Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 011949 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 345 PM EDT MON JUN 1 2015 .SYNOPSIS...A MID LEVEL LOW PRESSURE TROUGH AND SURFACE COLD FRONT OVER THE TENNESSEE VALLEY WILL MOVE SLOWLY EASTWARD THEN STALL OVER THE CAROLINAS THROUGH THE WORK WEEK... BRINGING UNSETTLED WEATHER. && .NEAR TERM /THROUGH TONIGHT/... AS OF 300 PM MONDAY... LATEST SURFACE ANALYSIS SHOWS A NORTHEAST-SOUTHWEST COLD FRONT SLOWLY MOVING ACROSS THE CREST OF THE SOUTHERN APPALACHIANS WITH A WEAK SURFACE LOW LOCATED NEAR WASHINGTON DC AND A WEAK LEE TROUGH EXTENDING SOUTH INTO THE PIEDMONT OF VA AND NC. THE AIR MASS ACROSS CENTRAL NC IS MODERATELY UNSTABLE WITH MLCAPE VALUES RANGING BETWEEN 1000-1500 J/KG. A DEEP LAYER SOUTHWESTERLY FLOW AT AROUND 15 KTS IS PRESENT WITH WEAK BULK SHEAR VALUES AROUND 10-15 KTS. SCATTERED SHOWERS AND THUNDERSTORMS HAVE DEVELOPED ACROSS THE WESTERN PIEDMONT DURING THE PAST HOUR OR TWO IN ASSOCIATION WITH A SHEARING SHORT WAVE. THE STORMS HAVE LARGELY BEEN PULSE IN NATURE WITH SHORT LIVED UPDRAFTS THAT OFTEN MERGE AND CONFLICT WITH EACH OTHER. WHILE ORGANIZED SEVERE WEATHER IS NOT EXPECTED...STEEP LOW LEVEL LAPSE RATES AND DCAPE VALUES AT OR JUST ABOVE 1000 J/KG SUGGESTS A LOCALIZED DAMAGING WIND GUST IS POSSIBLE. CONVECTION ALLOWING MODELS GRADUALLY SHIFT THE CONVECTION EASTWARD THIS AFTERNOON AND EARLY EVENING WITH THE COVERAGE AND INTENSITY GRADUALLY WANING AFTER MIDNIGHT. LATE THIS EVENING AND OVERNIGHT...CONVECTIVE COVERAGE DECREASES SIGNIFICANTLY WITH ONLY ISOLATED CONVECTION EXPECTED AFTER MIDNIGHT. LOWS TONIGHT WILL RANGE IN THE MID TO UPPER 60S. -BLAES && .SHORT TERM /TUESDAY AND TUESDAY NIGHT/... AS OF 345 PM MONDAY... THE COLD FRONT WILL STRETCH FROM SOUTHERN VIRGINIA SOUTHWEST TO NORTHWESTERN NC ON TUESDAY MORNING. THE FRONT WILL MAKE VERY SLOW SOUTHWARD PROGRESS ACROSS CENTRAL NC ON TUESDAY AND TUESDAY NIGHT BEFORE SETTLING NEAR THE NC/SC BORDER BY WEDNESDAY MORNING. THE FRONTAL PROGRESSION MAY BE VERY LIMITED EARLY IN THE DAY AND THEN AIDED BY CONVECTIVE OUTFLOW AND PRECIPITATION DURING THE AFTERNOON AND EVENING. THE UPPER LEVEL LOW ACROSS WESTERN TN/KY AT THE START OF THE PERIOD IS CUT OFF FROM THE WESTERLIES AND SLOWLY MOVES EASTWARD REACHING SOUTHEAST TN BY WEDNESDAY MORNING. AHEAD OF THE CLOSED LOW...A NARROW BUT MOIST FETCH OF MOISTURE WILL SPREAD INTO THE CAROLINAS. WITH SREF PW VALUES CLIMBING TO AROUND 1.75 INCHES. AS THE UPPER LOW APPROACHES...FORCING FOR ASCENT INCREASES AND SCATTERED TO WIDESPREAD CONVECTION IS LIKELY TO DEVELOP DURING THE AFTERNOON AND EVENING WITH MULTIPLE ROUNDS OF CONVECTION LIKELY TO SPREAD EAST ACROSS THE AREA. THE APPROACHING UPPER LOW RESULTS IN STRENGTHENING SHEAR WITH BULK SHEAR VALUES INCREASING TO 20-30 KTS BY TUESDAY AFTERNOON WHICH SHOULD SUPPORT A SLIGHTLY INCREASED SEVERE WEATHER THREAT BUT THE MAIN HAZARDOUS WEATHER THREAT WILL BE FROM LOCALLY HEAVY RAIN. WIDESPREAD CLOUDINESS AND THE INFILTRATION OF A COOLER AIR MASS WILL RESULT IN HIGHS ONLY IN THE LOWER TO MID 80S. -BLAES. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... AS OF 310 PM MONDAY... WET WEATHER WILL CONTINUE THROUGH WED. THE MID LEVEL LOW OVER ERN TN EARLY IN THE DAY WILL CONTINUE A VERY SLOW WOBBLE TO THE EAST DURING THE DAY... AS A LOBE OF VORTICITY ROTATES NORTHWARD THROUGH CENTRAL NC. PW VALUES WILL REMAIN ELEVATED (150-180% OF NORMAL) WITH A CONFLUENT LOW LEVEL ATLANTIC-SOURCE FLOW AND AT LEAST MODERATE UPPER DIVERGENCE AS WEAK JETLETS ROTATE ABOUT THE UPPER LOW. LATEST MODEL RUNS SHOW THE FRONT DROPPING INTO FAR NRN AND NW NC EARLY WED MORNING... WHICH SHOULD HELP FOCUS RAINFALL. MARGINAL INSTABILITY PERSISTS WITH PROJECTIONS OF 500-1000 J/KG OF MUCAPE MAINLY IN THE SW CWA. THE COMBO OF MOISTURE/LIFT/INSTABILITY SUPPORTS RETAINING LIKELY POPS (AND IF TRENDS CONTINUE THESE SHOULD GO UP TO CATEGORICAL IN LATER FORECASTS). RAIN TOTALS MAY BE LOCALLY HEAVY WITH POSSIBLE TRAINING CONVECTIVE ELEMENTS. ADJUSTMENT BY EARLIER SHIFTS OF TAKING WED MAX TEMPS DOWN ESPECIALLY N AND NW OF THE FRONT (NW CWA) LOOKS GOOD AND WILL STAY THAT COURSE... WITH HIGHS FROM THE LOWER 70S NW TO LOWER 80S SE... IN LINE WITH STATISTICAL GUIDANCE. THERE MAY BE A SLIGHT BIT OF DRYING (MARGINALLY LOWER PW AND A LULL IN DPVA) ROTATING ABOUT THE LOW AND WORKING INTO THE SW CWA WED NIGHT... BUT WITH PW STILL ABOVE NORMAL AND THE SURFACE WEDGE FRONTAL ZONE IN PLACE... WILL KEEP A CHANCE OF SHOWERS IN OVERNIGHT. LOWS 61-66 NW TO SE. MORE OF THE SAME THU WITH THE SYNOPTIC CONFIGURATION SIMILAR TO WED... EXCEPT THE MID LEVEL LOW TO OUR WEST WILL HAVE DRIFTED SLIGHTLY CLOSER... INTO FAR WRN NC. INSTABILITY MAY BE A TAD HIGHER (750-1500 J/KG AREAWIDE ON THE GFS) WITH SIMILAR WEAK DPVA... UPPER DIVERGENCE... PW 150-180% OF NORMAL... AND ONSHORE-DIRECTED LOW LEVEL FLOW FOCUSED ALONG THE FRONTAL ZONE. EXPECT ANOTHER ROUND OF NUMEROUS SHOWERS AND EMBEDDED STORMS... PEAKING IN THE AFTERNOON AND EVENING. THICKNESSES ARE EXPECTED TO BE 10 M BELOW NORMAL... AND FACTORING IN THE CLOUDS AND PRECIP... PREFER TO KEEP HIGHS BELOW NORMAL (MID 70S TO MID 80S)... AND EVEN THESE MAY BE TOO HIGH IN THE NW HALF OF THE CWA. WILL TREND PRECIP CHANCES DOWN BUT NOT OUT THU NIGHT AS THE BY-NOW-WEAKENING UPPER LOW STARTS TO SHIFT OVERHEAD. LOWS IN THE MID 60S. COOLER-THAN-NORMAL WEATHER IS LIKELY TO EXTEND INTO FRI... BUT MODERATING SLOWLY AS WE GO THROUGH THE SAT-MON TIME FRAME. THE UPPER LOW WILL OPEN UP AND WEAKEN TO A BAGGY TROUGH WHILE CONTINUING AN EASTWARD DRIFT OFF THE MIDATLANTIC COAST... HOWEVER THIS TROUGH AXIS IN THE MEAN MAY LINGER OVER OUR AREA THROUGH MON... AS WEAK ENERGY MAY DROP IN FROM THE NW TO RELOAD THE TROUGH OVERHEAD. THE ECMWF IS MORE ROBUST WITH THIS... RESULTING IN ANOTHER CLOSED LOW OVER THE CAROLINAS SUN INTO MON... WHILE THE GFS IS MUCH LESS AMPLIFIED... FOCUSING INSTEAD ON STRONG NRN STREAM TROUGHING DEVELOPING OVER SOUTH CENTRAL CANADA INTO THE UPPER MIDWEST. THE GFS HAS BEEN SLIGHTLY MORE CONSISTENT BUT OTHERWISE THERE IS NO CLEAR INDICATION OF WHICH SOLUTION IS MORE LIKELY. THE FRONTAL ZONE SHOULD HOLD IN PLACE (WITH NOTHING TO MOVE IT OUT) YET CONTINUE TO SLOWLY WASH OUT WITH TIME... AND THE GFS KEEPS PW VALUES ABOVE NORMAL. SO WITH WEAK (BUT NON-ZERO) FORCING FOR ASCENT AND ABOVE NORMAL MOISTURE IN PLACE WITH LIMITED FOCUS... WE SHOULD SEE DAILY SHOWERS AND STORMS... NEAR OR JUST ABOVE CLIMATOLOGICAL COVERAGE. WILL HAVE TEMPS SLIGHTLY BELOW NORMAL FRI... RISING BACK TOWARD NORMAL BY MON. -GIH && .AVIATION /18Z MONDAY THROUGH SATURDAY/... AS OF 100 PM MONDAY... VFR CONDITIONS WILL PERSIST THROUGH AT LEAST 06Z TONIGHT AT ALL CENTRAL NC SITES. THERE IS A CHANCE OF SUB-VFR (LIKELY IFR/LIFR) CIGS BETWEEN 08Z AND 13Z TONIGHT/TUE MORNING AT RDU/RWI/FAY... ALTHOUGH CONFIDENCE IS LOWER THAN USUAL DUE TO LACK OF AGREEMENT AMONG THE MODELS REGARDING STRATUS FORMATION. ANY SUB-VFR CIGS WILL LIFT/MIX OUT TO VFR BY 15Z TUE. SCATTERED STORMS ARE MOST PROBABLY NEAR INT/GSO THIS AFTERNOON/EARLY EVENING (17Z-23Z)... TRENDING TOWARD RDU THIS EVENING (23Z-04Z)... WHICH MAY CAUSE A BRIEF DROP IN VSBYS TO MVFR/IFR AND IN CIGS TO MVFR... BUT THESE CONDITIONS WILL NOT BE PREVAILING. BETTER CHANCE OF SHOWERS/STORMS FORMING EARLIER TUE... TOWARD THE END OF THE TAF VALID PERIOD AT 15Z-18Z. WINDS GENERALLY LIGHT FROM SOUTH OR SW EXCEPT IN/NEAR STORMS. LOOKING BEYOND 18Z TUE: THE MORE NUMEROUS SHOWERS/STORMS TUE AFTERNOON AND INTO THE NIGHT WILL MEAN A BETTER CHANCE OF BRIEF SUB- VFR CIGS/VSBYS AT ALL SITES... HOWEVER OUTSIDE OF SHOWERS/STORMS WE SHOULD HAVE VFR CONDITIONS TUE. A COLD FRONT DROPPING IN FROM THE NORTH TUE NIGHT INTO EARLY WED WILL BRING A GOOD CHANCE OF IFR/LIFR STRATUS AFTER 06Z TUE NIGHT... WITH AT LEAST MVFR IF NOT IFR CONDITIONS LASTING THROUGH MUCH OF WED WITH NUMEROUS SHOWERS AND ISOLATED STORMS. IFR CONDITIONS LIKELY BOTH WED NIGHT AND THU NIGHT MAINLY AT INT/GSO/RDU/RWI... NEAR A LINGERING FRONTAL ZONE... RISING SLOWLY TO MVFR EACH MORNING. SLIGHTLY DRIER AIR IS EXPECTED BY SAT... SUGGESTING VFR CONDITIONS WILL AGAIN PREVAIL. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...HARTFIELD NEAR TERM...BLAES SHORT TERM...BLAES LONG TERM...HARTFIELD AVIATION...HARTFIELD

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