Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 050239 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 939 PM EST WED MAR 4 2015 .SYNOPSIS... 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. && .NEAR TERM /THROUGH THURSDAY/... COLD FRONT HAS MOVED THROUGH MOST OF THE CWA...WITH LIGHT NORTHERLY WINDS ESTABLISHED AS FAR EAST AS THE I-95 CORRIDOR. THE FRONT WILL CONTINUE TO MOVE THROUGH THE REST OF THE CWA LATE THIS EVENING. SURFACE TEMPS BEHIND THE FRONT ARE COOLING...ALBEIT GRADUALLY AT THE START. MOST OF THE CWA REMAINS IN THE 40S...WITH SOME UPPER 30S OVER MD. THE NOTABLY COLDER AIR IS JUST TO THE NORTH AND WEST OF THE CWA...WITH TEMPS NEAR OR BELOW FREEZING ACROSS SOUTHWESTERN PA AND CENTRAL WV. MAIN ISSUE FOR TONIGHT WILL BE HOW QUICKLY THIS COLDER AIR IS ABLE TO MOVE INTO THE REGION AND PROMOTE PRECIPITATION TO TURN FROM RAIN TO SNOW/SLEET OVERNIGHT. HAVE NOT MADE CHANGES TO THE SNOW FORECAST WITH THE COLDER AIR SO CLOSE AT HAND. DENSE FOG HAS ALSO BEEN AN ISSUE THIS EVENING WITH ABUNDANT LOW LEVEL MOISTURE AND LIGHT WINDS AHEAD OF THE FRONT. EARLIER ADVISORY FOR BALTIMORE/WASHINGTON METROS HAS BEEN CANCELLED AS SLIGHTLY DRIER AIR AND LIGHT NW FLOW HAS ALLOWED VSBYS TO IMPROVE GRADUALLY. ADVISORY FOR ALBEMARLE/ORANGE COUNTIES IN EFFECT UNTIL MIDNIGHT. FOG WILL ALSO BE PREVALENT OVER THE REST OF THE PIEDMONT AND SRN MD LATE THIS EVENING UNTIL THE FRONTAL PASSAGE. OVERNIGHT...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. && .SHORT TERM /THURSDAY NIGHT/... 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 SIZABLE 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. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... 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. && .AVIATION /03Z THURSDAY THROUGH MONDAY/... MAINLY IFR CONDITIONS TONIGHT. RAIN WILL GRADUALLY CHANGE TO A MIX SNOW AND SLEET AND EVENTUALLY ALL SNOW LATE TONIGHT INTO EARLY MORNING. ADJUSTMENTS TO TIMING POSSIBLE WITH LATER UPDATES TONIGHT. GENERALLY N WINDS TONIGHT AND GRADUALLY INCREASING TO AROUND 10KT. WIND GUSTS UP TO AROUND 20KT EXPECTED THURSDAY. 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. && .MARINE... WINDS HAVE SHIFTED TO THE NORTH OVER MOST OF THE WATERS. WIND SPEED WILL GRADUALLY INCREASE TONIGHT. SCA GOES INTO EFFECT AT 1 AM AND CONTINUES UNTIL THURSDAY NIGHT. SCA LIKELY EXTENDS INTO FRIDAY BEFORE HIGH PRESSURE BUILDS OVERHEAD. DO NOT ANTICIPATE MARINE CONCERNS THROUGH THE REMAINDER OF THE WEEKEND. && .HYDROLOGY... 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.&& .LWX WATCHES/WARNINGS/ADVISORIES... 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. && $$ SYNOPSIS...HTS NEAR TERM...KCS/HTS SHORT TERM...HTS LONG TERM...MSE AVIATION...KCS/MSE MARINE...MSE/HTS/KCS HYDROLOGY...

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