Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 212100 AFDAKQ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WAKEFIELD VA 500 PM EDT MON APR 21 2014 .SYNOPSIS... HIGH PRESSURE REMAINS OVER THE AREA TONIGHT AS THE NEXT COLD FRONT APPROACHES FROM THE WEST. COLD FRONT WILL CROSS THE REGION TUESDAY AFTERNOON. COOL CANADIAN HIGH PRESSURE BUILDS BACK OVER THE REGION WEDNESDAY AND THURSDAY. ANOTHER COLD FRONT WILL CROSS THE AREA ON FRIDAY. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... UPPER/SFC HIGH PRESSURE HAS RESULTED IN NEAR SEASONABLE AFTERNOON TEMPS IN THE MID-UPPER 60S TO NEAR 70 AND SUNNY SKIES OVER THE LOCAL AREA. THE EXCEPTION IS ALONG THE COAST AS PERSISTENT NELY FLOW HAS PRODUCED TEMPS IN THE MID-UPPER 50S. COASTAL LOW CONTINUES TO SLOWLY PUSH OUT TO SEA. NRN STREAM SHORTWAVE OVER SRN CANADA WILL BEGIN TO PHASE WITH A SRN STREAM SHORTWAVE OVER THE MID-MS VALLEY TONIGHT OVER THE CNTRL CONUS...PUSHING AN ASSOCIATED COLD FRONT TOWARD THE REGION. MID-UPPER LEVEL CLOUDS WILL BEGIN TO SPREAD OVER THE REGION THIS EVENING AND TONIGHT. ALTHOUGH WINDS WILL DECOUPLE...INCREASING CLOUDS AND LOW LEVEL THICKNESSES WILL RESULT IN LOWS FALLING ONLY INTO THE UPPER 40S-LOW 50S. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/... TUESDAY... UPPER TROUGH WILL AMPLIFY AS ENERGY DIGS OVER THE GREAT LAKES REGION...AIDED BY A 100+ KT UPPER JET STREAK. A LEADING SHORTWAVE/VORTICITY MAXIMA WILL LIFT OVER THE LOCAL AREA...RESULTING IN A PRE-FRONTAL SFC TROUGH ON THE LEE SIDE OF THE APPALACHIANS. DEEP LAYER WLY FLOW WILL LIMIT THE AMOUNT OF MOISTURE ADVECTION INTO THE REGION...WITH MOST OF THE MOISTURE BEING SUPPLIED BY THE SYSTEM. PRECIP WATERS EXPECTED TO INCREASE TO NEAR ONE INCH...BUT DEWPOINTS ONLY EXPECTED TO BE IN THE LOW- MID 50S. TUES MORNING WILL REMAIN DRY...BUT MID-UPPER LEVEL CLOUDS WILL INCREASE. UPPER TROUGH WILL DIG SEWD OVER THE OH VALLEY INTO THE NRN MID-ATLANTIC REGION TUES. THE COLD FRONT WILL REACH THE LOCAL AREA EARLY TUES AFTERNOON...CROSSING THE REGION INTO EARLY TUES EVENING AND PUSHING OUT TO SEA LATE TUES EVENING. HI-RES MODELS INDICATE A NARROW AND UNORGANIZED BAND OF SHOWERS CROSSING THE AREA WITH THE FRONT DURING THE AFTERNOON. THIS SEEMS REASONABLE AS THE BEST DYNAMICS WILL REMAIN TO THE NORTH OF THE LOCAL AREA AND WITH WLY FLOW ALOFT. THETA-E ADVECTION AND TEMPS WARMING INTO THE UPPER 70S WILL RESULT IN A MARGINALLY UNSTABLE AIRMASS OVER THE REGION. THE BIGGEST LIMITATION TO INSTABILITY WILL BE RELATIVELY COOL DEWPOINTS. MLCAPE VALUES PROGGED TO BE LESS THAN 500 J/KG WHILE SREF CAPE PROBS >1K J/KG ARE ONLY 20 PCT. LI VALUES ALSO GENERALLY 0 TO -2. WITH THAT...DO ANTICIPATE AFTERNOON CONVECTION...BUT MARGINAL SHEAR (0-6KM BULK SHEAR 25-30 KT) WILL PREVENT OVERALL ORGANIZATION. THE MAIN THREAT FROM DEVELOPING STORMS WILL BE LOCALLY SUB-SEVERE WIND GUSTS DUE TO THE DRY LOW LEVELS. HAVE OPTED TO MAINTAIN SLIGHT CHANCE THUNDER BUT HAVE INCREASED POPS ACROSS THE NORTH TO LIKELY POPS (GENERALLY NORTH OF RICHMOND). QPF AMOUNTS WILL GENERALLY BE LESS THAN ONE QUARTER OF AN INCH. SHOWERS/THUNDERSTORMS PUSH OFFSHORE TUES EVENING. TUESDAY NIGHT-THURSDAY... SKIES WILL RAPIDLY CLEAR BEHIND THE FRONT TUES NIGHT AS COOL CANADIAN HIGH PRESSURE BUILDS IN FROM THE NW. BREEZY NW WINDS (10-15 MPH WITH GUSTS TO 25 MPH) WILL PROVIDE ENOUGH MIXING TO KEEP TEMPS FROM FALLING FARTHER THAN THE MID- UPPER 40S INLAND TO THE LOW 50S NEAR THE COAST. HIGH PRESSURE WILL CONTINUE TO BUILD IN FROM THE NW ON WEDS AS NW FLOW PERSISTS. REMNANT MID LEVEL MOISTURE UNDER A SUBSIDENCE INVERSION AND ADDITIONAL ENERGY DIVING DOWN THE BACK SIDE OF THE UPPER TROUGH (LOCATED JUST OFFSHORE) WILL RESULT IN AFTERNOON CU OVER THE REGION. TEMPS WILL ONLY WARM INTO THE MID-UPPER 60S. DEWPOINTS WILL MIX INTO THE LOW 30S...WITH MINIMUM RH VALUES IN THE MID 20S INLAND. DRY AGAIN ON THURS AS HIGH PRESSURE SLIDES OVER THE REGION...AND LOCATES OFF THE CAROLINA COAST LATE THURS. LOWS THURS MORNING FORECAST TO BE IN THE UPPER 30S-LOW 40S INLAND. HIGHS THURS GENERALLY IN THE UPPER 60S. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
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PROGRESSIVE FLOW ALOFT EXPECTED TO SLOWLY TRANSITION TO A MORE AMPLIFIED/BLOCKY PATTERN BY DAYS 6-7. SFC HIGH WILL SLIDE OFFSHORE THURS NIGHT...VEERING THE FLOW AROUND TO THE SOUTH AS THE UPPER RIDGE AXIS BUILDS OVERHEAD. MEDIUM RANGE GUIDANCE IS COMING INTO BETTER AGREEMENT...BUT CONTINUES TO STRUGGLE WITH THE EVOLUTION OF AN UPPER TROUGH OVER THE INTERMOUNTAIN WEST INTO THE NRN PLAINS THURS NIGHT. HOWEVER...GUIDANCE IS IN FAIRLY GOOD AGREEMENT WITH LIFTING A WARM FRONT OVER THE REGION IN THE AMPLIFYING FLOW FRI WITH A TRAILING COLD FRONT FORECAST TO CROSS THE REGION SAT. WLY FLOW OVER THE SRN PLAINS INTO THE GULF STATES WILL LIMIT THE AMOUNT OF MOISTURE ADVECTION INTO THE REGION...ESPECIALLY EAST OF THE APPALACHIANS. DEWPOINTS ONLY PROGGED TO WARM INTO THE LOW-MID 50S FRI. BEST DYNAMICS WILL ALSO REMAIN NORTH OF THE LOCAL AREA AS ZONAL FLOW PREVAILS OVER THE LOCAL AREA. HOWEVER...INCREASING SPEEDS ALOFT AND SMALL AMPLITUDE SHORTWAVES WILL BE ENOUGH TO MENTION SLIGHT CHANCE-LOW END CHANCE POPS ALONG THE FRONT ATTM. WITH THE LOCAL AREA IN THE WARM SECTOR FRI...TEMPS WILL WARM INTO THE MID-UPPER 70S (NEAR 80 INLAND). WARM TEMPS COMBINED WITH LOW LEVEL THETA-E ADVECTION WILL MAINTAIN A MARGINALLY UNSTABLE AIRMASS OVER THE REGION FRI AFTERNOON. THUS WILL CARRY A SLIGHT CHANCE OF THUNDER. SRN PORTION OF THE FRONT WILL LIKELY STALL OVER THE CAROLINAS FRI NIGHT-SAT IN WLY FLOW ALOFT. SHOULD REMAIN WARM SAT AS LOW LEVEL WESTERLY DOWNSLOPE FLOW PERSISTS...THUS DELAYING COOLER AIRMASS UNTIL SAT NIGHT. HAVE GONE ON WARM EDGE OF GUIDANCE IN THIS PATTERN WITH HIGHS AGAIN MAINLY 75-80 F. LOOKS DRY AS WELL WITH DYNAMICS WELL TO THE NORTH ALTHOUGH AN ISOLATED LATE DAY SHOWER COULD BRUSH NORTHERN ZONES. MORE SIGNIFICANT MODEL DISAGREEMENT ARISES SUN/MON AS THE GFS IS MUCH COOLER BUT DRY AS A DEEP UPPER LOW DEVELOPS OVER THE NE STATES INTO NEW ENGLAND...WHILE THE ECMWF IS LESS AMPLIFIED AND EVEN DEPICTS A LOW AMPLITUDE UPPER LEVEL RIDGE PUSHING BACK INTO REGION BY MON. RATHER LOW CONFIDENCE IN EITHER SOLUTION AT THIS TIME SO HAVE STAYED CLOSE TO WPC AND GEFS/ECMWF ENSEMBLE MEANS. WENT DRY SUN...THEN BRING SOME INCREASE IN CLOUDS AND A SLIGHT CHC POP BY MON AREA-WIDE. HIGH GENLY IN THE 60S TO LOWER 70S WITH LOWS IN THE 40S TO LOWER 50S.
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&& .AVIATION /21Z MONDAY THROUGH SATURDAY/... CLOUDS/LOW CIGS HAVE MOVED OFF TO THE SE OF ALL TAF SITES...GENLY SKC NOW WITH LIGHT WINDS INLAND AND NE WINDS 10-15 KT THROUGH 21Z NEAR THE COAST. FOR TONIGHT...SOME PATCHY FOG AND/OR LOW CIGS WILL BE POSSIBLE...MAINLY AT KPHF/KECG WHERE TEMP/DEW PT DEPRESSIONS ARE LIKELY TO BE LOW. HAVE INCLUDED SOME 4SM VSBYS AND JUST A LOW SCT CLOUD GROUP FOR NOW AS IT REMAINS QUESTIONABLE AS TO HOW WIDESPREAD CIGS BECOME. LIGHT/CALM WINDS SHIFT TO THE SW PRIOR TO DAYBREAK. A COLD FRONT MOVES ACROSS THE REGION LATE TUESDAY...AND THERE IS A GOOD CHANCE FOR SHOWERS AND A FEW THUNDERSTORMS TUESDAY AFTN AND EVENING WITH A BRIEF WINDOW OF FLIGHT RESTRICTIONS POSSIBLE. HIGH PRESSURE/DRY WX RETURNS WEDNESDAY AND THURSDAY...ALTHOUGH A PERIOD OF FAIRLY GUSTY NW FLOW WILL PREVAIL FOR ALL SITES FROM 06-21Z WED (GUSTS TO AROUND 25-30 KT). LESS WIND WED NIGHT/THU. THERE COULD BE A FEW SHOWERS AND THUNDERSTORMS ON FRIDAY...ALTHOUGH PROBABILITIES LOOK RATHER LOW AT THIS TIME. && .MARINE...
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LATEST OBS REFLECT CONTINUED NE WINDS OVER THE WATERS BUT SPEEDS ARE RAPIDLY DIMINISHING. WITH 10-11 SEC PERIOD SWELL HOWEVER..SEAS HAVE BEEN SLOW TO SUBSIDE ALONG THE COAST AND IN THE MOUTH OF THE BAY. HAVE EXTENDED SCA THROUGH 7 PM FOR MOUTH OF THE BAY FOR 3-4 FT WAVES. ALSO STILL NOTING SEAS OF 6-8 FT OVER THE COASTAL WATERS AT 20Z...THUS SCA REMAINS IN PLACE OVER THE ATLANTIC COASTAL WATERS THROUGH TONIGHT (MAY NEED TO EXTEND THROUGH LATE MORNING TUE ACRS SOUTHERN WATERS). FLOW VEERS AROUND TO THE SOUTH LATER TONIGHT IN ADVANCE OF A COLD FRONT APPROACHING FROM THE WEST. COULD HAVE A FEW GUSTS TO LOW END SCA OVER THE BAY/SND IN S-SW FLOW AHEAD OF THE FRONT TUESDAY AFTN BUT EXPECT PREDOMINANT CONDITIONS TO BE SUB-SCA. THE FRONT CROSSES THE WATERS TUESDAY NIGHT, WITH A PERIOD OF STRONG SCA CONDITIONS EXPECTED WITH RESULTANT N-NWLY CAA SURGE LATE TUESDAY NIGHT AND WEDNESDAY AS 850 MB TEMPERATURES DROP SIGNIFICANTLY. OFFSHORE NW FLOW PATTERN WILL GENLY KEEP SEAS FROM BUILDING TO RE THAN 5-6 FT..WITH 3-4 FT WAVES ON THE BAY AND 2-3 FT ON THE RIVERS. WILL SEE A SECONDARY SURGE WED NGT...FOLLOWED BY GRADUALLY IMPROVING MARINE CONDITIONS DURING THE DAY THU (ALTHOUGH TRENDS ARE A LITTLE SLOWER TO BUILD A SFC RIDGE INTO THE REGION SO IT WILL REMAIN FAIRLY BREEZY IN NW FLOW THROUGH THU AFTN FOR NRN COASTAL WATERS IN PARTICULAR). HIGH PRESSURE BUILDS OVER THE AREA FROM THE WEST BY LATE THU AFTN INTO FRI.
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&& .FIRE WEATHER...
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A COLD FRONT WILL CROSS THE LOCAL AREA TUESDAY AFTERNOON INTO TUESDAY NIGHT...BRINGING WITH IT A CHANCE OF SHOWERS AND AN ISOLATED THUNDERSTORM. HOWEVER...THE PROBABILITY OF A WIDESPREAD WETTING RAIN IS NOT ALL THAT GOOD. DRY AND BREEZY CONDITIONS ARE EXPECTED ON WEDNESDAY...WITH MIN RH VALUES DROPPING TO BETWEEN 25-30% FOR MOST LOCATIONS...AND 20FT WINDS ON THE ORDER OF 15-20 MPH WITH FREQUENT GUSTS BETWEEN 25-30 MPH. THESE CONDITIONS COUPLED WITH THE LACK OF SIGNIFICANT RAIN FOR ALMOST A WEEK MAY ENHANCE THE THREAT FOR WILDFIRES ON WEDNESDAY. THE GREATEST THREAT WILL BE ACROSS THE VA PIEDMONT WHERE MIN RH VALUES WILL BE THE LOWEST...AND WHERE THE LEAST AMOUNT OF RAIN HAS FALLEN RECENTLY.
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&& .AKQ WATCHES/WARNINGS/ADVISORIES...
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MD...NONE. NC...NONE. VA...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 7 PM EDT THIS EVENING FOR ANZ634. SMALL CRAFT ADVISORY UNTIL 6 AM EDT TUESDAY FOR ANZ650-652-654- 656-658.
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&& $$ SYNOPSIS...SAM/TMG NEAR TERM...SAM SHORT TERM...SAM LONG TERM...LKB AVIATION...LKB MARINE...LKB FIRE WEATHER...JDM

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