Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 221745 AFDAKQ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WAKEFIELD VA 145 PM EDT TUE APR 22 2014 .SYNOPSIS... A COLD FRONT APPROACHES FROM THE WEST THIS AFTERNOON...AND WILL CROSS THE REGION THIS EVENING. COOL CANADIAN HIGH PRESSURE BUILDS BACK OVER THE REGION WEDNESDAY AND THURSDAY. ANOTHER FRONT WILL CROSS THE AREA ON FRIDAY. && .NEAR TERM /THROUGH TONIGHT/... LATEST WX ANALYSIS FEATURES A WEAK LEE TROUGH DEVELOPING ACRS THE PIEDMONT AS SEEN IN OBS/PRESSURE FALLS. ACTUAL COLD FRONT STILL ALONG WEST SLOPE OF THE APPALACHIANS. DEEP LAYER SW FLOW WILL GRADUALLY SHIFT TO THE WSW LATER THIS AFTN. AREA LAPS AND BUFKIT SOUNDINGS SHOW AN INVERTED V PROFILE THAT WOULD SUGGEST THE POTENTIAL FOR GUSTY WINDS IN ANY SHOWERS AND TSTMS LATER TODAY. HOWEVER...THE FLOW BECOMING MORE WSW TYPICALLY TENDS TO DECREASE AREAL COVERAGE AND WOULD ALSO INHIBIT STORM ORGANIZATION TO SOME EXTENT. LATEST 12Z NAM SEEMS TO DEPICT CURRENT CONDITIONS FAIRLY WELL AND SHOWS MUCH OF THE CURRENT ACTIVITY OVER FAR NW ZONES DISSIPATING AS IT TRACKS TO THE EAST. HAVE SCALED BACK ON POPS THROUGH 20Z (4 PM) ACRS SE VA/NE NC WHILE MAINTAINING CHC TO LIKELY POPS ACRS THE FAR NW. WILL CONTINUE TO CARRY MAINLY CHC POPS FROM LATE AFTN INTO EARLY EVENING ACRS THE CWA (WITH LIKELY POPS OVER THE NORTH)...AS AREA OF ACTIVITY CURRENTLY OVER WRN NC AND ERN TN MOVES EAST. IN GENERAL...NOT A LOT OF SUPPORT FOR SEVERE WX GIVEN A SHORT WINDOW WITH ML CAPES EVEN GETTING TO 500-1000 J/KG BY LATE AFTN. DEEP LAYER SHEAR IS ONLY ON THE ORDER OF 25-30 KT AS WELL...BUT CAN`T RULE OUT AN ISOLATED STRONG STORM WITH GUSTY WINDS TO 40-45 MPH GIVEN THE DEEP MIXING. QPF AMOUNTS WILL GENERALLY BE LESS THAN ONE QUARTER OF AN INCH. HIGH TEMPERATURES TODAY GENERALLY WELL INTO THE 70S, WITH A FEW LOWER 80S POSSIBLE WEST OF THE BAY. 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. && .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 /18Z TUESDAY THROUGH SUNDAY/...
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BAND OF PRE-FRONTAL SHWRS NOW CROSSING THE PIEDMONT HAVE THE BEST CHC OF REACHING KRIC/KSBY OVER THE NEXT SVRL HRS SO HAVE ADDED A 2-3 HR TEMPO GROUP THERE. OTW...KEPT VCSH ACROSS SERN TAF SITES AFTR 20Z GIVING THE LATEST TRENDS OF THE PCPN WEAKENING AS IT CROSSES THE MTS. ALTHOUGH CONFIDENCE NOT HIGH ENOUGH TO PUT THUNDER IN ATTM... BEST LOCATION FOR ANY THUNDER TO OCCUR WOULD BE ACROSS SERN TAF SITES BEFORE 00Z. OTW...SCT-BKN MID LEVEL CLOUD COVERAGE EXPECTED AS THE ACTUAL COLD FRONT CROSSES THE AREA THIS EVENING. SKIES CLR BEHIND THE BOUNDARY AFTR 06Z. STRONG CAA SETS IN LATE TONIGHT AND WEDNESDAY MORNING WITH NW WINDS INCRG TO BTWN 15-25 KTS BY 12Z. HIGHER GUSTS POSSIBLE ALONG THE DELMARVA AND SERN COASTAL AREAS WEDNESDAY. VFR CONDITIONS CONTINUE THROUGH THURSDAY NIGHT. THE NEXT COLD FRONT CROSSES THE AREA FRIDAY WITH SCT SHWRS/TSTRMS.
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&& .MARINE...
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SEAS HAVE FINALLY SUBSIDED BELOW 5 FT IN THE COASTAL WATERS THANKS TO SLY FLOW. HAVE CANCELLED SCA HEADLINES FOR THE COASTAL WATERS FOR THIS AFTERNOON AND EVENING. HOWEVER...THE LULL WILL BE SHORT LIVED AS ANOTHER COLD FRONT CROSSES THE WATERS LATE THIS AFTERNOON INTO THIS EVENING. SOLID SCA CONDITIONS EXPECTED AFTER MIDNIGHT AS A STRONG NWLY SURGE ARRIVES OVER THE WATER. STRONG GRADIENT WILL PRODUCE 35-40 KT 925MB WINDS TONIGHT AND WEDNESDAY OVER THE WATER. WILL LEAVE AS SCA ATTM...BUT WILL RE-EVALUATE FOR THE AFTERNOON FORECAST PACKAGE. PREV DISCUSSION... LIGHT WINDS AROUND 5 KT ARE GRADUALLY TURNING FROM EAST TO SOUTH AS SFC HIGH PRESSURE BEGINS TO SLIDE OFFSHORE. MEANWHILE...A SFC COLD FRONT WILL PUSH ACROSS THE OHIO VALLEY THIS MORNING AND THEN CROSS THE WATERS THIS AFTN/EVENING. AS THE FRONT APPROACHES THE WATERS THIS AFTN...WINDS WILL BECOME SW AND INCREASE TO 10-15 KT. A FEW GUSTS AROUND 20 KT MAY BE POSSIBLE OVER CHES BAY/CURRITUCK SOUND DURING THIS TIME...BUT AM STILL ANTICIPATING PREDOMINANT CONDITIONS TO BE SUB-SCA. MEANWHILE FOR TODAY...ONSHORE SWELL WITH 10-11 SECOND PERIODS WILL PREVENT SEAS FROM SUBSIDING BELOW 5 FT FOR THE GREATER PART OF TODAY...ESPECIALLY OUT NEAR 20 NM. THEREFORE SCA FLAGS FOR ALL COASTAL WATERS HAVE BEEN EXTENDED THROUGH TODAY. SHOWERS AND ISOLATED THUNDERSTORMS ARE EXPECTED DURING THE FRONTAL PASSAGE AND MAY BE CAPABLE OF PRODUCING LOCALIZED GUSTY WINDS OF 25-35 KT. THE FRONT CROSSES THE WATERS THIS EVENING AND PUSHES OFFSHORE AFTER MIDNIGHT TONIGHT. A PERIOD OF STRONG POST-FRONTAL SCA CONDITIONS ARE ANTICIPATED DUE TO A DECENT CAA SURGE LATE TONIGHT INTO WEDNESDAY. A FAVORABLE NW WIND DIRECTION WILL FURTHER ENHANCE WIND SPEEDS...BUT WILL GENERALLY PREVENT SEAS FROM BUILDING ANY HIGHER THAN 5-6 FT...WITH 3-4 FT WAVES ON THE BAY (LOCALLY UP TO 5 FT SRN BAY LATE TONIGHT) AND 2-3 FT ON THE RIVERS. WILL SEE A SECONDARY...ALBEIT WEAKER... COLD AIR SURGE WED NIGHT...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. SCA FLAGS FOR ALL COASTAL WATERS WERE EXTENDED THROUGH WED NIGHT FOR A COMBINATION OF WINDS AND SEAS. ADDITIONAL FLAGS WERE HOISTED FOR THE BAY/SOUND/RIVERS BEGINNING AFTER MIDNIGHT TONIGHT AND PERSISTING INTO EARLY WED EVENING TO ACCOUNT FOR THE STRONG NW SURGE TONIGHT AND CONTINUED BREEZY CONDITIONS ON WED BEFORE WINDS DIMINISH.
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&& .FIRE WEATHER... A COLD FRONT WILL CROSS THE LOCAL AREA LATE 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...
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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 FROM 10 PM THIS EVENING TO 8 AM EDT THURSDAY FOR ANZ650-652-654-656-658.
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&& $$ SYNOPSIS...LKB NEAR TERM...LKB/MAM SHORT TERM...MAM LONG TERM...LKB AVIATION...BMD MARINE...BMD/SAM FIRE WEATHER...

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