Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 040528 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 127 AM EDT FRI SEP 4 2015 .SYNOPSIS...AN UPPER LEVEL DISTURBANCE WILL AMPLIFY ACROSS CENTRAL TODAY. MEANWHILE AT THE SURFACE...A BACKDOOR COLD FRONT WILL APPROACH FROM THE NORTH LATE TODAY...THEN PUSH SOUTHWARD THROUGH THE AREA TONIGHT...BEFORE SETTLING TO OUR SOUTH ON SATURDAY. HIGH PRESSURE WILL EXTEND INTO THE REGION 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 /06Z FRIDAY THROUGH TUESDAY/... AS OF 120 AM FRIDAY... 24 HR TAF PERIOD: EARLY MORNING FOG AND LOW STRATUS DEVELOPMENT IS UNDERWAY ACROSS CENTRAL NC... WITH LOCATIONS AGAIN ACROSS THE NORTHEAST PIEDMONT AND NORTHERN AND CENTRAL COASTAL EXPECTED TO SEE THE MOST COVERAGE AND IFR/LIFR CONDITIONS... THANKS IN PART TO MOIST SOILS FROM THE CONVECTION LATE WEDNESDAY AND EARLY THURSDAY MORNING. THUS... AGAIN THINK IFR/LIFR FOG AND LOW STRATUS WILL DEVELOP AT KRWI AND KRDU THIS MORNING... WITH GENERALLY MVFR VISBYS AT KFAY/KGSO/KINT. ANY FOG AND STRATUS THAT DEVELOPS EARLY THIS MORNING SHOULD LIFT WITHIN A FEW HOURS OF SUNRISE AGAIN... WITH SKIES BECOMING MOSTLY TO PARTLY SUNNY BY MID MORNING. HOWEVER... AS A MID/UPPER LEVEL DISTURBANCE CONTINUES TO MOVE INTO THE REGION COUPLED WITH THE APPROACH OF A BACKDOOR COLD FRONT... EXPECT CLOUD COVER SHOULD THICKEN THIS AFTERNOON INTO THE EVENING... WITH SCATTERED TO POTENTIALLY NUMEROUS SHOWERS AND STORMS DEVELOPING. THUS... HAVE ADDED A PROB30 GROUP FOR THE POTENTIAL FOR CONVECTION THIS AFTERNOON AND EVENING AT ALL TAF SITES. ANY STORMS THAT DEVELOP WILL HAVE THE POTENTIAL TO PRODUCE AT LEAST IFR CONDITIONS IN HEAVY RAIN... ALONG WITH GUSTY WINDS. OUTLOOK: LINGERING SHOWERS AND EVEN SOME ISOLATED STORMS MAY CONTINUE INTO THE EARLY MORNING HOURS OF SATURDAY... AS THE FRONT MOVES THROUGH THE AREA... WITH LOCATIONS ACROSS THE WESTERN PIEDMONT STANDING THE BEST CHANCE AS SEEING LINGERING CONVECTION (KGSO/KINT). 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. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...BSD/26 NEAR TERM...26 SHORT TERM...HARTFIELD LONG TERM...ELLIS AVIATION...BSD/BLAES

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