Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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905
FXUS62 KRAH 020832
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
432 AM EDT MON MAY 2 2016

.SYNOPSIS...
WARM SOUTHWEST FLOW WILL PREVAIL AHEAD OF A SLOW-MOVING COLD
FRONT...AND ASSOCIATED WAVES OF LOW PRESSURE...THAT WILL APPROACH
FROM THE NORTHWEST AND CROSS THE MIDDLE ATLANTIC STATES LATE TUE
THROUGH EARLY WED.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 425 AM MONDAY...

LOW PRESSURE NOW OVER THE OH VALLEY WILL MIGRATE SLOWLY EAST INTO
THE NORTHERN MIDDLE ATLANTIC STATES...WHERE IT WILL MERGE WITH AN
APPALACHIAN LEE TROUGH THAT WILL EXTEND SOUTHWESTWARD THROUGH THE
WEST-CENTRAL CAROLINAS TODAY. A PRECEDING EFFECTIVE WARM FRONT OVER
SOUTH-CENTRAL VA (MODULATED BY EARLIER STRONG TO SEVERE CONVECTION
OVER THE VIRGINIAS) WILL RETREAT QUICKLY NORTH ACROSS VA OWING TO
THE WARMTH JUST ABOVE THE SURFACE LAYER...WHICH WILL BE REALIZED
QUICKLY AS LOW CLOUDS ERODE AND DIABATIC HEATING/ MIXING OCCURS.

ASIDE FROM THE LEE TROUGH...A COUPLE OF OTHER OUTFLOW BOUNDARIES
OVER THE FAR NORTHERN NC PIEDMONT AND SOUTHERN PIEDMONT AND
SANDHILLS MAY SERVE AS FOCI FOR CONVECTIVE DEVELOPMENT TODAY...THE
LATTER OF WHICH MAY SUPPORT THE MAINTENANCE AND/OR RE-DEVELOPMENT OF
SHOWERS AND STORMS THERE THROUGH MIDDAY...AS AN UPSTREAM MCV OVER GA
APPROACHES FROM THE SW. SOME SUBSIDENCE BEHIND THIS FEATURE MAY
INITIALLY OTHERWISE INHIBIT CONVECTIVE DEVELOPMENT UNTIL EARLY-MID
AFTERNOON.

OTHERWISE...THE EROSION OF LOW CLOUDS WILL CAUSE TEMPERATURES TO
WARM THROUGH THE 70S...TO PROBABLE HIGHS IN THE LOWER 80S...WHICH IN
CONJUNCTION WITH SURFACE DEWPOINTS IN THE 60S...WILL YIELD A
MODERATELY UNSTABLE AIR MASS OVER CENTRAL NC THIS AFTERNOON.
LIKE SUNDAY...HOWEVER...THE MAIN BELT OF THE NORTHERN STREAM MID-
UPPER FLOW AND ASSOCIATED SHORTWAVE TROUGHS WILL REMAIN TO THE NORTH
OF CENTRAL NC TODAY...SO ONLY LOW AMPLITUDE IMPULSES IN THE SOUTHERN
STREAM AND/OR MCV/S FROM UPSTREAM CONVECTION WILL BE AVAILABLE TO
ENCOURAGE FORCING FOR ASCENT. THE RESULT WILL LIKELY BE RELATIVELY
SCATTERED...MULTI-CELLULAR STORMS THIS AFTERNOON...CAPABLE OF
PRODUCING STRONG WIND GUSTS AND PERHAPS SOME MARGINALLY SEVERE HAIL.

TONIGHT: A COUPLE OF NORTHERN STREAM SHORTWAVE TROUGHS STRETCHING
FROM OK TO THE FOUR CORNERS REGION WILL CAUSE MID LEVEL HEIGHTS TO
FALL ACROSS THE CENTRAL APPALACHIANS/OH VALLEY/NORTHERN MIDDLE
ATLANTIC STATES BY THIS EVENING. FORCING FOR ASCENT --IN THE
ASSOCIATED DIVERGENT RIGHT ENTRANCE REGION OF THE UPPER JET-- WILL
SPREAD EAST OF THE APPALACHIANS THIS EVENING...THEN PIVOT EAST
ACROSS VA/NC TONIGHT. THESE FEATURES WILL INTERACT WITH A CONTINUED
UNSEASONABLY MOIST AND CONDITIONALLY UNSTABLE AIR MASS AND SUPPORT
THE MAINTENANCE AND POSSIBLE UPSCALE GROWTH INTO LARGER CLUSTERS OF
SHOWERS AND STORMS OVERNIGHT.

THE ASSOCIATED GREATEST SEVERE WEATHER THREAT WOULD LIKELY OCCUR
OVER THE WESTERN PIEDMONT DURING THE EVENING...WHEN INSTABILITY WILL
STILL BE RELATIVELY MAXIMIZED AND OVERLAP IN SPACE AND TIME WITH
STRENGTHENING UVV/S AND MID LEVEL FLOW/SHEAR ACCOMPANYING THE
APPROACHING SHORTWAVE TROUGHS. DAMAGING WIND WILL POSE THE PRIMARY
THREAT...THOUGH SOME SEVERE HAIL WOULD ALSO BE POSSIBLE IN ANY
STORMS THAT REMAIN RELATIVELY DISCRETE. HEAVY RAIN AND LOCALIZED
FLOODING...PARTICULARLY IN URBAN AREAS...WILL ALSO BE OF CONCERN
GIVEN THE PRESENCE OF AN UNSEASONABLY MOIST AIRMASS CHARACTERIZED BY
PRECIPITABLE WATER VALUES OF 1.5-1.75". HUMID OTHERWISE...WITH LOWS
IN THE 60S.

&&

.SHORT TERM /TUESDAY AND TUESDAY NIGHT/...
AS OF 400 AM MONDAY...

A SHORTWAVE WILL DIVE SOUTH THROUGH THE PLAINS STATES ON TUESDAY AND
THEN SWING ACROSS THE DEEP SOUTH TUESDAY NIGHT.... FINALLY GIVING
THE STATIONARY FRONT CURRENTLY STRETCHING FROM EAST TX TO THE LOWER
GREAT LAKES A KICK TO THE EAST.  THE FRONT IS PROGGED TO CROSS NC
DURING THE DAY ON TUESDAY...THOUGH THE GFS IS SLIGHTLY FASTER THAN
THE ECMWF/NAM IN BRINGING THE FRONT THROUGH CENTRAL NC BY LATE
AFTERNOON. THE ECMWF AND NAM FAVOR A FRONTAL PASSAGE LATER IN THE
EVENING.  DEEP SHEAR IS INCREASINGLY FAVORABLE FOR ORGANIZED
CONVECTION TUESDAY AFTERNOON...WITH 40-50KT OF UNIDIRECTIONAL 0-6KM
BULK SHEAR AS THE UPPER JET SHIFTS EAST.  CAPE IS LITTLE MORE
UNCERTAIN GIVEN 1) THE POTENTIAL FOR ONGOING PRECIP OVER WESTERN NC
EARLY TUESDAY TO INHIBIT DESTABILIZATION OVER THE WESTERN PIEDMONT
AND 2) WESTERLY FLOW AND DEEPER MIXING TO LOWER DEWPOINTS (AGAIN
OVER THE WESTERN PIEDMONT).  GFS FORECAST SOUNDINGS SUGGEST100-
1500JKG MLCAPE IN THE COASTAL PLAIN.  THUS...THE COASTAL PLAIN IS
FAVORED FOR STRONGER STORMS TUESDAY AFTERNOON. HIGHS WILL BE IN THE
MID AND UPPER 70S.

THE SLOWER PASSAGE OF THE COLD FRONT SHOW IN THE ECMWF SUGGESTS THE
POTENTIAL FOR LINGERING SHOWERS IN THE COASTAL PLAIN TUESDAY NIGHT
AS A WEAK WAVE OF LOW PRESSURE DEVELOPS ALONG THE FRONT WHILE IT
APPROACHES THE COAST.  LOWS 54-59.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
AS OF 400 AM MONDAY...

AN OMEGA BLOCK PATTERN IS FORECAST TO DEVELOP FROM MID TO LATE
WEEK...WITH A STRONG UPPER RIDGE OVER THE WESTERN CONUS AND AN UPPER
LOW DROPPING SLOWLY OUT OF CANADA AND ACROSS THE MID-ATLANTIC STATES
AND CAROLINAS.  MEDIUM RANGE ENSEMBLES HAVE ADVERTISED THIS UPPER
LOW AS 2-3 STD BELOW NORMAL.  H10-H85 THICKNESSES DROPPING TO AROUND
1340M BY FRIDAY MORNING SUPPORT THE IDEA OF HIGHS SEVERAL DEGREES
BELOW NORMAL...WITH THE COOLEST MEX GUIDANCE INDICATING MID 60S TO
LOWER 70S THURS/FRI.  MULTIPLE DISTURBANCES WITH THE UPPER LOW AND
PERIODIC DCVA COMBINED WITH A POCKET OF COLD AIR ALOFT WILL SUPPORT
SHOWERS AND EVEN A FEW ISOLATED STORMS (MAINLY AFTERNOON) THROUGH
FRIDAY.  THE UPPER LOW SHOULD BEGIN TO FILL AND MOVE EAST BY
SATURDAY...WITH RIDGING OVER THE DEEP SOUTH AND NORTHWESTERLY FLOW
ACROSS NC.  TEMPS SHOULD BEGIN TO CLIMB BACK TO AND ABOVE NORMAL BY
THE END OF NEXT WEEKEND.

&&

.AVIATION /06Z TUESDAY THROUGH FRIDAY/...
AS OF 245 AM MONDAY...

AREAS OF STRATUS...IN MOIST/HUMID SSW LOW LEVEL FLOW BELOW A
TEMPERATURE INVERSION AROUND 1500 FT...WILL DEVELOP ACROSS CENTRAL
NC THIS MORNING...THOUGH COVERAGE AND CEILING HEIGHTS ARE BOTH
LIKELY TO BE MORE VARIABLE THAN IN RECENT DAYS. IN ADDITION...A
CHANCE OF SHOWERS AND STORMS WILL PERSIST IN A DEEPLY MOIST AND
CONDITIONALLY UNSTABLE AIR MASS THIS MORNING...WITH THE RELATIVE
MOST LIKELY OCCURRENCE AT KFAY.

OTHERWISE...LOW CLOUDS WILL LIFT THROUGH MVFR RANGE AND SCATTER
BETWEEN 13-16Z. SUBSEQUENT DIURNAL HEATING OF THE AFOREMENTIONED
HUMID AIR MASS WILL DESTABILIZE THE ATMOSPHERE AND SUPPORT SCATTERED
TO NUMEROUS STORMS THAT WILL LIKELY DEVELOP ALONG AN APPALACHIAN LEE
SURFACE TROUGH AND REMNANT OUTFLOW BOUNDARIES FROM EARLIER
CONVECTION - BEST CONVEYED WITH A PROB30 GROUP AT THIS TIME RANGE.
THE CHANCE OF SHOWERS AND STORMS WILL AGAIN LINGER OVERNIGHT...AS
LOW AMPLITUDE DISTURBANCES IN WSW FLOW ALOFT INTERACT WITH A
CONTINUED UNSEASONABLY MOIST AND CONDITIONALY UNSTABLE AIR MASS.

OUTLOOK: LATE NIGHT-MORNING LOW STRATUS...AND ABOVE AVERAGE CHANCES
OF SHOWERS AND STORMS...WILL PERSIST UNTIL A COLD FRONT CROSSES THE
MIDDLE ATLANTIC STATES AND MOVES OFFSHORE LATE TUE THROUGH EARLY
WED. A POLAR VORTEX WILL MEANWHILE MIGRATE FROM THE ARCTIC CIRCLE TO
THE MIDDLE ATLANTIC STATES THROUGH THE END OF THE WEEK...WITH
RESULTANT ENHANCED AFTERNOON CLOUDINESS AND SHOWERS/STORMS...AS
DIURNAL HEATING OCCURS BENEATH VERY COLD TEMPERATURES ALOFT
ATTENDING THE VORTEX.

&&

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

&&

$$
SYNOPSIS...26
NEAR TERM...26
SHORT TERM...22
LONG TERM...22
AVIATION...26



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