Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 041958 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 258 PM EST WED MAR 4 2015 .SYNOPSIS...
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A COLD FRONT WILL CROSS THE REGION TONIGHT. ASSOCIATED PRECIPITATION WILL CONTINUE INTO THURSDAY AS SNOWFALL DUE TO THE PASSAGE OF A CORE OF STRONGER WINDS IN THE JET STREAM. HIGH PRESSURE BUILDS OVERHEAD FRIDAY...THEN PERSISTS THROUGH THE WEEKEND.
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&& .NEAR TERM /THROUGH TONIGHT/...
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THE TWO SFC BNDRYS OF THIS MRNG SEEM TO HV COMBINED INTO ONE... STRETCHING FM INVOF MRB-BNA-SHV. GIVEN THE LACK OF FORCING...PCPN HAS BEEN SLOW IN ADVCG EWD TDA. HWVR...LTST RADAR COMPOSITE DEPICTS PCPN /ALL RAIN/ ACRS NRN CWFA. ANTICIPATE PCPN TO OVERSPREAD THE REST OF THE AREA TAFTN. DUE TO IN-SITU WEDGE...ITS BEEN TOUGH TO GET TEMPS OUT OF THE 40S TDA. W99 HAS BEEN THE ONE EXCEPTION. THE ARRIVAL OF RAFL WL PUT AN END TO ANY ADDTL TEMP RISE. LTST GDNC CYCLE REVEALS A DECENT AMT OF CONSISTENCY SYNOPTICALLY. HV SUBTLE THERMAL TIMING CHGS...WHICH IS XPCTD. BUT FROM AN ENSEMBLE VIEWPOINT...GDNC CONFIRMING THAT GOING FCST ON TRACK... AND HV NOT ADJUSTED MUCH. THE END RESULT IS TO COVERT THE SRN FRINGE OF THE CWFA FROM A WATCH TO A LOW END WARNING. PTYPES IN THIS AREA A BIT OF A CONCERN. AS ALREADY MENTIONED...IT WL BE RAINING AT THE BGNG OF THE TNGT PD. AS THE CDFNT WORKS SWD...COLDER AIR WL BE DRAINING SOUTH... WHILE BAROCLINICITY AND THE UPR JET WL PROVIDE FORCING FOR CONTD PCPN GENERATION. THE MSTR FEED WL COME FROM THE WRN GLFMEX AS WELL AS THE PACIFIC. PWAT FM RNK 12Z RAOB WAS 250 PCT OF NORMAL. CERTAINLY PLENTY OF MSTR IN PLAY. AM KEEPING FCST CONSISTENT IN TRANSITIONING FROM RA TO SNW W/ A SHORT PD OF PL IN BTWN. EXACT TIMING OF EACH STILL MAY NEED TO BE ADJUSTED BY AN HR OR TWO EITHER WAY. BTTM LINE...BY SUNRISE XPCTG ALL SNOW BY SUNRISE TMRW N OF SHD-DCA-NAK. HV A SNPL OR PLRA MIX TO THE S.
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&& .SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/...
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WL TAKE THE TRANSITION TO SNW FM SHD-DCA-NAK AT THE START OF PD SWD TO EDGE OF CWFA BY MID MRNG. UVV ALIGNS VERY WELL W/ SNOW GROWTH REGION A CPL HRS BHD TRANSITION TO SNOW. SCREAMING MESSAGE HERE...EVEN THOUGH IT MAY NOT LOOK BAD UPON WAKING UP...XPCT CONDS TO GET WORSE DURING THE DAY. WL HV THE RRQ OF 160 KT UPR JET... SNOW GROWTH REGION...AND FGEN FORCING ALL CROSSING CWFA DURING THE MIDDAY HRS-- A LTL ERLR TO THE N AND LATER CENTRAL VA/SRN MD. THAT IS WHEN THE BULK OF THE FCSTD SNOW WL ACCUMULATE. SMALL TWEAKS HERE CUD HV BIG IMPACTS ON STORM TTLS. DID NOT MASSAGE FCST AS ANY CHGS WUD BE MINOR WRT PSBL FCST ERRORS. GDNC HOLDS ONTO PL A BIT LONGER IN SRN MD. ULTIMATELY THAT WL IMPACT SNW TTLS...POTENTIALLY BY CUTTING THEM DOWN. CURRENT FCST REPRESENTS BEST ASSESSMENT AT THIS TIME. RECOGNIZE THAT THIS ASPECT OF THE FCST SUBJECT TO MORE SIZEABLE ERRORS THAN THE REST OF THE CWFA. BACK EDGE OF SNOW SHUD MV SE BY LATE DAY. ADDED A CHC SNW ELY EVENING TO ACCNT FOR LINGERING ACTIVITY/TIMING DIFFS. AFTER THAT ITLL ALL BE A TEMP FCST. TEMPS WL ALREADY BE DROPPING DUE TO CAA DURING THE DAY THU...AND THAT DROP WL ONLY BE ENHANCED AT NGT W/ THE LOSS OF DAYLIGHT. USED MOS MEAN W/ A SMALL CONTRIBUTION FM PRVS FCST FOR MIN-T. WL HV PLENTY OF LOWS INTHE SINGLE DIGITS AND TEENS...AND WL NEED TO BE CONSIDERING SUBZERO WIND CHILL FACTOR BY DAWN FRI MRNG.
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&& .LONG TERM /FRIDAY THROUGH WEDNESDAY/...
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NOT MUCH HAS CHANGED FROM PREVIOUS FORECASTS FOR THE EXTENDED PERIOD. AFTER AN EXTREMELY COLD START FRIDAY MORNING...TEMPERATURES WILL BE VERY SLOW TO RISE THROUGH FRIDAY...WITH WEAK CAA AND RESIDUAL SNOW PACK. VERY WEAK SOUTHERLY FLOW COMMENCES LATE FRIDAY NIGHT...BUT THE SNOWPACK AND STRONG RADIATIONAL COOLING WILL KEEP NIGHTTIME LOWS WELL BELOW NORMAL. WARMING BEGINS SATURDAY...AND DESPITE THE PASSAGE OF A WEAK COLD FRONT SATURDAY NIGHT...TEMPERATURES WILL SLOWLY WARM THROUGH THE REST OF THE WEEKEND AND THROUGH THE EARLY/MIDDLE PART OF NEXT WEEK. FOR NOW KEPT THE EXTENDED POP FREE DUE TO LARGE MODEL DIVERGENCE.
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&& .AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
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STILL HV VFR CIGS ACRS THE TERMINALS ATTM. RESTRICTIONS COMING FM VSBYS. THAT SHUD CHG AS RA OVERSPREADS TERMINALS BY DARK. HV CONDS DROPPING TO IFR AFTR MIDNIGHT WHEN RA MIXES WITH PL AND THEN SNOW. ALL TERMINALS WL HV JUST SNW BEFORE THE START OF THE MRNG PUSH TMRW. THE LOWEST CONDS WL OCCUR DURING THE MIDDAY OF THE DAY WHEN THE SNOW WL BE HEAVIEST. CONDS WL BE IMPRVG MID-LT AFTN. VFR PSBL BY THU EVNG...AND LKLY BY THU NGT. EXPECT VFR CONDITIONS FRIDAY AS WINDS CALM AND CEILINGS RISE. VFR CONDITIONS EXPECTED THROUGH THE REST OF THE WEEKEND.
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&& .MARINE...
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ASIDE FM TPLM2...ALL WNDS AOB 10 KT ATTM. STILL HV SLY FLOW. THE TRANSITION TO NNWLY FLOW WL OCCUR THIS EVNG AS CDFNT CROSSES WATERS. WNDS WL INCREASE THEREAFTR...W/ SCA CONDS FOR THE LATTER PART OF THE NGT INTO THU NGT. SCA LIKELY EXTENDS INTO FRIDAY BEFORE HIGH PRESSURE BUILDS OVERHEAD. DO NOT ANTICIPATE MARINE CONCERNS THROUGH THE REMAINDER OF THE WEEKEND.
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&& .HYDROLOGY...
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RAIN IS ONGOING ACROSS THE NORTHERN HALF OF THE FORECAST AREA...AND WILL SPREAD SOUTHWARD THIS EVENING. PRIOR TO THE CHANGEOVER TO WINTRY PRECIPITATION...ADDITIONAL RAIN WILL BE BETWEEN 1/4 AND 1 INCH. WITH NO DIRECT SUNSHINE...SNOWMELT HAS BEEN SLOW BUT STEADY. THE ONLY STREAM REACTIONS THROUGH MID AFTERNOON HAVE BEEN IN THE NORTH BRANCH POTOMAC...NORTH FORK SOUTH BRANCH POTOMAC...AND WILLS CREEK BASINS. THE NORTH BRANCH POTOMAC AT KITZMILLER HAS RISEN ABOVE ACTION STAGE AND WILL BE MONITORED FOR POSSIBLE FLOODING ALL NIGHT. OTHER STREAMS IN THOSE BASINS ARE SHOWING SOME ICE EFFECTS AND HAVE RISEN QUITE A BIT...BUT ARE STILL WELL BELOW BANKFULL. POOR DRAINAGE FLOODING AND PONDING ARE LIKELY WHERE NORMAL DRAINAGE PATTERNS ARE DISTURBED BY SNOWPACK AND/OR ICE. HOWEVER...LOCALIZED MINOR OUT-OF-BANK FLOODING OF STREAMS CANNOT BE RULED OUT... ESPECIALLY IN NRN MD AND THE HIGHLANDS.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...WINTER STORM WARNING FROM MIDNIGHT TONIGHT TO 9 PM EST THURSDAY FOR DCZ001. MD...WINTER STORM WARNING FROM 7 PM THIS EVENING TO 7 PM EST THURSDAY FOR MDZ003-501-502. WINTER STORM WARNING FROM 10 PM THIS EVENING TO 7 PM EST THURSDAY FOR MDZ004>006-011-503>508. WINTER STORM WARNING FROM MIDNIGHT TONIGHT TO 9 PM EST THURSDAY FOR MDZ013-014-016-018. WINTER STORM WARNING FROM 3 AM TO 10 PM EST THURSDAY FOR MDZ017. VA...WINTER STORM WARNING FROM 7 PM THIS EVENING TO 7 PM EST THURSDAY FOR VAZ028-503-504. WINTER STORM WARNING FROM 10 PM THIS EVENING TO 7 PM EST THURSDAY FOR VAZ025>027-029>031-040-501-505>508. WINTER STORM WARNING FROM MIDNIGHT TONIGHT TO 9 PM EST THURSDAY FOR VAZ038-039-050>055-502. WINTER STORM WARNING FROM 3 AM TO 10 PM EST THURSDAY FOR VAZ036-037-056-057. WV...WINTER STORM WARNING FROM 7 PM THIS EVENING TO 7 PM EST THURSDAY FOR WVZ050>052-055-501>506. WINTER STORM WARNING FROM 10 PM THIS EVENING TO 7 PM EST THURSDAY FOR WVZ053. MARINE...SMALL CRAFT ADVISORY FROM 1 AM THURSDAY TO 6 AM EST FRIDAY FOR ANZ530>543.
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&& $$ SYNOPSIS...HTS NEAR TERM...HTS SHORT TERM...HTS LONG TERM...MSE AVIATION...HTS/MSE MARINE...HTS/MSE HYDROLOGY...JE

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