Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 212049 AFDAKQ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WAKEFIELD VA 449 PM EDT THU AUG 21 2014 .SYNOPSIS... A FRONTAL BOUNDARY REMAINS NEARLY STATIONARY ACROSS THE AREA INTO THE UPCOMING WEEKEND. HIGH PRESSURE FROM NEW ENGLAND IS SLOW TO BUILD OVER THE REGION FROM SUNDAY INTO EARLY NEXT WEEK. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... THE CURRENT SURFACE ANALYSIS INDICATES WEAK BROAD LOW PRESSURE IN VICINITY OF THE GREAT LAKES WITH A BOUNDARY EXTENDING SOUTHWARD FROM E-CENTRAL PA THROUGH THE WESTERN SHORE OF THE CHESAPEAKE BAY. THUNDERSTORMS HAVE DEVELOPED ALONG THE BOUNDARY OVER PA AHEAD OF A ~100KT UPPER JET DIVING ACROSS THE ERN GREAT LAKES. SPC MESOANALYSIS INDICATES 35-40KT OF EFFECTIVE SHEAR FROM SE PA THROUGH THE LOWER MD ERN SHORE ALONG WITH AN AXIS OF 1500J/KG OF MLCAPE. THUNDERSTORM COVERAGE IS EXPECTED TO INCREASE OVER THE ERN SHORE LATER THIS AFTERNOON INTO THE EVENING HOURS AS THE JET DIVES SE. A FEW STRONGER STORMS ARE POSSIBLE BASED ON FAVORABLE DYNAMIC AND THERMODYNAMIC PARAMETERS...WITH THE PRIMARY THREAT BEING STRONG WIND GUSTS. THE MAIN LIMITING FACTOR WILL BE RATHER WEAK LAPSE RATES. OTHERWISE...A CHC (30-40%) OF GENERAL THUNDER IS EXPECTED OVERNIGHT AS THE UPPER JET ENERGY PASSES OVER THE AREA AND THE SURFACE BOUNDARY REMAINS IN PLACE. LESS FOG IS EXPECTED DUE TO THE PRESENCE OF MID/UPPER LEVEL CLOUD COVER. OVERNIGHT LOWS SHOULD RANGE FROM THE UPPER 60S TO LOW 70S. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/... MID/UPPER NW FLOW REMAINS OVER THE REGION FRIDAY INTO THE WEEKEND. A MORE VIGOROUS WAVE DROPS THROUGH THE FLOW ACROSS THE AREA FRIDAY NIGHT. THIS WILL PROVIDE BEST CHC OF AND GREATEST AREAL COVERAGE OF SHOWERS/TSTMS ACROSS THE LOCAL AREA DURING THE SHORT-TERM PERIOD DUE TO MORE FAVORABLE/STRONGER UPPER JET SUPPORT. POCKETS OF MODERATE TO HEAVY RAIN ARE POSSIBLE GIVEN MODEST MOISTURE AND FAVORABLE UPPER SUPPORT. HIGH PRESSURE BUILDS OVER NEW ENGLAND SATURDAY AND SLOWLY PUSHES INTO THE REGION BY SUNDAY. THIS WILL PUSH THE REMNANT FRONT S OF THE AREA. CHC POPS WILL CONTINUE EARLY SATURDAY...WITH A STEADY DRYING TREND COMMENCING SATURDAY AFTERNOON FROM NNE-SSW AS THE HIGH BUILDS INTO THE REGION. HIGHS FRIDAY SHOULD BE MAINLY 85-90...AND THEN FROM THE LOW TO MID 80S SATURDAY (UPPER 70S ALONG THE ATLANTIC BEACHES)...WITH UPPER 70S TO LOW 80S SUNDAY. LOWS SHOULD BE IN THE UPPER 60S TO LOW 70S SATURDAY...AND IN THE 60S SUNDAY MORNING. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... EXTENDED FORECAST PERIOD WILL CONSIST OF MAINLY NE FLOW AS HIGH PRESSURE TO THE NORTH RIDGES SOUTH WHILE AN AREA OF LOW PRESSURE EMERGES FROM THE BAHAMAS. THIS PATTERN WILL MAINTAIN A COOLER MARITIME AIRMASS IN PLACE OVER THE AREA THROUGH WED BEFORE HIGH PRESSURE AT THE SURFACE AND ALOFT BEGIN TO CENTER THEMSELVES OVER THE FA. AT THIS POINT SUBSIDENCE WILL PREVAIL AND WILL HELP TO DRY THE ATMOSPHERE. PRECIP ALONG THE VA/NC COAST CAN NOT BE COMPLETELY RULED OUT DUE TO THE INFLUX OF MOISTURE NORTH AS THE SURFACE LOW FORMS TO THE SOUTH. THERE IS SOME MODEL DISCREPANCY IN REGARDS TO THE POSITION AND STRENGTH OF THE LOW OVER THE EASTERN ATLANTIC. AND DUE TO THE LARGE DEGREE OF CHANGE IN MODEL RUNS...AT THIS POINT...WILL NOT MODIFY THE PREVIOUS FORECAST TOO MUCH. TEMPS WILL REMAIN BELOW AVERAGE FOR MUCH OF THE EXTENDED PERIOD WITH LOWS AROUND 80 MON AND TUES...WARMING SLIGHTLY INTO THE MID 80S WED AND THUR. SEASONAL LOW TEMPS IN THE LOW TO MID 60S ARE LIKELY AS THE MARITIME AIRMASS WILL LIMIT SIGNIFICANT OVERNIGHT COOLING. && .AVIATION /21Z THURSDAY THROUGH TUESDAY/... A WEAK FRONTAL BOUNDARY IS OVER THE NORTHEAST PART OF THE AREA. A STRONGER FRONT WILL MOVE INTO THE MID ATLANTIC TONIGHT AND FRIDAY. THESE FRONTS COMBINED WITH A MOIST AIR MASS WILL TRIGGER SCATTERED SHOWERS AND THUNDERSTORMS THIS AFTERNOON THROUGH FRIDAY. THUNDERSTORMS ARE EXPECTED TO BE MORE NUMEROUS ON FRIDAY. WITH A SEA BREEZE AND A WEAK FRONTAL BOUNDARY OVER THE EASTERN PART OF THE AREA THIS AFTERNOON WILL HAVE SCATTERED THUNDERSTORMS DEVELOP. VERY DIFFICULT TO TIME THESE BUT THESE SHOULD END BY AROUND 00Z. OUT TO THE WEST SEVERAL MESOSCALE CONVECTIVE SYSTEMS ARE MOVING TOWARD THE AREA. THESE SHOULD DIMINISH AS THEY CROSS THE MOUNTAIN BUT COULD STILL TRIGGER A SHOWER OR THUNDERSTORM NEAR KRIC THIS EVENING. THE THUNDERSTORMS TO THE WEST WILL PRODUCE PLENTY OF MID LEVEL CLOUDS ACROSS THE AREA TONIGHT. THIS SHOULD PREVENT ANY WIDE SPREAD FOG FROM FORMING. THE BEST CHANCE FOR THUNDERSTORMS WILL DEVELOP FRIDAY AFTERNOON AND EVENING ACROSS ALL TAF SITES. EXPECT CLEARING WEATHER FOR THE WEEKEND WITH VFR CONDITIONS RETURNING. WINDS WILL BE VERY LIGHT THROUGH FRIDAY WITH MAINLY SOME EAST WINDS NEAR THE COAST AND SOUTHWEST INLAND. ALL AREAS WILL SWITCH TO NORTH OR NORTHEAST BY SATURDAY. && .MARINE...
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LOW PRESSURE FORMS ALONG A STATIONARY BOUNDARY THAT IS CURRENTLY POSITIONED OVER THE EASTERN PORTIONS OF THE FORECAST AREA OVERNIGHT. THIS WEAK AREA OF LOW PRESSURE WILL MOVE OFF THE COAST FRIDAY AFTN. EARLY SAT MORNING...HIGH PRESSURE NOSES SOUTH FROM THE NORTHEASTERN US CAUSING A BACKDOOR COLD FRONT TO MOVE THROUGH THE AREA. ENERGY STREAMING SE WILL HELP FORM AN AREA OF LOW PRESSURE OFF THE CAROLINA COAST. THIS SYNOPTIC SETUP WILL ENHANCE THE PRESSURE GRADIENT ACROSS THE WATERS CAUSING NEAR SCA WIND GUST OVER THE BAY(18-20KT) AND THE COASTAL WATERS(23-25KT) ON SATURDAY. DUE TO THE WIND DIRECTION AND FETCH...EXPECT WAVES TO BUILD TO 4-6FT ACROSS MOST OF THE COASTAL WATERS LASTING EARLY SATURDAY THROUGH MONDAY NIGHT. HIGH PRESSURE BEGINS TO POSITION OVER THE AREA BY TUESDAY BUT LOW PRESSURE EMERGING FROM THE SOUTH MAY HELP TO MAINTAIN THE PRESSURE GRADIENT AND ONSHORE FLOW THROUGH WED.
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&& .AKQ WATCHES/WARNINGS/ADVISORIES... MD...MODERATE RIP CURRENT RISK UNTIL 8 PM EDT THIS EVENING FOR MDZ025. NC...MODERATE RIP CURRENT RISK UNTIL 8 PM EDT THIS EVENING FOR NCZ102. VA...MODERATE RIP CURRENT RISK UNTIL 8 PM EDT THIS EVENING FOR VAZ098>100. MARINE...NONE. && $$ SYNOPSIS...AJZ/ALB NEAR TERM...AJZ SHORT TERM...AJZ/ALB LONG TERM...DAP AVIATION...MAS/JAB MARINE...DAP

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