Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 241348 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 948 AM EDT THU APR 24 2014 .SYNOPSIS... HIGH PRESSURE WILL BUILD OVER THE AREA THROUGH TODAY BEFORE GRADUALLY SHIFTING TO THE EAST TONIGHT. A COLD FRONT WILL PASS THROUGH THE AREA FRIDAY AND ANOTHER COLD FRONT IS EXPECTED TO MOVE THROUGH LATE SATURDAY THROUGH SATURDAY NIGHT. HIGH PRESSURE WILL BUILD IN ON SUNDAY AS THE COLD FRONT STALLS TO OUR SOUTH. SEVERAL WAVES OF LOW PRESSURE WILL DEVELOP ALONG THE STALLED BOUNDARY...BRINGING UNSETTLED CONDITIONS TO THE AREA NEXT WEEK. && .NEAR TERM /THROUGH TONIGHT/...
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NORTHWEST WINDS WILL CONTINUE ACROSS MOST OF THE REGION THIS MORNING AS HIGH PRESSURE MOVES INTO THE WEST AND LOW PRESSURE DEPARTS ACROSS THE NRN ATLANTIC. THE TIGHT PRESSURE GRADIENT EAST OF THE POTOMAC RIVER AND BLUE RIDGE WILL LEAD TO BREEZY CONDITIONS FOR THE ABOVE MENTIONED AREA. THE GRADIENT WILL SHIFT TO THE EAST THIS AFTERNOON AND WINDS WILL DECREASE BY THIS AFTERNOON. TEMPS WILL RISE INTO THE 60S TODAY WHICH IS SLIGHTLY BELOW CLIMO. MOISTURE WILL MOVE AROUND AN UPPER LEVEL RIDGE ACROSS THE OHIO VALLEY AND MID TO HIGH LEVEL CLOUDS WILL MOVE ACROSS THE CENTRAL FOOTHILLS AND POTOMAC HIGHLANDS THIS MORNING. PREVIOUS DISCUSSION... THE HIGH WILL GRADUALLY SHIFT TOWARD MID-ATLANTIC COAST TONIGHT ALONG WITH THE UPPER-LEVEL RIDGING. A POTENT SHORTWAVE AND ITS ASSOCIATED SURFACE LOW WILL TRACK INTO THE MIDWEST DURING THIS TIME. THERE WILL BE SOME HIGH AND MID- LEVEL CLOUDS INCREASING OVERNIGHT...BUT DRY CONDITIONS WILL PERSIST. MIN TEMPS WILL RANGE FROM THE UPPER 30S ACROSS PORTIONS OF NORTHERN MARYLAND WHERE THERE MAY BE SOME RADIATIONAL COOLING TO NEAR 50 IN DOWNTOWN WASHINGTON AND BALTIMORE.
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&& .SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/... THE SHORTWAVE AND SURFACE LOW WILL TRACK INTO THE OHIO VALLEY FRIDAY MORNING BEFORE MOVING INTO OUR AREA FRIDAY AFTERNOON. THE COLD FRONT ASSOCIATED WITH THE SURFACE LOW WILL ALSO MOVE INTO OUR AREA DURING THIS TIME. A SOUTHERLY FLOW WILL INCREASE AHEAD OF THE BOUNDARY...ALLOWING FOR WARM AND MOIST AIR TO MOVE INTO THE REGION. GUIDANCE HAS TRENDED A BIT SLOWER WITH THIS SYSTEM...WHICH WILL ALLOW FOR SOME MORE MOISTURE TO MAKE IT INTO THE AREA BEFORE IT MOVES THROUGH. THEREFORE...POPS HAVE BEEN INCREASED AND WIDESPREAD SHOWERS ARE EXPECTED. THE BEST CHANCE FOR PRECIPITATION WILL BE FROM MID-MORNING THROUGH THROUGH FRIDAY AFTERNOON WEST OF THE BLUE RIDGE MOUNTAINS...AND FRIDAY AFTERNOON EAST OF THE BLUE RIDGE MOUNTAINS. THERE WILL BE ENOUGH WARM AND MOIST AIR FOR SOME INSTABILITY TO DEVELOP AS WELL. THEREFORE...A FEW THUNDERSTORMS CANNOT BE RULED OUT. CLOUD COVER AND MARINE AIR SHOULD KEEP INSTABILITY LIMITED ENOUGH TO KEEP THE SEVERE THREAT MAINLY TO OUR SOUTH. HOWEVER...SHOULD THERE BE MORE SUNSHINE THAT BREAKS OUT...THEN SEVERE THUNDERSTORMS WOULD BE POSSIBLE DUE TO FAVORABLE SHEAR PROFILES...ESPECIALLY ACROSS CENTRAL VIRGINIA. MOST MODELS STILL A BIT DIVERGENT IN THE PROGRESS/SPEED OF THE UPPER LEVEL FEATURE THAT IS EXPECTED TO SLIDE ACROSS OUR REGION ON FRI... EXITING LATE FRI NIGHT. A BULK OF THE PRECIP WILL HAVE ALREADY MOVED THRU EARLIER IN THE DAY...W/ THE BACK END SUBSIDENCE MOVING ANY LINGERING PRECIP OFF THE COAST LATE FRI NIGHT. THE DRIER AIR INFLUX WILL HELP DROP DEWPOINTS A FEW DEGREES FROM THEIR EARLIER VALUES...BUT STILL PLENTY MOIST WHICH WILL KEEP OVERNIGHT LOWS IN THE U40S-L50S. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... OVER THE PAST SEVERAL YEARS...HAVE SEEN A NUMBER OF LATE APRIL CLOSED UPPER LOWS THAT MEANDER AND DRIFT OVER A PORTION OF EITHER THE UPPER MIDWEST/OHIO VLY OR DEEP SOUTH AND EVENTUALLY OFF THE ATLC COAST. CANNOT REMEMBER SEEING/FORECASTING ONE AS LARGE AS THE ONE LONG RANGE GUIDANCE IS DEPICTING FOR THE BETTER PART OF NEXT WEEK. ONE OF THE REASONS THIS SYSTEM WILL LIKELY BE SO VAST IS THAT IT ORIGINALLY WILL HAVE STARTED OUT AS TWO SEPARATE UPPER WAVES THAT COMBINE OVER THE UPPER MIDWEST. THE FRIDAY UPPER WAVE AFFECTING OUR AREA WILL SLIDE OFF THE MID ATLC COASTLINE AND STALL BASICALLY OFF THE SRN NEW ENGLAND COAST THIS WEEKEND. MEANWHILE...A COLD AND DEEP UPPER WAVE OVER THE INTER-MTN WEST WILL BE GEARING UP FOR AN INTENSIFICATION ONCE IT MOVES EAST OF THE ROCKIES THIS COMING WEEKEND. THE STALLED NEW ENGLAND COASTAL LOW WILL PREVENT THE FORWARD PROGRESS OF THE NOW LARGE-SCALE UPPER SYSTEM OVER THE NRN PLAINS SUN/MON...AND ALSO SQUEEZE DOWN A COLDER UPPER VORT DOWN FROM HUDSON VLY IN BETWEEN THE TWO LARGER SYSTEMS. THE CONTINUAL ROTATION OF SMALLER VORT LOBES AROUND THE PARENT SYSTEM WILL KEEP AN ACTIVE PERIOD OF WX FOR ROUGHLY THE ENTIRE ERN HALF OF THE CONUS FOR MOST OF NEXT WEEK. CLOSED UPPER LOWS TYPICALLY PRESENT A NUMBER OF FORECAST CHALLENGES...AND THE DAILY DEPICTIONS OF THIS FEATURE WILL BE AN INTRIGUING STORY FOR THE NEXT SEVERAL DAYS. EACH PHASING PERIOD OF THIS SYSTEM COULD CAUSE ANOTHER ROUND OR WAVE OF PRECIP ACROSS OUR REGION W/ PERIODIC BREAKS IN BETWEEN. COMPARING THE GFS AND EURO`S LATEST VERSIONS - THE GFS IS A MUCH COLDER AND COMPACT UPPER LOW SLIDING OVER THE UPPER MIDWEST WHILE THE EURO...THOUGH SHOWING SOME SIMILAR PROGRESS AND INTERACTIONS - NOT AS STRONG AS THE GFS. THE CURRENT FORECAST FOR OUR AREA REVOLVES ESSENTIALLY AROUND A WET MIDDLE OF THE WEEK PERIOD...W/ A SLOW BUILD UP TO IT THIS WEEKEND INTO EARLY NEXT WEEK. TEMPS UNDER THIS TYPE OF REGIME WOULD BE WELL BELOW AVG BUT NOT VERY COLD - MORE LIKE A MODERATED ENVIRONMENT W/ LITTLE DIURNAL CHANGE. && .AVIATION /14Z THURSDAY THROUGH MONDAY/... VFR CONDITIONS ARE EXPECTED THROUGH TONIGHT. NORTHWEST WINDS WILL GUST AROUND 15 TO 20 KNOTS THIS MORNING THROUGH MID-AFTERNOON ACROSS THE EASTERN TERMINALS. HIGH PRESSURE WILL ALLOW FOR LIGHT WINDS TONIGHT. SOUTHERLY WINDS WILL INCREASE AHEAD OF A COLD FRONT FRIDAY WITH GUSTS AROUND 15 TO 20 KNOTS EXPECTED IN THE AFTERNOON. SHOWERS ARE EXPECTED...ESPECIALLY DURING THE AFTERNOON. CIGS/VSBYS WILL LOWER TO MVFR LEVELS AND POSSIBLY IFR LEVELS IN BANDS OF HEAVIER SHOWERS. A QUIET WX WEEKEND IN STORE...AS ONE UPPER LEVEL SYSTEM MOVES OFF THE COAST FRI NIGHT - ALLOWING HIGH PRESSURE TO SQUEEZE IN OVER THE AREA SAT/SUN AND LASTING THRU LATE MON. HOWEVER...THE FRI/FRI NIGHT SYSTEM WILL HANG OUT OFF THE NEW ENGLAND COAST AND HELP STEER A COLD UPPER LOW INTO A LARGE AND POTENT LOW PRESSURE SYSTEM OVER THE NRN PLAINS. THESE FEATURES WILL EVENTUALLY COMBINE INTO A LARGER SYSTEM THAT WILL SLOWLY DRIFT TOWARD AND OVER THE AREA FOR MUCH OF NEXT WEEK...STARTING LIKELY TUE AND ONWARD. PERIODS OF RAIN AND PERIODICALLY LOWERED FLIGHT CATEGORIES WILL LIKELY BE COMMON INTO THE MIDDLE AND LATTER PARTS OF NEXT WEEK. && .MARINE...
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A SMALL CRAFT ADVISORY IS IN EFFECT FOR THE WATERS TODAY. MIXING WILL CONTINUE THIS MORNING AND SHOULD CAUSE GUSTS AROUND 20 KNOTS LATER THIS MORNING INTO EARLY THIS AFTERNOON. THE PRESSURE GRADIENT WILL DECREASE THIS AFTERNOON AND WINDS WILL DIMINISH DURING THIS TIME FROM WEST TO EAST. THE SMALL CRAFT ADVISORY MAY BE ABLE TO BE CANCELLED LATER THIS AFTERNOON, HIGH PRESSURE WILL ALLOW FOR LIGHTER WINDS TONIGHT. NO MARINE HEADLINES ARE EXPECTED. A SOUTHERLY FLOW WILL INCREASE AHEAD OF A COLD FRONT FRIDAY. A SMALL CRAFT ADVISORY IS IN EFFECT FOR THE WATERS FRIDAY AFTERNOON. SHOWERS WILL DEVELOP DURING THE AFTERNOON. A SFC LOW IS EXPECTED TO PASS BY THE NRN PART OF THE BAY FRI NIGHT...BUT THEN WINDS WILL PICK UP AGAIN BEHIND THE LOW. WINDS WILL THEN CONTINUE TO GUST INTO SAT...W/ PERIODS OF BREEZY CHANNELING WINDS OVER THE BAY/TP INTO NEXT WEEK. A BREEZY SAT WILL GIVE WAY TO A QUIET START TO NEXT WEEK...AS HIGH PRESSURE MOVES IN - THEN OUT BY LATE MON/EARLY TUE. ONSHORE FLOW WILL THEN BEGIN AHEAD OF ANOTHER SYSTEM FOR MID NEXT WEEK.
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&& .FIRE WEATHER... A NORTHWEST FLOW HAS CAUSED DEWPOINTS TO DROP SEVERAL DEGREES COMPARED TO WEDNESDAY. THEREFORE...THE RELATIVE HUMIDITY WILL BE SIGNIFICANTLY LOWER TODAY WITH MIN RH VALUES AROUND 15 TO 25 PERCENT THIS AFTERNOON. GUSTY NORTHWEST WINDS ARE STILL EXPECTED ACROSS NORTHEASTERN MARYLAND SO A RED FLAG WARNING IS IN EFFECT. ELSEWHERE...WINDS MAY GUST AROUND 15 TO 20 MPH THIS MORNING INTO EARLY THIS AFTERNOON...ESPECIALLY EAST OF THE BLUE RIDGE MOUNTAINS. HOWEVER...WINDS SHOULD DIMINISH THIS AFTERNOON AS HIGH PRESSURE BUILDS OVERHEAD. THEREFORE...NO FIRE WEATHER HEADLINES ARE IN EFFECT. WINDS WILL BE LIGHT TONIGHT WITH A STRONG NOCTURNAL INVERSION. SOUTHERLY WINDS WILL INCREASE FRIDAY AND SHOWERS WILL DEVELOP AHEAD OF A COLD FRONT. THE BEST CHANCE FOR SHOWERS WILL BE FRIDAY MORNING AND FRIDAY AFTERNOON WEST OF THE BLUE RIDGE MOUNTAINS...AND FRIDAY AFTERNOON INTO FRIDAY NIGHT EAST OF THE BLUE RIDGE MOUNTAINS. RAINFALL AMOUNTS WILL AVERAGE BETWEEN ONE-QUARTER AND ONE-HALF INCH ACROSS MOST LOCATIONS. HOWEVER...LOCALLY HIGHER AMOUNTS ARE LIKELY SINCE THERE WILL BE A CONVECTIVE ELEMENT TO THE PRECIPITATION. && .TIDES/COASTAL FLOODING... A SOUTHERLY FLOW WILL STRENGTHEN AHEAD OF A COLD FRONT FRIDAY AFTERNOON THROUGH FRIDAY EVENING. THIS WILL CAUSE TIDAL ANOMALIES TO SHARPLY INCREASE. THE FLOW WILL TURN OFFSHORE BEHIND A COLD FRONT AFTER MIDNIGHT...CAUSING TIDAL ANOMALIES TO DECREASE BY SATURDAY MORNING. MINOR COASTAL FLOODING IS POSSIBLE NEAR TIMES OF HIGH TIDE FRIDAY NIGHT...ESPECIALLY IF THE ARRIVAL OF THE OFFSHORE FLOW IS DELAYED A BIT. && .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE. MD...RED FLAG WARNING UNTIL 6 PM EDT THIS EVENING FOR MDZ005>007- 010-011-014. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EDT THIS EVENING FOR ANZ530>543. SMALL CRAFT ADVISORY FROM NOON TO 6 PM EDT FRIDAY FOR ANZ530>543.
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&& $$ SYNOPSIS...BJL NEAR TERM...BJL/HAS SHORT TERM...BJL/GMS LONG TERM...GMS AVIATION...BJL/GMS MARINE...BJL/GMS FIRE WEATHER...BJL TIDES/COASTAL FLOODING...BJL

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