Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 141050 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 650 AM EDT MON APR 14 2014 .SYNOPSIS...SOUTHERLY FLOW WILL ADVECT AN INCREASINGLY MOIST AND UNSTABLE AIRMASS INTO THE REGION TODAY AND TONIGHT AS A POTENT UPPER LEVEL TROUGH AND ASSOCIATED COLD FRONT TRACK EAST INTO THE TENNESSEE VALLEY. THE COLD FRONT WILL PROGRESS EAST THROUGH THE CAROLINAS TUESDAY AFTERNOON AND EVENING. && .NEAR TERM /THROUGH TONIGHT/... AS OF 330 AM MONDAY... OVERVIEW: AN UPPER LEVEL TROUGH OVER THE CENTRAL ROCKIES THIS MORNING WILL DIG SOUTHEAST THROUGH THE LOWER MIDWEST TODAY...THROUGH THE CENTRAL MS RIVER VALLEY THIS EVENING...PROGRESSING INTO THE TENNESSEE VALLEY LATE TONIGHT. MULTIPLE WAVES OF LOW PRESSURE ARE EXPECTED TO DEVELOP ALONG AN ATTENDANT COLD FRONT TRACKING INTO THE TN VALLEY LATE TONIGHT. PRECIPITATION CHANCES: INCREASING HEIGHT FALLS AND STRENGTHENING /DIFFLUENT/ SW FLOW ALOFT DOWNSTREAM OF THE AFOREMENTIONED UPPER LEVEL TROUGH WILL RESULT IN AN INCREASINGLY MOIST SOUTHERLY FLOW OVER THE CAROLINAS TODAY...WITH RAPID LOW-LEVEL MOISTENING OCCURRING THIS MORNING (12-16Z) UNDERNEATH A LINGERING MID-LEVEL CAP ASSOC/W THE SOUTHERN PERIPHERY OF AN ELEVATED MIXED LAYER IN THE MID- ATLANTIC. RAPID LOW-LEVEL MOISTENING COMBINED WITH DIURNAL HEATING WILL RESULT IN SHALLOW DESTABILIZATION AND A CHANCE FOR ISOLD TO SCT LOW-TOPPED CONVECTION (~10 KFT ECHO TOPS) LATER THIS MORNING THROUGH EARLY AFTERNOON...WITH ISOLD/SCT SHOWERS AND THUNDERSTORMS POSSIBLE BY LATE AFTERNOON AND EARLY EVENING (BY 21-00Z) AS THE SOUTHERN FRINGE OF THE EML /CAP/ ERODES IN THE PRESENCE OF DPVA IN STRENGTHENING SW FLOW ALOFT. CONVECTION SHOULD BECOME MORE NUMEROUS IN COVERAGE OVER CENTRAL NC THIS EVENING INTO TONIGHT DUE TO ONGOING MOISTENING...STRENGTHENING HEIGHT FALLS...AND PERIODIC DPVA IN SW FLOW ALOFT...ESPECIALLY IN WESTERN PORTIONS OF THE STATE. HOWEVER... SEVERAL LARGE MESOSCALE CONVECTIVE SYSTEMS ARE EXPECTED TO DEVELOP UPSTREAM IN THE DEEP SOUTH IN THIS PERIOD...ONE THIS AFTERNOON AND PERHAPS ANOTHER LATE TONIGHT...AND HOW THESE FEATURES EVOLVE/ INTERACT WITH THE LARGER SCALE PATTERN WILL MOST CERTAINLY AFFECT PRECIP CHANCES DOWNSTREAM IN CENTRAL NC...LENDING A FAIR AMOUNT OF UNCERTAINTY TO THE PRECISE COVERAGE/AMOUNT OF CONVECTION TONIGHT. TEMPERATURES: HIGHS TODAY WILL BE TEMPERED BY CLOUD COVER AND ISOLD/SCT SHOWER ACTIVITY...RANGING FROM THE MID 70S NW PIEDMONT TO UPPER 70S COASTAL PLAIN/SANDHILLS. A VERY MOIST/BREEZY SOUTHERLY FLOW THROUGHOUT THE WARM SECTOR IN THE CAROLINAS WILL MAINTAIN TEMPS IN THE MID 60S OVERNIGHT. SEVERE POTENTIAL: THOUGH QUITE CONDITIONAL/UNCERTAIN...IF DEEP CONVECTION DEVELOPS AND PROGRESSES INTO CENTRAL NC THIS EVENING AND TONIGHT...AN ISOLD SEVERE STORM WOULD BE POSSIBLE GIVEN INCREASINGLY IMPRESSIVE LOW/DEEP-LAYER SHEAR. -VINCENT && .SHORT TERM /TUESDAY THROUGH THURSDAY NIGHT/...
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AS OF 330 AM MONDAY... TUE/TUE NIGHT: EXPECT CHANCES FOR CONVECTION NEAR 100% ON TUESDAY AS A POTENT UPPER LEVEL TROUGH AND ATTENDANT COLD FRONT PROGRESS THROUGH THE CAROLINAS IN THE PRESENCE OF A MOIST AND UNSTABLE AIRMASS VIA PERSISTENT SOUTHERLY LOW-LEVEL FLOW OFF THE ATLANTIC. AT THIS TIME...FROPA IS EXPECTED TO OCCUR BETWEEN 18-21Z IN THE NW PIEDMONT AND BY 00-03Z IN THE COASTAL PLAIN...WITH STRONG COLD ADVECTION THEREAFTER. EXPECT HIGHS RANGING FROM THE MID/UPPER 60S IN THE NW PIEDMONT WHERE CLOUD COVER/CONVECTION WILL PREVENT MUCH OF A RISE IN TEMPS PRIOR TO FROPA...TO THE MID/UPPER 70S POTENTIALLY IN THE COASTAL PLAIN WHERE FROPA WILL BE LATER. STRONG LOW/DEEP LAYER SHEAR...FAVORABLE DIURNAL TIMING...AND MARGINAL TO MODERATE DESTABILIZATION (500-1000 J/KG MLCAPE) CERTAINLY INDICATE A POTENTIAL FOR SEVERE THUNDERSTORMS...THOUGH THE PRECISE NATURE OF THE THREAT IS STILL DIFFICULT TO ASCERTAIN GIVEN A POTENTIAL FOR UPSTREAM CONVECTION /MCS ACTIVITY/ LATE TONIGHT AND TUE MORNING. DAMAGING WINDS AND ISOLD TORNADOES WILL BE THE PRIMARY THREAT(S)... THE LATTER OF WHICH COULD BE FURTHER ENHANCED BY BACKED SFC WINDS /LARGE CLOCKWISE CURVED HODOGRAPHS/ POSSIBLE ON THE EASTERN PERIPHERY OF ANY SFC WAVES WHICH COULD DEVELOP ALONG THE FRONT IN CENTRAL/EASTERN NC...PARTICULARLY ALONG AND EAST OF I-95 WHERE DIURNAL TIMING AND DESTABILIZATION WILL BE MOST FAVORABLE. STRONG COLD ADVECTION WILL RESULT IN A STARK CONTRAST IN TEMPERATURES IN COMPARISON TO THE PREVIOUS FEW DAYS...WITH LOWS RANGING FROM THE LOWER TO UPPER 30S...POTENTIALLY NEAR FREEZING ALONG/WEST OF HWY 1. A FREEZE WATCH MAY BE NEEDED FOR PORTIONS OF THE AREA TUE NIGHT/WED MORNING. SINCE LOWS WILL PRIMARILY DEPEND UPON COLD ADVECTION... SUFFICIENT UNCERTAINTY EXISTS TO PRECLUDE ANY FROST/FREEZE PRODUCT ISSUANCE AT THIS TIME. -VINCENT AS OF 245 AM MONDAY...RISING HEIGHTS ALOFT/DNVA AND ASSOCIATED STRONG SUBSIDENCE WILL RESULT IN FURTHER DEEP LAYER DRYING WED...FOLLOWED BY GENERALLY NEUTRAL VERTICAL MOTION BUT WITH STILL A RESIDUALLY DRY AND STRONGLY CAPPED REGIME OVER OUR REGION. SURFACE HIGH PRESSURE WILL CONSEQUENTLY BECOME UNSEASONABLY STRONG - INTO THE 1040-1045 MB RANGE AS IT BUILDS FROM THE OH VALLEY TO NEW ENGLAND. UNSEASONABLY COOL NORTHEASTERLY FLOW...WITH TEMPERATURES 10 TO 20 DEGREES BELOW AVERAGE...WILL RESULT OVER CENTRAL NC. INITIALLY CLEAR SKIES WED WILL BECOME PARTLY CLOUDY...TO PERHAPS MOSTLY SO IN THE COASTAL PLAIN...BY THU AFTERNOON...AS MOISTURE FLAT STRATOCUMULUS IS ADVECTED INLAND BENEATH THE CAP. PROJECTED LOW LEVEL THICKNESS VALUES IN THE 1300-1310 METER RANGE AT 12Z THU AND CLEAR SKIES WOULD SUPPORT SUB-FREEZING TEMPERATURES THU MORNING...BUT CONFIDENCE IS LOW REGARDING THE DEGREE OF CALM GIVEN A PROJECTED 4-6 MB RISE IN MSL PRESSURE WITH THE STRENGTHENING HIGH WED NIGHT. WILL ADJUST LOWS TO REFLECT MOSTLY LOWER TO MIDDLE 30S...COOLEST WEST...BUT THESE MAY NEED FURTHER DOWNWARD ADJUSTMENT (OR AT LEAST OPEN THE RANGE) TO INCLUDE SOME UPPER 20S (AROUND RECORD LOWS) IF IT INDEED APPEARS ANY PERIOD OF APPRECIABLE CALM WILL BE ATTAINED. SIMILARLY COOL IN THE MIDDLE 50S WED...WHICH MAY THREATEN THE RECORD LOW MAX OF 56 DEGREES AT KFAY FOR THE DATE. SEE CLIMATE SECTION BELOW. SLOW MODERATION TO AROUND 60 AND 40 DEGREES FOR HIGHS AND LOWS...RESPECTIVELY...THU AND THU NIGHT. -MWS
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&& .LONG TERM /FRIDAY THROUGH SUNDAY/... AS OF 300 AM MONDAY... THOUGH MODEL SOLUTION SPREAD REMAINS ABOVE AVERAGE DURING THE LONG TERM...THE EMERGING SIGNAL FROM THE MAJORITY OF BOTH THE ENSEMBLE AND SOLUTIONS OS FOR A DOMINANT NORTHERN STREAM ACROSS THE NORTHERN THIRD OF THE US...ONE THAT WILL INCLUDE AT LEAST ONE PRIMARY SHORTWAVE TROUGH AND ACCOMPANYING SURFACE CYCLONE FORECAST TO CROSS THE UPPER MIDWEST AND LOWER GREAT LAKES FRI-SAT - A STORM TRACK THAT WOULD RESULT IN A MOSTLY DRY COLD FRONTAL PASSAGE SAT-SAT NIGHT AS DEPICTED BY AT LEAST THE LAST SEVERAL RUNS OF THE GFS. ON THE OTHER HAND...THE LAST COUPLE OF RUNS OF THE OPERATIONAL ECMWF...WHICH HAVE MINIMAL SUPPORT FROM THE EC ENSEMBLE MEAN...SUGGEST MORE IN THE WAY OF SOUTHERN STREAM TROUGHING/INTERACTION THAT WOULD RESULT IN SOME DEGREE OF COASTAL CYCLOGENESIS AND A WETTER PATTERN FOR AT LEAST THE EASTERN HALF OF NC DURING THE SAME TIME FRAME. IN EITHER SCENARIO...THE BEST CHANCES OF RAIN WOULD BE LATE FRI NIGHT-SAT EVENING...SO MENTIONABLE POP WILL BE CONFINED TO THAT TIME UNTIL A CLEARER PICTURE EMERGES. && .AVIATION /12Z MONDAY THROUGH SATURDAY/... AS OF 600 AM MONDAY... 24-HR TAF PERIOD: LOW-LEVEL MOISTENING /WARM ADVECTION/ IS EXPECTED TO RESULT IN THE RAPID DEVELOPMENT OF MVFR OR IFR CEILINGS BY 12-15Z ACROSS MUCH OF CENTRAL NC. SHALLOW CONVECTION (SHRA) WITH TOPS AROUND 10 KFT WILL BE POSSIBLE THROUGH EARLY AFTERNOON IN ASSOC/W AN ONSHORE FLOW IN THE LOWER-LEVELS...WITH ISOLD TO SCT SHOWERS AND THUNDERSTORMS POSSIBLE BY LATE THIS AFTERNOON AND EVENING IN ADVANCE OF A COLD FRONT PROGRESSING EAST INTO THE TN VALLEY. THERE SHOULD BE SOME MARGINAL IMPROVEMENT TO CEILINGS IN ASSOC/W DIURNAL HEATING... HOWEVER...DUE TO CONTINUED LOW-LEVEL MOISTENING CEILINGS MAY REMAIN IN THE MVFR CATEGORY...AT OR BELOW 2000 FT AGL. EXPECT CEILINGS TO DETERIORATE TO IFR/LIFR TONIGHT ALONG WITH AN INCREASING LIKELIHOOD OF SHOWER ACTIVITY IN ADVANCE OF THE APPROACHING COLD FRONT. SOUTHERLY WINDS AT 7-12 KT EARLY THIS MORNING WILL INCREASE TO 10-15 KT WITH GUSTS UP TO 22-25 KT DURING THE DAY...LIKELY REMAINING BREEZY AND GUSTING UP TO 20 KT OVERNIGHT AS THE MSLP GRADIENT TIGHTENS FROM THE WEST. LOOKING AHEAD: ADVERSE AVIATION CONDITIONS ASSOCIATED WITH WIDESPREAD SHOWERS AND THUNDERSTORMS ARE EXPECTED ON TUESDAY AS THE AFOREMENTIONED COLD FRONT PROGRESSES EAST ACROSS THE CAROLINAS. ISOLD SEVERE THUNDERSTORMS WILL BE POSSIBLE...ESPECIALLY AT THE RDU/FAY/RWI TERMINALS. SOUTHERLY OR SSW WINDS AT 15 KT WITH GUSTS UP TO 25 KT CAN BE EXPECTED IN ADVANCE OF THE FRONT THROUGH 18Z TUE...BECOMING NW/NNW AT 15 KT WITH GUSTS UP TO 25 KT BETWEEN ROUGHLY 18-21Z TUE AFTERNOON (INT/GSO) TO 00-03Z WED (FAY/RWI). IFR/LIFR CEILINGS MAY LINGER FOR A WHILE IN THE WAKE OF THE FRONTAL PASSAGE...EVENTUALLY CLEARING FROM WEST-EAST AND BECOMING VFR AFTER MIDNIGHT WED MORNING. VFR CONDITIONS WILL PREVAIL IN THE WAKE OF THE FRONT WED-FRI. -VINCENT && .CLIMATE... THE FOLLOWING ARE THE RECORD LOW TEMPERATURES FOR WED AND THU MORNING... AND THE RECORD LOW MAXIMUM TEMPERATURES FOR THU: WED 04/16 THU 04/17 LOW/YEAR LOW MAX/YEAR LOW/YEAR FAY: 28/1943 56/1950 31/1953 GSO: 25/1943 48/1929 29/1953 RDU: 28/1950 46/1890 29/1962 && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...VINCENT NEAR TERM...VINCENT SHORT TERM...VINCENT LONG TERM...MWS AVIATION...VINCENT CLIMATE...MWS

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