Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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920 FXUS62 KRAH 210849 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 449 AM EDT THU MAY 21 2015 .SYNOPSIS...LOW PRESSURE WILL TRACK EAST ALONG A QUASI-STATIONARY FRONT OVER NC TODAY. WEAK HIGH PRESSURE WILL FOLLOW FOR TONIGHT AND FRI. && .NEAR TERM /THROUGH TONIGHT/...
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AS OF 445 AM THURSDAY... AT THE BASE OF AN ELONGATED NORTHERN STREAM SHORTWAVE TROUGH THAT INCLUDES A COUPLE OF NOTABLE VORTICITY CENTERS OVER THE EASTERN GREAT LAKES AND NW IOWA...RESPECTIVELY...A PAIR OF SOUTHERN STREAM IMPULSES INITIALLY OVER THE EASTERN TN VALLEY AND LOWER MS VALLEY THIS MORNING...RESPECTIVELY...WILL TRACK EAST AND ACROSS THE SOUTHERN APPALACHIANS AND CAROLINAS TODAY. AMIDST GENERALLY WEAK/~20 METER HEIGHT FALLS AT THE BASE OF THE NORTHERN STREAM SHORTWAVE TROUGH...THE MODELS SUGGEST THE SOUTHERN STREAM IMPULSES WILL PROVIDE FOR A CORRIDOR OF RELATIVELY MAXIMIZED 30-40 METER/12 HR HEIGHT FALLS ACROSS CENTRAL NC AROUND 18Z AND AND EASTERN NC BY 00Z. AT THE SURFACE...AN ELONGATED AREA OF LOW PRESSURE STRETCHED AT 08Z FROM NE TN TO THE WESTERN CAROLINAS. MEANWHILE...A SUB-SYNOPTIC LOW ACCOMPANYING SCATTERED ELEVATED SHOWERS AND ISOLATED THUNDER OVER THE NW NC PIEDMONT...DRIVEN BY STRONG LOW-MID LEVEL WAA...HAS WEAKENED AS IT MOVED INTO LOW LEVEL RIDGING EXTENDING INTO THE NORTHERN NC PIEDMONT FROM THE MIDDLE ATLANTIC STATES. IT IS PROBABLE THAT A SERIES OF WAVES OF LOW PRESSURE WILL TRACK EAST ALONG A PRECEDING WARM FRONT THAT WILL BECOME QUASI-STATIONARY OVER CENTRAL NC TODAY. ONCE THE ELEVATED MORNING CONVECTION MOVES INTO SE VA BY AROUND 15Z...THE RETREAT OF THE WARM FRONT TO NEAR THE HIGHWAY 64 CORRIDOR...IN CONJUNCTION WITH DIURNAL DESTABILIZATION...WILL RESULT IN THE DEVELOPMENT OF WEAK TO MODERATE INSTABILITY OVER SOUTHERN AND ESPECIALLY SOUTHEASTERN NC. THE MODELS SUGGEST A PRIMARY SURFACE WAVE WILL TRACK ALONG THE FRONT FROM THE SOUTHERN PIEDMONT TO THE CENTRAL COASTAL PLAIN BETWEEN 15-18Z...COINCIDENT WITH THE DEVELOPMENT AND MAINTENANCE OF A BAND OR TWO OF STORMS PER AN OVERWHELMING SIGNAL FROM THE CONVECTION ALLOWING MODELS. STRENGTHENING MID LEVEL FLOW TO BETWEEN 35-45 KTS OWING TO THE INFLUENCE OF THE SHORTWAVE TROUGHS NOTED ABOVE WILL PROVIDE SUFFICIENT BULK SHEAR FOR ORGANIZED STORM MODES...WHICH MAY INCLUDE BOTH MULTI-CELLULAR AND SUPERCELLULAR ONES...THE LATTER OF WHICH AND ASSOCIATED FOCUS FOR AN ISOLATED TORNADO AND/OR DAMAGING STRAIGHT LINE WIND...WILL BE MORE LIKELY IN THE RELATIVE BACKED LOW LEVEL FLOW IMMEDIATELY PRECEDING THE SURFACE WAVE...AND WHERE BOUYANCY IS MAXIMIZED AND CAN OFFSET OTHERWISE MARGINAL BULK SHEAR THAT WILL INCREASE WITH NORTHERN EXTENT/AWAY FROM THE WARM SECTOR. WHILE DAMAGING WINDS WILL OTHERWISE POSE THE PRIMARY HAZARD...HAIL WILL ALSO BE POSSIBLE IN ANY SUPERCELL...THOUGH GENERALLY WEAK MID LEVEL LAPSE RATES (AOB 5.5-6 C/KM) SHOULD DETER THE OCCURRENCE OF HAIL MUCH BEYOND THE SIZE OF QUARTERS. GIVEN THE DIURNAL TIMING OF THE LEAD SURFACE WAVE AND PROBABLE STORMS...AREAS ALONG AND SOUTH OF HIGHWAY 64 AND EAST OF HIGHWAY 1 STILL APPEAR FAVORED FOR MOST OPTIMAL TIMING/DESTABILIZATION/SEVERE THREAT. CONVERGENCE ALONG THE FRONT AND ANY ADDITIONAL SURFACE WAVES...WHICH WOULD LIKELY MIGRATE EAST ON A MORE SOUTHERLY TRACK ACROSS FAR SOUTHERN NC OR SC...MAY SUPPORT WIDELY SCATTERED SHOWERS AND STORMS THAT MAY LINGER THROUGH THE AFTERNOON AND EVENING... PARTICULARLY IF THE AIR MASS DESTABILIZES IN THE WAKE OF THE EXPECTED FIRST BAND(S) OF STORMS THROUGH EARLY AFTERNOON. HIGH TEMPERATURES WILL BE WIDE-RANGING GIVEN BOTH THE PRESENCE OF THE FRONT AND CONVECTION - AROUND 70 NORTH TO MID-UPPER 80S SOUTH. WHILE SOME LOW CLOUDS MAY LINGER INTO THE EVENING...PARTICULARLY OVER THE NE PIEDMONT AND NORTHERN COASTAL PLAIN...SKIES WILL OTHERWISE BEGIN TO CLEAR AS DRIER AIR SETTLES SOUTH...WITH LOWS IN THE 50S.
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&& .SHORT TERM /FRIDAY AND FRIDAY NIGHT/...
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AS OF 355 AM THURSDAY... A TROUGH ALOFT WILL AMPLIFY ACROSS THE NORTHEAST AND MIDDLE ATLANTIC STATES FRI...THEN OFFSHORE FRI NIGHT. DESPITE THE AMPLIFICATION OF THE TROUGH...HEIGHT RISES ALOFT AND ASSOCIATED SUBSIDENCE WILL BE UNDERWAY OVER VA AND THE CAROLINAS...IN THE WAKE OF A LEAD SHORTWAVE TROUGH FORECAST TO CROSS THE MIDDLE ATLANTIC STATES TONIGHT. SURFACE HIGH PRESSURE WILL CONSEQUENTLY BUILD EAST FROM THE TN VALLEY ON FRI IN ASSOCIATION WITH THE LEAD MIDDLE ATLANTIC SHORTWAVE TROUGH... FOLLOWED BY THE FRI NIGHT PASSAGE OF A DRY COLD FRONT RESULTING FROM THE LARGER SCALE TROUGH AMPLIFICATION OVER THE NORTHEAST. TEMPERATURES WILL BE IN THE 70S ON FRI...WITH LOWER HUMIDITY VALUES OWING TO SURFACE DEWPOINTS IN THE 40S. TEMPERATURES FRI NIGHT WILL LIKELY VARY WILDLY...WITH PE-FRONTAL RADIATIONAL COOLING INITIALLY; THEN MIXING AND ASSOCIATED WARMING WITH FROPA; AND ENDING WITH CAA LATE...WITH LOWS BY THE END OF THE NIGHT IN THE 50S.
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&& .LONG TERM /SATURDAY THROUGH WEDNESDAY/... AS OF 220 AM THURSDAY... SATURDAY THROUGH WEDNESDAY: VERY LITTLE SIGNIFICANT WEATHER IS EXPECTED DURING THE LONG TERM PERIOD WITH HIGH PRESSURE DOMINATING THE PATTERN FOR MUCH OF THE PERIOD. INITIALLY...SURFACE HIGH PRESSURE WILL BE TO THE NORTH OF THE AREA BRINING COOLER NORTHEASTERLY FLOW TO CENTRAL NC FOR SATURDAY BEFORE THE HIGH SLIDES OFFSHORE AND SETS UP EAST OF THE AREA. THIS WILL SHIFT WINDS TO SOUTHERLY (ALTHOUGH LIGHT) AND BEGIN A WARMING TREND THAT WILL CONTINUE THROUGH WEDNESDAY. INITIALLY...EXPECT TEMPERATURES IN THE UPPER 70S TO NEAR 80 DEGREES ON SATURDAY BUT STEADILY RISING A FEW DEGREES EACH DAY UP TO NEAR 90 DEGREES BY WEDNESDAY AFTERNOON. LOWS WILL FOLLOW A SIMILAR PATTERN...RISING A COUPLE DEGREES EACH DAY FROM THE UPPER 50S ON SATURDAY NIGHT UP TO THE UPPER 60S BY TUESDAY NIGHT/WEDNESDAY MORNING. MUCH OF THE PERIOD LOOKS DRY AS HIGH PRESSURE KEEPS MUCH OF THE PRECIPITATION THREAT WELL AWAY FROM THE AREA. LATE IN THE PERIOD...A FRONTAL SYSTEM WILL APPROACH FROM THE WEST AND THERE IS A LITTLE DISCREPANCY ON TIMING BUT MODELS THIS MORNING LOOK TO HOLD OFF PRECIPITATION WITH THIS FRONT A LITTLE LONGER THAN THE PREVIOUS DAYS RUNS AND THEREFORE HAVE CUT BACK POPS ON TUESDAY AND WEDNESDAY...INTRODUCING A SLIGHT CHANCE IN THE WEST ON TUESDAY AFTERNOON AND THEN CHANCE IN THE WEST...SLIGHT CHANCE IN THE EAST ON WEDNESDAY AFTERNOON. && .AVIATION /06Z THURSDAY THROUGH MONDAY/... AS OF 230 AM THURSDAY... A WARM FRONT AND ASSOCIATED LIFT AND FOCUS FOR THE DEVELOPMENT OF BOTH MVFR-IFR CEILINGS AND SCATTERED ELEVATED SHOWERS/STORMS WILL CONTINUE TO RETREAT NORTH INTO CENTRAL NC THIS MORNING...WITH THE RELATIVE BEST CHANCE OF SHOWERS AND STORMS AT GSO/INT/RDU THROUGH 15Z. A WAVE OF LOW PRESSURE WILL TRACK EAST ALONG THE FRONT...WHICH IS EXPECTED TO STALL IN THE VICINITY OF A LINE FROM NEAR RDU TO RWI. THE LOW PRESSURE WILL BE ACCOMPANIED BY A BAND OF THUNDERSTORMS THAT WILL LIKELY DEVELOP NEAR THE TRIAD TERMINALS BETWEEN 15-17Z AND GAIN STRENGTH AS IT MOVES EAST INTO AN INCREASINGLY UNSTABLE AIR MASS DOWNSTREAM...PARTICULARLY SOUTH OF THE WARM FRONT -AT FAY- WHERE DESTABILIZATION WILL BE MAXIMIZED. OTHERWISE...THE FRONT WILL ALSO SERVE AS THE BOUNDARY BETWEEN CONTINUED MVFR-IFR CEILINGS TO THE NORTH AND VFR CEILINGS AND A GUSTY S TO SW SURFACE WIND TO THE SOUTH. WHILE THE ASSOCIATED SUB-VFR CEILINGS MAY LINGER AT NORTHERN TAF SITES INTO HE AFTERNOON...OR EVENING EARLY EVENING AT RWI...DRIER AIR WILL EVENTUALLY SETTLE SOUTH INTO OUR AREA IN THE WAKE OF THE PASSING LOW PRESSURE SYSTEM...WITH AN ASSOCIATED RETURN TO VFR CONDITIONS FOR TONIGHT. OUTLOOK: VFR...UNDER THE INFLUENCE OF HIGH PRESSURE. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...26 NEAR TERM...26 SHORT TERM...26 LONG TERM...ELLIS AVIATION...26

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