Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 021856 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 255 PM EDT TUE SEP 2 2014 .SYNOPSIS...AN AREA OF HIGH PRESSURE WILL EXTEND OVER THE REGION TODAY. A WEAK SURFACE FRONT WILL SETTLE SOUTHWARD ACROSS CENTRAL NC ON WEDNESDAY. HIGH PRESSURE WILL BUILD BACK OVER THE AREA FOR THE REMAINDER OF THE WORK WEEK. && .NEAR TERM /THROUGH TONIGHT/... AS OF 1030 AM TUESDAY... LITTLE CHANGE REQUIRED TO NEAR TERM FORECAST BASED ON UPPER AIR AND SATELLITE ANALYSIS. MID-UPPER RIDGE REMAINS ANCHORED OVER THE SE U.S. WITH THE 850MB AND 700 MB ANTI-CYCLONE CENTERED OVER THE SAVANNAH RIVER VALLEY. THE POSITION OF THIS HIGH AND STRENGTH (322-323DM) SUPPORT AFTERNOON TEMPS WELL INTO THE 90S ACROSS CENTRAL NC. THESE HOT TEMPERATURES COMBINED WITH THE HUMIDITY WILL CREATE HEAT INDICES IN THE 100-104 DEGREE RANGE FOR LOCATIONS GENERALLY ALONG AND EAST OF HIGHWAY 1 WITH THE HIGHEST VALUES EXPECTED IN THE SANDHILLS. IN ADDITION...THE HOT AND HUMID AIR MASS WILL YIELD MODERATE INSTABILITY. THIS SHOULD INITIATE/SUPPORT ISOLATED CONVECTION PRETTY MUCH ANYWHERE IN THE FORECAST AREA. THE CHANCES FOR CONVECTION WILL LIKELY INCREASE TOWARD SUNSET AS A S/W IN THE NORTHERN STREAM PASSES TO OUR NORTH...DRAGGING A WEAK SURFACE BOUNDARY TOWARD OUR NORTHERN COUNTIES. THIS FEATURE INTERACTING WITH AVAILABLE LOW LEVEL MOISTURE/INSTABILITY SHOULD MAINTAIN A FEW SHOWERS/STORMS THIS EVENING ACROSS THE NORTHERN PIEDMONT...AND POSSIBLY WELL PAST MIDNIGHT OVER THE REST OF THE FORECAST AREA. A STRONG OR SEVERE STORM MAY OCCUR LATE THIS AFTERNOON AS LOW LEVEL LAPSE RATES WILL BE IN THE 9-10 DEGREE RANGE...SUPPORTIVE OF A LOCALIZED DOWNBURST. THE BIG STORY MAY BE THE AMOUNT OF LIGHTNING ASSOCIATED WITH THE STORMS. DUE TO PROJECTED PARAMETERS ALOFT...A STORM OR TWO MAY PRODUCE FREQUENT TO EXCESSIVE AMOUNT OF LIGHTING STRIKES...ESPECIALLY ACROSS THE SOUTHERN PIEDMONT AND SANDHILLS. && .SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/... AS OF 330 AM TUESDAY... THE WEAK FRONTAL ZONE...MAINLY JUST SURFACE TROUGH...WILL SETTLE OVER CENTRAL ON WEDNESDAY AS ITS PRIMARY SHORTWAVE LIFTS WELL OFF TO THE NORTHEAST. THE AXIS OF HIGHER PW NEAR 2 INCHES WILL SHIFT SOUTH ACROSS THE SOUTHERN TIER OF THE AREA. WEAK WESTERLY FLOW ALOFT MAY CONTAIN A DISTURBANCE OR TWO TO HELP TRIGGER SCATTERED SHOWERS AND STORMS...MAINLY ALONG AND SOUTH OF THE SURFACE TROUGH WHERE MODERATE INSTABILITY WILL DEVELOP. THE AIRMASS WONT CHANGE MUCH ON WEDNESDAY BUT H85 TEMPS ARE KNOCKED BACK A DEGREE OR TWO...AND ADDITIONAL CLOUD COVER SHOULD ALSO HELP TO KEEP HIGHS IN THE LOWER 90S. OVERNIGHT LOWS IN THE UPPER 60S AND LOWER 70S. && .LONG TERM /THURSDAY THROUGH TUESDAY/...
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AS OF 255 PM TUESDAY... FOR THU/FRI: CONTINUED WARM/HUMID WITH DAILY SCATTERED SHOWERS AND STORMS. AT THE SURFACE... THE WEAK FRONTAL ZONE WILL LIKELY HAVE WASHED OUT BY THU MORNING... AND THE SURFACE HIGH CENTERED OFF THE SOUTHEAST COAST WILL INTRODUCE A MOIST CONFLUENT LOW LEVEL FLOW OFF THE ATLANTIC INTO NC. A POSITIVELY TILTED TROUGH WILL SHIFT FROM MT/DAKOTAS/SCENTRAL CANADA EARLY THU ACROSS ONT/QUE BY FRI NIGHT... PROPELLING A COLD FRONT THROUGH THE GREAT LAKES/MID MISS VALLEY. AS THE FLAT RIDGE HOLDS ACROSS THE SOUTHEAST/MIDSOUTH/GULF STATES HOWEVER... WE`LL STAY WITHIN AN ENVIRONMENT CHARACTERIZED BY WEAK SHEAR AND MODERATE INSTABILITY (TEMPERED BY WARM MID LEVELS). PW VALUES SHOULD STAY ABOVE NORMAL AT 1.7-1.9"... NOT UNEXPECTED GIVEN THE TROPICAL NATURE OF THE INCOMING AIR MASS... AND SUFFICIENT TO SUPPORT SCATTERED CONVECTION ALONG THE SEA BREEZE... DYING FRONTAL ZONE... OR ANY OTHER SUBTLE BOUNDARY. WILL RETAIN AFTERNOON AND EVENING STORM CHANCES BOTH DAYS... WITH TEMPS HOLDING ABOUT A CATEGORY ABOVE NORMAL AS THICKNESSES STAY AROUND 10 M ABOVE NORMAL. FOR SAT-TUE: STILL EXPECT A TRANSITION FROM THE WARM/HUMID WEATHER TO MORE SEASONABLE CONDITIONS LATE IN THE WEEKEND. THE INITIAL MID LEVEL TROUGH OVER ERN QUEBEC WILL CONTINUE SHIFTING EAST OVER THE MARITIMES... WHILE A STRONG SLUG OF STRONG VORTICITY EMANATING FROM A STRONG COLD VORTEX OVER THE BEAUFORT SEA WILL PUSH EASTWARD CLOSE ON ITS HEELS... CROSSING HUDSON BAY ON SUNDAY. THIS SHOULD PUSH THE SURFACE COLD FRONT TO JUST NW OF NC BY SUN... AND WELL INTO THE STATE BY EARLY MON. BOTH THE GFS AND ECMWF TRACK THEIR COOL PARENT HIGHS OVER THE ST LAWRENCE VALLEY/SRN QUEBEC MON/TUE... WITH THE COLD FRONT PUSHING TO ERN NC AND ACROSS NWRN SC. THIS MODEL AGREEMENT LEADS TO GROWING CONFIDENCE THAT THE PARENT HIGH WILL BE DENSE ENOUGH TO PUSH THIS COOLER AIR WELL INTO CENTRAL NC... ALTHOUGH IT MAY NOT HAPPEN UNTIL LATE SUN NIGHT INTO MON MORNING. WILL FOLLOW THIS TREND WITH TEMPS HOLDING ABOVE NORMAL SAT/SUN (BUT NOT AS WARM IN THE NORTH SUN DUE TO MORE CLOUDS) WITH HIGHS IN THE MID 80S TO NEAR 90... BUT THEN EXPECT TEMPS TO PLUNGE FOR MON/TUE WITH THICKNESSES DROPPING TO 10-20 M BELOW NORMAL... YIELDING HIGHS NEAR 80 TO LOWER 80S. REGARDING PRECIP CHANCES... WE`RE LIKELY TO SEE SCATTERED TO PERHAPS NUMEROUS SHOWERS AND STORMS LATE SAT THROUGH AT LEAST SUN NIGHT... BOTH ALONG THE PREFRONTAL PIEDMONT TROUGH AND AHEAD OF AND WITH THE FRONT ITSELF. SHOWER/STORM CHANCES ARE EXPECTED TO PEAK SUN AFTERNOON. WITH THE MID LEVEL TROUGH AXIS SWINGING THROUGH THE REGION MON... WE MAY SEE LINGERING CHANCES FOR RAIN ESPECIALLY SOUTH AND EAST. THE SURFACE RIDGE NOSING IN FROM THE NORTH LATE MON INTO TUE ACCOMPANIED BY LOWERING PW VALUES SHOULD MEAN MOSTLY DRY WEATHER TUE... AS THE MID LEVEL TROUGH AXIS LIFTS NE AWAY FROM THE REGION FOLLOWED BY WEAK MID LEVEL SHORTWAVE RIDGING OVER THE CAROLINAS. -GIH
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&& .AVIATION /18Z TUESDAY THROUGH SUNDAY/... AS OF 110 PM TUESDAY... EXPECT VFR CONDITIONS TO PERSIST ACROSS CENTRAL NC THROUGH THIS EVENING. THERE WILL BE ISOLATED THUNDERSTORMS THIS AFTERNOON AND TONIGHT WITH BRIEF INSTANCES OF MVFR/IFR CONDITIONS IN VICINITY OF THE STORMS ALONG WITH WIND GUSTS 25-40KTS AND FREQUENT LIGHTNING. A FEW STORMS MAY PERSIST PAST MIDNIGHT AS A SURFACE FRONT SETTLES SOUTHWARD INTO CENTRAL NC. THIS SAME FEATURE MAY POOL MOISTURE LONG IT...CAUSING AREAS OF FOG AND/OR LOW CLOUDS TO DEVELOP. THIS ADVERSE CONDITIONS ARE EXPECTED TO BE SPOTTY WITH THE KRWI AND KFAY TERMINALS HAVING THE BEST CHANCE OF EXPERIENCING SUB-VFR CONDITIONS EARLY WEDNESDAY MORNING. SCATTERED CONVECTION WILL BE MORE PROMINENT WEDNESDAY AFTERNOON- EVENING...MAINLY ACROSS THE SOUTHERN COUNTIES INCLUDING IN VICINITY OF THE KFAY TERMINAL. OTHERWISE VFR CONDITIONS ARE EXPECTED TYPICAL SUMMERTIME WEATHER CONDITIONS ANTICIPATED THURSDAY THROUGH SATURDAY WITH AREAS OF EARLY MORNING FOG AND LOW CLOUDS GIVING WAY TO VFR CONDITIONS ASIDE FROM SUB-VFR CONDITIONS IN VICINITY OF SCATTERED AFTERNOON-EARLY EVENING CONVECTION. ON SUNDAY...A FRONT WILL BE APPROACHING FROM THE NW. THIS WEATHER SYSTEM WILL LIKELY ENHANCE THE PROBABILITY OF CONVECTION ACROSS CENTRAL NC. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...WSS NEAR TERM...WSS SHORT TERM...BLS LONG TERM...HARTFIELD AVIATION...WSS

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