Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 231402 AAA AFDLWX AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 1002 AM EDT THU APR 23 2015 .SYNOPSIS... UPPER LEVEL LOW PRESSURE WILL CONTINUE MOVE EAST TO NEW ENGLAND TODAY WHERE IT WILL MERELY DRIFT EAST THROUGH SATURDAY BEFORE IT RETROGRADES BACK ACROSS THE NORTHEASTERN STATES FOR EARLY NEXT WEEK. MEANWHILE...A SECOND LOW WILL CROSS THE MID-ATLANTIC SATURDAY INTO SUNDAY. && .NEAR TERM /THROUGH TONIGHT/...
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ANOTHER UPPER WAVE ASSOCIATED W/ A CANADIAN AIRMASS IS MAKING THE WX ACROSS THE NERN QUADRANT OF THE CONUS LOOK MORE LIKE EARLY SPRING THAN LATE SPRING. SCTD SNOW SHOWERS SLIDING ACROSS NRN/CNTRL PA...WHILE THE ACTIVITY IN SRN PA DISSIPATES BEFORE MOVING ACROSS THE MD LINE. UPPER FLOW IS NEARLY ZONAL SO THE WINDS ALOFT ARE CARRYING THIS ACTIVITY FAIRLY QUICKLY FROM WEST TO EAST. A MINOR SLY COMPONENT WILL INCH THE DENSE OVERCAST STRATUS DOWN INTO NRN MD INTO THE COMING HRS...AS TEMPS SLOWLY INCH THEIR WAY UP INTO THE 50S THIS AFTN. THE INCOMING UPPER VORT ALSO HELPING TO MIX DOWN A STEADY DOSE OF 20-30KT WINDS AT THE SFC AND WILL CONTINUE TO DO SO THROUGHOUT THE DAY. EVEN W/ TEMPS REACHING NEAR 60F THIS AFTN...A SOLID 10F BELOW AVG...THE DRY AND GUSTY WNW WINDS WILL KEEP A BIT OF A CHILL IN THE AIR. STEEP LLVL LAPSE RATES AND THE OVERHEAD UPPER SUPPORT MAY ALLOW FOR SOME SCTD SPRINKLES LATER THIS AFTN AS THE STRONGEST PART OF THE VORT SLIDES THRU. FROM PREV DISC... THE LOW PIVOTS TOWARD MAINE TONIGHT WHILE THE HIGH SETTLES TOWARD THE OHIO VALLEY. THE LOW TEMP FORECAST WILL BE COMPLICATED BY LINGERING CLOUDS AND A CONTINUED PRESSURE GRADIENT. NUMEROUS GUIDANCE DATASETS HAVE AT LEAST PARTS OF THE AREA FALLING BELOW FREEZING. HOWEVER WITH ONLY MARGINAL LOWS (30-35F) IN A MAJORITY OF THE ZONES AND THE COMPLICATING FACTORS...HAVE ELECTED TO RAISE A FREEZE WATCH FOR THE SHENANDOAH VALLEY AND NRN MD AT THIS TIME AND ALLOW LATER SHIFTS TO ANALYZE THE LATEST DATA. DO NOT THINK FROST WILL BE A WIDESPREAD ISSUE DUE TO THE WINDS. A FEW SNOW SHOWERS REMAIN POSSIBLE IN UPSLOPE AREAS.
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&& .SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/... FRIDAY WILL BE DRY AS HIGH PRESSURE INCHES CLOSER BUT THERE WILL STILL BE ENOUGH GRADIENT WITH DEEP MIXING TO PERMIT GUSTS OF 20-30 MPH AGAIN. ONLY MARGINAL WARMING OF THE THERMAL PATTERN...WITH HIGHS RANGING FROM THE MID 50S TO LOWER 60S. FRIDAY NIGHT...UPR LOW OVER GULF OF MAINE WITH MID-CONTINENT LOW MOVING FROM THE CENTRAL GREAT PLAINS TO THE MIDWEST. SFC HIGH PRESSURE IN BETWEEN SETTLES AS A RIDGE FROM CNTRL PA TO SERN VA BY SUNRISE SATURDAY. WITH CANADIAN AIR IN PLACE AND THE SFC DECOUPLED...EXPECT FROST/FREEZE CONCERNS. HOWEVER...IT IS NOT THAT SIMPLE AS THE JET ON THE SOUTH SIDE OF THE UPR LOW OFF MAINE WILL BE DIRECTLY OVER HEAD AND HIGH CLOUDS FROM THE APPROACHING MID- CONTINENT LOW WILL BE BUILDING IN EARNEST. FOR NOW WENT FOR A MAV/MET/SREF BLEND WHICH HAS NRN AND SHENANDOAH ZONES GENERALLY BELOW FREEZING WITH AN EXPANSE OF MID 30S FOR N-CNTRL AND NRN VA/CNTRL MD. ADDED AREAS OF FROST TO AREAS EXPECTED TO GET INTO THE LOW 30S. WILL ENHANCE FROST/FREEZE WORDING IN THE HWO. OTW DRY. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... LOW PRESSURE CROSSES THE AREA SATURDAY INTO SUNDAY PER 00Z GFS/ECMWF OPERATIONAL CONSENSUS. LET CONFIDENCE INCREASE IN POPS WITH LIKELIES FOR ALL OF THE AREA EXCEPT NE OF BALTIMORE AS THE LOW LOOKS TO TRACK JUST SOUTH OF THE CWA. FOLLOWED WPC QPF OF GENERALLY 0.25 INCHES DC AREA AND 0.5 INCHES CHARLOTTESVILLE/CNTRL SHEN VLY. GFS HOLDS ONTO RAIN LONG WITH A TRAILING COLD FRONT THAT STALLS WELL INTO SUNDAY...EXTENDED POPS THROUGH SUNDAY MORNING. UPR LOW RETROGRADES BACK TO NERN CONUS/NY STATE BY SUNDAY NIGHT WITH SHORTWAVE TROUGH ENERGY ROUNDING THE LOW AND BRINGING SOME POPS TO THE CWA MONDAY AFTERNOON (SOME SNOW ABOVE ABOUT 3000 FT MONDAY MORNING) THEN SOME MORE RAIN TUESDAY. LIMITED MAX TEMPS MONDAY AS POPS WERE INCREASED FROM WPC GUIDANCE. NEXT LOW MOVES OVER THE SERN CONUS...WILL NEED TO WATCH HOW FAR NORTH IT TRACKS. 00Z GFS SUGGESTS AN EXTENDED PERIOD OF RAIN THROUGH THE MIDDLE OF NEXT WEEK. && .AVIATION /13Z THURSDAY THROUGH MONDAY/... VFR CONDITIONS EXPECTED THROUGH FRIDAY. THERE COULD BE A CIG AROUND 6KFT AT NRN TERMINALS TODAY INTO THIS EVENING. A LIGHT SHOWER/SPRINKLE WILL BE POSSIBLE THIS AFTERNOON/EARLY EVENING...BUT WOULD NOT BE ENOUGH TO CAUSE VSBY REDUCTIONS. WNW WINDS WILL CONTINUE TO GUST TO 25 KT TODAY...DIMINISHING TONIGHT...THEN INCREASE AGAIN TO 25 KT FRIDAY. VFR FRIDAY NIGHT AS WINDS BECOME CALM AND HIGH CLOUDS MOVE IN. LOW APPROACHES FROM THE WEST SATURDAY WITH INCREASING RAIN/MVFR CHANCES THROUGH THE DAY...CONTINUING THROUGH SUNDAY MORNING. VFR/CANADIAN HIGH PRESSURE SUNDAY NIGHT WITH WEAK DISTURBANCES THEN THROUGH THE MIDDLE OF NEXT WEEK. && .MARINE... STRONG GRADIENT BETWEEN LOW PRESSURE TO NE AND HIGH PRESSURE TO WEST WILL ALLOW GUSTY WNW WINDS TO CONTINUE ON THE WATERS THROUGH FRIDAY. A SCA HAS BEEN EXTENDED THROUGH FRIDAY FOR THE BAY AND LOWER TIDAL POTOMAC AS IT APPEARS THERE WILL NOT BE COMPLETE DECOUPLING TONIGHT. WINDS IN THE MID/UPPER POTOMAC SHOULD DROP OFF TONIGHT. THE STRONGEST WIND GUSTS OF 20-30 KT CAN BE EXPECTED IN THE AFTERNOONS. SCA LIKELY CONTINUES FOR NWLY FLOW THROUGH FRIDAY EVENING FOR MAIN PORTIONS OF THE WATER...CALMS LATE FRIDAY NIGHT WITH SLY FLOW SATURDAY AND INCREASING RAIN CHANCES THAT CONTINUE THROUGH SUNDAY MORNING. WEAK DISTURBANCES THEN THROUGH THE MIDDLE OF NEXT WEEK. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...FREEZE WATCH FROM LATE TONIGHT THROUGH FRIDAY MORNING FOR MDZ003>006-507. VA...FREEZE WATCH FROM LATE TONIGHT THROUGH FRIDAY MORNING FOR VAZ025>031-507-508. WV...FREEZE WATCH FROM LATE TONIGHT THROUGH FRIDAY MORNING FOR WVZ051>053. MARINE...SMALL CRAFT ADVISORY UNTIL 8 PM EDT FRIDAY FOR ANZ530>534- 537>543. SMALL CRAFT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR ANZ535- 536. SMALL CRAFT ADVISORY FROM 10 AM TO 8 PM EDT FRIDAY FOR ANZ535- 536. && $$ UPDATE...GMS PREV DISCUSSION...ADS/BAJ

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