Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 010056 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 856 PM EDT TUE MAR 31 2015 .SYNOPSIS...A COLD FRONT WILL MOVE THROUGH SOUTHERN VA AND NC TONIGHT...FOLLOWED BY HIGH PRESSURE FOR THE MIDDLE OF THE WEEK. && .NEAR TERM /THROUGH TONIGHT/... AS OF 320 PM TUESDAY... REMAINDER OF THE AFTERNOON... SHARPENING LEE SIDE TROUGH WILL MAINTAIN A BREEZY SW SFC WIND THROUGH 23Z. THIS WARM FLOW WILL RESULT IN LATE AFTERNOON TEMPS IN THE LOW-MID 70S. TONIGHT... A S/W CROSSING SOUTHERN NEW ENGLAND WILL EXIT OFF THE COAST THIS EVENING. THIS FEATURE WILL DRAG A SFC COLD FRONT SOUTHWARD ACROSS CENTRAL NC AFTER MIDNIGHT...EXITING OUR SOUTHERN COUNTIES JUST BEFORE DAYBREAK. LIMITED MOISTURE ASSOCIATED WITH THIS FEATURE THOUGH DECENT SPEED CONVERGENCE IN THE 850-700MB LAYER DOES PROVIDE SOME LIFT IN THE MOIST LAYER. BULK OF WRF MODELS AS WELL AS GLOBAL MODELS SUGGEST A DRY COLD FRONTAL PASSAGE THOUGH NMM DOES DEPICT A WEAKENING BAND OF LIGHT SHOWERS DRIFTING SWD ACROSS THE NORTHERN PIEDMONT/NORTHERN COASTAL PLAIN. PER LATEST RADAR IMAGERY...WRF MODELS MAY BE TOO AGGRESSIVE. HOWEVER WRF MODELS DEPICT DECENT SHOWER COVERAGE OCCURRING BY 21-22Z OVER SECTIONS OF NORTHERN AND CENTRAL VA. WILL CONTINUE TO MONITOR RADAR TRENDS THROUGH 22Z...AND ADJUST FORECAST ACCORDINGLY WITH A POSSIBLE INTRODUCTION OF A SLIGHT CHANCE/SMALL CHANCE POP...MAINLY OVER THE COASTAL PLAIN COUNTIES...LATE TONIGHT. OTHERWISE EXPECT A NARROW BAND OF CLOUDS WITH THE FRONT. SFC WINDS WILL VEER FROM A SW TO A NLY DIRECTION WITH THE FROPA. THIS MIXING WILL LEAD TO OVERNIGHT TEMPS SEVERAL DEGREES WARMER COMPARED TO LAST NIGHT. MIN TEMPS LOWER 40S FAR NORTH TO THE MID-UPPER 40S ELSEWHERE. && .SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/... AS OF 320 PM TUESDAY... WEDNESDAY...COOL SFC HIGH WILL EXTEND INTO OUR REGION FROM THE NORTH. THE SOUTH END OF THE 850MB THERMAL TROUGH WILL BRUSH ACROSS OUR FAR NORTHERN-NE COUNTIES. SUBSIDENCE THROUGH THE COLUMN WILL SUPPORT SUNNY SKIES. EXPECT AFTERNOON TEMPS TO VARY FROM AROUND 70 ACROSS THE FAR SOUTH-SW...TO LOW-MID 60S OVER THE NE COUNTIES. CLEAR AND SEASONABLY COOL WEDNESDAY NIGHT AS THE SFC RIDGE EXTENDS ACROSS THE REGION AND MID-UPPER LEVEL HEIGHTS INCREASE. EXPECT COOLEST OVERNIGHT TEMPS IN CLOSE PROXIMITY TO THE PARENT HIGH (WHERE SFC DEWPOINTS WILL BE COOLEST). MIN TEMPS WILL VARY FROM THE MID- UPPER 30S OVER THE NE TO THE LOWER 40S WEST WHERE A RETURN FLOW MAY SET-UP AS THE PARENT HIGH MOVES AWAY FROM THE REGION. && .LONG TERM /THURSDAY THROUGH TUESDAY/... AS OF 255 PM TUESDAY... FOR THU/THU NIGHT: A WEAK MID LEVEL SHORTWAVE TROUGH OVER THE LOWER MISS VALLEY EARLY THU WILL CROSS THE CAROLINAS THU AFTERNOON AND NIGHT. 925-800 MB MOISTURE IS PROJECTED TO INCREASE MAINLY ACROSS THE NORTHWEST HALF OF THE FORECAST AREA THU WITH PASSAGE OF THE 850 MB WARM FRONT TO OUR NE WITH STRENGTHENING LOW LEVEL SW WINDS IN THE WARM CONVEYOR BELT... ATTENDING THE WARM FRONT MOVING IN FROM THE SW. THE NAM DEPICTS MORE MOISTURE AND THUS MORE CLOUDS THAN THE GFS... BUT NONETHELESS THIS SHOULD EQUATE TO A DAY OF INCREASING CLOUDINESS (EARLIER NW AND MUCH LATER IN THE DAY SE)... AS PW VALUES RISE TO ABOVE NORMAL VALUES. A VEIL OF HIGH CLOUDS ASSOCIATED WITH THE DAMPENING SHORTWAVE TROUGH WILL AUGMENT THE LOWER LEVEL SCT-BKN STRATOCU ESPECIALLY LATER IN THE DAY. MOISTURE IS OVERALL FAIRLY SHALLOW... AND THE NEWEST NAM/GFS RUNS INDICATE ONLY LIGHT PATCHY PRECIP AT BEST IN OUR FAR WESTERN COUNTIES. WITH LIFT MECHANISMS LARGELY LIMITED TO WEAK MOIST UPGLIDE OVER WRN NC AND VERY WEAK DPVA... NO EXPECTED INSTABILITY... AND AGREEMENT FROM THE SREF PROBABILITIES SHOWING A LESS THAN 10 PERCENT CHANCE OF MEASURABLE PRECIP THROUGH THU NIGHT... WILL CUT POPS TO JUST ISOLATED IN THE NW AND FAR W ONLY LATE THU THROUGH THU NIGHT. HIGHS 70-75 WITH SLIGHTLY ABOVE NORMAL THICKNESSES. MILD LOWS IN THE UPPER 50S TO AROUND 60 WITH WIDESPREAD LOW CLOUDS AND PATCHY FOG OVERNIGHT. FOR FRI/SAT: CHANCES STILL LOOK GOOD FOR GETTING SOME RAINFALL ALONG AND BEHIND AND APPROACHING COLD FRONT. SHORTWAVE ENERGY ASSOCIATED WITH A COLD VORTEX OVER WRN HUDSON BAY EARLY FRI WILL ZIP THROUGH SE CANADA FRI... WHILE A SEPARATE WAVE (AND ATTENDING 120+ KT UPPER SPEED MAX) MOVES FROM CO/KS EARLY FRI THROUGH THE OH VALLEY AND MIDATLANTIC REGION THROUGH SAT. THESE FEATURES WILL PUSH A SURFACE COLD FRONT TO THE SPINE OF THE APPALACHIANS BY FRI EVENING THEN SOUTHEASTWARD THROUGH NC BY SAT AFTERNOON. MODELS HAVE TRENDED MUCH DRIER FOR FRI... WHEN WE`LL BE FIRMLY IN THE WARM SECTOR... AND THIS IS REASONABLE CONSIDERING THE LACK OF A FOCUS FOR LIFT AND AND NO OBVIOUS TRIGGERS. HOWEVER... FEEL COMPELLED TO RETAIN A SMALL CHANCE OF A SHOWER FRI AFTERNOON MAINLY EAST... WITH A THUNDERSTORM POSSIBLE EAST OF HIGHWAY 1 GIVEN MODEL MUCAPE PREDICTIONS OF MUCAPE VALUES OVER 500 J/KG FROM THE TRIANGLE SOUTH AND EAST... AND 35-40 KTS OF DEEP LAYER BULK SHEAR. EXPECT RAIN CHANCES TO RAMP UP FRIDAY EVENING AND REACH A MAXIMUM OVERNIGHT ALONG AND JUST BEHIND THE COLD FRONT. MECHANISMS TO FORCE ASCENT SHOULD INCLUDE POTENT HEIGHT FALLS... LOW LEVEL CONVERGENT FLOW... ACCELERATING 850 MB SW FLOW TO OVER 50 KTS... AND THE ARRIVAL OF DECENT (BUT NOT PARTICULARLY STRONG) UPPER DIVERGENCE ASSOCIATED WITH THE UPPER JET STREAK. HAVE BUMPED UP POPS TO 50-60%... HIGHEST NORTH... FRI NIGHT... MAINLY AFTER MIDNIGHT. THE FRONT SHOULD BE PUSHING SOUTHEASTWARD OUT OF THE CWA SAT MORNING... AND WILL RETAIN JUST A CHANCE OF RAIN OVER THE SOUTHEAST THROUGH MID MORNING... ALTHOUGH THE 00Z ECMWF IS SEVERAL HOURS SLOWER... AND IF IT COMES TO PASS... WILL MEAN MORE LIGHT RAIN LINGERING LONGER OVER THE PIEDMONT INTO SAT MORNING. EITHER WAY... EXPECT IMPROVING BUT COOLING WEATHER ON SAT WITH CLEARING SKIES. THE DROP IN THICKNESSES BACK TO JUST UNDER NORMAL WILL MEAN COOLER HIGHS ON SAT IN THE 60S... STILL FAIRLY SEASONABLE BUT QUITE A DROP AFTER FRIDAY HIGHS IN THE UPPER 70S TO LOWER 80S. FOR SAT NIGHT/SUN: COOL HIGH PRESSURE WILL BUILD OVERHEAD BEHIND THE FRONT THROUGH SAT NIGHT... BEHIND THE SHORTWAVE EXITING SWIFTLY OFF THE MIDATLANTIC AND NORTHEAST COAST. THICKNESSES ARE PROJECTED TO BE 20-30 M BELOW NORMAL SUN MORNING AND WITH SURFACE WINDS BECOMING LIGHT OR CALM AND CLEAR SKIES... EXPECT GOOD RADIATIONAL COOLING WITH LOW IN THE UPPER 30S. HIGHS EASTER SUNDAY WILL BE MOSTLY IN THE MID 60S WITH A STABLE AND DRY COLUMN YIELDING LOTS OF SUNSHINE. FOR MON/TUE: THE SURFACE HIGH WILL MOVE OFF THE CAROLINA COAST SUN NIGHT AND MON... AND THE ONSET OF RETURN FLOW WITH A LOW LEVEL FEED OUT OF THE BAHAMAS WILL BRING WARMER WEATHER MONDAY WITH A FEW MORE CONVECTIVE CLOUDS. THE MID LEVEL FLOW BRIEFLY FLATTENS MON BEFORE BECOMING BROADLY FROM THE WSW ACROSS THE SRN CONUS IN RESPONSE TO A PROMINENT TROUGH SHIFTING INTO THE PACIFIC NORTHWEST. THE GFS IS WETTER EARLIER DUE TO A WEAK MID LEVEL WAVE PASSAGE ON MONDAY... WHICH COULD EASILY BE A SPURIOUS ARTIFACT... AND WILL STICK WITH VERY LOW OR NO POPS FOR MON AT THIS TIME. THE COLUMN SHOULD CONTINUE TO MOISTEN WITH A STEADY RISE IN RAIN CHANCES MON NIGHT/TUE WITH THE COMBINATION OF SW MID LEVEL FLOW AND A LOWER LEVEL FEED OUT OF THE GULF AND ATLANTIC. BUT THE LACK OF ANY FOCUS OR STRONG TRIGGER FOR LIFT PRECLUDES GOING ANY HIGHER THAN CHANCE POPS AT THIS TIME. EXPECT A TREND TO PARTLY THEN MOSTLY CLOUDY SKIES MON NIGHT THROUGH TUE. -GIH && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/... AS OF 840 PM TUESDAY... 24 HOUR TAF PERIOD: A GENERALLY DRY COLD FRONT WILL PUSH SOUTH- SOUTHEASTWARD ACROSS CENTRAL NC LATE THIS EVENING INTO THE OVERNIGHT. OUTSIDE OF POSSIBLY A SPRINKLE ALONG OR JUST IN ADVANCE OF THE FRONT... EXPECT DRY CONDITIONS WITH ONLY SOME SCATTERED TO AT TIME BROKEN CLOUDS ACCOMPANYING THE FRONTAL PASSAGE... GENERALLY IN THE 5 TO 7 KFT RANGE. WINDS WILL SWING AROUND TO MORE OF A NORTHWEST TO NORTHERLY DIRECTION BEHIND THE FRONT TONIGHT. SURFACE HIGH PRESSURE WILL BUILD INTO THE AREA ON WEDNESDAY... RESULTING IN GENERAL MOSTLY SUNNY SKIES. HOWEVER... A BRIEF PERIOD OF 2-3 KFT (MOSTLY SCATTERED AT BEST) CLOUDS MAY DEVELOP IN THE 12- 16Z TIME FRAME ACROSS THE EASTERN TAF SITES (KRDU/KRWI/KFAY) AS LOW LEVEL WINDS BECOME NORTH-NORTHEAST TO NORTHEAST. CANNOT COMPLETELY RULE OUT A BRIEF PERIOD OF MVFR CIGS... BUT CONFIDENCE IS WAY TOO LOW TO INCLUDE ANY MENTION OF SUB-VFR CIGS IN THE TAFS. OTHERWISE... VFR CONDITIONS ARE EXPECTED ON TUESDAY WITH GENERALLY NORTH TO NORTHEASTERLY WINDS IN THE 5 TO 10 KT RANGE. AN APPROACHING FRONTAL SYSTEM WILL INCREASE THE THREAT FOR SUB VFR CONDITIONS THURSDAY NIGHT THROUGH FRIDAY NIGHT. THE HIGHEST PROBABILITY FOR SHOWERS AND WIDESPREAD MVFR/IFR CEILINGS WILL BE FRIDAY NIGHT. THE FRONTAL SYSTEM WILL MOVE EAST OF THE REGION EARLY SATURDAY...LEADING TO A RETURN OF VFR CONDITIONS WHICH WILL PERSIST THROUGH SUNDAY. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...RAH NEAR TERM...WSS SHORT TERM...WSS LONG TERM...HARTFIELD AVIATION...BSD/WSS

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