Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 210802 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 402 AM EDT THU AUG 21 2014 .SYNOPSIS... A STATIONARY FRONT WILL WAVER ACROSS THE MID ATLANTIC AS RIPPLES OF LOW PRESSURE MOVE ALONG THE BOUNDARY. THE LAST IMPULSE WILL TRAVERSE THE FRONT FRIDAY NIGHT...WHICH WILL PUSH IT SOUTH AS A COLD FRONT. HIGH PRESSURE FROM NEW ENGLAND WILL DOWN DOWN THE EAST COAST THIS WEEKEND. && .NEAR TERM /THROUGH TONIGHT/... THE UPPER-LEVEL PINWHEEL A FEW HUNDRED MILES TO OUR NORTH WILL SLINGSHOT ANOTHER WAVE OF MOISTURE ACROSS THE REGION LATER TODAY...BEFORE DISSIPATING AND BEING BECOMING PART OF A LARGER UPPER TROUGH. OUR MOIST AIRMASS WILL UNDERGO VERY LITTLE CHANGE OVER THE NEXT COUPLE OF DAYS. THIS MODIFIED SUB-TROPICAL REGIME HAS A CORRIDOR OF DRY AIR ATOP A DENSE AND VERY MOIST BOUNDARY/SFC LAYER. NW FLOW ALOFT WILL CARRY WAVES OF EMBEDDED VORT MAXES...WHICH ARE ESSENTIALLY AREAS OF LIFT...BUT IN AN INTERMITTENT AND RANDOM NATURE. LATER TODAY/THIS EVE...A MORE COMPACT AREA OF UPPER ENERGY WILL BE SHOVED QUICKLY DOWN ACROSS THE UPPER MIDWEST AND OVER THE MID-ATLC REGION. LIKE WED HOWEVER...THE UPPER LOW WILL FORCE THIS WAVE DOWN TOWARD THE AREA BUT KIND OF STABLE COASTAL BLOCK WILL DISSIPATE THE ENERGY AS IT APPROACHES THE ATLC COASTLINE. BUT BEFORE THEN...PLENTY OF MOISTURE AND MARGINAL INSTABILITY WILL BE AVAILABLE FOR THE INCOMING SHORTWAVE ENERGY TO DEVELOP CONVECTION. ONE OF THE KEY FACTORS WILL BE OUR HIGH TEMPS...AGAIN EXPECTED TO REPEAT IN THE M-U80S. THESE VALUES COMBINED W/ SFC DEWPOINTS IN THE U60S/L70S WILL BE MORE THAN ENOUGH TO AT LEAST BREAK THE WEAK CAP AND FORCE FOR THE CONDITIONALLY UNSTABLE ATMOS TO DEVELOP SCATTERED SHOWERS/TSTMS. A HANDFUL OF ISOLATED SHOWERS COULD DOT THE MAP OVER THE COMING HRS...BUT NOT UNTIL MID-LATE AFTN IS MORE ORGANIZED/WIDESPREAD DEVELOPMENT EXPECTED. TIMING/LOCATIONS/INTENSITIES WILL DEPEND ON EARLY OUTFLOWS AND STORM MOMENTUM FACTORS BUT THE LOW LEVEL SHEAR WILL CERTAINLY BE ENOUGH /20-30KT BOUNDARY LAYER/ TO SUSTAIN A LINEAR FEATURE. AS W/ THE CONVECTION ON WED AFTN/EVE...THE ACTIVITY LEVEL WILL QUICKLY DROP OFF AFT SUNSET AND W/IN A COUPLE HRS AFTERWARD. OVERNIGHT LOWS WILL DROP ONLY INTO THE U60S/L70S AGAIN SINCE DEWPOINTS WON`T BUDGE - SETTING UP FOR ANOTHER WAVE OF SHOWERS/TSTMS ON FRI AFTN. && .SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/... MOST SHORT/MED RANGE MODELS...INCLUDING THE TAIL END OF SOME LOCAL WRF MEMBERS ARE IN GOOD AGREEMENT ON A FRI AFTN AND INTO LATE EVE HRS HEIGHTENED LEVEL OF SHOWER/TSTM ACTIVITY ACROSS PORTIONS OF THE AREA. POPS ARE HIGHER THAN THE GARDEN-VARIETY ISOLATED AFTN REGIME. THIS COULD MEAN THAT A MORE STRATIFORM/DISSIPATED REGION OF EARLIER CONVECTION WILL DROP A REGIONAL-SCALE BATCH OF LIGHT/MODERATE RAIN OVER THE AREA...ESPEC ACROSS THE WRN HALF OF THE CWA AS MODELS SUGGEST. INCREASING CLOUD COVER FROM LATE TONIGHT INTO EARLY FRI COULD ALSO INHIBIT CONVECTIVE POTENTIAL AND LIMIT IT TO AREAS FURTHER S AND E WHERE TEMPS ARE EXPECTED TO PEAK IN THE M80S. MODEL ADJUSTED VALUES ARE GIVING L80S FOR HIGHS...ACCOUNTING FOR THE CLOUD COVER INCREASE...A LIGHT NLY WIND THAT IS EXPECTED TO TURN MORE ELY OVER TIME AND CERTAINLY INTO THE LATE NIGHT HRS - WHICH IS A MORE STABLE FLOW. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... H5 PTTN WL BE EVEN MORE AMPLIFIED IN THE XTNDD PD...W/ RDGG IN THE CENTER OF THE CONUS AND TROFFING ALONG THE ERN SEABOARD. THAT WL PERMIT SFC HIPRES OVER THE CNDN MARITIMES AND DOWNEAST MAINE TO BLD DOWN THE COAST. THEREFORE...AM BCMG INCRSGLY CONFIDENT THAT THE WET PTTN OF THIS WK WL BREAK. SAT WL BE THE TRANSITION DAY. WL STILL HV ELY SFC LOW AND MODEST INSTBY. MEANWHILE...THE JET STREAM WL STILL BE OVHD...PROVING A ZONE OF SHEAR. WITH A MARITIME AMS IN THE LLVL AND LIFT W/IN THE COLUMN...NEED TO PAINT A GLOOMY PICTURE. WL BE HOLDING POPS AT CHC...AND EMPHASIZING POINTS E OF THE BLURDG /UPSLP FLOW/. AM NOT GOING AS LOW ON MAXT AS PSBL. SINCE AM NOT GOING FOR A WASHOUT...WL BE HOLDING OUT SOME HOPE THAT THERE WL BE SOME OPPORTUNITY FOR TEMPS TO RISE FM DEWPTS. THOSE DEWPTS SHUD BE UPR 60S TO NEAR 70F...SO ITLL BE A MUGGY DAY EVEN W/O SUNSHINE. WL BE PUSHING PCPN BACK INTO THE MTNS SAT NGT-SUN AS RDGG BLDS. STILL HV PROLONGED ELY FLOW...SO SUN WL BE THE DAY WHEN AIR TEMPS WL BE STRUGGLING TO RISE ABV WATER TEMPS. THERE MAY BE ENUF AIR MVMT SO THAT FOG WONT BE AN ISSUE SAT NGT. IF IT TURNS OUT THAT FLOW DCPLS INSTEAD...IT WL BE A WHOLE DIFFERENT STORY. SFC HIPRES WL RUN THE SHOW FOR THE REST OF THE XTNDD. AM MUCH MORE GENEROUS W/ SUNSHINE. MAXT UPR 70S-LWR 80S/MIN-T 50S TO LWR 60S STILL BELOW CLIMO...BUT REACHING TIME OF YR WHEN NRMLS STARTING TO DROP. && .AVIATION /08Z THURSDAY THROUGH MONDAY/... GROUND/VLY FOG HAS SETTLED OVER PARTS OF THE REGION...ESPEC ALONG THE NRN VA PIEDMONT IN TYPICAL FOG PRONE VLYS AND AREAS THAT RECEIVED RAIN LAST EVE. THE METRO AREAS WILL ONLY SEE A BRIEF PERIOD OF HIGH-END VSBY GROUND FOG AND POTENTIALLY A BRIEF MVFR/IFR STRATUS DECK FROM THE MOIST OVERHEAD ENVRMNT TOWARD SUNRISE. SKIES AFTER SUNRISE WILL WAVER IN/OUT OF PARTLY SUNNY/MOSTLY CLOUDY SINCE WE STILL HAVE A MOIST ATMOS. AN UPPER-LEVEL DISTURBANCE WILL SWING ACROSS THE REGION LATER TODAY...POTENTIALLY CARRYING ANOTHER WAVE OF SHOWERS/TSTMS TO THE AREA. CONDS WILL IMPROVE AGAIN OVERNIGHT...THOUGH A FEW ISOLATED SHOWERS AND MORE DENSE CLOUD COVER IS EXPECTED INTO EARLY FRI. MORE SHOWER/TSTMS EXPECTED ON FRI AFTN/EVE AS WELL. SAT-SUN...LOCLDS AND VSBYS MAY BE AN ISSUE AS A MARINE AMS SPREADS INLAND. THINK FLG RESTRICTIONS WL BE MORE PRONOUNCED AND PROLONGED SAT. MON...VFR. && .MARINE... SCA CONDITIONS NOT ANTICIPATED THROUGH THE END OF THE WORK WEEK...AS WINDS HAVE DROPPED OFF OVERNIGHT. A FEW TSTMS POSSIBLE THIS AFTN/EVE OVER THE WATERS...CALM AGAIN OVERNIGHT W/ ANOTHER ROUND EXPECTED ON FRI AFTN/EVE. ELY FLOW WL DOMINATE THIS WKND AS HIPRES BLDS DOWN THE COAST. THERE ARE SOME HINTS THAT WNDS MAY TOUCH SCA CRIT AT TIMES...PRIMARILY IN THE MID BAY. THAT ALL DEPENDS UPON STRENGTH OF THE SFC HIGH AND RELATIVE LOPRES OFF THE CAROLINAS. NOT TOO CONFIDENT AT A TIGHT P-GRAD ATTM...AND HV CAPPED WNDS BLO SCA CRIT. && .TIDES/COASTAL FLOODING... WATER LVLS ABOUT 3/4 TO 1 FT ABV ASTRO NORMS. THAT PLACED ANNAPOLIS AT RISK FOR THE EARLY MORNING TIDE CYCLE. GAUGE READINGS CAME BACK ARND MIDNGT...AND WE/RE TOPPING OFF JUST ABOVE MINOR CRITERIA. DEPARTURES ELSEWHERE SHOULD NOT TRIGGER ANY ADVYS...BUT A FEW CAUTION STAGES SHOULD BE REACHED. ONLY OTHER CONCERN MAY BE ALEXANDRIA/SWDC...WHERE A 1.1 FT DEPARTURE WOULD TIP THE SCALE. THINK WE MAY BE ABLE TO SNEAK THAT ONE OUT...BUT ADMITTEDLY ITS GONNA BE CLOSE. WE WILL HV SLY FLOW TODAY BECOMING LIGHT TNGT. FORTUNATELY THE 2ND TIDE CYCLE OF THE DAY IS THE LOWER OF THE TWO ASTRONOMICALLY. GUIDANCE SUGGESTING WE WL HV JUST ENOUGH OPPORTUNITY FOR A LITTLE WATER TO OOZE OUT OF THE ESTUARY BY THEN. SO...TOMORROW MORNINGS TIDE WL BE HIGH...BUT AM NOT ANTICIPATING REACHING CRITERIA ATTM. HOWEVER...WE ARE WORKING ON A MARGIN OF INCHES...WHICH IS PUSHING CURRENT SKILL LEVEL...SO ITS ADVISABLE TO CONTINUE TO MONITOR THE SITUATION. FLOW WL BE NLY FRI BEFORE ONSHORE /ELY/ FLOW RETURNS FOR THE WKND. THUS...IF WATER DOESNT EVACUATE BY THE END OF THE WEEK...THERE COULD BE MORE NUISANCE ISSUES THIS WKND. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...COASTAL FLOOD ADVISORY UNTIL 6 AM EDT EARLY THIS MORNING FOR MDZ014. VA...NONE. WV...NONE. MARINE...NONE. && $$ SYNOPSIS...HTS NEAR TERM...GMS SHORT TERM...GMS LONG TERM...HTS AVIATION...GMS/HTS MARINE...GMS/HTS TIDES/COASTAL FLOODING...HTS

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