Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 310801 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 400 AM EDT TUE MAR 31 2015 .SYNOPSIS...HIGH PRESSURE WILL BUILD BRIEFLY OVER THE CAROLINAS THIS MORNING...AHEAD OF A CLIPPER LOW THAT WILL CROSS THE MIDDLE ATLANTIC STATES TODAY. A TRAILING COLD FRONT WILL MOVE THROUGH VA AND NC TONIGHT...FOLLOWED BY HIGH PRESSURE FOR THE MIDDLE OF THE WEEK. && .NEAR TERM /THROUGH TONIGHT/...
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AS OF 345 AM TUESDAY... BENEATH A PAIR OF AMPLIFYING SHORTWAVE TROUGHS IN NW FLOW ALOFT...A CLIPPER SURFACE LOW OVER SOUTHERN LAKE MI THIS MORNING WILL DIVE ESE ACROSS THE OH VALLEY AND MIDDLE ATLANTIC STATES TODAY. TO THE SOUTH OF THE CLIPPER LOW...A SURFACE TROUGH WILL SHARPEN IN THE LEE OF THE CENTRAL APPALACHIANS THIS AFTERNOON...WHILE THE TRAILING COLD FRONT PRESSES SOUTH...THEN CROSSES CENTRAL NC THIS EVENING. A TIGHTENING MSLP PRESSURE GRADIENT SURROUNDING THE CLIPPER LOW AND LEE TROUGH WILL CAUSE SOUTHWEST WINDS TO STEADILY INCREASE AFTER THE MORNING INVERSION BREAKS BETWEEN 10-11 AM...WITH SUSTAINED WINDS PEAKING IN THE 15-20 KT RANGE...WITH GUSTS BETWEEN 25-30 KTS - STRONGEST OVER THE NORTHERN PIEDMONT AND COASTAL PLAIN BETWEEN 300-630 PM. WHILE DRY ADIABATIC MIXING OF 00Z H85 TEMPERATURES SUPPORTS HIGHS IN THE LOWER 70S...STRONG AND INCREASINGLY WESTERLY (VEERING FROM SW) FLOW IN THE H85-925 LAYER THIS AFTERNOON WILL LIKELY SUPPORT FURTHER ADIABATIC WARMING OF THE AIR MASS...WITH RESULTANT HIGHS IN THE LOWER TO MIDDLE 70S - WARMEST SW. THE TRAILING COLD FRONT WILL PASS WITH LITTLE EXCITEMENT...ASIDE FROM AN ACCOMPANYING BAND OF CUMULUS THIS EVENING. BUFR SOUNDINGS DO DEPICT A SHALLOW LAYER OF WEAK ELEVATED INSTABILITY (MUCAPE GENERALLY AOB 100 J/KG) AT THE BASE OF A PERSISTENT SUBSIDENCE INVERSION BETWEEN 850-800 MB...AND THE HIRES-NMM IN FACT INDICATES SCATTERED SIMULATED REFLECTIVITY OVER CENTRAL NC BETWEEN 00-06Z. HOWEVER...LIMITED FORCING FOR ASCENT (ASIDE FROM FRONTAL CONVERGENCE) AND A LACK OF DEEP MOISTURE SUGGESTS ANY WEAK ELEVATED INSTABILITY WILL LIKELY GO UNREALIZED...OR ASSOCIATED CUMULUS OVERCOME BY ENTRAINMENT...AND THE FORECAST WILL CONSEQUENTLY BE KEPT DRY. CAA-DRIVEN LOWS IN THE LOWER 40S NORTH TO UPPER 40S SOUTH.
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&& .SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/...
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AS OF 355 AM TUESDAY... DEEP LAYER RIDGING...INCLUDING A 1020 MB OR SO SFC HIGH...WILL BUILD EAST ACROSS THE CAROLINAS WED AND WED NIGHT. THE RESULT WILL BE MAINLY CLEAR AND COOLER THAN AVG CONDITIONS...WITH TEMPERATURES MOSTLY IN THE 60S FOR HIGHS...TO AROUND 70 DEGREES OVER THE SANDHILLS AND SOUTHERN PIEDMONT. LOWS IN THE MIDDLE 30S TO LOWER 40S...PER PROJECTED LL THICKNESS VALUES AROUND 1345 METERS AT 12Z THU...WITH GOOD TO EXCELLENT RADIATIONAL COOLING.
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&& .LONG TERM /THURSDAY THROUGH MONDAY/... AS OF 335 AM TUESDAY... THE WEAK CUT OFF LOW CURRENTLY OFF THE CALIFORNIA BAJA WILL DEAMPLIFY AS IT CROSSES THE SOUTHERN US WEDNESDAY AND THEN LIFTS ACROSS THE CAROLINAS THURSDAY AFTERNOON/EVENING. MEANWHILE...HIGH PRESSURE WILL MOVE OFF THE VIRGINIA COAST ON THURSDAY...ALLOWING SOME DEWPOINT RECOVERY DURING THE DAY. HOWEVER... GUIDANCE ONLY INDICATES DEWPOINTS REACHING THE LOW/MID 50S ACROSS THE SOUTHERN PIEDMONT THURSDAY AFTERNOON...LEADING TO LITTLE TO NO INSTABILITY TO AID THE WEAKENING FORCING ASSOCIATED WITH AFOREMENTIONED UPPER DISTURBANCE. WE MAY SEE A LITTLE BETTER CHANCE OF SOME SHOWERS THURSDAY NIGHT AS THE LOW-LEVEL FLOW INCREASES AND MOIST WARM ADVECTION BRINGS PW UP TOWARD 1.25". THE ECMWF IS THE MAIN GUIDANCE TO SUPPORT THIS...SUGGESTING JUST ISOLATED SHOWERS AFTER MIDNIGHT. HIGHS THURSDAY IN THE LOW/MID 70S FOR MOST AREAS...WHILE LOWS WILL BE IN THE UPPER 50S. WARMING WILL CONTINUE ON FRIDAY WITH A BREEZY SOUTHWEST WIND AHEAD OF A STRONGER SHORTWAVE CROSS THE CENTRAL PLAINS AND ITS ASSOCIATED SURFACE LOW AND COLD FRONT. SOME WEAK INSTABILITY OF UP TO 500 J/KG SHOULD DEVELOP ON FRIDAY BUT THERE WON`T BE MUCH OF A FOCUS TO KICK OFF ANY SHOWERS OR STORMS...SO PREFER TO KEEP POPS TO JUST SLIGHT CHANCE DURING THE AFTERNOON. MOST OF THE PRECIP WILL COME WITH THE COLD FRONT FRIDAY NIGHT...AND DESPITE STRONG SHEAR OF UP TO 40KT...THE PRECIP SHOULD BE MAINLY COME FROM SHOWERS GIVEN THE POOR DIURNAL TIMING AND LACK OF INSTABILITY SHOWN IN MODEL SOUNDINGS. HIGHS SHOULD REACH TO THE UPPER 70S AND LOWER 80S FRIDAY AS 1000- 850MB THICKNESSES EXCEED 1380M. AS THE FRONT MOVES EAST OF THE AREA SATURDAY...MODIFIED HIGH PRESSURE WILL BUILD IN FROM THE WEST AND DOMINATE THE REGION THROUGH THE WEEKEND AND EARLY NEXT WEEK. THICKNESSES FALL BACK BELOW NORMAL BY ABOUT 15-20M (COOLEST SUNDAY) AND SUGGEST HIGHS JUST SLIGHTLY BELOW NORMAL IN THE MID/UPPER 60S SUNDAY BEFORE REBOUNDING INTO THE UPPER 60S MONDAY AS THE SURFACE HIGH MOVES OFFSHORE. THE GFS IS MUCH FASTER TO GENERATE PRECIP THAN THE ECMWF IN THE RETURN FROM ON MONDAY... SO WILL ONLY INTRODUCE A SMALL CHANCE POP IN THE WEST AT THIS TIME. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/... AS OF 150 AM TUESDAY... ASIDE FROM A SMALL CHANCE OF FLEETING AND SHALLOW FOG AT RWI THIS MORNING...VFR CONDITIONS ARE EXPECTED TO PREVAIL THROUGH THE TAF PERIOD. THE MAIN CONCERN WILL BE STRONG SOUTHWESTERLY WINDS THAT WILL STEADILY INCREASE AFTER 14Z...PEAKING IN THE 15-20 KT RANGE WITH GUSTS OF 25-30 KTS...AHEAD OF A CLIPPER LOW THAT WILL CROSS THE MIDDLE ATLANTIC STATES TODAY. AN ASSOCIATED DRY COLD FRONT...WITH AN ACCOMPANYING BAND OF CUMULUS WITH BASES BETWEEN 5 AND 7 THOUSAND FT...AND A SURFACE WIND SHIFT TO WNW...WILL CROSS THE FORECAST AREA THIS EVENING. THE FRONT WILL BE A MAINLY DRY ONE OWING TO BOTH LIMITED MOISTURE AND LIFT OVER NC...HOWEVER...WITH THE RELATIVE BEST CHANCE OF AN ISOLATED SHOWER NEAR RWI AND GSB BETWEEN 01-05Z. OUTLOOK: THE PASSAGE OF A WARM FRONT WILL RESULT IN A CHANCE OF MVFR- IFR CEILINGS AND SHOWERS LATE THU THROUGH EARLY FRI...PARTICULARLY AT INT AND GSO...FOLLOWED BY SUB-VFR CONDITIONS AND WIDESPREAD SHOWERS...IN ASSOCIATION WITH A PASSING COLD FRONT...FRI NIGHT. && .FIRE WEATHER... AS OF 310 PM MONDAY... BREEZY SW SFC WINDS TUESDAY WILL LEAD TO A WARM AFTERNOON WITH AFTERNOON TEMPS NEAR 70-LOWER 70S. THESE TEMPS COMBINED WITH A DRY AIR MASS WILL RESULT IN MINIMUM RELATIVE HUMIDITY VALUES BETWEEN 25- 30 PERCENT. SFC WINDS ARE EXPECTED TO FREQUENTLY GUSTS BETWEEN 23-28 MPH. WINDS OF THIS MAGNITUDE IN CONJUNCTION WITH THE LOW RH WILL QUICKLY DRY OUT FINE FUELS. WHILE THESE PARAMETERS ARE JUST SHORT OF RED FLAG CONDITIONS...ANY UNATTENDED FIRES MAY QUICKLY BECOME UNCONTROLLABLE IF THE FIRE OCCURS IN A RECEPTIVE FUEL. AFTER COORDINATING WITH NC FORESTRY OFFICIALS...WILL ISSUE A SPECIAL WEATHER STATEMENT FOR INCREASE FIRE DANGER IN EFFECT TUESDAY AFTERNOON. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...RAH NEAR TERM...RAH SHORT TERM...RAH LONG TERM...22 AVIATION...RAH FIRE WEATHER...WSS

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