Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 202116 AFDAKQ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WAKEFIELD VA 516 PM EDT MON APR 20 2015 .SYNOPSIS... SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS WILL ACCOMPANY A COLD FRONT AS IT CROSSES THE AREA THIS EVENING. HIGH PRESSURE BUILDS BACK IN FROM THE SOUTHWEST ON TUESDAY. ANOTHER COLD FRONT CROSSES THE AREA LATE WEDNESDAY INTO WEDNESDAY NIGHT. HIGH PRESSURE RETURNS THURSDAY AND FRIDAY. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... SEVERE THUNDERSTORM WATCH 89 HAS BEEN ISSUED FOR PORTIONS OF THE ERN VA PIEDMONT...CNTRL VA AND NRN VA UNTIL 10 PM. LATEST REGIONAL RADAR MOSAIC DEPICTS SCATTERED SHOWERS/THUNDERSTORMS DEVELOPING ACROSS THE VA/NC PIEDMONT THIS AFTERNOON. THUNDERSTORMS ARE DEVELOPING IN A FAVORABLE AIRMASS IN ADVANCE OF AN APPROACHING COLD FRONT. THETA-E ADVECTION AND TEMPS IN THE MID-UPPER 70S WITH DEWPOINTS IN THE MID 50S TO LOW 60S HAS RESULTED IN A MARGINALLY UNSTABLE AIRMASS...WITH MLCAPE VALUES BETWEEN 500 AND 1000 J/KG. VERY LITTLE INHIBITION ANALYZED WITH MLCAPE ON THE RNK SOUNDING -35 J/KG. NOSE OF HIGHER PWATS AROUND 1 TO 1.2 INCHES ADVECTING INTO THE REGION IN ADVANCE OF THE FRONT. ALOFT...SHORTWAVE VISIBLE ON WATER VAPOR LIFTING OVER THE CAROLINAS WILL PROVIDE ADEQUATE UVM OVER THE REGION. THE RESULT WILL BE ADDITIONAL DEVELOPMENT ACROSS THE PIEDMONT THRU LATE THIS AFTERNOON. LATEST HI-RES GUIDANCE CONTINUES TO INDICATE DISCRETE CELLS THIS AFTERNOON...BUT BASED ON 30-40 KT OF EFFECTIVE SHEAR EXPECT CELLS TO BECOME LINEAR EARLY THIS EVENING OVER THE PIEDMONT. STORMS THEN LIFT QUICKLY NEWD IN 30-40 KT MEAN FLOW AS THE COLD FRONT REACHES THE LOCAL AREA THIS EVENING. DAMAGING WINDS AND LARGE HAIL ARE STILL THE MAIN CONCERNS WITH THE STRONGEST STORMS IN THE WATCH AREA. WHILE THERE IS SOME DIRECTION SHEAR/HELICITY...LCL HEIGHTS OF 1000-1500 M WILL LIMIT THE TORNADO THREAT. BRIEF HEAVY RAINFALL ALSO EXPECTED. ISOLATED STRONG TO SEVERE STORMS POSSIBLE OVER SE VA/NE NC...BUT TIMING IS NOT FAVORABLE AND INSTABILITY WILL BE ON THE DECREASE. COLD FRONT REACHES THE COAST AROUND MIDNIGHT...PUSHING OFFSHORE SHORTLY THEREAFTER. EXPECT ALL PRECIP TO BE OFFSHORE BY MIDNIGHT...WITH CLEARING W TO E LATE. LOWS RANGE FROM THE LOW 50S NW TO LOW 60S NEAR THE COAST. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/... STACKED UPPER LOW ANCHORS OVER THE GREAT LAKES REGION AND SRN CANADA THRU THE SHORT TERM PERIOD THANKS TO BLOCKY FLOW OVER THE HIGH LATITUDES. IN WAKE OF TONIGHTS (MON NIGHTS) COLD FRONT...HIGH PRESSURE FORECAST TO BUILD ACROSS THE SE STATES TUES...EXTENDING NEWD OVER THE LOCAL AREA. THE RESULT WILL BE DRY CONDITIONS AND A WLY WIND. HIGHS FORECAST IN THE UPPER 60S E TO LOW 70S W UNDER A MOSTLY SUNNY SKY. SERIES OF UPPER LEVEL DISTURBANCES WILL ROUND THE BASE OF THE UPPER LOW...WITH THE FIRST ROUNDING THE BASE TUES NIGHT- WEDS. ASSOCIATED FAST MOVING COLD FRONT DROPS INTO THE OH VALLEY WEDS. HIGH PRESSURE PUSHES OFF THE SE COAST WEDS...WITH INCREASING SWLY LOW LEVEL FLOW OVER THE LOCAL AREA. WEAK FRONT REACHES THE CNTRL APPALACHIANS WEDS AFTERNOON. WILL MAINTAIN SLIGHT CHANCE- CHANCE POPS ACROSS THE NRN LOCAL AREA WEDS AFTERNOON...CLOSEST TO BEST MOISTURE/DYNAMICS. HIGHS WEDS GENERALLY IN THE LOW-MID 70S. FRONT DROPS ACROSS THE LOCAL AREA WEDS NIGHT. WILL MAINTAIN SLIGHT CHANCE-CHANCE POPS ALONG THE COAST WEDS NIGHT. FRONTAL BOUNDARY STALLS JUST SOUTH OF THE LOCAL AREA EARLY THURS MORNING. WAVE OF LOW PRESSURE PROGGED TO DEVELOP ALONG THE STALLED BOUNDARY THURS MORNING AS SRN STREAM ENERGY TRAVERSES THE GULF STATES. GFS/ECMWF SOLUTIONS KEEP MEASURABLE PRECIP SOUTH OF THE LOCAL AREA THURS...BUT NAM/SREF SOLUTIONS SPREAD PRECIP INTO S AND SE VA/NE NC. WILL CARRY SLIGHT CHANCE POPS THURS ACROSS THOSE AREAS BASED ON UNCERTAINTY. COOLER THURS WITH WNW FLOW BEHIND THE FRONT. HIGHS GENERALLY IN THE LOW-MID 60S. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... COLD FRONT MOVES SOUTH OF THE AREA THURS NIGHT FOLLOWED BY COOL HIGH PRESSURE BUILDING IN FROM THE NW. DRY WITH LOWS BOTH THURS AND FRI NIGHTS 40-50 XCPT A FEW U30S NWRN MOST CNTYS. HIGHS FRI M-U60S. NXT SYSTM PROGGED TO TRACK ACROSS THE CAROLINAS SAT. ECMWF SOMEWHAT FRTHR SOUTH WITH ITS MOISTURE FIELDS THAN GFS. BEST SPRT FOR PCPN WILL BE ACROSS SRN HALF OF FA WHERE CHC POPS WILL BE MAINTAINED. SLGHT CHC ACROSS THE NRTH. COOL SAT WITH HIGHS 60-65. PCPN ENDS SAT EVE AS SYSTM EXITS OFF THE COAST. LOWS IN THE 40S. CANADIAN HIGH PRESSURE DOMINATES ERLY NEXT WEEK WITH ANY PCPN STAYING SOUTH OF FA. DRY WITH A SLOW MODERATING TREND. HIGHS SUN IN THE L-M60S. LOWS SUN NIGHT IN THE 40S. HIGHS MON M-U60S. && .AVIATION /21Z MONDAY THROUGH SATURDAY/... SHOWERS AND THUNDERSTORMS ARE ANTICIPATED TO MOVE ACROSS VA AHEAD OF A COLD FRONT THAT IS CURRENTLY STRETCHING FROM THE GREAT LAKES THROUGH GA. SCATTERED STRONG TO SEVERE THUNDERSTORMS ARE EXPECTED TO FORM ACROSS THE VA PIEDMONT THIS AFTN AND EVENING BEFORE A LINE OF SHOWERS AND THUNDERSTORMS MAKES ITS WAY WEST TO EAST OVERNIGHT. THE COLD FRONT MOVES OFF THE COAST LATE TONIGHT...WITH HIGH PRESSURE BUILDING INTO THE REGION TUESDAY. EXPECT EXTREMELY REDUCED VISIBILITIES...STRONG GUSTY WINDS AND HAIL DURING ANY THUNDERSTORM ACTIVITY. THE SURFACE HIGH MOVES OFFSHORE WEDNESDAY. A COLD FRONT CROSSES THE AREA WEDNESDAY NIGHT WITH A SLIGHT CHC OF SHOWERS. && .MARINE... SEAS REMAIN AT OR ABOVE 5 FT...SO WILL CONT THE SCA HEADLINES WITH AN EMPHASIS ON SUBSIDING CONDITIONS THROUGH TUES. A COLD FRONT CROSSES THE AREA LATE TONIGHT. SW WINDS AHEAD OF THIS BOUNDARY WILL SHIFT TO THE WEST BUT REMAIN BLO 20 KTS...SO NO HEADLINES (WIND WISE) XPCTD BEHIND THE FRNT. NEXT TROF / FRONT PROGGED ACROSS THE WATERS WED NIGHT / ERLY THURSDAY SWITCHING THE WNDS TO A NW THEN N DIRECTION. ONCE AGAIN...SURGE BEHIND THIS BOUNDARY NOT STRONG ENUF TO GENERATE HEADLINES. NW FLOW SETS UP BEHIND THIS BOUNDARY INTO THE WEEKEND WITH CONDITIONS REMAINING BLO SCA LEVELS. && .HYDROLOGY... OVERNIGHT RAINFALL OF ONE TO ONE HALF INCH RESULTED IN RISES OVER AREA RIVERS DURING THE DAY. A FLOOD WARNING HAS BEEN POSTED FOR THE RIVANNA RIVER AT PALMYRA...WHERE MINOR FLOODING IS EXPECTED. RISES ARE EXPECTED OVERNIGHT TONIGHT FOR THE JAMES RIVER...WITH THE RICHMOND WESTHAM GAUGE APPROACHING MINOR FLOODING. && .TIDES/COASTAL FLOODING...
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SOUTHERLY FLOW INTO THIS EVENING WILL HELP MAINTAIN ~1.0 FT ANOMALIES IN THE MIDDLE BAY THROUGH TONIGHT. TIDAL ANOMALIES WILL BEGIN TO SUBSIDE TUESDAY AS THE FLOW BECOMES OFFSHORE.
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&& .AKQ WATCHES/WARNINGS/ADVISORIES... MD...NONE. NC...NONE. VA...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 7 AM EDT TUESDAY FOR ANZ654-656-658. SMALL CRAFT ADVISORY UNTIL 1 PM EDT TUESDAY FOR ANZ650-652. && $$ SYNOPSIS...JDM/SAM NEAR TERM...SAM SHORT TERM...SAM LONG TERM...MPR AVIATION...DAP MARINE...AJZ/MPR HYDROLOGY... TIDES/COASTAL FLOODING...

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