Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 300800 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 400 AM EDT TUE JUN 30 2015 .SYNOPSIS...
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LOW PRESSURE WILL SLIDE EASTWARD OVER THE EASTERN GREAT LAKES TODAY. A COLD FRONT WILL SLIDE SOUTHEAST INTO THE MID ATLANTIC ON WEDNESDAY...AND THEN STALL ACROSS THE REGION ON THURSDAY. THE STALLED FRONT WILL LINGER IN THE AREA THROUGH THE WEEKEND BEFORE LIFTING NORTHWARD AGAIN ON MONDAY.
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&& .NEAR TERM /THROUGH TONIGHT/...
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LIGHT SHOWERS HAVE BEEN CROSSING NW PARTS OF THE CWA EARLY THIS MORNING IN ASSOCIATION WITH WEAK SHORTWAVE ENERGY. MOST OF THESE SHOULD EXIT THE AREA SHORTLY AFTER DAYBREAK...AND THERE MAY BE A BIT OF A LULL INTO THE MID MORNING...BUT CAN/T TOTALLY RULE OUT AN ISOLATED SHOWER...MAINLY OVER NORTHERN AREAS. VERY SUBTLE ATMOSPHERIC FORCING TODAY. LOW PRESSURE WILL BE SLOWLY TRACKING ALONG A NEARLY-STATIONARY FRONT THROUGH THE GREAT LAKES. RETURN FLOW TO BE ESTABLISHED LOCALLY...WITH THETA-E ADVECTION EAST OF THE BLUE RIDGE. VORTICITY MAXIMA OVER THE OHIO AND TN VALLEYS WILL MAKE A RUN AT THE AREA THIS AFTERNOON/EVENING...BUT MODEL DEPICTIONS ARE SLIGHTLY DIFFERENT. TERRAIN AND LEE TROUGHING MAY BE AS MUCH OF A FACTOR IN STORM INITIATION. INSTBY SHOULD BUILD DURING THE AFTN AS TEMPS RISE THROUGH THE 80S TO PERHAPS AROUND 90...HOWEVER MID-LEVEL LAPSE RATES WILL NOT BE VERY STEEP. AMOUNT OF CLOUD COVER COULD ALSO BE A FACTOR. MODELS CONTINUE TO ADVERTISE DEEP LAYER SHEAR AOA 30 KT...SO IF ENOUGH INSTBY IS REALIZED...SOME STRONG TO SEVERE STORMS COULD DEVELOP. THE PRIMARY THREAT WOULD BE LOCALIZED DAMAGING WIND GUSTS AS STORM STRUCTURES MAY BE TRANSIENT. CONTINUED HIGHEST POPS IN NORTHERN CWA CLOSER TO FORCING/HEIGHT FALLS...ALTHOUGH COVERAGE IS LOW CONFIDENCE. WHILE THERE SHOULD BE AN OVERALL EASTWARD PROGRESSION AND DIURNAL WEAKENING OF ACTIVITY THIS EVENING...MODELS MAINTAIN ELEVATED INSTBY OVERNIGHT...AND MID/UPPER LEVEL TROUGH WILL BE APPROACHING TOWARD DAYBREAK. THEREFORE SOME SHOWERS AND STORMS MAY LINGER WELL INTO THE OVERNIGHT PERIOD. MIN TEMPS IN THE LOWER/MID 60S WEST AND UPPER 60S/LOWER 70S EAST.
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&& .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
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MID LEVEL TROUGH AXIS WILL BE LIFTING NORTH DURING THE MORNING HOURS. SFC COLD FRONT WILL BE APPROACHING FROM THE NORTHWEST BUT LIKELY WON/T ENTER THE AREA DURING THE DAYTIME HOURS. TIMING AND COVERAGE OF PRECIP QUITE UNCERTAIN WITHOUT STRONG FORCING MECHANISMS. IF FORECAST SOUNDINGS ARE CORRECT IN DECREASING INSTBY BEHIND THE TROUGH PASSAGE IN THE AFTERNOON...CONVECTION MAY BE RATHER LIMITED. HAVE MAINTAINED LOW CHANCE POPS THROUGHOUT DAY. ON WEDNESDAY NIGHT...THE COLD FRONT WILL STALL OUT OVER THE MID ATLANTIC JUST TO OUR SOUTH. SUPPORT ALOFT WILL WANE AS THE TROUGH PASSES SO EXPECT CONVECTION TO QUICKLY DISSIPATE OR MOVE AWAY. WITH THE FRONT STALLED IN THE AREA...GUIDANCE IS BEGINNING TO HONE IN ON A WAVE OF LOW PRESSURE MOVING EAST ALONG THE FRONT FROM THE MID MISSISSIPPI VALLEY THURSDAY OR THURSDAY NIGHT. HOWEVER...TIMING IS STILL MUCH IN QUESTION...SO GENERALLY KEEP CHANCE POPS AROUND WITH LIKELYS TO THE SOUTH CLOSER TO THE STALLED FRONT. WITH THE FRONT TO THE SOUTH AND INCREASED CLOUD COVER...TEMPS SHOULD BE COOLER ON THURSDAY.
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&& .LONG TERM /FRIDAY THROUGH MONDAY/...
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THROUGH THE LONG TERM THE PATTERN WILL REMAIN FAIRLY STATIC WITH A BROAD TROUGH OVER CANADA...AND A STRONG RIDGE OUT WEST. THIS WILL KEEP FUNNELLING DISTURBANCES SOUTHEAST AND EAST ACROSS OUR AREA AS A FRONTAL BOUNDARY REMAINS STALLED OUT OVER THE REGION. SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE EACH DAY WITH THE FRONT NEARBY BUT TIMING DISTURBANCES WILL BE INCREASINGLY DIFFICULT AS WE GO FURTHER OUT. RIGHT NOW ONE SYSTEM MAY AFFECT US SATURDAY...AND ANOTHER MONDAY...BUT CONFIDENCE ON TIMING IS NOT HIGH. SO...GENERALLY HAVE KEPT TEMPS A BIT BELOW NORMAL...WITH A CHANCE OF SHOWERS AND THUNDERSTORMS IN THE FORECAST EACH DAY. AS WE GET CLOSER...WE SHOULD HAVE BETTER CLARITY AS FAR AS DAYS WHICH WILL TURN OUT MOSTLY RAIN-FREE...AND THOSE WHICH WILL BE PRETTY WET.
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&& .AVIATION /08Z TUESDAY THROUGH SATURDAY/...
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VFR EXPECTED THROUGH THE MORNING HOURS...ALTHOUGH A PASSING LIGHT SHOWER OR SPRINKLE WILL BE POSSIBLE AT MRB THROUGH DAYBREAK. SOUTHERLY WINDS WILL INCREASE DURING THE MIDDAY WITH OCNL GUSTS TO 20 KT. THUNDERSTORM COVERAGE AND TIMING LOW CONFIDENCE TODAY. LIKELY TO BE LARGELY DIURNAL IN NATURE...FAVORING 21-01Z TIME FRAME...BUT CAN/T RULE OUT ACTIVITY BEFORE/AFTER. BRIEF MVFR OR IFR CONDITIONS AND STRONG WIND GUSTS COULD ACCOMPANY ANY STORM. DISTURBANCE CROSSES AREA LATE TONIGHT/WED MORNING...SO A SHOWER OR STORM WILL REMAIN POSSIBLE...BUT LOWER POTENTIAL FOR CIG/VSBY REDUCTIONS. QUESTIONABLE HOW MUCH OF THIS ACTIVITY LINGERS/REDEVELOPS WED AFTERNOON...LOW CHANCE OF IMPACTS. MAIN CONCERN THROUGH EXTENDED IS POTENTIAL FOR SCATTERED THUNDERSTORMS EACH DAY. WINDS WILL BE UNCERTAIN GIVEN THE FRONT WILL CONTINUE TO MEANDER IN THE AREA AFTER ARRIVING WEDNESDAY. WAVE OF LOW PRESSURE MAY PROVIDE A MORE CONCENTRATED PERIOD OF RAIN AND IFR CIGS/VIS AT SOME POINT THURSDAY...FRIDAY OR SATURDAY BUT LOW CONFIDENCE RIGHT NOW ON WHEN THIS IS...OR IF IT EVEN HAPPENS.
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&& .MARINE...
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S/SE CHANNELING OCCURING OVER THE WATERS NOW WITH GUSTS TO 15 KT. WILL MONITOR THE NEED TO START SCA EARLY SHOULD GUSTS INCREASE. OTHERWISE WILL GO INTO EFFECT FOR ALL WATERS AT 10AM WITH SOUTHERLY GUSTS OF 20-25 KT POSSIBLE. THUNDERSTORMS WILL DEVELOP IN THE AREA FROM LATE AFTERNOON INTO THE EVENING WITH THE POTENTIAL FOR STRONG WIND GUSTS...AND SOME SMW/S ARE POSSIBLE. GRADIENT WINDS WILL DIMINSH OVERNIGHT. SW FLOW THROUGH WED AROUND 10 KT...ALTHOUGH MAY BE SLIGHTLY STRONGER TOWARD TANGIER SOUND. LOWER CHANCE OF STORMS THROUGH WED. WINDS EXPECTED TO REMAIN BELOW SCA CRITERIA THROUGH THE EXTENDED...THOUGH WILL NEED TO MONITOR AS FRONT WILL BE NEAR AREA EACH DAY. SHOWERS AND TSTMS ARE ALSO POSSIBLE EACH DAY...WHICH COULD IMPACT MARINE CONCERNS.
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&& .TIDES/COASTAL FLOODING...
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WATER LVLS WL BE INCREASING TONIGHT THRU MID WEEK. THE WATER LVLS MAY APPROACH MINOR THRESHOLDS AROUND SW DC HIGH TIDE THIS MORNING...AND THEN AGAIN WED ALONG THE WESTERN CHESAPEAKE DURING THE HIGHER HIGH TIDE...WHICH IS THE AM CYCLE /MIDNGT THRU NOON/.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY FROM 10 AM THIS MORNING TO 4 AM EDT WEDNESDAY FOR ANZ531>534-536-537-539>543. SMALL CRAFT ADVISORY FROM 10 AM THIS MORNING TO 8 PM EDT THIS EVENING FOR ANZ530-535-538.
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&& $$ SYNOPSIS...RCM NEAR TERM...ADS SHORT TERM...ADS/RCM LONG TERM...RCM AVIATION...ADS/RCM MARINE...ADS/RCM TIDES/COASTAL FLOODING...

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