Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 241146 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 746 AM EDT THU APR 24 2014 .SYNOPSIS...HIGH PRESSURE WILL BUILD SOUTH ACROSS THE MIDDLE ATLANTIC STATES TODAY...THEN OFFSHORE TONIGHT. A WARM FRONT WILL LIFT NORTH THROUGH NC AND VA FRIDAY MORNING...FOLLOWED BY THE PASSAGE OF A COLD FRONT FRIDAY EVENING. && .NEAR TERM /THROUGH TONIGHT/... AS OF 245 AM THURSDAY... A REINFORCING BACKDOOR COLD FRONT...EVIDENT AS A RADAR FINE LINE ON KAKQ/KRAX/KMHX BETWEEN 00-06Z...HAD SETTLED INTO THE SOUTHERN COASTAL PLAIN/SANDHILLS/SOUTHERN PIEDMONT DURING THE PAST HOUR OR TWO. THIS BOUNDARY MARKS THE LEADING EDGE OF A 1021 MB HIGH OVER EASTERN MI...WHICH WILL BUILD SOUTH ACROSS THE MIDDLE ATLANTIC STATES TODAY...AND RESULT IN TEMPERATURES 2-3 DEGREES COOLER THAN THOSE OF WED. SKIES WILL BE SUNNY TO START...BECOMING MOSTLY TO PARTLY SO FROM SOUTH TO NORTH...AS A RESULT OF A BAND OF 10-15 THOUSAND FT MOISTURE OVER THE UPPER MIDWEST AND OH VALLEY FORECAST TO SKIRT IN NW MID LEVEL FLOW MAINLY THE NORTHERN HALF OF THE FORECAST AREA THIS AFTERNOON. OTHERWISE SOME PASSING THIN CIRRUS OVER THE TN VALLEY THIS MORNING WILL ARRIVE AREA-WIDE ABOUT THE SAME TIME. THE SURFACE RIDGE AXIS WILL HAVE SHIFTED OFFSHORE BY THIS EVENING AND PROMOTE A DEVELOPING RETURN/SOUTHERLY FLOW (PARTICULARLY JUST ABOVE A STABLE/NOCTURNAL INVERSION)...AND CONSEQUENTLY ALLOW THE SURFACE BOUNDARY TO RETREAT NORTH AS A WARM FRONT IN ADVANCE OF A SHORTWAVE TROUGH ALOFT AND ATTENDANT SURFACE LOW LIFTING TOWARD THE OH VALLEY/LOWER GREAT LAKES. THE APPROACH AND PASSAGE OF THE BOUNDARY VERY LATE TONIGHT THROUGH EARLY FRI WILL RESULT IN THE DEVELOPMENT OF STRATUS...LOWEST AND WITH GREATEST COVERAGE OVER THE WESTERN/SOUTHERN PIEDMONT. SCATTERED ELEVATED SHOWERS ARE ALSO APT TO DEVELOP NORTHWARD WITH THE PASSAGE OF THE FRONT...AS MOISTENING AT THE NOSE OF THE LLJ AND INVOF THE BOUNDARY DRIVE WEAK/SHALLOW ELEVATED INSTABILITY AMIDST A LIFT-INDUCING REGIME OF LOW LEVEL WAA AND HEIGHT FALLS ALOFT (AHEAD OF THE AFOREMENTIONED SHORTWAVE TROUGH). WIDE RANGING LOWS FROM THE MID 40S IN CLOSEST PROXIMITY TO THE DEPARTING SFC RIDGE AXIS AND PERIODS OF CALM OVER THE COASTAL PLAIN...TO LOWER 50S OVER THE SOUTHERN PIEDMONT. && .SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/... AS OF 300 AM THURSDAY... FRI AND FRI NIGHT: EARLY MORNING SCATTERED ELEVATED SHOWERS...AND STRATUS...BOTH INVOF THE RETREATING WARM FRONT...WILL PLAY A ROLE IN HOW MUCH DIABATIC HEATING WILL OCCUR AND WHERE IT WILL BE MAXIMIZED...AMIDST AN OTHERWISE WARMING AND BREEZY SW LOW LEVEL FLOW ON FRI. THE COLD FRONT ATTENDING THE PRIMARY LOW REFERENCED IN THE NEAR TERM WILL START THE DAY WELL TO OUR WEST/WEST OF THE APPALACHIANS; AND IT IS LIKELY THAT A SECONDARY WEAK TRIPLE POINT SURFACE WAVE WILL DEVELOP ALONG THE RETREATING WARM FRONT FROM WESTERN NC TO NORTH-CENTRAL VA THROUGH THE AFTERNOON. LOW AND DEEP LAYER SHEAR WILL INCREASE TO LEVELS MARGINALLY SUPPORTIVE OF SEVERE THUNDERSTORMS...IN AN ENVIRONMENT CHARACTERIZED BY RELATIVELY STEEP MID LEVEL LAPSE RATES AROUND 6.5 C/KM (GOOD THERMODYNAMICS)...AHEAD OF THE APPROACHING COLD FRONT FORECAST TO CROSS CENTRAL NC MAINLY DURING THE EVENING HOURS. THOUGH SEVERE HAIL AND DAMAGING WIND GUSTS WILL BE THE PRIMARY THREATS AMIDST THE AFOREMENTIONED STEEP MID LAPSE RATES AND 40-45 KTS OF MID LEVEL FLOW...CYCLONICALLY-CURVED CHARACTER OF FORECAST HODOGRAPHS/SRH IN THE 100-300 M2/S2 RANGE (STRONGEST NMM)...WOULD ALSO SUPPORT A LOW TORNADO PROBABILITY - PARTICULARLY INVOF ANY REMNANT DIABATICALLY- INDUCED MESOSCALE BOUNDARIES OVER CENTRAL NC FROM EARLIER DAY CLOUDS/CONVECTION...AND IN VA INVOF THE PASSING TRIPLE POINT LOW. HIGH TEMPERATURES...ENTIRELY DEPENDENT UPON LOW PREDICTABILITY LOCATION/EVOLUTION OF CLOUDS AND CONVECTION...IN THE MIDDLE 70S TO AROUND 80 DEGREES. THE PASSAGE OF THE COLD FRONT DURING THE EVENING WILL USHER A COOLER AND DRIER AIR MASS ACROSS NC FRI NIGHT...RESULTING IN CLEARING SKIES...AND LOWS IN THE LOWER TO MIDDLE 50S. -MWS SATURDAY THROUGH SUNDAY NIGHT: DRY WEATHER WITH SEASONABLE TEMPERATURES WILL ENSUE FOR THE WEEKEND IN THE WAKE OF THE COLD FRONT FRIDAY NIGHT AS A MILD SURFACE HIGH SURFACE BUILDS INTO THE AREA LOWER MS VALLEY/NORTHERN GULF COAST STATES. A COMPACT UPPER LOW/TROUGH OVER THE UPPER GREAT LAKES WILL MOVE EASTWARD-SOUTHEASTWARD THROUGH SOUTHERN NEW ENGLAND ON SUNDAY. ATTENDANT HEIGHT FALLS ALOFT ACROSS THE NORTHERN MID-ATLANTIC STATES WILL ATTEMPT TO DRIVE A BACK-DOOR COLD FRONT SOUTHWARD INTO THE AREA ON SUNDAY...BUT GIVEN S/W RIDGE ALOFT BUILDING IN FROM THE WEST...THINK THIS WIL CURTAIL SOUTHWARD PUSH OF THE FRONT...WITH EXPECTATIONS OF THE FRONT STALLING NORTH OF THE AREA. HIGHS IN THE 70S. LOWS IN THE 50S. && .LONG TERM /MONDAY THROUGH SATURDAY/... AS OF 300 AM THURSDAY... AN ACTIVE AND UNSETTLED WEATHER PATTERN LOOKS TO BE SETTING UP ANYWHERE FROM THE SOUTHERN PLAINS EASTWARD FOR AT LEAST THE FIRST HALF OF NEXT WEEK..IF NOT LONGER OWING TO THE BLOCKING PATTERN OVER THE SOUTHEAST CANADA TOWARDS GREENLAND THAT WILL HAMPER THE EASTWARD PROGRESSION OF A STRONG CLOSED LOW FROM THE SOUTHWEST INTO THE CENTRAL CONUS. REGARDING SENSIBLE WEATHER IMPACTS...WHILE MODEL SPREAD IS CURRENTLY TOO HIGH TO ELABORATE ON FORECAST SPECIFICS/DETAILS...GIVEN SUCH A POTENT SYSTEM WITH A HIGH LIKELIHOOD OF DEEP GULF MOISTURE TRANSPORT NORTHWARD INTO THE AREA DURING THE CLIMATOLOGICALLY FAVORED SPRING CONVECTIVE SEASON OF LATE APRIL/EARLY MAY...CENTRAL NC WILL HAVE TO BE ON THE LOOKOUT FOR THE POSSIBILITY OF EXCESSIVE RAINFALL AND SEVERE STORMS MONDAY THROUGH WEDNESDAY. PROSPECTS OF WIDESPREAD CLOUDS AND PRECIP WILL KEEP TEMPERATURES NEAR NORMAL. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... AS OF 300 PM WEDNESDAY... HIGH PRESSURE OVER THE AREA ON SUNDAY WILL RESULT IN QUIET WEATHER FOR CENTRAL NC...WITH TEMPS NEAR TO SLIGHTLY ABOVE NORMAL. THE HIGH WILL SHIFT OFFSHORE LATE SUNDAY INTO MONDAY AHEAD OF A STRONG SYSTEM THAT WILL LIKELY BE A BIG SEVERE WEATHER MAKER FOR THE CENTRAL CONUS OVER THE WEEKEND AND EARLY NEXT WEEK. THERE IS STILL A LOT TO BE WORKED OUT WITH REGARD TO THE DETAILS OF THIS SYSTEM...THEREFORE FORECAST UNCERTAINTY REMAINS HIGH. OVERALL THIS CUTOFF LOW WILL SLOWLY MAKE ITS WAY EAST THROUGH THE MIDDLE OF NEXT WEEK...WITH OUR BEST PRECIP CHANCES LOOKING TO BE ON TUESDAY...ALTHOUGH SOME OVERRUNNING PRECIP WILL BEGIN EARLY MONDAY MORNING. TEMPS SHOULD BE NEAR TO SLIGHTLY BELOW NORMAL...BUT WILL ULTIMATELY DEPEND ON THE AMOUNT/TIMING OF CLOUDS/PRECIP. && .AVIATION /12Z THURSDAY THROUGH MONDAY/...
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AS OF 745 AM THURSDAY... HIGH PRESSURE WILL BUILD SOUTH FROM THE GREAT LAKES AND RESULT IN A HIGH CONFIDENCE OF VFR CONDITIONS THROUGH AT LEAST THE FIRST THREE QUARTERS OF THE TAF PERIOD. IN ANTICYCLONIC FLOW AROUND THE HIGH...NNE SURFACE WINDS THIS MORNING WILL BECOME LIGHT AND VARIABLE BENEATH THE RIDGE AXIS BY MIDDAY...THEN LIGHT SOUTHERLY...THIS AFTERNOON AT TRIAD TERMINALS...AND THIS EVENING ELSEWHERE. PASSING MID CLOUDS (BETWEEN 10 AND 15 THOUSAND FEET) IN NW FLOW ALOFT WILL SKIRT THE NORTHERN PIEDMONT THIS AFTERNOON AND EVENING. THE DEVELOPING SOUTHERLY RETURN FLOW AND ASSOCIATED APPROACH OF A SURFACE WARM FRONT FROM THE SOUTH WILL RESULT IN THE DEVELOPMENT OF IFR-MVFR STRATUS LATE TONIGHT AND EARLY FRI...LOWEST AND MOST LIKELY AT TRIAD TERMINALS. THE PASSAGE OF THE WARM FRONT WILL ALSO SUPPORT SCATTERED SHOWERS FRI MORNING...FOLLOWED BY A BREEZY SW SURFACE WIND AND ANOTHER ROUND OF SCATTERED SHOWERS - AND THUNDERSTORMS - ALONG AND AHEAD OF A COLD FRONT FRI AFTERNOON AND EVENING. UNSETTLED WEATHER WILL RETURN AGAIN EARLY NEXT WEEK..AND WILL LIKELY LINGER THROUGH MID-WEEK.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...MWS NEAR TERM...MWS SHORT TERM...MWS/CBL LONG TERM... CBL AVIATION...MWS

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