Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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839 FXUS62 KRAH 031745 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 145 PM EDT TUE MAY 3 2016 .SYNOPSIS... LOW PRESSURE WILL MOVE OFF THE MIDDLE ATLANTIC COAST EARLY TODAY. A SECONDARY WAVE OF LOW PRESSURE WILL DEVELOP ALONG THE TRAILING COLD OVER NC THIS AFTERNOON AND EVENING...BEFORE MOVING SLOWLY TO THE COAST AND OFFSHORE LATE TONIGHT AND WED. && .NEAR TERM /THROUGH TONIGHT/... AS OF 1120 AM TUESDAY... THE MID LEVEL DISTURBANCE...RESPONSIBLE FOR THE WIDESPREAD PRECIPITATION AND THUNDERSTORMS OVER THE EASTERN HALF OF NC THIS MORNING...WILL CONTINUE TO LIFT OUT OF THE AREA THROUGH 16Z. ANOTHER UPPER WAVE AND IT`S ASSOCIATED DPVA...SEEN MOVING INTO THE SOUTHERN APPALACHIANS PER 13Z WATER VAPOR IMAGERY...WILL SLIDE OVER THE WESTERN PIEDMONT BY EARLY AFTERNOON...PROVIDING FORCING FOR STORM INITIATION. ANOTHER MID-LEVEL WAVE IS EXPECTED TO MOVE IN ON IT`S HEELS...FURTHER PROVIDING UPPER LEVEL SUPPORT TO SUSTAIN CONVECTION THROUGH THE EARLY OVERNIGHT HOURS. PRECIPITATION CHANCES: SHOWERS ASSOCIATED WITH WITH THIS MORNING`S UPPER DISTURBANCE SHOULD CONTINUE TO MOVE TO THE EAST THROUGHOUT THE REMAINDER OF THE MORNING AND INTO THE EARLY AFTERNOON. FOCUS THEN TURNS TO THE WESTERN PIEDMONT...WHERE CLEARING IS ALREADY OCCURRING AS OF 14Z AND IS EXPECTED TO CONTINUE AS WE EXPERIENCE SUBSIDENCE IN THE WAKE OF THIS MORNINGS WAVE. 14Z SPC MESO ANALYSIS ALREADY SHOWS 500J/KG OF CAPE MOVING INTO THE SW PIEDMONT...WITH HIGHER VALUES ADVECTING INTO THE CWA BY AFTERNOON...COURTESY OF LOW LEVEL SOUTHERLY FLOW ADVECTING MOISTURE NORTHWARD INTO THE CWA. CONVECTIVE INITIATION SHOULD OCCUR BY 16-18Z IN THE WESTERN PIEDMONT...AS DPVA BEGINS TO OVERSPREAD THE AREA FROM THE AFOREMENTIONED UPPER DISTURBANCE TO OUR SW. STORMS WILL QUICKLY BECOME WIDESPREAD IN THE LARGELY UNCAPPED ENVIRONMENT...POSSIBLY EVOLVING INTO A CONVECTIVE LINE OVER THE EASTERN 1/2 OF THE CWA BY LATE AFTERNOON. WITH WESTERLY FLOW ALOFT...CONVECTION WILL FIRST AFFECT THE WESTERN PIEDMONT AND TRIAD AFTER 16Z...THE CENTRAL PIEDMONT AND TRIANGLE AFTER 18Z AND THE EASTERN PIEDMONT AFTER 20Z. CONVECTION WILL LIKELY CONTINUE OVER THE AREA THROUGH THE EARLY OVERNIGHT...AS UPPER- SUPPORT REMAINS OVER THE AREA PROVIDING FORCING FOR CONVECTION. DESPITE A VERY MOIST ATMOSPHERE...PWATS OVER 1.5" EAST OF US-1...AND THE POTENTIAL FOR STORMS TO HAVE VERY HEAVY RAIN...STORM MOTIONS SUGGEST TRAINING IS UNLIKELY...AND WIDESPREAD FLASH FLOODING IS UNLIKELY. SEVERE THREAT: WITH SBCAPE VALUES EXCEEDING 1500J/KG...ESPECIALLY OVER THE SOUTHERN AND EASTERN CWA...STORMS WILL HAVE PLENTY OF ENERGY TO FEED OFF OF. SPEEDY FLOW ALOFT...ASSOCIATED WITH THE SERIES OF UPPER DISTURBANCES MOVING OVERHEAD...WILL RESULT IN DEEP LAYER SHEAR VALUES IN EXCESS OF 45KTS THIS AFTERNOON. THIS COMBINED WITH 0-3KM SRH VALUES APPROACHING 100M2/S2, SHOULD RESULT IN THE DEVELOPMENT OF A FEW SUPERCELLS BY THE AFTERNOON. HOWEVER...AS PREVIOUSLY MENTIONED...WITH THE UPPER SUPPORT OVERHEAD AND AN UNCAPPED ENVIRONMENT...STORM MODE MAY BECOME MESSY QUICKLY...WITH ALL STORM MODES POSSIBLE OVER THE CWA BY THIS AFTERNOON. REGARDLESS...THE STRONGEST STORMS WILL BE CAPABLE OF LARGE HAIL...500-700HPA LAPSE RATES ARE RATHER STEEP AND FREEZING LEVELS ARE ~9000FT...AND STRONG WINDS...DCAPE VALUES >800-1000J/KG. THE SEVERE THREAT MAY SHIFT AWAY FROM HAIL AND MORE TOWARD WIND BY LATE AFTERNOON...AS STORMS WILL LIKELY GROW UPSCALE INTO A CONVECTIVE LINE..WHICH AS SUGGESTED BY THE CAMS THIS MORNING...COULD CONTAIN BOWING SEGMENTS...ESPECIALLY OVER THE EASTERN CWA. THE TOR THREAT WILL REMAIN LOW THIS AFTERNOON AND INTO TONIGHT...MOSTLY DUE TO STRAIGHT-LINE HODOGRAPHS AND A LACK OF LOW LEVEL SHEAR/HELICITY. -SCR/WSS THE FRONTAL ZONE AND EMBEDDED WAVE OF LOW PRESSURE...AND ASSOCIATED DEEP MOISTURE AND SHOWERS...WILL MOVE GRADUALLY EAST OVERNIGHT... WITH JUST A LINGERING SLIGHT-LOW CHANCE OF SHOWERS EAST OF I-95 BY WED MORNING...AND DRYING ELSEWHERE. COOLER WITH LOWS IN THE MID- UPPER 50S. -26 && .SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/... AS OF 405 AM TUESDAY... A PAIR OF NOTABLE CURLS IN WATER VAPOR OVER OVER IOWA AND NEBRASKA THIS MORNING WILL ELONGATE AND MOVE EAST BENEATH A DEEPER TROUGH DEVELOPING FROM A WAVE DIVING SOUTH OUT OF CENTRAL CANADA. THIS LEAD WAVE WILL CROSS CENTRAL NC EARLY WEDNESDAY... AND IN RESPONSE A BROAD WAVE OF LOW PRESSURE IS FORECAST TO DEVELOP OVER EASTERN NC WEDNESDAY AFTERNOON. DESPITE THE AIRMASS CHANGE IN THE WAKE OF TODAYS COLD FRONT... SLIGHTLY ELEVATED DEWPOINTS IN THE UPPER 50S IN THE COASTAL PLAIN AND WEAK LOW LEVEL MASS CONVERGENCE BENEATH STRONG COOLING ALOFT AND 60M HEIGHT FALLS SHOULD BE ENOUGH TO KICK OFF SOME SHOWERS AND ISOLATED STORMS...MAINLY IN THE NORTHERN COASTAL PLAIN. THE FREEZING LEVEL WILL DROP TO AROUND 9000 FT...SO SOME SMALL HAIL CANT BE RULED OUT WITH WEAK DESTABILIZATION. HIGHS WILL BE INT HE LOW/MID 70S...WITH FURTHER COOLING BENEATH AN UPPER LOW THAT WILL SETTLE OVER THE CAROLINAS LATE WEEK. ANY CONVECTION SHOULD DIE OFF AS THE UPPER FORCING DEPARTS TO THE EAST AND NOCTURNAL COOLING SETS IN. HOWEVER...WITH THE AFOREMENTIONED CANADIAN SHORTWAVE DROPPING THROUGH THE MIDWEST... SOME ADDITIONAL SHOWERS MAY DROP SOUTH THROUGH VA EARLY THURSDAY. MAINLY INT HE LOWER 50S. && .LONG TERM /THURSDAY THROUGH MONDAY/... AS OF 405 AM TUESDAY... A STRONG SHORTWAVE OVER MANITOBA THIS MORNING WILL DIVE SOUTH THROUGH THE MIDWEST WEDNESDAY AND CUT OFF OVER THE CAROLINAS ON THURSDAY...DEEPENING 3 TO 4 STD BELOW NORMAL THURSDAY AFTERNOON AS AN OMEGA BLOCK DEVELOPS OVER THE CONUS. STRONG HEIGHT FALLS AND A PERSISTENT AREA OF LOW PRESSURE/TROUGHING OVER NC SHOULD AGAIN PROMOTE THE DEVELOPMENT OF SHOWERS... SOME OF WHICH COULD PRODUCE A LITTLE GRAUPEL. H10-H85 THICKNESSES DIPPING TO AROUND 1340M SUPPORTS HIGHS IN THE MID 60S TO AROUND 70S ON THURSDAY...WHICH IS INCREASINGLY SUPPORTED BY MEDIUM RANGE GUIDANCE. THE CHANCE OF SCATTERED SHOWERS WILL CONTINUE FRIDAY AND DECREASE RAPIDLY INTO THE WEEKEND AS THE UPPER LOW BEGINS TO FILL AND MOVE EAST. RIDGING ALOFT WILL SHIFT EAST TOWARD THE REGION AND ALLOW FOR A WARMING TRENDING THROUGH THE WEEKEND AND INTO NEXT WEEK. THE GFS AND ECMWF THEN INDICATE A SHORTWAVE DIVING SOUTHEAST OUT OF CANADA...WHICH ULTIMATELY WEAKENS THE RIDGE AND ALLOWS A COLD FRONT TO APPROACH NC FROM THE NORTHWEST LATE SUNDAY AND MONDAY. GIVEN THE EXPECTED STRENGTH OF THE RIDGE...CONFIDENCE IN THE FRONT MOVING TO OUR LATITUDE IS A LITTLE LOW AT THIS POINT AND THE FORECAST WILL REMAIN DRY. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/... AS OF 145 PM TUESDAY... VARIABLE AVIATION CONDITIONS ACROSS CENTRAL NC...WAVERING BETWEEN VFR AND MVFR DUE TO CEILINGS...WILL PERSIST THROUGH MOST OF THE AFTERNOON...WITH A GENERAL TREND TOWARD VFR BY EVENING. AS THE ATMOSPHERE CONTINUES TO DESTABILIZE DUE TO AFTERNOON HEATING AND THE APPROACH OF AN MID LEVEL DISTURBANCE...SCATTERED-NUMEROUS SHOWERS AND A FEW STRONG/SEVERE STORMS WILL ERUPT BY MID AFTERNOON IN THE WESTERN PIEDMONT...SPREADING EAST BY 22Z-00Z. THE STRONGER STORMS WILL PRODUCE LARGE AND WIND GUSTS AROUND 50-55KTS. THE THREAT FOR STORMS WILL DECREASE AFTER 01Z THOUGH A FEW SHOWERS WILL PERSIST WELL INTO THE NIGHT. AVIATION CONDITIONS WILL REMAIN HIGHLY VARIABLE AS AN AREA OF LOW PRESSURE ALOFT WILL CAUSE PERIODS OF UNSETTLED WEATHER AND ATTENDANT SUB VFR CEILINGS THROUGH FRIDAY. VFR PARAMETERS ASSOCIATED WITH AN AREA OF HIGH PRESSURE WILL RETURN TO CENTRAL NC FOR THE WEEKEND. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...26 NEAR TERM...SCR/WSS SHORT TERM...22 LONG TERM...22 AVIATION...WSS

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