Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 200141 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 941 PM EDT SAT APR 19 2014 .SYNOPSIS...
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HIGH PRESSURE WILL BUILD INTO THE AREA...AND 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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AS HAS BEEN THE CASE FOR THE DAYTIME HRS...MAIN FCST ISSUE FOR THE EVNG HAS BEEN HI CLDS. NOT ONLY HV THEY NOT BEEN DSPTG...BUT THEYVE ACTUALLY BEEN INCRSG...BLOWOFF FM UPR LOW. GDNC KEEPING H3 RH HIGH THRU THE NGT...AND HV BEEN BUMPING UP SKYCVR IN THE GRIDS. SINCE CLDS HV BEEN IN PLACE ALL PM...TEMPS HVNT DROPPED MUCH FM DAYTIME HIGHS. HWVR...DEWPTS QUITE LOW...SPCLY ALONG THE PA BRDR. HV MADE AN UPWD ADJUSTMENT...BUT NOT AS LARGE AS OTRW GIVEN POTL FOR QUICK RADL COOLING.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... 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. && .LONG TERM /MONDAY THROUGH SATURDAY/... 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. && .AVIATION /02Z SUNDAY THROUGH THURSDAY/...
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VFR CONDITIONS XPCTD THRU VALID TAF PD. ONLY ISSUE HIGH CLDS...NOT OF OP IMPACT. NE WNDS AOB 10 KT. 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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WNDS MAINLY AOB 10 KT...W/ A HINT OF VRBL ONSHORE FLOW. WRF-ARW4 SUGGESTS INCRSG NELY FLOW LT TNGT...AND FLLWD ALONG SINCE PRVS FCSTS BASED ON THAT TOO. GREATEST WNDS TMRW MRNG-MIDDAY...BUT SHUD START A LTL SOONER AND LAST A LTL LONGER MAIN CHANNEL OF BAY/LWR PTMC/MID BAY INLETS. 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- 535-536-538>540. SMALL CRAFT ADVISORY FROM 4 AM TO 8 PM EDT SUNDAY FOR ANZ531>534-537-541>543.
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&& $$ SYNOPSIS...HTS/CAS NEAR TERM...HTS SHORT TERM...LEE LONG TERM...CAS/CEB AVIATION...HTS/LEE/CAS/CEB MARINE...HTS/CAS/CEB

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