMBINATION OF COLD AIR ADVECTION... TYPICAL
NOCTURNAL COOLING FACILITATED BY CLEAR SKIES...AND DIMINISHING
SURFACE WINDS WILL MAKE FOR A CHILLY OVERNIGHT. PREFER LOWS ON THE
LOW END OF STATISTICAL GUIDANCE... 24-31.

FOR WEDNESDAY THROUGH THURSDAY NIGHT: COOL AND FAIRLY QUIET. THE
SURFACE HIGH WEAKENS A BIT AS IT DRIFTS OVERHEAD WED... THEN A
SECONDARY MID LEVEL TROUGH AND REINFORCING SURFACE COLD FRONT
APPROACH FROM THE WNW AND MOVE QUICKLY THROUGH CENTRAL NC BETWEEN
03Z AND 09Z WED NIGHT. THE COLUMN WILL REMAIN DRY AND FAIRLY
STABLE... SO EXPECT NO PRECIP WITH THIS FRONTAL PASSAGE... ALTHOUGH
THE VERTICAL WIND AND THERMAL STRUCTURE COMBINED WITH A POCKET OF
SOMEWHAT MOIST AIR AROUND 500 MB MAY LEAD TO DEVELOPMENT OF
OROGRAPHICALLY ENHANCED HIGH CLOUDS OVERNIGHT INTO EARLY THU
MORNING. OTHERWISE... EXPECT GENERALLY CLEAR SKIES AND BELOW-NORMAL
TEMPS. LOW LEVEL THICKNESSES START OUT ROUGHLY 25 M BELOW NORMAL
WED... THEN IN THE WAKE OF THE REINFORCING FRONT WED NIGHT...
THICKNESSES DROP FURTHER TO AROUND 35-40 M BELOW NORMAL. EXPECT
HIGHS 45-50 WED AND 39-46 THU. LOWS 24-31 WED NIGHT AND LOW-MID 20S
THU NIGHT AS AN ARCTIC-SOURCE HIGH BUILDS OVERHEAD. -GIH
-- End Changed Discussion --

&&

.LONG TERM /FRIDAY THROUGH SUNDAY/...
-- Changed Discussion --
AS OF 330 AM MONDAY...

FRIDAY...RELATIVELY TRANQUIL WEATHER PERIOD ANTICIPATED FROM MID
WEEK TO THE END OF THE WEEK AS BROAD UPPER TROUGH COVERS THE EASTERN
TWO-THIRDS OF THE NATION. THE NORTHERN BRANCH WILL BE DOMINATE IN
THE BEGINNING...KEEPING THE STORM TRACK MAINLY ACROSS THE NORTHERN
PLAINS-GREAT LAKES AND NEW ENGLAND. THE SURFACE HIGH THAT COVERS OUR
REGION WEDNESDAY WILL QUICKLY SCOOT EWD BY LATE WEDNESDAY BUT IS
REPLACED BY ANOTHER CHILLY HIGH THAT BUILDS INTO THE MID ATLANTIC IN
THE WAKE OF A MID LEVEL S/W CROSSES THE GREAT LAKES INTO NEW
ENGLAND.  THUS OUR CURRENT STRETCH OF BE LOW NORMAL TEMPS WILL
CONTINUE. HIGH TEMPS WED AND THU WILL BE IN THE 40S WHILE MIN TEMPS
WILL BE IN THE 20S TO AROUND 30.

SATURDAY INTO SUNDAY...OPERATIONAL GFS AND ECMWF OFFER A SIMILAR
SOLUTION FOR THE UPCOMING WEEKEND WEATHER PATTERN...IN SHARP
CONTRAST TOT E 12Z MODEL RUNS WHICH DEPICTED A SOLUTION VERY SIMILAR
TO OUR CURRENT WEATHER PATTERN. MODEL GUIDANCE NOW ADVERTISING A
RETURN FLOW REGIME BECOMING ESTABLISHED FRIDAY NIGHT INTO
SATURDAY...AHEAD OF A FRONTAL SYSTEM DOMINATED BY A S/W IN THE
NORTHERN STREAM. THIS FRONTAL SYSTEM CROSSES OUR REGION SATURDAY
NIGHT WITH CHILLY HIGH PRESSURE BUILDING INTO OUR REGION SUNDAY. FOR
NOW WILL CONFINE THE BEST CHANCE FOR PRECIP TO SATURDAY AND KEEP IT
ALL LIQUID. IF PRECIP COMES INTO THE REGION EARLY ENOUGH FRIDAY
NIGHT...MAY START OUT AS A WINTRY MIX BEFORE QUICKLY TRANSITIONING
TO ALL RAIN. TEMPS EXPECTED TO REMAIN BELOW NORMAL AND HIGHLY
DEPENDENT UPON PRECIP COVERAGE. HIGHS IN THE 40S TO AROUND 50. LOWS
TEMPS IN THE 30S FRIDAY NIGHT AND 30S TO AROUND 40 SATURDAY NIGHT.
-- End Changed Discussion --

&&

.AVIATION /18Z MONDAY THROUGH FRIDAY/...
AS OF 1250 PM MONDAY...

WITH A PERSISTENT MOIST SOUTHWESTERLY FLOW IN PLACE...LOW CLOUDS
CONTINUE TO CAUSE LIFR CONDITIONS THIS AFTERNOON WITH POCKETS OF
RAIN...DRIZZLE AND LOW VSBYS.  THERE IS HIGH CONFIDENCE THAT AT
LEAST IFR CONDITIONS WILL CONTINUE...AND IT IS VERY POSSIBLE THAT
LIFR CONDITIONS MAY PERSIST THROUGH THE NIGHT.  A COLD FRONT WILL
SLIP INTO NC FROM THE NORTH-NORTHWESTER LATE TONIGHT...WITH WINDS
TURNING TO NORTHERLY BEHIND THE FRONT.  MEANWHILE...A 40-50KT LOW
LEVEL JET WILL SURGE BACK ACROSS THE AREA..CAUSING PRECIP TO
CONTINUE BEHIND THE FRONT.  IMPROVEMENT IN CEILINGS AND VSBYS WONT
BEGIN UNTIL AFTER AROUND 18Z TUESDAY OR THEREAFTER.  LOW LEVEL WIND
SHEAR SHOULD DIMINISH THIS EVENING AS WINDS ABOVE THE SURFACE
RELAX...BUT WILL REDEVELOP TONIGHT WITH THE ARRIVAL OF THE LOW-LEVEL
JET ATOP WEAK SURFACE WINDS.

LOOKING AHEAD: VFR CONDITIONS WILL RETURN TUE NIGHT AS DRY HIGH
PRESSURE BUILDS INTO THE REGION FROM THE WEST. VFR/DRY CONDITIONS
ARE EXPECTED TO PREVAIL THROUGH THE REMAINDER OF THE WORK WEEK.

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

SYNOPSIS...SMITH
NEAR TERM...SMITH
SHORT TERM...HARTFIELD
LONG TERM...WSS
AVIATION...SMITH