Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 191917 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 317 PM EDT SAT APR 19 2014 .SYNOPSIS...
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HIGH CLOUDS WILL ERODE THROUGH THE EVENING TODAY AS HIGH PRESSURE BUILDS INTO THE AREA. THIS HIGH WILL REMAIN IN CONTROL OF THE REGION`S WEATHER THROUGH MONDAY. A COLD FRONT WILL BRING SHOWERS TO THE AREA TUESDAY INTO TUESDAY EVENING BEFORE HIGH PRESSURE BUILDS BACK IN FOR THE SECOND HALF OF THE WORKWEEK. NEXT UP IS ANOTHER COLD FRONT LATER FRIDAY OR SATURDAY.
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&& .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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HIGH CLOUDS HUNG ON LONGER THAN ANTICIPATED THIS AFTERNOON AS TAIL END OF UPPER JET EXITING NEW ENGLAND COMBINED WITH LOW PRESSURE OVER SE US TO GIVE AGEOSTROPHIC LIFT IN UPPER LEVELS. THIS CIRRIUS BKN-OVC SKY COVER WILL CONTINUE THROUGH TONIGHT. NE WIND FLOW 5-10 KTS WILL CONTINUE TONIGHT...BUT WILL LOSE THE GUSTINESS IN IN THE UPPER TEENS AS WE`VE SEEN ON INLAND LOCATIONS THIS AFTERNOON. TEMPERATURES ARE COUPLED AND WENT WITH A BLEND OF SREF AND NAM FOR OVERNIGHT MINS.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
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EXPECTING HIGH CLOUDS TO START EASTER SUNDAY BUT DIMINISH THROUGH THE DAY. SLIGHTLY LOWER MAX TEMPERATURES AS HIGH PRESSURE GETS ESTABLISHED OVER SOUTHERN NEW ENGLAND AND OUR AREA RECEIVES A DEEP LLVL MARINE/NE INFLOW ORIGINATING FROM THE GULF OF MAINE. TEMPS WILL REACH THE LOWER 60S IN MOST AREAS EXCEPT DIRECTLY ON THE WESTERN SHORE OF THE CHESAPEAKE WHERE THEY`LL BE IN THE UPPER 50S TO NEAR 60. NOTHING MUCH OF A CHANGE FOR SUN NIGHT AS MARINE FLOW CONTINUES. NIGHTTIME MINS ON SUN NIGHT WILL BE FLIRTING ONCE AGAIN WITH FROST ADVISORIES AS DRYER AIR WORKS IN AND CALMER WINDS.
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&& .LONG TERM /MONDAY THROUGH SATURDAY/...
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MONDAY THROUGH TUESDAY... NORTHERN JET STREAM GETS A BIT MORE AMPLIFIED BETWEEN MON AND TUE. WE START WITH AN AXIS OF SURFACE HIGH PRESSURE OVER THE EAST MONDAY MORNING. BUT A NORTHERN STREAM 500MB TROUGH WILL DIP DOWN INTO THE NE AND BRING A COLD FRONT IN FROM THE WEST. THERE IS SOME DISAGREEMENT BETWEEN THE VARIOUS MODELS AS TO TIMING AND HOW QUICKLY IT WILL PASS THRU. WENT WITH THE SREF ENSEMBLE FOR POPS AND CLOUDS TO ACCOUNT FOR THE POSSIBLE DIFFS. IN ANY CASE...EXPECT THE COLD FRONT TO CROSS THE APPALACHIANS TUESDAY MORNING AND MOVE THRU THE FORECAST AREA DURING THE DAY TUESDAY. HOW QUICKLY IT WILL CLEAR IS IN QUESTION...PARTIALLY DUE TO ITS INTERACTION WITH THE LIFTING AREA OF LOW PRESSURE MOVING SLOWLY NE OFFSHORE. FOR TEMPS RELIED ON THE BIAS CORRECTED SREF AND BIAS CORRECTED ADJUSTED NAM MOS...BOTH OF WHICH HAVE BEEN DOING WELL RECENTLY. SHOWERS WITH THE COLD FRONT ARE NOT EXPECTED TO LEAVE A LOT OF RAIN...FORECAST IS FOR 0.15 TO A QUARTER OF AN INCH. HOWEVER LOOKING AT A SMALL AMOUNT OF FORECAST ATMOSPHERIC INSTABILITY...THERE IS A CHANCE FOR A THUNDERSTORM EMBEDDED WITH THE SHOWERS IN OUR SOUTHERN HALF WHICH COULD BOOST RAINFALL IN TARGETED AREAS IF IT COMES TO PASS. TUESDAY NIGHT THROUGH SATURDAY... PRECIP WILL EXIT THE EASTERN EXTENT OF THE CWA OVERNIGHT TUES AS COOL DRY AIR FILLS IN IN BREEZY NW FLOW BEHIND THE FRONT. SKIES WILL BE PARTLY TO MOSTLY SUNNY FOR SUNRISE ON WED AND SHOULD CONTINUE TO CLEAR THROUGH THE MORNING. A WEAK VORT MAX MAY LEAD TO A SLIGHT INCREASE IN CLOUD COVER NEAR THE MASON DIXON LINE FOR WED AFTERNOON/EVENING...BUT EVERYWHERE WILL STAY DRY. MODEST COLD AIR ADVECTION WILL KEEP HIGHS 5 TO 10 DEGREES COOLER THAN TUES...IN THE UPPER 50S TO MID 60S. HIGH PRESSURE WILL FILL IN OVER THE AREA BEGINNING OVERNIGHT WED AND THURS WILL BE A COOL BUT PLEASANT SPRING DAY. LOWS THURSDAY MORNING WILL BE NEAR 40 WITH HIGHS REACHING INTO THE MID 60S UNDER MOSTLY SUNNY SKIES. THE HIGH WILL MOVE OFF THE COAST ON THURS NIGHT AND WE WILL SEE WARMING IN THE SOUTHERLY RETURN FLOW FOR THE DAY ON FRI AS A COLD FRONT APPROACHES FROM THE WEST. DETERMINISTIC MODELS DISAGREE ON THE EXACT TIMING OF THE COLD FRONTAL PASSAGE WITH THE EURO BRINGING RAIN THROUGH THE DAY FRI AND THE GFS KEEPING US WARM AND DRY DURING THE DAY BUT WET OVERNIGHT ON FRI. LARGE SPREAD AMONGST ENSEMBLE MEMBERS JUSTIFIED KEEPING CHANCE POPS IN THE FORECAST THROUGH THE DAY AND NIGHT ON FRI AND INTO SAT. TIMING OF THE FRONTAL PASSAGE WILL DETERMINE HIGHS SAT...BUT FAVORING SLOWER PROGRESSION OF FRONT EXPECT HIGH TEMPS SLIGHT COOLER THAN FRI...MID 70S FRI AND LOWER 70S SAT.
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&& .AVIATION /19Z SATURDAY THROUGH THURSDAY/...
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VFR CONDITIONS ALL TERMS THROUGH 36 HOURS WITH WIND GENERALLY 03008KT THROUGH THE ENTIRE TAF PERIOD. VFR CONDS ARE XPCTD FOR MONDAY AND MONDAY NIGHT. LARGELY VFR ON TUE AS WELL BUT IFR POSSIBLE FOR FEW HOURS AROUND COLD FRONTAL PASSAGE. IFR CONDITIONS ARE POSSIBLE IN LINGERING LOW CEILINGS AND RAIN SHOWERS AS A COLD FRONT DEPARTS THE AREA TUESDAY NIGHT.
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&& .MARINE...
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THRESHOLD SCA LATE TONIGHT ON BIG WATER OF OUR MARINE ZONES...THEN EXPECTING THE ENTIRE MARINE AREA TO HAVE SCA CONDITIONS FROM 8 AM SUNDAY THROUGH EARLY AFTERNOON. AGAIN BIG WATER WILL CONTINUE SCA THROUGH EARLY SUNDAY EVENING AS THE SE US SFC LOW MAKES IT WAY OFFSHORE. WIND SHIFT ON TUESDAY INTO TUE NIGHT...BUT NO HAZARDS DURING THAT TIME. A SMALL CRAFT ADVISORY MAY BE NECESSARY TUESDAY NIGHT THROUGH THURSDAY MORNING IN BREEZY POST FRONTAL NORTHWEST FLOW.
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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 6 AM TO 2 PM EDT SUNDAY FOR ANZ530>532-535-536-538>540. SMALL CRAFT ADVISORY FROM 4 AM TO 8 PM EDT SUNDAY FOR ANZ533- 534-537-541>543. SMALL CRAFT ADVISORY UNTIL 6 PM EDT THIS EVENING FOR ANZ534- 537-543.
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&& $$ SYNOPSIS...CAS NEAR TERM...LEE SHORT TERM...LEE LONG TERM...CAS/CEB AVIATION...LEE/CAS/CEB MARINE...LEE/CAS/CEB

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