Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 010744 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 344 AM EDT WED APR 1 2015 .SYNOPSIS...A COLD FRONT WILL MOVE SOUTH THROUGH NC THIS MORNING. COOL HIGH PRESSURE WILL FOLLOW FOR WED AND THU. A WARM FRONT MOVE NORTH THROUGH THE REGION THU NIGHT...FOLLOWED BY THE PASSAGE OF A STRONG COLD FRONT FRI NIGHT AND EARLY SAT. && .NEAR TERM /THROUGH TONIGHT/...
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AS OF 340 AM WEDNESDAY... OBSERVATIONAL DATA INDICATE THE SFC COLD FRONT HAD MOVED INTO THE SOUTHERN PIEDMONT/SANDHILLS/SOUTHERN COASTAL PLAIN AT 0730Z...AND THE FRONT WILL CONTINUE TO MOVE SOUTH AND OUT OF NC THROUGH 12Z. NORTH TO NE SFC WINDS WILL BE BRIEFLY GUSTY TO AROUND 15-20 KTS BOTH IN THE FEW HOUR WAKE OF THE FRONT...AND AGAIN AS THE MIXED LAYER DEEPENS WITH HEATING BETWEEN 12-15Z...MAINLY EAST OF 1-95. WHILE A FEW PATCHES OF ALTOCUMULUS IN THE VICINITY OF THE FRONT WILL DOT THE SKY THIS MORNING...IT WILL BE SHORT-LIVED AS THE PARENT S/W TROUGH ALOFT MOVES AWAY FROM THE MIDDLE ATLANTIC COAST. CLEARING AND HEIGHT RISES IN DEEP LAYER RIDGING ALOFT WILL FOLLOW...AND CAUSE A 1018 MB SFC HIGH OVER SOUTHERN OH TO STRENGTHEN A FEW MB AS IT BUILDS SOUTHEASTWARD ACROSS VA/NC TODAY. ASSOCIATED NE FLOW WILL RESULT IN COOLER (THAN TUE) TEMPERATURES...WITH DRY ADIABATIC MIXING NEAR H85 SUPPORTIVE OF HIGHS IN THE LOWER 60S NE TO LOWER 70S SW. SKIES WILL REMAIN CLEAR OR MOSTLY SO TONIGHT...WITH PERHAPS THE SOUTHERN FRINGE OF CIRRUS IN NW FLOW ALOFT GRAZING THE NORTHERN PIEDMONT THIS EVENING. H85-925 FLOW WILL BECOME SOUTHWESTERLY LATE TONIGHT AS THE CENTER OF THE ANTI-CYCLONE IN THAT LAYER DRIFTS OFF THE SC COAST...AND ASSOCIATED MOISTURE ADVECTION WILL CAUSE SOME STRATOCUMULUS TO DEVELOP AND CREEP TOWARD THE YADKIN BY DAYBREAK. BASED ON CURRENT AND PREVIOUS MODEL PROGS...IT IS UNLIKELY THAT THIS CLOUD COVER WILL ARRIVE SOON OR THICK ENOUGH TO HAVE A LARGE IMPACT ON OVERNIGHT TEMPERATURES. GIVEN THE RELATIVE CLEAR AND CONTINUED NEARBY PRESENCE OF THE AFOREMENTIONED SFC HIGH NEAR THE VA/NC COAST THAT GUIDANCE SUGGESTS WILL STRENGTHEN FURTHER BENEATH THE SUBSIDENT RIDGING ALOFT (TO NEAR 1028 MB) GOOD TO EXCELLENT RADIATIONAL COOLING CONDITIONS ARE EXPECTED...WITH PROJECTED LL THICKNESS VALUES AROUND 1345 METERS AT 12Z THU SUPPORTIVE OF MIDDLE 30S TO AROUND 40 DEGREES - COOLEST EAST...NEARER THE CENTER OF THE SFC HIGH.
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&& .SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
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AS OF 320 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.
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&& .LONG TERM /FRIDAY THROUGH TUESDAY/...
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AS OF 255 PM TUESDAY... 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
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&& .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... AS OF 210 AM WEDNESDAY... VFR. A COLD FRONT AND ASSOCIATED WIND SHIFT TO NORTHERLY WITH TEMPORARY GUSTINESS INTO THE MID TEENS TO NEAR 20 KTS...WILL CONTINUE TO MOVE SOUTH THROUGH CENTRAL NC THIS MORNING. THE FRONT HAD ALREADY CLEARED ALL BUT FAY AS OF THE 06Z TAF ISSUANCE...AND FRONTAL PASSAGE THERE WILL BE BETWEEN 0730-08Z. WINDS WILL THEN GRADUALLY VEER TO NE LATER THIS MORNING...WITH A BRIEF PERIOD OF HIGHER SUSTAINED SPEEDS...AND GUSTS...THROUGH AROUND 15Z. OTHERWISE...SKIES WILL BE MAINLY CLEAR...WITH THE EXCEPTION BEING A BAND OF ALTOCUMULUS AND ASSOCIATED 8-11 THOUSAND FT CEILINGS IN THE VICINITY OF THE FRONT THIS MORNING...AND PERIODS OF THIN CIRRUS LATER TODAY AND TONIGHT. OUTLOOK: THE PASSAGE OF A WARM FRONT WILL RESULT IN A GOOD CHANCE OF MVFR-IFR CEILINGS THU NIGHT THROUGH EARLY FRI...WITH THE RELATIVELY HIGHEST PROBABILITY OF OCCURRENCE AND LOWEST CEILINGS AT INT AND GSO. A FEW SHOWERS WILL ALSO BE POSSIBLE DURING THAT TIME...ALSO MAINLY AT INT AND GSO. WARM AND WINDY FRI...WITH SUSTAINED SW WINDS NEAR 20 KTS AND GUSTS 30-35 KTS...FOLLOWED BY SUB-VFR CONDITIONS AND WIDESPREAD SHOWERS IN ASSOCIATION WITH A PASSING COLD FRONT...FRI NIGHT AND EARLY SAT. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...RAH NEAR TERM...RAH SHORT TERM...WSS LONG TERM...HARTFIELD AVIATION...RAH

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