AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
1044 PM EST SAT NOV 22 2014

.SYNOPSIS...A WARM FRONT WILL APPROACH THE REGION FROM THE SOUTH 
SUNDAY MORNING...THEN SURGE NORTHWARD THROUGH THE CAROLINAS AND MID-
ATLANTIC LATE SUNDAY INTO SUNDAY NIGHT AS A POWERFUL LOW PRESSURE 
SYSTEM TRACKS NORTHEAST FROM THE LOWER MIDWEST TO THE GREAT LAKES. 
AN ASSOCIATED COLD FRONT WILL SWEEP EASTWARD THROUGH THE CAROLINAS 
MONDAY NIGHT.

&&

.NEAR TERM /OVERNIGHT/... 
AS OF 1030 PM SATURDAY...

OVERVIEW: A POTENT UPPER LEVEL LOW IN CENTRAL TX AT 03Z WILL TRACK 
EAST TO THE TX/LA BORDER BY 12Z SUN. MEANWHILE...SMALL AMPLITUDE 
WAVES IN SW FLOW ALOFT WILL TRACK NORTHEAST FROM THE DEEP SOUTH GULF 
COAST INTO THE CAROLINAS. IN THE LOWER LEVELS...AN H85 WARM FRONT 
OVER GA/FL AT 03Z WILL LIFT NORTH TO THE GA/SC BORDER BY 12Z SUN.

00Z RAOB DATA SHOWED RAPID/PRONOUNCED MOISTENING UNDERWAY IN THE 
CAROLINAS. FOR EXAMPLE...34 DEGREE 925 MB DEWPOINT DEPRESSION ON THE 
12Z/MHX RAOB DECREASED TO 5 DEGREES BY 00Z. SOUTHERLY FLOW /WARM 
ADVECTION/ ALONG THE WESTERN PERIPHERY OF THE DEPARTING LOW-LEVEL 
RIDGE WILL RAPIDLY STRENGTHEN OVERNIGHT AS HEIGHT FALLS COMMENCE 
DOWNSTREAM OF A POTENT UPPER LEVEL LOW TRACKING TOWARD THE LOWER MS 
RIVER VALLEY...AS EVIDENCED BY RADAR ECHOES EXPANDING IN COVERAGE 
OVER GA/SC THIS EVENING. STRENGTHENING WARM ADVECTION IN ADVANCE OF 
THE SFC-H85 WARM FRONT APPROACHING FROM THE SOUTHWEST COMBINED WITH 
DPVA ATTENDANT SMALL AMPLITUDE WAVES IN SW FLOW ALOFT WILL RESULT IN 
A RAPID INCREASE IN CLOUD COVER FROM SW-NE OVERNIGHT...WITH LIGHT 
RAIN LIKELY ALONG PORTIONS OF THE SW PIEDMONT/SANDHILLS NEAR THE SC 
BORDER BY SUNRISE. W/REGARD TO TEMPERATURES...LOWS HAVE ALREADY 
OCCURRED IN MOST LOCATIONS WITH TEMPS STEADYING AND EVENTUALLY 
RISING LATE TONIGHT IN ASSOC/W INCREASING LOW-LEVEL MOISTURE AND 
CLOUD COVER. -VINCENT

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... 
AS OF 410 PM SATURDAY...

A SHORTWAVE TROUGH CURRENTLY OVER SOUTHWEST TX WILL EJECT 
NORTHEASTWARD SUNDAY MORNING...DEAMPLIFYING AS IT LIFTS TOWARD THE 
GREAT LAKES REGION.  WHILE THE SURFACE LOW WILL ALSO LIFT WELL WEST 
OF THE MOUNTAINS...A 50-60KT LLJ WILL BRING PW OF OVER 1.75 INCHES 
WITHIN THE ASSOCIATED WARM CONVEYOR BELT LATE SUNDAY EVENING/NIGHT.  
BASED ON A CONSENSUS OF MODEL ISENTROPIC FIELDS...RAIN WILL BEGIN TO 
SPREAD INTO THE AREA FORM THE SOUTH MID-MORNING... THOUGH PRECIP 
WILL INITIALLY HAVE TO OVERCOME THE RATHER DRY AND ONLY SLOW 
MOISTENING AIRMASS OVER NC.  THE HEAVIER PRECIP ACCOMPANYING THE 
SURFACE/850MB WARM FRONTS WILL BEGIN TO SPREAD INTO THE AREA AFTER 
21Z...AND IT LOOKS AS THOUGH THE 00-06Z TIME FRAME WILL BE THE BEST 
FOR THE HEAVIEST RAIN.

TEMPS... WITH DEWPOINTS IN THE 30S IN THE WESTERN PIEDMONT EARLY 
SUNDAY...EVAPORATIVE COOLING WILL LIKELY LEAD TO AT LEAST A 
WEAK...STABLE WEDGE AIRMASS OVER THE NORTHWEST PIEDMONT.  HIGHS IN 
THE TRIAD MAY STRUGGLE TO GET OUT OF THE UPPER 40S...WHILE TEMPS 
WILL HAVE LITTLE MORE TIME TO WARM INTO THE 50S TO LOWER 60S TO THE 
EAST.  TEMPS ARE THEN EXPECTED TO HOLD STEADY OR CONTINUE RISING 
SLOWLY INTO THE UPPER 50S TO MID 60S OVERNIGHT AS THE WARM FRONT 
SURGES NORTH THROUGH THE AREA.  WHETHER OR NOT THE WEDGE AIRMASS IS 
ERODED IN THE NORTHWEST PIEDMONT...AS MODELS INDICATE...IS 
UNCERTAIN.  BUT FOR MANY AREAS...HIGHS WILL LIKELY OCCUR WELL AFTER 
SUNSET.

SEVERE THREAT... STRONG WARM ADVECTION WILL LEAD TO SOME WEAK 
DESTABILIZATION...ELEVATED TO THE NORTHWEST AND NEAR SURFACE BASED 
IN THE SOUTHEAST.  MODELS HAVE TRENDED A LITTLE FURTHER INLAND WITH 
THE BETTER PUSH OF THE MARITIME AIR...WITH THE NAM SHOWING AS MUCH 
AS 200-600 J/KG MLCAPE AT KFAY AS DEWPOINTS RISE INTO THE MID 60S.  
THIS APPEARS TO BE THE HIGHEST MLCAPE GENERATED BY ANY OPERATIONAL 
NWP...WITH THE GFS/SREF SHOWING 100-300 J/KG...AND NOCTURNAL 
STABILIZATION WILL FURTHER LIMIT CAPE. EFFECTIVE DEEP LAYER SHEAR 
INCREASING TO 50-70KT SHOULD SUPPORT SOME LOW-TOPPED SUPERCELLULAR 
STORMS EMBEDDED WITHIN THE BANDS OF SHOWERS AND STORMS CROSSING SC 
AND SOUTHEASTERN NC.  IN ADDITION...THERE WILL BE A 4-6 HOUR WINDOW 
LATE SUNDAY EVENING WHEN THE WEAK INSTABILITY WILL LINE UP WITH 
STRONG CYCLONICALLY CURVED LOW-LEVEL HODOGRAPHS...AND LOW-END 
TORNADO THREAT MAY EXIST ALONG AND EAST OF I-95.  FURTHER TO THE 
NORTHWEST...ELEVATED INSTABILITY WILL ALSO BE WEAK..BUT DPVA FROM 
THE VORT LOBE ATTENDANT TO THE MAIN SHORTWAVE MAY ALSO BE ENOUGH FOR 
AN ISOLATED STORM EVEN BACK TOWARD THE TRIAD. -BLS

MON AND MON NIGHT: THE AXIS OF A 50 KT LLJ...IN DEEP SW FLOW 
ALOFT...WILL CROSS CENTRAL NC DURING THE DAY MONDAY...IN ADVANCE OF 
THE SURFACE COLD FRONT THAT IS FORECAST TO CROSS THE AREA LATE MON 
AND MON EVENING - A SOLUTION BEST REPRESENTED BY THE SLOWER 12Z 
ECMWF/NAM GUIDANCE. THE PASSAGE OF THE LLJ AND ASSOCIATED MOISTURE 
TRANSPORT...THEN LATER FRONTAL FORCING/LOW LEVEL CONVERGENCE...WILL 
SUPPORT SCATTERED SHOWERS - AND ISOLATED THUNDER IN AN AXIS OF LOWER 
TO MIDDLE 60S SURFACE DEWPOINTS IN THE COASTAL PLAIN - ENDING FROM 
WEST TO EAST DURING THE AFTERNOON AND EVENING HOURS. STRONG AND 
INCREASINGLY UNIDIRECTIONAL DEEP LAYER FLOW...AFTER THE EARLY 
MORNING WARM FRONTAL PASSAGE...WILL SUPPORT A CONDITIONAL RISK OF 
SEVERE WEATHER IN THE COASTAL PLAIN. IN ADDITION...MIXING OF THE 
STRONG LLJ WILL RESULT IN A VERY BREEZY SW WIND...SUSTAINED AROUND 
20 MPH...WITH GUSTS BETWEEN 30 AND 40 MPH PROBABLE PER ~35 KT MIXED 
LAYER WIND FORECASTS. HIGHS GENERALLY IN THE LOWER TO MIDDLE 70S. 

AFTER PERHAPS A LINGERING SHOWER IN THE COASTAL PLAIN DURING THE 
EVENING...COLD AND DRY ADVECTION...AND CLEARING...WILL DEVELOP 
EASTWARD AND RESULT IN LOWS RANGING FROM AROUND 40 WEST TO LOWER 50S 
EAST.  -MWS

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/... 
AS OF 350 PM SATURDAY...

TUE-WED: 1025 MB SURFACE HIGH PRESSURE WILL BUILD SOUTHEAST ACROSS 
THE HIGH PLAINS TUE...THEN EASTWARD INTO THE MIDDLE ATLANTIC STATES 
TUE NIGHT. MEANWHILE...THE APPROACH OF A POSITIVELY-TILTED TROUGH 
ALOFT FROM THE MS VALLEY WILL INDUCE COASTAL CYCLOGENESIS...ALONG AN 
OLD FRONTAL ZONE OFF THE SOUTH EAST...REFERENCED IN THE SHORT TERM 
DISCUSSION ABOVE. THERE REMAINS CONSIDERABLE MODEL SPREAD WITH THE 
DEVELOPMENT AND TRACK OF THIS COASTAL LOW AS IT LIFTS UP THE 
SOUTHEAST AND MIDDLE ATLANTIC COASTS THROUGH MID WEEK...RANGING FROM 
THE WELL OFFSHORE AND TOTALLY DRY-FOR-CENTRAL-NC CANADIAN SOLUTIONS 
OF RECENT DAYS...TO THE CLOUDY AND WET SOLUTIONS DEPICTED BY THE 
PAST FEW ECMWF AND GFS RUNS. GIVEN THE POSITIVE TILT AND ONLY SLOW 
EASTWARD PROGRESSION OF THE TROUGH ALOFT...THE MORE WESTWARD (AND 
WET) SOLUTIONS OF THE OFFSHORE FRONT AND INCIPIENT COASTAL LOW ARE 
FAVORED...WITH A LOW TRACK MOST PROBABLE ALONG THE WESTERN WALL OF 
THE GULF STREAM. 

THE RESULT WOULD BE RAIN DEVELOPING FROM THE SOUTH LATE TUE AND 
ESPECIALLY TUE NIGHT...WITH A COLD RAIN LIKELY AND  TEMPERATURES IN 
THE UPPER 30S TO MIDDLE 40S...ON WED. THOUGH THE AFOREMENTIONED 
PARENT POLAR HIGH IS FORECAST TO BE RELATIVELY WEAK (AROUND 1025 MB) 
AND POSITIONED FARTHER SOUTH (OVER THE MIDDLE ATLANTIC STATES) THAN 
IS TYPICAL FOR SNOW IN CENTRAL NC...THE TRACK OF THE COASTAL LOW AND 
RESULTANT PARTIAL THICKNESSES ON THE WEST/NW SIDE SUGGEST AT LEAST A 
THREAT OF A LITTLE WEST SNOW MIXING IN WITH THE RAIN OVER THE 
PIEDMONT. GIVEN THE MARGINALLY COLD THERMODYNAMIC PROFILES...AND 
FREEZING LEVELS AROUND 1000 FT OVER THE PIEDMONT PER GFS BUFR 
FORECAST SOUNDINGS...ANY SUCH SNOW WOULD LIKELY BE DRIVEN BY 
PRECIPITATION RATES...AND THE EXCEPTION RATHER THAN THE RULE.  

WED NIGHT-SAT: MEDIUM RANGE GUIDANCE HAS COME INTO SOMEWHAT BETTER 
AGREEMENT (THAN RECENT DAYS) REGARDING THE DEVELOPMENT OF A BROAD 
TROUGH ALOFT FROM NORTH-CENTRAL CANADA TO THE MIDDLE ATLANTIC COAST 
LATE WEEK INTO NEXT WEEKEND. SUCH A PATTERN WOULD FAVOR THE RE-
ESTABLISHMENT OF ARCTIC HIGH PRESSURE ACROSS THE NORTHERN HALF OF 
THE CONUS EAST OF THE ROCKIES (JUST TO THE NORTH OF NC)...AND 
MILDER/MORE MODIFIED HIGH PRESSURE OVER THE SOUTHEAST STATES. THIS 
PATTERN OF NW TO WNW FLOW ALOFT WOULD RESULT IN DRY AND COOL 
CONDITIONS OVER CENTRAL NC.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/... 
AS OF 700 PM SATURDAY...

VFR CONDITIONS ARE EXPECTED TO CONTINUE ACROSS MOST OF THE AREA 
THROUGH THE OVERNIGHT HOURS AS HIGH PRESSURE REMAINS JUST OFFSHORE. 
HOWEVER...RETURN FLOW ON THE BACK SIDE OF THE DEPARTING HIGH 
(ESPECIALLY ACROSS THE WESTERN PORTIONS OF NC) MAY BRING SOME 
STRATUS ACROSS THE TRIAD LATE TONIGHT...BUT CONFIDENCE IN THIS 
OCCURRENCE IS NOT VERY HIGH. ANY SUB VFR CONDITIONS THAT MAY DEVELOP 
WILL IMPROVE BY MID-MORNING. HOWEVER...THESE VFR CONDITIONS WILL BE 
SHORT LIVED AS AVIATION CONDITIONS DETERIORATE FROM THE SOUTH/WEST 
TO NORTH/EAST AS A LOW PRESSURE SYSTEM APPROACHES FROM THE 
SOUTHWEST. CIGS/VSBYS WILL GRADUALLY FALL INTO THE IFR RANGE THROUGH 
THE AFTERNOON HOURS...AS PRECIP OVERSPREADS THE AREA FROM SOUTH TO 
NORTH.

OUTLOOK...ADVERSE AVIATION CONDITIONS WILL CONTINUE INTO SUNDAY 
NIGHT AS RAIN...HEAVY AT TIMES...IMPACTS THE AREA. A STRONG 50-60KT 
LOW LEVEL JET MAY CAUSE SOME LOW-LEVEL WIND SHEAR...ESPECIALLY AT 
KGSO/KINT...WHILE SOME 30-40KT WIND GUSTS MAY BE POSSIBLE OVER 
EASTERN NC WHERE THUNDERSTORMS DEVELOP. CONDITIONS WILL IMPROVE SOME 
ON MONDAY AS DRIER AIR ALOFT MOVES IN FROM THE WEST...THOUGH LOW 
CEILINGS MAY LINGER AT EASTERN TERMINALS. THERE MAY ALSO BE SOME 
GUSTY SOUTHWESTERLY WINDS (GUSTS UP TO 35-40 MPH) MONDAY AFTERNOON 
AHEAD OF A COLD FRONT. BEYOND MONDAY..ANOTHER SYSTEM WILL IMPACT THE 
REGION BY MIDWEEK...THOUGH THERE IS SOME UNCERTAINTY AS TO HOW MUCH 
OF THE AREA WILL BE IMPACTED BY PRECIPITATION AND ADVERSE AVIATION 
CONDITIONS AS A SURFACE LOW MOVES ALONG THE EAST COAST.

&&

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

&&

$$

SYNOPSIS...VINCENT 
NEAR TERM...VINCENT 
SHORT TERM...BLS/MWS 
LONG TERM...MWS 
AVIATION...KRD/BLS


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