Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 040256
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
1056 PM EDT THU SEP 3 2015

.SYNOPSIS...A VORT MAX WILL AMPLIFY ACROSS CENTRAL NC THROUGH FRI.
MEANWHILE AT THE SURFACE...A BACKDOOR COLD FRONT WILL APPROACH FROM
THE NORTH LATE FRIDAY...THEN PUSH SOUTHWARD THROUGH THE AREA FRIDAY
NIGHT...BEFORE SETTLING TO OUR SOUTH ON SATURDAY. HIGH PRESSURE WILL
NOSE IN FROM THE NORTH OVER THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 1050 PM THURSDAY...

EVENING WATER VAPOR IMAGERY DEPICTED AN ELONGATED AXIS OF SHEAR
VORTICITY STRETCHING FROM WESTERN NC NORTHWESTWARD TO A WELL-DEFINED
SHORTWAVE TROUGH OVER WISCONSIN. NWP GUIDANCE INDICATES THE
VORTICITY AXIS WILL BECOME MORE CONCENTRIC WITH TIME AND
SOUTHEASTWARD EXTENT/NEAR THE BASE OF THE PARENT TROUGH AXIS OVER
THE CAROLINAS...ULTIMATELY CULMINATING IN A CLOSED UPPER LOW AND
POCKET OF -9 TO -10 C 500 MB TEMPERATURES OVER CENTRAL NC DURING THE
DAY FRI. THE PRECEDING ASSOCIATED DYNAMIC FORCING FOR ASCENT IS
FORECAST TO SPREAD EAST OF THE APPALACHIANS AND ACROSS CENTRAL VA
AND CENTRAL NC BETWEEN 06-12Z. SHOWERS HAVE BEEN PERCOLATING OVER
WESTERN NC DURING THE PAST COUPLE OF HOURS (AFTER SUNSET/DURING A
TIME THAT SOLELY-DIURNALLY-DRIVEN CONVECTION SHOULD BE DIMINISHING);
AND THIS ACTIVITY IS PRESUMABLY INDICATIVE OF THE INFLUENCE OF THE
AMPLIFYING VORT MAX. THAT FORCING...IN CONJUNCTION WITH LOW LEVEL
CONVERGENCE ALONG A LEE SURFACE TROUGH THAT NEARLY PERFECTLY BISECTS
THE RAH CWFA FROM NNE TO SSW THIS EVENING...MAY YET FOCUS SOME
ISOLATED SHOWERS OVERNIGHT...MAINLY ALONG AND EAST OF THE TROUGH
AXIS/WHERE LOW LEVEL MOISTURE AND ASSOCIATED INSTABILITY FIELDS
ARE/WILL CONTINUE TO BE RELATIVELY MAXIMIZED.

OTHERWISE...SURFACE VISIBILITY IS ALREADY DECREASING ACROSS CENTRAL
NC...AND BOTH STATISTICAL GUIDANCE AND HRRR VISIBILITY FORECASTS
SUGGEST VISIBILITY RESTRICTIONS WILL CONTINUE TO EXPAND AND LOWER IN
A RELATIVELY CALM...CLEAR...AND MOIST (IN THE BOUNDARY LAYER)
ENVIRONMENT OVER CENTRAL NC OVERNIGHT. LOWS AGAIN IN THE UPPER 60S
TO LOWER 70S.

&&

.SHORT TERM /FRIDAY AND FRIDAY NIGHT/...
AS OF 325 PM THURSDAY...

OUR BEST SHOT AT SCATTERED TO NUMEROUS SHOWERS AND STORMS WILL BE
LATE FRI INTO FRI NIGHT... WITH SEVERAL FAVORABLE FACTORS IN PLAY.
FIRST... MODELS DEPICT A POCKET OF ABOVE-NORMAL PW SLIDING SOUTHWARD
FROM VA INTO/THROUGH CENTRAL NC TOMORROW... IN CONJUNCTION WITH WEAK
DPVA SPREADING IN FROM THE NW AND NE AND IMPROVING UPPER DIVERGENCE
FROM THE NORTH... ALL AHEAD OF THE INCOMING BACKDOOR COLD FRONT. THE
LARGE-SCALE MODELS INCLUDING THE NAM/GFS/ECMWF/SREF ARE IN AGREEMENT
ON CONVECTION DEVELOPING DURING THE EARLY TO MID AFTERNOON OVER
CENTRAL NC... FOCUSING THE BEST COVERAGE AND HIGHEST AMOUNTS OVER
THE FAR NW PIEDMONT. GIVEN THE EXPECTED MID-UPPER LEVEL DYNAMIC
CONTRIBUTIONS TO ASCENT... DESTABILIZATION WITH GOOD HEATING DURING
THE DAY... AND RISING MOISTURE THROUGH THE COLUMN... CONVECTIVE
COVERAGE LOOKS SUFFICIENT TO RAISE POPS A BIT... TO LIKELY IN THE NW
CWA WITH GOOD CHANCES ELSEWHERE FOR NOW (ALTHOUGH THESE MAY GO UP TO
LIKELY HERE AS WELL IN LATER FORECASTS IF TRENDS HOLD). THE WEAK
DEEP LAYER SHEAR SHOULD LIMIT STORM STRENGTH... ALTHOUGH THE PROFILE
AND DCAPE NOTED ON NAM FORECAST SOUNDINGS WOULD SUGGEST A MARGINAL
WIND THREAT. THE ANTICIPATED SLOW MOVEMENT WITH HIGH WATER CONTENT
WILL BRING A RISK OF SLOW-MOVING STORMS GENERATING URBAN FLOODING.
EXPECT HIGHS OF 90-95 WITH DECENT PREFRONTAL HEATING AND CONTINUED
ABOVE NORMAL THICKNESSES. POPS SHOULD TREND DOWNWARD AFTER NIGHTFALL
WITH LOSS OF INSOLATION... HOWEVER WITH LOW LEVEL CONFLUENT FLOW
NEAR THE BACKDOOR FRONT AND INCREASED ATLANTIC-SOURCE FEED WITH
PERSISTENT UPPER DIVERGENCE OVERNIGHT... WILL KEEP A MENTION OF
SCATTERED SHOWERS AND STORMS THROUGH THE NIGHT... WITH THE BEST
CHANCES WEST. LOWS 67-71. -GIH

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
AS OF 150 PM THURSDAY...

COOLER TEMPERATURES EXPECTED FOR MUCH OF THE LONG TERM AS THE COLD
FRONT THAT IS PROGGED TO COME THROUGH FRIDAY NIGHT WILL BRING A
CHANGE IN AIRMASS FROM THE NORTHEAST. WITH THIS WILL COME A GREATER
FETCH OF MOISTURE FROM OFFSHORE...DRIVEN BY SEVERAL SHORTWAVE
IMPULSES THAT ARE EXPECTED TO MOVE INTO THE STATE DURING THE WEEKEND
AND INTO EARLY NEXT WEEK.

FOR THE WEEKEND...THE GREATEST THREAT FOR RAIN WILL BE IN THE WEST
ON SATURDAY AS THE FRONT MOVES THROUGH AND A CAD-LIKE SCENARIO SETS
UP. AS THE WEEKEND PROGRESSES HOWEVER...AN INVERTED TROUGH ALONG THE
EAST COAST WILL SHARPEN AND THUS BRING A MORE NORTHERLY COMPONENT TO
THE WIND AND SHUT OFFSHORE MOISTURE FEED INTO THE NW PIEDMONT AND
INSTEAD BEGIN TO FOCUS THE BEST CHANCE FOR CONVECTION OVER THE
EASTERN PART OF THE STATE. THUS RAIN CHANCES FOR SUNDAY WILL BE
BETTER IN THE EAST THAN IN THE WEST. THIS PATTERN WILL CONTINUE INTO
LABOR DAY WITH SOUTHEASTERN COUNTIES HAVING THE BEST CHANCE FOR
SHOWERS AND THUNDERSTORMS. HIGHS IN THE LOW TO MID 80S FOR THIS
PERIOD WITH THE POTENTIAL FOR SOME UPPER 70S IN THE NW IF CLOUD
COVER LOCKS IN.

THE BERMUDA HIGH BEGINS TO TAKE BACK OVER FOR MIDWEEK AND THE
SURFACE HIGH OVER OUR AREA AND THE INVERTED TROUGH WILL BEGIN TO
BREAK DOWN. THIS WILL SEE A RETURN TO WARMER TEMPERATURES...ALTHOUGH
GRADUALLY...WITH DIURNAL CHANCES FOR SHOWERS AND ISOLATED
THUNDERSTORMS THROUGH THURSDAY. AT THIS TIME...ANY THUNDERSTORMS
THAT DO OCCUR EITHER THIS WEEKEND OR NEXT WEEK ARE NOT EXPECTED TO
BE SEVERE...BUT A FEW STRONG STORMS CANNOT BE RULED OUT.

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
AS OF 810 PM THURSDAY...

THE 24 HR TAF PERIOD...VFR CONDITIONS WILL PERSIST THROUGH THE
EVENING HOURS AND IN MOST LOCATIONS OVERNIGHT. AREAS OF FOG WILL
DEVELOP LATE TONIGHT TOWARD FRIDAY MORNING WITH MAINLY VFR-MVFR
VSBYS WITH THE POTENTIAL FOR IFR/LIFR VSBY/CIG RESTRICTIONS FOR A
SHORT PERIOD TOWARD DAYBREAK AT KRWI AND PERHAPS KFAY. RESTRICTIONS
WILL GRADUALLY IMPROVE AFTER SUNRISE WITH MULTIPLE CLOUD LAYERS
EXPECTED DURING THE DAY FRIDAY. MOST LOCATIONS WILL HAVE BKN MID
LEVEL CLOUDS THROUGHOUT THE DAY WITH A LOWER SCT CLOUD DECK AT 4-
6KFT BECOMING BKN TOWARD MIDDAY AND THE EARLY AFTERNOON. SCATTERED
SHOWERS AND THUNDERSTORMS WILL DEVELOP DURING THE MID TO LATE
AFTERNOON HOURS...FOCUSED ACROSS THE NORTHEAST PIEDMONT AND NORTHERN
COASTAL PLAIN AND THEN SHIFTING TOWARD THE WEST AND SOUTHWEST WITH
LOCALLY REDUCTIONS IN VSBYS AND CEILINGS. MAINLY CALM WINDS ARE
EXPECTED OVERNIGHT WITH A LIGHT NORTH TO NORTHEAST WIND AT LESS THAN
7KTS EXPECTED ON FRIDAY...EXCEPT HIGHER IN THUNDERSTORMS.

LOOKING BEYOND 00Z SATURDAY...SCATTERED SHOWERS AND
THUNDERSTORMS WILL CONTINUE INTO THE EVENING HOURS ON FRIDAY. MORE
WIDELY SCATTERED CONVECTION IS POSSIBLE DURING THE AFTERNOON AND
EVENING ON SATURDAY AND SUNDAY WITH A DECREASE IN COVERAGE AND A
FOCUS TOWARD THE COASTAL PLAIN ON MONDAY AND TUESDAY. LATE NIGHT
AND MORNING FOG AND STRATUS WITH POTENTIALLY SIGNIFICANT
RESTRICTIONS APPEAR PROBABLE ON SATURDAY AND SUNDAY MORNINGS. -BLAES

&&

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

&&

$$

SYNOPSIS...26/HARTFIELD
NEAR TERM...26
SHORT TERM...HARTFIELD
LONG TERM...ELLIS
AVIATION...HARTFIELD


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