Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 220814 AFDAKQ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WAKEFIELD VA 414 AM EDT TUE APR 22 2014 .SYNOPSIS... A WEAK COLD FRONT APPROACHES FROM THE WEST THIS MORNING...AND WILL CROSS THE REGION THIS AFTERNOON THROUGH THIS EVENING. COOL CANADIAN HIGH PRESSURE BUILDS BACK OVER THE REGION WEDNESDAY AND THURSDAY. ANOTHER COLD FRONT WILL CROSS THE AREA ON FRIDAY. && .NEAR TERM /THROUGH TONIGHT/...
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LATEST WX ANALYSIS FEATURES MID-UPPER LEVEL TROUGH ORIENTED FROM SOUTHEASTERN ONTARIO INTO THE MID-SOUTH THIS MORNING, WITH THE ATTENDANT SFC COLD FRONT EXTENDING FROM THE EASTERN GREAT LAKES INTO THE LOWER MISSISSIPPI VLY. UPPER LEVEL TROUGH WILL PUSH EAST TODAY, PUSHING THE COLD FRONT ACROSS THE REGION LATE THIS AFTN/TNGT. DEEP LAYER W TO W-SW FLOW AHEAD OF THE FRONTAL PASSAGE WILL LIMIT THE AMOUNT OF MOISTURE ADVECTION INTO THE REGION...WITH MOST OF THE MOISTURE BEING SUPPLIED BY THE SYSTEM. EXPECT A PARTLY TO MOSTLY SUNNY MORNING TO START...AND CWA SHOULD REMAIN DRY WITH LITTLE MORE THAN SOME INCREASING CLOUDS THROUGH MIDDAY. HIGH TEMPERATURES TODAY GENERALLY WELL INTO THE 70S, WITH LOWER 80S EXPECTED WEST OF THE BAY. EXPECT SOME SHRAS TO DEVELOP ALONG PRE-FRONTAL LEE TROUGH BY AROUND/JUST AFTER 18Z, WITH ADDITIONAL SCT SHRAS AS THE COLD FRONT ADVANCES INTO THE LOCAL AREA BY MID TO LATE AFTERNOON THROUGH EARLY EVENING. HI-RES MODELS CONTINUE TO INDICATE A NARROW AND UNORGANIZED BAND OF SHOWERS AND A FEW ISOLATED THUNDERSTORMS CROSSING THE AREA WITH THE FRONT DURING THE AFTERNOON. THIS SEEMS REASONABLE GIVEN DOWNSLOPE FLOW ALOFT AND WITH THE BEST DYNAMICS WILL REMAIN TO THE NORTH OF THE LOCAL AREA. THETA-E ADVECTION AND TEMPS WARMING INTO THE UPPER 70S WILL RESULT IN A MARGINALLY UNSTABLE AIRMASS OVER THE REGION. HOWEVER, COOL TD VALUES, MEAGER MLCAPE VALUES (PROGGED TO BE LESS THAN 500 J/KG) AND RATHER SHALLOW MID-LVL LAPSE RATES ALL SEEM TO POINT TOWARDS ISOLATED CONVECTIVE ACTIVITY. FURTHER, MARGINAL SHEAR (0-6KM BULK SHEAR 25-30 KT) SHOULD PREVENT OVERALL STORM ORGANIZATION. THE MAIN THREAT FROM ANY DEVELOPING STORMS WILL BE LOCALLY SUB-SEVERE WIND GUSTS DUE TO THE DRY SUB-CLOUD LYR, AND WILL REFLECT THIS IN TODAY`S HWO. LIKELY POPS ARE IN PLACE MAINLY ALONG AND NORTH OF I-64, WITH A CHC (40-50%) POP FARTHER SOUTH. DID RETAIN ISOLATED THUNDER WORDING ACROSS THE ENTIRE CWA. QPF AMOUNTS WILL GENERALLY BE LESS THAN ONE QUARTER OF AN INCH. TONIGHT... SHOWERS/ISO THUNDERSTORMS PUSH OFFSHORE THIS EVENING W/ A QUICKLY CLEARING SKY THROUGH MIDNIGHT, AS COOL CANADIAN HIGH PRESSURE BUILDS IN FROM THE NW. WELL MIXED ATMOSPHERE SHOULD PREVENT TEMPS FROM FALLING AS QUICKLY AS PROGGED BY COOLER MAV GUIDANCE...SO HAVE OPTED TOWARDS WARMER ENVELOPE OF MOS GUIDANCE ACROSS THE BOARD. EARLY MORNING LOWS GENERALLY IN THE UPPER 40S INLAND AND OVER THE EASTERN SHORE...TO LOW 50S SE COAST.
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&& .SHORT TERM /WEDNESDAY THROUGH THURSDAY/... MODIFYING CANADIAN HIGH PRESSURE BUILDS IN FROM THE NW ON WED, AS NW FLOW PERSISTS. REMNANT MID LEVEL MOISTURE UNDER A SUBSIDENCE INVERSION AND ADDITIONAL SHORTWAVE ENERGY DIVING DOWN THE BACK SIDE OF THE UPPER TROUGH (LOCATED JUST OFFSHORE) WILL RESULT IN AFTERNOON CU OVER THE LOCAL AREA...ESPECIALLY OVER NORTHEASTERN COASTAL ZONES. LOCAL THICKNESS TOOLS INDICATE HIGHS ONLY IN THE LOWER TO MIDDLE 60S OVER THE LOCAL AREA. HOWEVER, WITH DEWPOINTS WILL MIX INTO THE UPR 20S/LOW 30S (YIELDING MINIMUM RH VALUES IN THE MID 20S INLAND) AND WITH DOWNSLOPE FLOW COMPONENT, BUMPED TEMPS INTO THE MID TO UPPER 60S INLAND, WITH LOWER 60S OVER THE LOWER EASTERN SHORE. CONCERN DOES EXIST FOR FIRE WX CONDITIONS WED...SEE FIRE WX SECTION BELOW FOR DETAILS. EARLY MORNING LOWS THU MORNING IN THE U30S TO AROUND 40...UNDER A MAINLY CLEAR SKY. DRY AGAIN ON THU AS HIGH PRESSURE SLIDES OVER THE REGION, BEFORE SLIDING OFF OFF THE CAROLINA COAST LATE THU/ERY FRIDAY. HIGHS THURS GENERALLY IN THE UPPER 60S. ONCE AGAIN, MIN RH VALUES FALL INTO THE 20S THU AFTN. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... 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. && .AVIATION /08Z TUESDAY THROUGH SATURDAY/... AS OF 22/0540Z...LIGHT WINDS ARE GRADUALLY TURNING FROM EAST TO SOUTH AS SFC HIGH PRESSURE BEGINS TO SLIDE OFFSHORE. MEANWHILE... A SFC COLD FRONT WILL PUSH ACROSS THE GREAT LAKES REGION AND INTO THE OHIO VALLEY DURING THE REMAINDER OF THE OVERNIGHT HOURS. BKN CIGS AROUND 25 KFT AGL HAVE BEGUN TO OVERSPREAD THE MID ATLANTIC REGION AND WILL CONTINUE TO DO SO INTO TUE MORNING. THE APPROACHING COLD FRONT IS EXPECTED TO CROSS THE AREA DURING TUE AFTN/EVENING. THERE IS ENOUGH INSTABILITY PRESENT FOR THUNDERSTORMS TO DEVELOP JUST AHEAD OF THE FRONT...POTENTIALLY RESULTING IN BRIEF REDUCTIONS TO VIS/CIGS UNDER STRONGER STORM CORES. THE APPROACHING FRONT WILL CAUSE WINDS TO BECOME MORE SW-W TODAY...WHICH WILL THEN INCREASE TO AROUND 10 KT WITH GUSTS OF 15-20 KT DURING THE AFTN. THUNDERSTORM WIND GUSTS OF 30-40 KT WILL ALSO BE POSSIBLE. BEHIND THE FRONT...WINDS QUICKLY TURN TO THE NW AFTER MIDNIGHT AND SPEEDS ARE EXPECTED TO INCREASE ALONG THE CHES BAY AND ATLANTIC COASTS DUE TO POST-FRONTAL COLD AIR ADVECTION. COOLER AIR CONTINUES TO FLOW INTO THE MID ATLANTIC REGION ON WED...MAKING FOR A BREEZY DAY. AREAS WELL INLAND SHOULD EXPERIENCE NW WINDS 10-15 KT WITH GUSTS OF 20-25 KT. AREAS CLOSER TO THE CHES BAY AND ATLANTIC COASTS (INCLUDING THE MD/VA EASTERN SHORE) SHOULD EXPERIENCE NW WINDS OF 15-20 KT WITH GUSTS OF 25-30 KT. DIMINISHING WIND SPEEDS ARE ANTICIPATED TO OCCUR THROUGHOUT WED EVENING...BECOMING CALM INLAND BY 24/0400Z WHILE SPEEDS STAY AROUND 10-15 KT NEAR THE COAST. HIGH PRESSURE/DRY WX CONTINUES THU WITH NW WINDS TURNING TO THE W DURING THE DAY. SPEEDS WILL STAY SOMEWHAT BREEZY NEAR THE COAST AS A TIGHTENED SFC PRESSURE GRADIENT PERSISTS. ANOTHER COLD FRONT CROSSES THE ARE ON FRI AND THERE COULD BE A FEW SHOWERS AND THUNDERSTORMS...ALTHOUGH PROBABILITIES LOOK RATHER LOW AT THIS TIME. && .MARINE... 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. && .FIRE WEATHER... A COLD FRONT WILL CROSS THE LOCAL AREA THIS AFTERNOON INTO TONIGHT, 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. && .AKQ WATCHES/WARNINGS/ADVISORIES... MD...NONE. NC...NONE. VA...NONE. MARINE...SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO 7 PM EDT WEDNESDAY FOR ANZ633-635>638. SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO 8 AM EDT THURSDAY FOR ANZ630>632-634. SMALL CRAFT ADVISORY UNTIL 8 AM EDT THURSDAY FOR ANZ650-652- 654-656-658. && $$ SYNOPSIS...MAM NEAR TERM...MAM/SAM SHORT TERM...MAM LONG TERM...LKB AVIATION...BMD MARINE...LKB FIRE WEATHER...

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