Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 030712 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 310 AM EDT THU SEP 3 2015 .SYNOPSIS...A DISTURBANCE ALOFT WILL CROSS EASTERN PORTIONS OF CENTRAL NC THIS MORNING. A LEE TROUGH WILL OTHERWISE LINGER OVER CENTRAL NC UNTIL A BACK DOOR COLD FRONT MOVES SOUTHWEST ACROSS THE AREA LATE FRI AND FRI NIGHT. && .NEAR TERM /THROUGH TONIGHT/... AS OF 3 AM THURSDAY... REST OF THIS MORNING AND TODAY: LINGERING CONVECTION... ASSOCIATED WITH A DISTURBANCE ALOFT MOVING ACROSS THE AREA THIS MORNING... SHOULD GENERALLY SHIFT TO THE EAST OF CENTRAL NC WITHIN A COUPLE OF HOURS... GENERALLY ENDING ANY LINGERING THREAT THIS MORNING OF ANY SHOWERS AND STORMS. HOWEVER... SOME PATCHY FOG AND STRATUS HAS AND WILL LIKELY DEVELOP ACROSS PORTIONS OF THE AREA THIS MORNING... MAINLY ACROSS LOCATIONS THAT SAW A DECENT AMOUNT OF PRECIP FROM THE AFOREMENTIONED DISTURBANCE... AS SKIES ARE CLEARING OFF BEHIND THE DISTURBANCE. ANY FOG AND LOW STRATUS THAT DEVELOPS THIS MORNING SHOULD LIFT AFTER SUNRISE. EXPECT GENERALLY DRY CONDITIONS FOR TODAY WITH... ONLY A LOW CHANCE OF SEEING ANY SHOWERS AND STORMS THIS AFTERNOON... MAINLY ALONG AND EAST OF A WEAK SURFACE TROUGH... EXPECTED TO BE LOCATED ACROSS THE EASTERN/SOUTHEASTERN THIRD OF CENTRAL NC. IN ADDITION... A TRAILING LINGERING PIECE OF THE DISTURBANCE ALOFT... WHICH IS PASSING THROUGH THE AREA CURRENTLY... MAY ALLOW FOR THE BEST CHANCE OF SEEING SOME SHOWERS AND STORMS ACROSS OUR FAR SOUTHEASTERN COUNTIES... THIS IS WHERE WE SHOULD HAVE THE BEST SURFACE INSTABILITY AS WELL. HOWEVER... WITH WEAK DEEP LAYER SHEAR AND ONLY MODEST INSTABILITY AT BEST... WE DO NOT EXPECT ANY SEVERE STORMS TODAY. HIGH TEMPS WILL AGAIN BE IN THE UPPER 80S TO LOWER 90S... WITH A FEW LOCATIONS MAKING IT INTO THE MID 90S... THANKS TO A FAIRLY DEEP MIX LAYER AND AFTERNOON LOW LEVEL THICKNESS VALUES NEAR 1430 METERS. TONIGHT: A FAIRLY WEAK NORTHWEST MID LEVEL FLOW ALOFT MAY ALLOW FOR A WEAK DISTURBANCE OR TWO TO CROSS THE AREA THIS EVENING OR OVERNIGHT TONIGHT. HOWEVER... WITH THE LOSS OF DAYTIME HEATING WE WILL ONLY KEEP A SLIGHT CHANCE OF SHOWERS ACROSS THE NORTHERN PORTION OF THE AREA FOR TONIGHT (WITH MOST LOCATIONS LIKELY REMAINING DRY). OVERNIGHT LOW ARE EXPECTED TO BE IN THE UPPER 60S TO LOWER 70S. && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... AS OF 333 PM WEDNESDAY... THE MID LEVEL VORTICITY MAX SHOULD BE SHIFTING OFF THE NRN NC COAST THU MORNING... ALBEIT WITH A WEAK TRAILING SHEAR AXIS EXTENDING BACK ACROSS THE NRN CWA. THIS TRAILING VORTICITY WILL SINK SLOWLY SOUTHWARD THROUGH THE DAY BUT REMAIN EXTENDED ACROSS THE SRN CWA LATE THU THROUGH THU NIGHT. PW VALUES WILL HAVE FALLEN WITH A SLIGHTLY MORE STABLE AND SUBSIDING COLUMN BEHIND THE CORE OF THE EXITING WAVE... SO EXPECT ANY SHOWER/STORM COVERAGE TO BE FAIRLY SMALL GIVEN THE WEAK WIND FIELD... LACK OF STRONG FORCING FOR ASCENT... AND LIMITED CAPE. WILL RETAIN AN ISOLATED POP JUST ACROSS THE SOUTH AND SE NEAR THE SHEAR AXIS AND WHERE LOW LEVEL DEWPOINTS WILL LIKELY BE HIGHER. ANOTHER MUCH WEAKER WAVE WILL PUSH INTO THE REGION FROM THE SW LATE THU INTO THU NIGHT... BUT THIS APPEAR TO CONTRIBUTE VERY LITTLE DYNAMIC FORCING... AND WITH LACK OF HEATING AFTER SUNSET... COVERAGE SHOULD BE ISOLATED AT BEST WITH THIS SECOND WAVE. WILL KEEP A MENTION OF ISOLATED STORMS IN THE NE CWA THROUGH THE EVENING... THEN TREND POPS DOWN BELOW 15% OVERNIGHT. THIS PATTERN CORRELATES WITH THE LOCATION OF THE SREF`S HIGHER CHANCES OF MEASURABLE PRECIP. WITH GOOD MIXING AND CONTINUED ABOVE NORMAL THICKNESSES... EXPECT STEAMY HIGHS OF 90-95. LOWS 67-72 UNDER PARTLY CLOUDY SKIES. -GIH && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... AS OF 310 AM THURSDAY... LOW LEVEL NELY FLOW WILL DEVELOP OVER THE REGION SATURDAY IN THE WAKE OF THE DEPARTING SURFACE BOUNDARY AS A SFC HIGH OVER SOUTHERN NEW ENGLAND NOSES SOUTHWARD. THIS LOW LEVEL FLOW APPEARS TO HAVE A DECENT FETCH OFF THE ATLANTIC. THUS...THIS WILL SET UP A BATTLE BETWEEN THE DRIER AIR MASS UNDERNEATH THE SURFACE RIDGE AND THE MOIST AIR INTRUDING WESTWARD OFF THE ATLANTIC. THE ORIENTATION/POSITION OF THE SURFACE RIDGE SUGGEST THE DRIER AIR WILL LIKELY BE IMMEDIATELY TO OUR WEST (OVER THE HIGHER TERRAIN OF WESTERN NC). IN ADDITION...LOW LEVEL FLOW WILL HAVE AN UPSLOPE COMPONENT. THUS...EXPECT TO SEE A GOOD DEAL OF CLOUDINESS BOTH SATURDAY AND SUNDAY ACROSS THE REGION. STILL MUCH UNCERTAINTY AS TO THE EXTENT OF SHOWER COVERAGE TO OCCUR. THE GFS HAS BEEN TRENDING TOWARD THE WETTER ECMWF SOLUTION THE PAST FEW RUNS. BOTH MODELS SUGGEST EITHER A LINGERING SHEAR AXIS OVERHEAD OR A SERIES OF WEAK PERTURBATIONS WORKING THEIR WAY WEST OFF THE ATLANTIC. PRESENCE OF A COASTAL TROUGH SHOULD FOCUS BEST LOW LEVEL CONVERGENCE OVER THE COASTAL PLAIN...WHILE AFTERNOON HEATING AND LOW LEVEL UPSLOPE COMPONENT SHOULD AID ADDITIONAL DEVELOPMENT IN THE AFTERNOON-EARLY EVENING OVER CENTRAL NC. STILL...FORCING APPEARS WEAK SO FAVOR POPS IN THE SLIGHT CHANCE-CHANCE RANGE SATURDAY AND SUNDAY. ONCE A DISCERNIBLE FEATURE NOTED...THEN POPS MAY HAVE TO BE TWEAKED HIGHER OR CONCENTRATED OVER A CERTAIN SECTION OF THE FORECAST REGION. STILL FEEL FAIRLY CERTAIN THAT WE SHOULD SEE NEAR OR BELOW NORMAL TEMPS THIS WEEKEND. IF CLOUDS AND/OR PRECIP MORE EXTENSIVE THAN CURRENT THINKING...THEN MUCH OF THE PIEDMONT MAY NOT REACH ABOVE 80 BOTH DAYS. FOR NOW WILL TARGET MAX TEMPS IN THE PIEDMONT NEAR 80- LOWER 80S WITH MID 80S COMMON OVER THE EAST AND SE. THE LOW LEVEL E-NE FLOW WILL BEGIN TO ABATE MONDAY AND MORE SO TUESDAY INTO WEDNESDAY. THIS SIGNALS A RETURN TO SLIGHTLY DRIER AND WARMER CONDITIONS THROUGH THIS PERIOD WITH THE BULK OF THE PRECIP DIURNALLY DRIVEN. LOW LEVEL THICKNESSES BY MID WEEK AVERAGE 20M ABOVE NORMAL. THIS SUGGEST AFTERNOON TEMPS REBOUNDING BACK INTO THE 85-90 DEGREE RANGE BY TUESDAY AND WEDNESDAY. && .AVIATION /06Z THURSDAY THROUGH MONDAY/... AS OF 145 AM THURSDAY... AND AREA OF SCATTERED TO NUMEROUS SHOWERS AND STORMS HAS PUSHED TO THE EAST AND SOUTH OF ALL CENTRAL NC TAF SITES EXCEPT KFAY. HOWEVER... THE GREATEST COVERAGE AND INTENSITY SHOULD REMAIN TO THE EAST OF KFAY THIS MORNING. THUS... WILL JUST INCLUDE A TEMPO FOR SHOWERS IN THE 06-08Z TIME FRAME AT KFAY. WRT OF ANY SUB-VFR CONDITIONS THIS MORNING... EXPECT ANY SUB-VFR CONDITIONS SHOULD BE ACROSS THE EASTERN TAF SITES... WITH THE GREATEST PROBABILITY OF OCCURRENCE AT KRDU AND KRWI (WHERE CONVECTION OCCURRED YESTERDAY EVENING AND THIS MORNING)... WITH KRWI POSSIBLY SEEING SOME IFR/LIFR FOG AND LOW STRATUS. ANY SUB-VFR CONDITIONS SHOULD QUICKLY DIMINISH BY 13Z... WITH VFR CONDITIONS GENERALLY EXPECTED FOR THE REMAINDER OF THE TAF PERIOD... WITH ONLY A VERY SMALL CHANCE OF SEEING ANY ISOLATED SHOWERS AND/OR STORMS ACROSS CENTRAL NC TODAY. LOOKING AHEAD: CONVECTION WILL BE POSSIBLE IN ASSOC/W A COLD FRONTAL PASSAGE ON FRIDAY. HIGH PRESSURE WILL EXTEND INTO THE REGION FROM THE N/NE IN THE WAKE OF THE FRONT...RESULTING IN A SYNOPTIC PATTERN REMINISCENT OF COLD AIR DAMMING. AS A RESULT...SUB-VFR CEILINGS WILL BE POSSIBLE AT ALL TERMINALS OVER THE WEEKEND. -VINCENT && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...77/26 NEAR TERM...BSD SHORT TERM...HARTFIELD LONG TERM...WSS AVIATION...BSD/VINCENT

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