Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 020315 AAB AFDLWX AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 1015 PM EST SUN MAR 1 2015 .SYNOPSIS... A COLD FRONT WILL CROSS THE AREA LATE TONIGHT. HIGH PRESSURE BUILDS ON MONDAY AND CONTINUES THROUGH TUESDAY. A WARM FRONT WILL CROSS THE AREA TUESDAY NIGHT. THEN A STRONG COLD FRONT WILL CROSS THE REGION LATE WEDNESDAY AS COLD HIGH PRESSURE BUILDS IN FOR THURSDAY AND CONTINUES INTO THE WEEKEND. && .NEAR TERM /THROUGH MONDAY/... HEADLINE UPDATE...THE WINTER STORM WARNING FOR PORTIONS OF ERN MD HAS BEEN CANCELLED. A WINTER WX ADZY WILL REMAIN IN EFFECT OVERNIGHT FOR UPSLOPE SNOW SHOWERS. THE MAIN CONCERN NOW TURNS TO WHAT IS LEFTOVER AFTER A DAY OF ACCUMULATED SNOW/SLEET/ICE. TRAVEL WILL BE DANGEROUS EVEN AFTER PRECIP IS OUT OF THE AREA COMPLETELY. A SOLID GLAZE TO NEAR/JUST OVER A QUARTER-INCH OF ICE HAS BEEN REPORTED ACROSS MUCH OF THE NRN/ERN HALVES OF THE CWA - ESPEC E OF THE BLUE RIDGE AND THE ENCOMPASSING ALL THE DC/BALT METRO AREAS. AIR TEMPS WILL HOVER RIGHT AROUND THE FREEZING MARK ALL-NIGHT...AT TIMES BOUNCING ABOVE AND BELOW IT. SFC TEMPS HOWEVER WILL VARY FROM EVEN NEAR-SFC AIR TEMPS...KEEPING MOST ICED-OVER PLACES FROM ALLOWING MUCH/IF ANY MELTING OVERNIGHT. THE COLD FRONT ASSOCIATED WITH THE LOW WILL PASS THROUGH LATE TONIGHT INTO EARLY MONDAY MORNING. A DRY NORTHWEST FLOW IS EXPECTED BEHIND THE FRONT. THERE WILL BE ENOUGH SUNSHINE AND DOWNSLOPING WINDS FOR MILDER CONDITIONS. MAX TEMPS WILL RANGE FROM THE 20S IN THE ALLEGHENY HIGHLANDS...TO THE LOWER 40S NEAR WASHINGTON AND BALTIMORE...TO THE UPPER 40S/NEAR 50 IN CENTRAL VIRGINIA. && .SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/... HIGH PRESSURE OVER THE OHIO VALLEY WILL MOVE EASTWARD TOWARD NEW ENGLAND BY MONDAY NIGHT. WITH DEWPOINTS DROPPING INTO THE TEENS AND LIGHT WINDS...TEMPERATURES SHOULD FALL WELL INTO THE 20S...SETTING THE STAGE FOR YET ANOTHER WINTRY PRECIP THREAT. TUESDAY MORNING SHOULD BE FINE...WITH PRECIP JUST BEGINNING TO SPREAD NORTHWARD INTO WRN VA AND WVA. AT THIS POINT...MODEL SOLUTIONS HAVE SOME SIMILARITY TO TODAY...WITH VERTICAL PROFILES FROM THE NAM AND GFS SHOWING PRECIP IN THE HIGHLANDS STARTING AS SNOW IN THE MORNING...FOLLOWED BY A CHANGEOVER TO SLEET AND FREEZING RAIN DURING THE DAY. LOOKING BACK THROUGH SEVERAL PREVIOUS MODEL RUNS...FORECAST SOUNDINGS HAVE VARIED IN P-TYPE...SO RATHER THAN CARRYING THE FULL GAMUT OF P-TYPE ON DAY 3...HAVE ELECTED TO KEEP THE WORDING AS RAIN-OR-SLEET AT THIS TIME AS THOSE APPEAR THE MORE LIKELY TWO. P-TYPE SHOULD BE ALL RAIN BY SUNSET...BUT AS THE SFC HIGH SHIFTS OFFSHORE AND WAA SURGES NORTH...TEMPERATURES SHOULD ACTUALLY RISE OVERNIGHT...WITH MOST AREAS AT LEAST APPROACHING 40 AND COMMUNITIES WEST OF THE BLUE RIDGE POSSIBLY PUSHING 50 BY DAYBREAK. KEPT A BRIEF PERIOD OF FZRA IN THE EVENING FOR AREAS THAT MAY STAY NEAR FREEZING LONGER. THE COLD FRONT WILL BE SLOW TO APPROACH...ALLOWING WAA TO CONTINUE AND HIGHS TO REACH INTO THE 50S OR PERHAPS EVEN LOWER 60S ON WEDNESDAY. MODEL SOLUTIONS DIFFER ON FROPA TIMING...SO I TOOK A MIDDLE GROUND CLOSE TO THE GFS. SEE HYDROLOGY SECTION FOR ADDITIONAL INFORMATION ON RAIN/SNOWMELT/RIVER ICE. && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... CAA INCREASES AFTER FRONTAL PASSAGE WEDNESDAY NIGHT WITH MUCH COOLER/DRIER AIR MOVING IN. SOME GUIDANCE HAS BEEN CONSISTENTLY INDICATING ANAFRONTAL QPF OVERNIGHT WEDNESDAY AND THROUGH THE DAY ON THURSDAY. IF THIS WERE TO OCCUR...WOULD EXPECT A QUICK TRANSITION FROM RAIN TO SLEET TO SNOW AS THE THERMAL COLUMN QUICKLY COOLS IN THE STRONG CAA. HIGH PRESSURE SETTLES INTO THE REGION OVERNIGHT THURSDAY...AND WITH STRONG RADIATIONAL COOLING...EXPECT LOWS FRIDAY MORNING TO BE VERY COLD. AIRMASS MODIFICATION BEGINS FRIDAY WITH WAA OVER THE AREA. NEXT COLD FRONT APPROACHES THE REGION SATURDAY...AT THIS POINT IT APPEARS TO PASS THROUGH DRY. && .AVIATION /03Z MONDAY THROUGH FRIDAY/... FREEZING DRIZZLE DISSIPATING OFF JUST AHEAD OF A COLD FRONT. CIGS E OF THE BLUE RIDGE WILL REMAIN IN THE MVFR/IFR RANGE THRU NEAR 6Z BEFORE A GRADUAL IMPROVEMENT TOWARD 12Z AND IN THE COUPLE HRS AFTER. WINDS WILL SHIFT TO THE NORTHWEST EARLY MON MRNG. CIGS/VSBYS WILL IMPROVE TO VFR LEVELS AND NORTHWEST WINDS WILL GUST AROUND 20 TO 25 KNOTS BY THE LATE MRNG HRS. VSBY/CIG RESTRICTIONS EXPECTED TUESDAY AFTERNOON THROUGH WEDNESDAY WITH PRECIPITATION. GUSTY SOUTHERLY WINDS ALSO EXPECTED ON WEDNESDAY. SUB-VFR CONDITIONS POSSIBLE THURSDAY IN ANY REGIONS OF PRECIPITATION. && .MARINE... WINDS WILL SHIFT TO THE NORTHWEST OVERNIGHT BEHIND A COLD FRONT. A SMALL CRAFT ADVISORY IS IN EFFECT MONDAY FOR NORTHWEST WINDS GUSTING AROUND 20 TO 25 KNOTS. SCA CONDITIONS POSSIBLE TUESDAY NIGHT AND WEDNESDAY AHEAD OF AN APPROACHING COLD FRONT. POSSIBILITY OF SCA WEDNESDAY NIGHT THROUGH THURSDAY IN THE CAA BEHIND THE COLD FRONT. && .HYDROLOGY... WE HAVE BEEN ADVERTISING THE POTENTIAL OF MIDWEEK FLOODING IN THE HAZARDOUS WEATHER OUTLOOK. LIQUID PRECIP FCST FROM WPC PUTS MUCH OF THE FCST AREA IN A MINIMA FOR AMOUNTS...AROUND AN INCH OR LESS IN MANY AREAS. WITH TEMPERATURES EXPECTED TO RISE INTO THE 50S ON WEDNESDAY...THERE WILL BE SOME...POSSIBLY A LOT OF...MELTING OF THE EXISTING SNOWPACK...WHICH COMPUTER MODELS AND OBSERVATIONS INDICATE CONTAINS ANYWHERE FROM 3/4 INCH TO 2 INCHES OF SNOW WATER EQUIVALENT. THIS COMBINATION MAY LEAD TO MINOR FLOODING AS THE RAIN FALLS ON WEDNESDAY. ALTHOUGH RIVER ICE IS NOT ESPECIALLY THICK...IT WILL HAVE TO BE MONITORED FOR POTENTIAL ROLE IN AFFECTING RUNOFF. ALSO...PLOWED SNOW IS LIKELY COVERING SOME OF THE DRAINS OUT THERE...WHICH COULD CAUSE MORE POOR DRAINAGE FLOODING THAN WOULD OTHERWISE USUALLY BE EXPECTED. WORTH NOTING...CURRENT FORECAST RAIN TOTALS ARE ON THE LOWER SIDE OF THE ENSEMBLE SUITES OF THE GEFS AND SREF. PLEASE CONTINUE TO MONITOR THE FORECAST FOR UPDATES AS THE EVENT GETS CLOSER. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...WINTER WEATHER ADVISORY UNTIL 6 AM EST MONDAY FOR MDZ501. VA...WINTER WEATHER ADVISORY UNTIL 6 AM EST MONDAY FOR VAZ503. WV...WINTER WEATHER ADVISORY UNTIL 6 AM EST MONDAY FOR WVZ501-503- 505. MARINE...SMALL CRAFT ADVISORY FROM 9 AM TO 6 PM EST MONDAY FOR ANZ530>543. && $$ UPDATE...GMS PREV DISCUSSION...BJL/JCE/HAS/MSE

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