Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 211146 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 746 AM EDT TUE OCT 21 2014 .SYNOPSIS....A LEAD SHORTWAVE TROUGH ALOFT WILL CROSS OUR REGION THIS MORNING...FOLLOWED BY THE PASSAGE OF A COLD FRONT THIS AFTERNOON AND EVENING. AN UPPER LEVEL LOW WILL SETTLE SOUTHEAST ACROSS THE MIDDLE ATLANTIC REGION TONIGHT THROUGH WEDNESDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 330 AM TUESDAY... A LEAD SHORTWAVE TROUGH ALOFT AND ASSOCIATED MID LEVEL (AOA 9-10 THOUSAND FT) CLOUD BAND AND VIRGA - OR ISOLATED SPRINKLE AT THE SURFACE - WILL MOVE EAST ACROSS CENTRAL NC THROUGH 12Z. SKIES WILL CONSEQUENTLY BECOME MOSTLY CLEAR FROM WEST TO EAST THROUGH MID- MORNING...WHICH WILL PROVIDE AN OPPORTUNITY TO SEE THE ORIONID METEOR SHOWER IN THE COUPLE HOURS PRIOR TO DAYBREAK OVER THE PIEDMONT COUNTIES. ANOTHER STRONG NORTHERN STREAM SHORTWAVE TROUGH WILL AMPLIFY SHARPLY SSE FROM NORTHERN MI AT 07Z TO THE CENTRAL APPALACHIANS BY THIS EVENING...THEN ULTIMATELY CULMINATE IN THE DEVELOPMENT OF AN UPPER LOW OVER THE MIDDLE ATLANTIC REGION BY EARLY WED. A PRECEDING SURFACE COLD FRONT...ANALYZED FROM WESTERN NY TO NORTHERN AR AT 07Z...WILL MOVE EAST ACROSS CENTRAL NC THIS AFTERNOON AND EVENING. WITH MOSTLY SUNNY SKIES PRECEDING THE FRONT...AND A WEST TO NW DOWNSLOPE WIND AHEAD AND BEHIND IT...TEMPERATURES WILL CLIMB INTO THE LOWER 70S OVER THE WESTERN PIEDMONT TO UPPER 70S OVER EASTERN SANDHILLS AND SOUTHERN COASTAL PLAIN. THOUGH MOISTURE AND INSTABILITY ARE FORECAST TO REMAIN LIMITED OVERALL...THE FORMER CONFINED TO A THIN LAYER BETWEEN 850-750 MB AND THE LATTER AOB 150 J/KG PER BUFR SOUNDINGS AND SREF PROBABILITIES... LOW LEVEL CONVERGENCE ALONG THE FRONT AMIDST FALLING HEIGHTS ALOFT LATE IN THE DAY MAY SUPPORT A BAND OF WIDELY SCATTERED SHOWERS OR SPRINKLES MAINLY ACROSS THE NORTHERN PIEDMONT AND NORTHERN COASTAL PLAIN...WHERE VERY WEAK INSTABILITY AND DEEPER LIFT SHOULD BE RELATIVELY MAXIMIZED IN CLOSEST PROXIMITY TO THE AMPLIFYING SHORTWAVE TROUGH AND ASSOCIATED COLD POOL ALOFT. ANY SCATTERED SHOWERS SHOULD MOVE EAST AND/OR DISSIPATE WITH THE ONSET OF NOCTURNAL COOLING AND THE PASSAGE OF THE COLD FRONT BY EVENING. TONIGHT: THE CENTER OF THE STRONGEST MID LEVEL HEIGHT FALLS...ON THE ORDER OF 100 M/12 HR...WILL CROSS THE NORTHEAST HALF OF THE CWFA AS THE POTENT SHORTWAVE TROUGH CONTINUES TO AMPLIFY SSE OVERNIGHT. THIS FORCING FOR ASCENT IN CONJUNCTION WITH THE ARRIVAL OF THE COLD POOL/STEEPENING LAPSE RATES ALOFT WILL SUPPORT A RENEWED CHANCE OF SPRINKLES OR LIGH RAIN SHOWERS OVER THE NORTHEAST PIEDMONT AND NORTHERN COASTAL PLAIN. DRY AND VARIABLY CLOUDY ELSEWHERE. LOWS MOSTLY 45 TO 50 DEGREES. && .SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/... AS OF 340 AM TUESDAY... THE UPPER LOW WILL DRIFT ACROSS THE CHESAPEAKE BAY AND DELMARVA ON WED...THEN LIFT SLOWLY UP THE MIDDLE ATLANTIC COAST WED NIGHT AND BEYOND. ASSOCIATED SURFACE COASTAL LOW PRESSURE WILL DEEPEN BY ABOUT 10 MB (FROM JUST UNDER 1010 MB TO JUST UNDER 1000 MB) FROM 12Z WED TO 12Z THU...AS IT TOO LIFTS UP THE MIDDLE ATLANTIC COAST. THE COLDEST TEMPERATURES/STEEPEST LAPSE RATES ALOFT ASSOCIATED WITH THE UPPER LOW...THE FORMER IN EXCESS OF MINUS 20 C AND THE LATTER BETWEEN 6.5-7 C/KM...WILL CONSEQUENTLY BRUSH THE NORTHEAST PIEDMONT AND NORTHERN-CENTRAL COASTAL PLAIN...AND RESULT IN A CHANCE OF "INSTABILITY" SHOWERS OR SPRINKLES WITH DIURNAL HEATING. IT WILL OTHERWISE BE COOLER AND BREEZY...WITH NORTHWESTERLY DAYTIME WIND GUSTS UP TO 25 MPH OWING TO THE DEEPENING COASTAL LOW...AND HIGHS IN THE 60S. CLEARING AND SIMILARLY COOLER WED NIGHT...WITH LOWS MOSTLY IN THE LOWER TO MIDDLE 40S. && .LONG TERM /THURSDAY THROUGH MONDAY/... AS OF 320 AM TUESDAY... DEEP NORTHWESTERLY FLOW WILL CONTINUE ON THURSDAY BETWEEN THE UPPER LOW DRIFTING NORTHEAST ALONG THE NEW ENGLAND COAST AND A SHORTWAVE RIDGE OVER THE MISSISSIPPI RIVER VALLEY. LOW-LEVEL THICKNESSES ARE FORECAST TO BE AROUND 1335M THURSDAY MORNING...AND FULL INSOLATION DURING THE AFTERNOON SUPPORTS HIGHS IN THE 63-68 RANGE. THE ALREADY LOW AMPLITUDE RIDGE WILL BREAK DOWN ON THURSDAY NIGHT INTO FRIDAY AS ANOTHER WAVE DIVES DOWN THE BACKSIDE OF THE DEPARTING UPPER LOW AND CROSSES NC FRIDAY NIGHT. WE SHOULD SEE SOME HIGH CLOUDS SPREAD ACROSS THE AREA LATE THURSDAY NIGHT AND FRIDAY AS AN UPPER JET STRENGTHENS OVER THE SOUTHEAST AHEAD OF THE TROUGH...THOUGH ITS NOT CLEAR HOW THICK THE CLOUD COVER WILL BE. HAVE NUDGED THURSDAY NIGHT LOWS UP A COUPLE DEGREES INTO THE MID 40S. HIGHS FRIDAY IN THE MID/UPPER 60S. MODELS HAVE TRENDED TOWARD A MUCH MORE COMPACT AND CLOSED OFF WAVE WITH A STRONG SHOT OF DCVA FRIDAY NIGHT...BUT WITH NO QPF EAST OF THE MOUNTAINS AS IT ENCOUNTERS A VERY DRY AIRMASS OVER CENTRAL NC. THE PROGRESSIVE NATURE OF THE TROUGH LOOKS LIKE IT WILL ALSO KEEP A POTENTIAL (SUB)TROPICAL SYSTEM AND ASSOCIATED MOISTURE IN THE CARIBBEAN WELL TO OUR SOUTH. THUS THE FORECAST WILL BE DRY THROUGH THE PERIOD. ONCE THE TROUGH PASSES...THE ECMWF AND GFS ROUGHLY AGREE THAT UPPER RIDGING WILL BUILD ACROSS THE SOUTHERN US...WITH THICKNESSES CLIMBING BACK TOWARD 1370M...WHICH IS SLIGHTLY ABOVE NORMAL. && .AVIATION /12Z TUESDAY THROUGH SATURDAY/...
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AS OF 745 AM TUESDAY... A LIGHT SSW SURFACE WIND WILL INCREASE INTO THE 5-10 KT FROM THE WSW AHEAD OF A COLD FRONT THAT WILL MOVE SOUTHEAST ACROSS THE AREA BETWEEN 20Z-01Z THIS AFTERNOON AND EVENING. THE PASSAGE OF THE FRONT WILL CAUSE SURFACE WINDS TO VEER TO WNW AND INCREASE INTO THE 8-14 KT RANGE WITH A FEW GUSTS INTO THE MID-UPPER TEENS KTS. SCATTERED TO BROKEN CUMULUS WITH BASES BETWEEN 4500-7000 FT AND TOPS BETWEEN 9-15 THOUSAND FT - THE DEEPEST OF WHICH WILL BE CAPABLE OF PRODUCING A LIGHT SHOWER OR SPRINKLE - WILL ALSO DEVELOP IN THE VICINITY OF THE PASSING FRONT...WITH THE RELATIVE GREATER CLOUD COVERAGE AND CHANCE OF A SHOWER AT KRDU AND KRWI. A STEADY WNW TO NW SURFACE WIND...WITH AN OCCASIONAL GUST INTO THE MID-UPPER TEENS KTS...WILL CONTINUE AS COLDER AIR MOVES IN BEHIND THE FRONT THIS EVENING. OUTLOOK: THE DEVELOPMENT OF AN UPPER LOW OVER THE MIDDLE ATLANTIC STATES TONIGHT AND WED WILL RESULT IN PERIODS OF LOW VFR CEILINGS (BETWEEN 3500-5000 FT) AND A CHANCE OF SHOWERS MAINLY AT KRWI NORTHEAST TOWARD THE CHESAPEAKE BAY. COASTAL LOW PRESSURE ALONG THE MIDDLE ATLANTIC AND NORTHEAST COAST WILL PRODUCE NW SURFACE WINDS IN THE LOW-MID TEENS KTS WITH GUSTS AROUND 20 KTS WED...AND TO A LESSER DEGREE ON THU.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...MWS NEAR TERM...MWS SHORT TERM...MWS LONG TERM...BLS AVIATION...MWS

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