Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 171403 AFDAKQ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WAKEFIELD VA 1003 AM EDT SUN AUG 17 2014 .SYNOPSIS... A WEAK TROUGH OF LOW PRESSURE WILL LINGER OVER EASTERN VIRGINIA INTO CENTRAL NORTH CAROLINA THIS AFTERNOON. ANOTHER COOL FRONT WILL DROP SOUTH TOWARDS THE REGION LATE TONIGHT AND MONDAY. LOW PRESSURE WILL MOVE ALONG THE FRONT FROM THE OHIO VALLEY TOWARDS THE MID-ATLANTIC REGION LATE TONIGHT THROUGH MONDAY NIGHT...BEFORE SHIFTING OFF THE COAST ON TUESDAY. && .NEAR TERM /THROUGH TONIGHT/... LATEST UPPER AIR ANALYSIS FEATURES UPPER TROUGH AXIS OVER THE EAST COAST LATE THIS MORNING...RESULTING IN THE FCST AREA IN W-NW FLOW ALOFT. MEANWHILE TO THE WEST...A DEVELOPING MID/UPPER LEVEL LOW WAS OVER THE MID MS VLY WITH SEVERAL SPOKES OF SHORTWAVE ENERGY SLIDING EAST OVER THE LOWER OH VLY AND THE MID-SOUTH REGION. AT THE SFC...THE NEXT COLD FRONT WAS STILL DRAPED ACROSS NORTHERN NEW ENGLAND BACK INTO THE EASTERN GREAT LAKES AND ACROSS NORTHERN IN/IL. MAINLY DRY WX IS EXPECTED ACROSS THE LOCAL AREA THIS AFTN...ALBEIT WITH SLIGHTLY WARMER TEMPERATURES AND HUMIDITY. WEAK TROF OVER THE AREA WILL WASH OUT THROUGH THE AFTN IN ADVANCE OF A SLOW MOVING COLD FRONT...WHICH WILL DROP SOUTH TOWARDS THE AREA. APPRECIABLE FORCING IS LACKING OVER THE REGION AND DESPITE MODEST MODELED LLVL INSTABILITY...STRONG MID-LEVEL CAPPING ABOVE H7 OWING TO DOWNSLOPE FLOW ALOFT AND A LACK OF AVAILABLE CONVECTIVE TRIGGER SHOULD KEEP THE DAY DRY FOR MOST. WILL MAINTAIN A SLIGHT CHANCE/ISOLATED POP ACROSS THE NRN THIRD OF THE LOCAL AREA CLOSEST TO THE APPROACHING FRONTAL ZONE TO THE NORTH AND INCREASING MOISTURE. ALSO KEPT ISO TSRA WORDING OVER THE SE COAST BY LATE THIS AFTN THROUGH EARLY EVENING IVOF THE OLD SFC BOUNDARY. GENERALLY PARTLY SUNNY WITH MAX TEMPS RANGING FM THE MID 80S TO NEAR 90. GIVEN AFOREMENTIONED LACK OF FORCING, ANY ISOLATED CONVECTIVE ACTIVITY QUICKLY WANES WITH LOSS OF HEATING. VARIABLY CLOUDY AND MILD TNGT WITH LOWS IN THE UPPER 60S TO LWR 70S. && .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... RAIN CHANCES STEADILY INCREASE THROUGH THE SHORT TERM PERIOD, THOUGH CONSIDERABLE UNCERTAINTY REMAINS WITH RESPECT TO THE AMPLITUDE AND PLACEMENT OF AFOREMENTIONED MIDWEST UPPER TROUGH AND ASSD SFC LOW...AS IT TRANSLATES EAST. HV STAYED CLOSE TO A CANADIAN GEM/ECMWF BLEND MONDAY TUESDAY, THOUGH THE 00Z/17 GFS COMING IN LINE WITH A FASTER, LESS AMPLIFIED SOLUTION. THE DAMPENING UPPER TROUGH IS STILL PROGGED TO REACH THE CENTRAL APPALACHIANS MON AFTERNOON, WITH THE ASSOCIATED SFC FRONT DROPPING SOUTH ACROSS THE NRN PORTIONS OF THE LOCAL AREA MONDAY AFTN. MODELS REMAIN IN GOOD AGREEMENT THAT THE MAIN VORT MAX/ENERGY WILL SLIDE ACROSS NRN VA TOWARDS THE UPPER EASTERN SHORE MONDAY INTO MON NGT IN THE PRESENCE OF AN INCREASINGLY UNSTABLE AIRMASS. RESULTANT LOW LEVEL LEE/THERMAL TROUGHING AND INCREASING SW FLOW WILL RESULT IN INCREASING MOISTURE ACROSS THE AREA, WITH PW VALUES ~2" BY LATE MONDAY. THE APPROACH AND PASSAGE OF SFC LOW PRES ACRS THE AREA...MODERATE DIURNAL INSTABILITY (MLCAPE IN THE 1500-2500 J/KG RANGE) AND INCREASING FORCING FOR ASCENT SHOULD ALLOW FOR A GREATER COVERAGE OF SCT SHOWERS DEVELOPING MON AFTERNOON AND EVENING...AND CONTINUE SHOWERS MONDAY NIGHT INTO TUESDAY MORNING. HV GONE WITH CHC TO LOW END LKLY POP AREA WIDE MONDAY AFTN/EVENING (30-60%) WITH HIGHEST POP NORTH ACROSS THE LWR EASTERN SHORE. AS OF RIGHT NOW, EXPECT A RELATIVE LULL IN ACTIVITY TUESDAY AFTN IN ASSOCIATION WITH SUBSIDENCE BEHIND THE DEPARTING WAVE AND WITH QUASI-DOWNSLOPE FLOW DEVELOPING TUESDAY AFTN-EARLY WEDNESDAY. LOW LEVEL THICKNESSES YIELD TEMPS IN THE LOW-MID 90S MON IN ADVANCE OF THE FRONT. HOWEVER, ONCE AGAIN, CLOUD COVER AND HIGHER TD`S WILL LIKELY PREVENT TEMPS FROM REACHING THE WARMER MAV NUMBERS, SO AGAIN UNDERCUT BLENDED GUIDANCE SOLUTION BY 1-2 DEGS EACH DAY. LOOK FOR HIGHS IN THE MID TO UPPER 80S BOTH DAYS. WARM AND MODERATELY HUMID, ESPECIALLY IN COMPARISON TO THE PAST FEW NIGHTS. LOWS WILL RANGE FROM THE UPPER 60S TO LOW 70S BOTH TUESDAY AND WEDNESDAY MORNINGS. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... BLOCKY PATTERN OVER THE NRN ATLANTIC AND SPLIT FLOW OVER THE NRN CONUS WILL RESULT IN AN UNSETTLED WEATHER PATTERN THROUGH THE PERIOD. TEMPS WILL BE NEAR SEASONABLE...LATE SUMMER NORMS. SPLIT FLOW IS TYPICALLY PROBLEMATIC FOR MEDIUM RANGE GUIDANCE...AND THIS TIME IS NO EXCEPTION. HAVE TRENDED FORECAST MORE TOWARD THE ECMWF AND ENSEMBLE MEANS BASED ON RUN TO RUN CONSISTENCY AND WPC GUIDANCE. WITH THAT SAID...WEAK SRN STREAM JET WILL PUSH A SHORTWAVE OVER THE GREAT LAKES WEDS AS THE PREVIOUS DAYS WEAK COLD FRONT PUSHES INTO NC. THE PARENT SFC LOW WILL PUSH OFFSHORE AS WEAK HIGH PRESSURE BUILDS OVER THE NE STATES. WEAK WLY FLOW ALOFT PARALLEL TO THE FRONT WILL LIKELY KEEP THE FRONT OVER THE REGION THRU THE END OF THE WEAK AS THE MID LEVEL WAVE SLOWLY PUSHES INTO THE NE STATES. WEAK ENERGY IN THE WLY FLOW WILL LIKELY LEAD TO WAVES OF LOW PRESSURE DEVELOPING ALONG THE STALLED FRONTAL BOUNDARY...BUT TIMING THEM AT THIS POINT IS QUITE DIFFICULT. WARM/HUMID AIRMASS WILL BE IN PLACE WITH DEWPOINTS IN THE UPPER 60S TO LOW 70S. PWATS WILL BE TYPICAL FOR LATE SUMMER...AVG BTWN 1.5 AND 2.0 INCHES. EXPECT TYPICAL DIURNAL CONVECTION AS INSTABILITY INCREASES DURING THE AFTERNOON AND EVENING THRU THE END OF THE WEEK. HOWEVER...THE AIRMASS MAY SUPPORT SHOWERS AND THUNDERSTORMS INTO THE OVERNIGHT...SO WILL MAINTAIN SLIGHT CHANCE POPS. UPPER LOW REMAINS OVER THE NE STATES SAT WITH TROUGHING IN VICINITY OF THE ERN SEABOARD. WILL CONTINUE WILL SLIGHT CHANCE-CHANCE POPS SAT AFTERNOON AND EVENING. WARM/HUMID WITH TEMPS RIGHT AROUND SEASONABLE NORMS IN THE MID-UPPER 80S WITH LOWS IN THE MID-UPPER 60S TO LOW 70S. && .AVIATION /14Z SUNDAY THROUGH THURSDAY/... VFR CONDITIONS WILL PREVAIL TODAY WITH SW-W WINDS AROUND 10 KT OR LESS. A STALLED BOUNDARY FROM THE DELMARVA TO THE NC PIEDMONT WILL WASH OUT INTO A THERMAL TROUGH TODAY AS WNW FLOW ALOFT STREAMS MOISTURE AND ENERGY INTO THE MID ATLANTIC REGION. AS THIS ENERGY INTERACTS WITH THE THERMAL TROUGH...THUNDERSTORMS MAY DEVELOP BY THIS AFTN/EVENING BUT ARE EXPECTED TO BE VERY ISOLATED AT THIS TIME. THE THERMAL TROUGH GETS SHUNTED SWD OVER THE CAROLINAS ON MONDAY AND LOW PRESSURE IS EXPECTED TO DEVELOP ALONG THIS FEATURE...AS A COLD FRONT APPROACHES THE REGION FROM THE NORTH AND MERGES WITH THE LOW MONDAY NIGHT. THIS WILL INCREASE THUNDERSTORM CHANCES ACROSS THE AREA MON/MON NIGHT. FOR TUESDAY...THE LACK OF UPSTREAM FEATURES AND GENERALLY LIGHT STEERING FLOW ALOFT (LESS THAN 25 KT) WILL KEEP THE LOW PRESSURE SYSTEM ALONG THE MID ATLANTIC COAST ON TUESDAY AND ONCE AGAIN RESULT IN WIDESPREAD SHOWERS/STORMS. INCREASING DEWPOINTS AND MOISTURE WILL AID FOG DEVELOPMENT EACH NIGHT BUT WILL GENERALLY FORM IN AREAS THAT RECEIVE RAINFALL DURING THE AFTN/EVENING HOURS. && .MARINE... SW-W WINDS AOB 10 KT WILL PREVAIL TODAY THROUGH THIS EVENING AS A FRONTAL BOUNDARY WASHES INTO A THERMAL TROUGH LOCATED ALONG THE MID ATLANTIC COAST INTO THE NC COASTAL PLAIN. THUNDERSTORMS MAY BE POSSIBLE DURING THE AFTN/EVENING HOURS (PRIMARILY IN THE SRN WATERS) BUT WILL BE VERY ISOLATED. WINDS TURN NW-N OVERNIGHT AND REMAIN LIGHT AT 5-10 KT. WAVES/SEAS AVERAGE 1-2 FT THE THERMAL TROUGH GETS SHUNTED SWD OVER THE CAROLINAS ON MON AND LOW PRESSURE IS EXPECTED TO DEVELOP ALONG THIS FEATURE...AS A COLD FRONT APPROACHES THE REGION FROM THE NORTH AND MERGES WITH THE LOW MON NIGHT. WINDS BECOME E-SE UP TO 10 KT AND GRADUALLY INCREASE LATE IN THE DAY INTO THE EVENING...AVERAGING AOB 15 KT BY NIGHTFALL. MEANWHILE...THUNDERSTORM CHANCES INCREASE ACROSS THE WATERS MON/MON NIGHT. FOR TUESDAY...THE LACK OF UPSTREAM FEATURES AND GENERALLY LIGHT STEERING FLOW ALOFT (LESS THAN 25 KT) WILL KEEP THE LOW PRESSURE SYSTEM ALONG THE MID ATLANTIC COAST ON TUESDAY AND ONCE AGAIN RESULT IN WIDESPREAD SHOWERS/STORMS. WINDS WILL BE VARIABLE FROM A GENERAL NE DIRECTION AOB 10 KT. UNSETTLED CONDITIONS PREVAIL THROUGH AS LOW PRESSURE LINGERS NEAR THE MID ATLANTIC COAST. WINDS WILL GENERALLY BE ONSHORE AOB 10 KT. WAVES 1-2 FT MON THROUGH FRI. SEAS WILL AVERAGE 1-2 FT MON THROUGH THU...SLOWLY BUILDING TO 3-4 FT NRN WATERS FRI AFTN. && .AKQ WATCHES/WARNINGS/ADVISORIES... MD...NONE. NC...NONE. VA...NONE. MARINE...NONE. && $$ SYNOPSIS...MAM NEAR TERM...MAM/TMG SHORT TERM...MAM LONG TERM...SAM AVIATION...BMD MARINE...BMD

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