Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 031706 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 105 PM EDT THU SEP 3 2015 .SYNOPSIS...WEAK HIGH PRESSURE WILL HOLD OVER THE REGION TODAY... WITH A WEAK DISTURBANCE PASSING THROUGH TONIGHT. A BACKDOOR COLD FRONT WILL APPROACH FROM THE NORTH LATE FRIDAY... THEN PUSH SOUTHEAST THROUGH THE AREA FRIDAY NIGHT INTO EARLY SATURDAY. HIGH PRESSURE WILL NOSE IN FROM THE NORTH OVER THE WEEKEND. && .NEAR TERM /THROUGH TONIGHT/... AS OF 1045 AM THURSDAY... CONVECTION CHANCES OVERALL LOOK PRETTY SLIM FOR THE DAYLIGHT HOURS IN CENTRAL NC. THE MSLP PATTERN REMAINS VERY WEAK WITH THE LATEST SURFACE ANALYSIS SHOWING WEAK TROUGHING ACROSS THE SE CWA AND THE RIDGE HOLDING JUST WEST OF THE MOUNTAINS ACROSS THE OH/TN VALLEY AND LOWER MISS VALLEY. THIS MORNING`S FOG/STRATUS WHICH FORMED IN THE WAKE OF LAST NIGHT`S CONVECTION HAS LARGELY DISSIPATED/MIXED OUT... LEAVING FAIR SKIES WITH PATCHES OF HIGH CLOUDS ASSOCIATED WITH THE WEAK SHEAR AXIS TRAILING OFF THE POTENT WAVE WHICH PASSED SE THROUGH THE REGION LAST NIGHT. MODELS ARE FOCUSING ON THE SRN AND EXTREME SE CWA FOR CONVECTION CHANCES TODAY... ALTHOUGH A NUMBER OF CONVECTION ALLOWING MODELS INCLUDING THE LATEST RAP... NSSL WRF... AND NCAR WRF ENSEMBLE ARE NOT EXCITED ABOUT MUCH COVERAGE AND/OR KEEP MOST ACTIVITY JUST TO OUR SOUTH AS THE SHEAR AXIS CONTINUES TO SINK SLOWLY SOUTHWARD. BUT THERE WILL BE SUFFICIENTLY HIGH PW (ALTHOUGH STILL JUST SLIGHTLY ABOVE NORMAL) AND SURFACE DEWPOINTS IN THE SOUTHEAST TO SUPPORT ISOLATED TO SCATTERED SHOWERS/STORMS THIS AFTERNOON INTO EARLY EVENING. MODELS ARE SUBDUED WITH INSTABILITY WITH MARGINAL CAPE... AND DEEP LAYER SHEAR WILL BE EVEN LOWER THAN YESTERDAY AT JUST 15-20 KTS. WILL KEEP POPS AS IS... LOW CHANCES CONFINED TO THE SOUTH AND SE CWA WITH MINOR SPATIAL AND TEMPORAL TWEAKS. THICKNESSES ARE STILL WELL ABOVE NORMAL BY ABOUT 15 M BUT SLIGHTLY LOWER THAN YESTERDAY... ALL SUPPORTING HIGHS NEAR 90 TO THE LOWER 90S WITH PARTLY TO MOSTLY SUNNY SKIES. -GIH 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 /FRIDAY AND FRIDAY NIGHT/... AS OF 320 AM THURSDAY... A S/W DISTURBANCE AND ASSOCIATED SURFACE LOW WILL TRACK EASTWARD AND OFF OF SE CANADIAN COAST ON LATE TODAY AND TONIGHT. THE TRAILING COLD FRONT ASSOCIATED WITH THIS SYSTEM WILL PUSH SOUTH/SOUTHWESTWARD IN BACKDOOR FASHION ACROSS CENTRAL NC LATE FRIDAY INTO FRIDAY NIGHT. THIS COUPLED WITH ANOTHER WEAK DISTURBANCE PASSING THROUGH THE REGION IN THE WEAK NORTHWESTERLY FLOW ALOFT WILL ALLOW FOR SCATTERED SHOWERS AND STORMS TO DEVELOP LATE INTO THE DAY AND INTO THE EVENING... POSSIBLY LINGERING INTO THE EARLY MORNING HOURS OF FRIDAY ACROSS THE WESTERN/SOUTHWESTERN PORTION OF THE AREA. DESPITE BETTER INSTABILITY... LOW LEVEL CONVERGENCE WILL REMAIN WEAK ALONG WITH THE DEEP LAYER SHEAR. THUS... WE DO NOT EXPECT TO SEE ANY SEVERE WEATHER. HOWEVER... WITH SUCH A WEAK FLOW AND PW`S OF AROUND 1.75"... WE COULD SEE SOME LOCALIZED FLOODING... MAINLY IN URBAN AREAS AND POOR DRAINAGE AREAS (THOUGH THIS SHOULDN`T BE WIDESPREAD). HIGHS ON FRIDAY ARE EXPECTED TO BE IN THE LOWER 90S... WITH PERHAPS A FEW LOCATIONS TOUCHING THE MID 90S AGAIN. LOWS SATURDAY MORNING ARE EXPECTED TO BE IN THE UPPER 60S TO LOWER 70S. && .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 /18Z THURSDAY THROUGH TUESDAY/... AS OF 105 PM THURSDAY... VFR CONDITIONS WILL HOLD TODAY INTO THIS EVENING. A WEAK LOW PRESSURE TROUGH WILL REMAIN STRETCHED ACROSS SE NC AS WEAK HIGH PRESSURE HOLDS OVER NRN AND WRN NC. THERE IS A SMALL CHANCE OF A SHOWER OR STORM GENERATING BRIEF SUB-VFR CONDITIONS AT FAY TODAY MAINLY 19Z-01Z... BUT CHANCES ARE TOO LOW TO MENTION AT THIS TIME. THERE IS A RISK OF MVFR-IFR FOG LATE TONIGHT INTO EARLY FRI MORNING AT RDU/FAY AND ESPECIALLY RWI... WITH WINDS GOING CALM AND LITTLE IN THE WAY OF CLOUD COVER WITH RESIDUAL GROUND MOISTURE ALL FACILITATING FOG DEVELOPMENT ESPECIALLY IN LOW LYING AREAS. ISOLATED SHOWERS ARE POSSIBLE TONIGHT NEAR RDU/RWI... HOWEVER MODELS ARE NOT IN GOOD AGREEMENT ON THIS... AND ANY COVERAGE SHOULD BE LOW ANYWAY... SO WILL NOT MENTION IN THE TERMINAL FORECASTS FOR NOW. VFR CONDITIONS WILL AGAIN DOMINATE MID-LATE MORNING FRI... HOWEVER WE`LL SEE A TREND TOWARD NUMEROUS SHOWERS AND STORMS AREAWIDE TOWARD THE END OF THIS 24-HR FORECAST PERIOD... LIKELY STARTING NEAR OR JUST AFTER 16Z... AS A BACKDOOR COLD FRONT APPROACHES FROM THE NORTH. OUTSIDE OF ANY SHOWERS/STORMS... SURFACE WINDS WILL REMAIN LIGHT. LOOKING BEYOND 18Z FRI... CONFIDENCE IS HIGH THAT NUMEROUS SHOWERS AND STORMS WITH SLOW MOVEMENT WILL BRING A PERIOD OF ADVERSE AVIATION CONDITIONS TO ALL CENTRAL NC TERMINALS FRI AFTERNOON THROUGH MID EVENING. SUB-VFR CIGS/VSBYS... HEAVY DOWNPOURS... AND ENHANCED SURFACE WIND GUSTS WILL BE POSSIBLE IN/NEAR THIS ACTIVITY. THE COLD FRONT WILL PUSH SOUTHWARD THROUGH CENTRAL NC FRI NIGHT AND SETTLE TO OUR SOUTH SAT... HOLDING THERE WHILE WEAKENING THROUGH TUE AS HIGH PRESSURE NOSES IN FROM THE NORTH AND NE. SUB-VFR LOW CLOUDS AND FOG ARE LIKELY AT ALL SITES EACH LATE NIGHT/EARLY MORNING SAT/SUN/MON. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...HARTFIELD NEAR TERM...HARTFIELD/BSD SHORT TERM...BSD LONG TERM...WSS AVIATION...HARTFIELD

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