Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 180630 AFDAKQ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WAKEFIELD VA 230 AM EDT MON AUG 18 2014 .SYNOPSIS... A TROUGH OF LOW PRESSURE WILL SLIDE OFF THE COAST TONIGHT. A 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 MOVING OFF THE COAST DURING TUESDAY. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... UPDATE OF THE POPS ACROSS THE MD EASTERN TO ACCOUNT FOR A WEAK WAVE IN THE UPPER LEVELS WHICH IS PRODUCING SOME ISOLD TO SCT SHOWERS. THE RAP AND HRRR BOTH HAVE A DECENT HANDLE ON THESE SHOWERS WHICH COULD HOLD ON THROUGH AROUND 06Z. THE SHOWERS SHOULD BE LIMITED IN OVERALL COVERAGE...BUT WILL TRAIN OVER A FEW LOCATIONS THROUGH 06Z. SHOWER ACTIVITY SHOULD DECREASE AND SHIFT OFF THE COAST SHORTLY AFTER 06Z. A TROF OF LO PRES WILL SLIDE OFF THE CST TNGT. SOME WEAK ENERGY COMBINED WITH MARGINAL INSTABILITY COULD TRIGGER AN ISLTD SHOWER OR TSTM THIS EVENG. OTHERWISE...GENERALLY PARTLY CLOUDY AND MILD TNGT WITH LOWS RANGING FM THE MID 60S TO LWR 70S. && .SHORT TERM /6 AM THIS MORNING THROUGH WEDNESDAY/... WARM AND MORE HUMID MON THRU WED...AS WESTERLY (ZONAL) FLO ALOFT DOMINATES THE REGION. AN AREA OF DEEPER LO LVL MOIST ASSOCIATED WITH A MID LVL TROF AND SFC LO PRES WILL AFFECT THE REGION MON AFTN INTO AT LEAST MIDDAY TUE. THUS...WILL HAVE THE HIGHEST POPS (30-60%) FOR SHOWERS AND POSSIBLE TSTMS DURING THIS TIME PERIOD. THE PRESENCE OF AN INCREASINGLY UNSTABLE AIRMASS AND PW VALUES ~1.75-2.00 INCHES WILL ALSO MEAN STRONGER SHOWERS OR TSTMS COULD CONTAIN HEAVY RAINFALL. POPS DECREASE TO SLGT CHC OR NO CHC (14%) LATE TUE INTO WED MORNG...DUE TO SUBSIDENCE BEHIND THE DEPARTING WAVE OF LO PRES. MORE SHRTWV ENERGY IN WEAK UPR AIR TROFINESS WILL RESULT IN SLGT (20%) TO SML CHC (30%) POPS ACRS THE AREA ON WED...ESPLY IN THE AFTN/EVENG. MAX TEMPS WILL MAINLY RANGE FM THE MID 80S TO NEAR 90 THRU THE PERIOD...WITH MIN TEMPS RANGING FM THE MID 60S TO LWR 70S. && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... BLOCKY PATTERN OVER ERN CANADA AND THE NRN ATLANTIC WILL RESULT IN AN UNSETTLED WEATHER PATTERN THROUGH THE PERIOD. TEMPS WILL BE NEAR SEASONABLE...LATE SUMMER NORMS. SPLIT/BLOCKY FLOW IS TYPICALLY PROBLEMATIC FOR MEDIUM RANGE GUIDANCE...AND THIS TIME IS NO EXCEPTION. CONTINUE TO TREND FORECAST TOWARD THE ECMWF AND ENSEMBLE MEANS BASED ON RUN TO RUN CONSISTENCY AND WPC GUIDANCE...BUT CONFIDENCE IS NOT HIGH ATTM. THIS GUIDANCE REMAINS BTWN THE MORE AMPLIFIED 17/12Z GFS AND THE NEARLY ZONAL 17/12Z CANADIAN. WITH THAT SAID...FLOW AMPLIFIES OVER THE ERN CONUS AS MID LEVEL HIGH PRESSURE BUILDS OVER THE GULF STATES. MEANWHILE...ANOMALOUS HIGH PRESSURE BUILDS OVER ERN CANADA. SRN STREAM ENERGY OVER THE GREAT LAKES/NE STATES WILL PUSH A SHORTWAVE INTO THE NE STATES WITH TROUGHING EXTENDING SWD ALONG THE ERN SEABOARD. QUASI-STATIONARY BOUNDARY WILL SETTLE ACROSS THE MID-ATLANTIC REGION (ABOUT 100 MILES FARTHER SOUTH THAN 24 HOURS AGO) DURING THE PERIOD AS FLOW ALOFT REMAINS GENERALLY WLY. THE FRONT WILL BE THE FOCUS FOR SHOWERS/THUNDERSTORMS THRU THE PERIOD AS WEAK PERTURBATIONS IN THE FLOW PRODUCE WAVES OF LOW PRESSURE ALONG THE BOUNDARY. WARM/HUMID AIRMASS WILL BE IN PLACE WITH DEWPOINTS IN THE UPPER 60S TO LOW 70S AND TYPICAL LATE SUMMER PWATS BTWN 1.5 AND 2 INCHES. HOWEVER...LACK OF CONFIDENCE FACTORS INTO RELATIVELY LOW CHANCE POPS. CLIMO THIS TIME OF YEAR IS AROUND 20 PCT...BUT WILL GO HIGHER DURING THE AFTERNOON (30-40%) AND NEAR CLIMO OVERNIGHT DUE TO MOIST AND MARGINALLY UNSTABLE AIRMASS. IF THE TROUGH PUSHES OFFSHORE FRI NIGHT-SAT...PERTURBATIONS IN THE NW FLOW COULD BRING ADDITIONAL CHANCES OF PRECIP TO THE REGION THRU THE WEEKEND...ESPECIALLY IN THE NE. WARM THURS AND FRI WITH HIGHS IN THE UPPER 80S TO AROUND 90...COOLING OFF DUE TO CLOUDS/PRECIP THIS WEEKEND. LOW LEVEL THICKNESSES YIELD TEMPS GENERALLY IN THE MID 80S SAT AND SUN. OVERNIGHT LOWS GENERALLY IN THE UPPER 60S TO LOWER 70S THRU THE PERIOD. && .AVIATION /07Z MONDAY THROUGH FRIDAY/...
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VFR CONDITIONS WILL PREVAIL THE REST OF TONIGHT WITH PATCHY FOG REDUCING VISIBILITIES FROM 3 TO 5SM...INCLUDING TAF SITES KSBY AND KECG. A COLD FRONT APPROACHES THE REGION FROM THE NORTH AND STALLS ACROSS THE AREA MONDAY AFTN. THE FRONT COUPLED WITH A WEAK SURFACE TROUGH WILL INCREASE THUNDERSTORM CHANCES ACROSS THE AREA MON/MON NIGHT. SE-S WINDS AOB 10 KT MON WILL VEER TO SW-W MON NIGHT. FOR TUESDAY AND WEDNESDAY...THE FRONT REMAINS STATIONARY ACROSS THE REGION AND CONTINUES A CHANCE FOR WIDESPREAD SHOWERS/STORMS. THE LACK OF UPSTREAM FEATURES AND GENERALLY LIGHT STEERING FLOW ALOFT (LESS THAN 25 KT) COULD LEAD TO MODERATE TO HEAVY RAINFALL IN SLOW-MOVING STORMS...THUS REDUCING VIS/CIGS UNDER THE STRONGEST STORM CORES. FOG WILL CONTINUE TO BE A POSSIBILITY OVERNIGHT AND SHOULD GENERALLY FORM IN AREAS THAT RECEIVE RAINFALL DURING THE AFTN/EVENING HOURS. DEVELOPING NW FLOW ALOFT WILL KEEP UNSETTLED CONDITIONS ACROSS THE AREA THURSDAY AND FRIDAY.
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&& .MARINE... UNSETTLED WEATHER PATTERN WILL PREVAIL OVER THE WATERS THRU THE FORECAST PERIOD...BUT SCA CONDITIONS ARE NOT ANTICIPATED. WEAK SFC TROUGH REMAINS OVER THE WATERS THIS AFTERNOON WITH WSW WINDS AVG 5-10 KT AND WAVES/SEAS 1-2 FT. A COLD FRONT HAS DROPPED INTO SRN PA LATE THIS AFTERNOON AS AN AREA OF LOW PRESSURE PROPAGATES EWD OVER THE MID MS/LOWER OH VALLEY. THE FRONT WILL DROP SWD TONIGHT OVER THE NRN WATERS AS HIGH PRESSURE BUILDS OVER NEW ENGLAND. FLOW BECOMES NE ON THE BACKSIDE OF THE FRONT WITH WLY FLOW TO THE SOUTH...REMAINING AOB 10 KT. SFC LOW WILL WEAKEN OVER THE CNTRL APPALACHIANS AS A SECONDARY LOW DEVELOPS OVER THE WATERS. FLOW WILL INCREASE SOUTH OF THE WATERS...BUT ANTICIPATE SPEEDS AROUND 10 KT TUES-TUES NIGHT. HIGH PRESSURE SLIDES OVER NEW ENGLAND TUES...LOCATING OFFSHORE TUES NIGHT WEDS. MEANWHILE...LOW PRESSURE REMAINS OVER THE WATERS. THE RESULT WILL BE PERIODS OF ONSHORE FLOW...ESPECIALLY OVER THE NRN WATERS. NE FETCH WILL LIKELY PUSH SEAS UPWARDS OF 3-4 FT...BUT NOT ANTICIPATING SCA CONDITIONS ATTM. FRONTAL BOUNDARY REMAINS OVER THE REGION THRU THE WEEK...RESULTING IN AN UNSETTLED WX PATTERN...BUT SUB-SCA CONDITIONS. && .AKQ WATCHES/WARNINGS/ADVISORIES... MD...NONE. NC...NONE. VA...NONE. MARINE...NONE. && $$ SYNOPSIS...TMG NEAR TERM...TMG/JAO SHORT TERM...TMG LONG TERM...SAM AVIATION...BMD MARINE...SAM

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