Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 250219 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 919 PM EST SAT JAN 24 2015 .SYNOPSIS... HIGH PRESSURE BUILDS IN BRIEFLY SUNDAY. LOW PRESSURE WILL PASS SOUTH OF THE AREA SUNDAY NIGHT...THEN STRENGTHEN AS IT MOVES UP THE COAST MONDAY AND TUESDAY. HIGH PRESSURE IS THEN EXPECTED THROUGH MIDWEEK. && .NEAR TERM /THROUGH SUNDAY/... CWFA IN NW FLOW THIS EVNG. SFC RDGG RESIDES IN/NW OF OHVLY. HV HAD A FEW HIER WND GUSTS PAST CPL HRS...REFLECTIVE OF A WEAK VORT EMBEDDED W/IN THE MEAN FLOW. MDL SNDGS SUGGEST THAT SFC WNDS SHUD DECOUPLE SOMEWHAT...WHILE WINDS REMAIN BRISK BTWN 1-5 KFT. HV HIER WINDS ACRS THE RIDGETOPS. CLDS ACRS THE APLCNS HV BEEN CREEPING TWD THE BLURDG. WHILE BELIEVE THAT PCPN WL BE HELD BACK BY THE APLCNS...MEAN LYR RH DOES INCREASE THRU MRNG. MADE SUBTLE CLDCVR ADJUSTMENTS. CLDS AND WINDS SUGGEST THAT TEMPS WL HV TROUBLE FALLING MUCH. HV LEFT PRVS MIN-T FCST AS IS. LASTLY...RADAR ACRS WRN PA/WVA HV STARTED TO FILL IN SLGTLY. UNFORTUNATELY UPSTREAM OBS INDICATE FZDZ...NOT SHSN. THE FACT THAT LERI LARGELY ICE COVERED IS A CONCERN. MORESO...THE DRIER AIR ALOFT AND SWWLY WINDS ALSO TROUBLING. WL HOLD ONTO UPSLOPE SHSN FOR NOW. RECOGNIZE PSBLTY THAT AN OVNGT FRZG RAIN ADVY MAY ULTIMATELY BE REQD. FOR SUNDAY...DRY EVERYWHERE IN THE MORNING EXCEPT AGAIN THE ALLEGHENY FRONT WHICH WILL HAVE SCT SNOW SHOWERS. HEADING INTO THE AFTN...ATTENTION WILL BE TURNED TO THE APPROACHING CLIPPER SYSTEM AS IT DIPS SOUTH THROUGH THE GREAT LAKES WITH IT NEARING KENTUCKY BY 00Z MONDAY. UPPER LVL ENERGY NUDGING AHEAD OF THE APPROACHING ASSOCIATED CLOSED LOW COULD BRING LIGHT PCPN TO AREAS WEST OF THE BLUE RIDGE AND ALONG THE MASON DIXON LINE SUN AFTN...BUT THE BULK OF THE PCPN FOR MOST OF THE AREA LOOKS TO HOLD OFF UNTIL AFTER 00Z MON. TEMPS WARMING INTO THE 40S COULD RESULT IN THE LIGHT PCPN BEING A RAIN/SNOW MIX OR EVEN ALL RAIN. AT THE MOMENT NOT ANTICIPATING ACCUMULATING SNOWS OUTSIDE THE POTOMAC HIGHLANDS/ALLEGHENY REGION UNTIL SUNDAY EVENING. && .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/... CLIPPER LOW PRESSURE SYSTEM WILL REACH THE CENTRAL OHIO VALLEY BY SUNDAY EVENING...AND NEARLY VERTICALLY STACKED WITH AN UPPER LOW. 12Z ECMWF/GFS/NAM ALL IN AGREEMENT OVERALL SYNOPTIC SCENARIO. BOTH THE UPPER TROUGH AND SURFACE LOW WILL TRACK SEWD INTO THE CAROLINAS SUNDAY NIGHT. ASSOCIATED PRECIPITATION WILL SPREAD ACROSS THE AREA DURING THE EVENING AND OVERNIGHT HOURS. TEMP GUIDANCE IS A FEW DEGREES WARMER THAN PREVIOUS RUNS. THIS WILL RESULT IN SOME AREAS STARTING WITH RAIN OR A RAIN/SNOW MIX BEFORE CHANGING OVER TO SNOW SUNDAY NIGHT...INCLUDING THE SOUTHERN TIER COUNTIES OF MARYLAND AND VIRGINIA...UP TO THE WASHINGTON DC METRO. ALTHOUGH MODELS ARE CONSISTENT WITH GENERAL FEATURES...THERE ARE STILL SPECIFIC DIFFERENCES REGARDING BANDING AND LOCALLY HIGHER QPF AMOUNTS. A WINTER STORM WATCH HAS BEEN ISSUED STARTING SUNDAY EVENING FOR THE NORTHWESTERN PORTION OF THE CWA...INCLUDING SEVERAL COUNTIES IN WV...WESTERN AND NORTH CENTRAL MD...AND WESTERN LOUDOUN...CLARK AND FREDERICK COUNTIES IN VA. LOW TEMPS RANGE FROM THE UPPER 20S IN THE WATCH AREA AND THE POTOMAC HIGHLANDS TO THE THE LOW 30S ACROSS THE PIEDMONT AND SRN MD. ON MONDAY...ENERGY TRANSFERS FROM THE CAROLINAS TO THE OFFSHORE WATERS...WITH RAPID CYCLOGENESIS TAKING PLACE EAST OF NORFOLK. THIS WILL CONTINUE TO DRAW MOISTURE INTO THE REGION ALONG WITH COLD AIR FROM THE NORTH. SNOW WILL CONTINUE...ALTHOUGH LIKELY TRENDING LIGHTER DURING THE DAY AS MOST ENERGY TRANSFERS EWD TOWARDS THE OFFSHORE LOW. FOR THE BALTIMORE/WASHINGTON METROS... EXPECTING AN ADVISORY LEVEL SNOW OF AROUND 2-4 INCHES. SIMILAR AMOUNTS EXPECTED OVER SOUTHERN PORTIONS OF THE SHENANDOAH VALLEY... BLUE RIDGE AND THE PIEDMONT..WITH LESSER AMOUNTS TO THE SOUTH. WITH THE FORECAST ADVISORY-LEVEL SNOWFALL...HAVE NOT ISSUED A WINTER STORM WATCH FOR THESE AREAS. CERTAINLY HEADLINES WILL BE REFINED AS THE EVENT DRAWS CLOSER. SYSTEM PULLS OUT MONDAY NIGHT. LOWS DROP INTO THE 20S ACROSS THE CWA. && .LONG TERM /TUESDAY THROUGH SATURDAY/... ANOTHER PIECE OF ENERGY BEHIND THE DEPARTING ALBERTA CLIPPER WILL ALLOW FOR THE OPPORTUNITY OF ADDITIONAL SNOW SHOWERS TUESDAY. SOME UPSLOPE SNOW SHOWERS MAY STILL LINGER IN THE POTOMAC HIGHLANDS TUESDAY NIGHT WHILE HIGH PRESSURE INFLUENCES DRY CONDITIONS ELSEWHERE. TEMPERATURES TUESDAY AND TUESDAY NIGHT WILL BE 8 TO 10 DEGREES BELOW NORMAL. HIGH PRESSURE WILL BUILD ACROSS THE REGION WEDNESDAY AND WEDNESDAY NIGHT...KEEPING CONDITIONS DRY BUT TEMPERATURES 5 TO 10 DEGREES BELOW NORMAL. HIGH PRESSURE WILL MOVE EAST THURSDAY TO ALLOW FOR A GREAT LAKES LOW PRESSURE SYSTEM TO DRAG A COLD FRONT ACROSS THE REGION LATE THURSDAY AND THURSDAY NIGHT. THERE IS A CHANCE OF SNOW SHOWERS THURSDAY INTO THURSDAY NIGHT. SOME LIGHT RAIN MAY ALSO MIX FURTHER SOUTH AS HIGHS MAY HOVER NEAR 40 DEGREES. OVERALL...TEMPERATURES SHOULD NOT BE AS CHILLY AS EARLIER IN THE WEEK. A CHANCE OF A FEW LINGERING SNOW SHOWERS NEAR THE CHESAPEAKE BAY DUE TO TRAILING UPPER LEVEL ENERGY FRIDAY. HOWEVER A DEVELOPING DOWNSLOPING EFFECT COULD PROHIBIT SNOW SHOWERS EAST OF THE BLUE RIDGE MOUNTAINS. ELSEWHERE...SNOW SHOWERS IN THE POTOMAC HIGHLANDS. HIGH PRESSURE WILL BUILD INTO THE REGION LATE FRIDAY THROUGH SATURDAY...ALLOWING FOR DRYING OUT. TEMPERATURES SHOULD REMAIN BELOW NORMAL. && .AVIATION /02Z SUNDAY THROUGH THURSDAY/... VFR CONDITIONS ACROSS ALL TAF SITES OVERNIGHT...CONTINUING THRU SUNDAY. SCT LOW-MID LVL CLOUDS WILL FORM AHEAD OF THE APPROACHING PCPN...BUT NOT EXPECTING SUB-VFR CONDITIONS UNTIL AFTR 00Z MON...THE EXCEPTION BEING KMRB WHICH COULD SEE LOWER CIGS AFTER 21Z. OVERALL...SUNDAY SHOULD BE DRY WITH THE PCPN MOVING IN SUNDAY EVENING. WINDS WILL BE LIGHT AND VRB. IFR CONDITIONS LIKELY WITH SNOW SUNDAY NIGHT INTO MONDAY. TAF SITES OTHER THAN KMRB MAY START AS RAIN OR A RAIN/SNOW MIX FOR A WHILE SUNDAY NIGHT. LIGHT E-ENE WINDS SUNDAY NIGHT...BECOMING N-NW MONDAY. GUSTS POSSIBLE MONDAY OVER THE BALTIMORE/WASHINGTON TERMINALS. CONDITIONS IMPROVE MONDAY NIGHT. LINGERING LIGHT SNOW OR SNOW SHOWERS COULD POSE A THREAT FOR MVFR TO IFR CONDITIONS TUESDAY. OTHERWISE...VFR CONDITIONS TUESDAY NIGHT AND WEDNESDAY. NORTHWEST WINDS COULD GUST 20 TO 25 KNOTS TUESDAY THROUGH WEDNESDAY. && .MARINE... WINDS THIS EVENING HV BEEN TRICKY. WHILE SFC FLOW HAS DIMINISHED AFDK...30 KT WINDS RESIDE JUST 1K FT UPSTAIRS. THERE HAS BEEN SPORADIC MIXING...MOST NOTABLY AT TPLM2. SCA ENDS AT 03Z. AM MONITORING SITUATION FOR A POTL SHORT-FUSED EXTENSION. WINDS REMAIN MAINLY BELOW SCA CRITERIA SUNDAY. HIGHER CONFIDENCE OF GUSTS INTO THE 20S LATE SUN NIGHT AND INTO MONDAY WITH NORTHERLY FLOW SO SCA COULD BE NEEDED AS EARLY AS 06Z MON BUT MORE LIKELY AFTER 12Z MON. SCA WILL LIKELY BE NEEDED OVER AT LEAST CHESAPEAKE BAY AND THE LOWER TIDAL POTOMAC MONDAY AND MONDAY NIGHT FOR GUSTY NORTH WINDS AS LOW PRESSURE STRENGTHENS OFFSHORE. SMALL CRAFT ADVISORY MAY BE NEEDED TUESDAY THROUGH WEDNESDAY AS NORTHWEST WINDS GUST 20 TO 25 KNOTS. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...WINTER STORM WATCH FROM SUNDAY EVENING THROUGH MONDAY AFTERNOON FOR MDZ003-501-502. WINTER STORM WATCH FROM SUNDAY EVENING THROUGH MONDAY EVENING FOR MDZ004-005-503-505. VA...WINTER STORM WATCH FROM SUNDAY EVENING THROUGH MONDAY EVENING FOR VAZ028-031-505. WV...WINTER STORM WATCH FROM SUNDAY EVENING THROUGH MONDAY AFTERNOON FOR WVZ050-051-055-501>504. WINTER STORM WATCH FROM SUNDAY EVENING THROUGH MONDAY EVENING FOR WVZ052-053. MARINE...SMALL CRAFT ADVISORY UNTIL 10 PM EST THIS EVENING FOR ANZ530>534-537>541-543. && $$ SYNOPSIS...SEARS/KCS NEAR TERM...HTS/SEARS SHORT TERM...KCS LONG TERM...KLW AVIATION...HTS/SEARS/KCS/KLW MARINE...HTS/SEARS/KCS/KLW

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