Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 090831 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 331 AM EST TUE FEB 9 2016 .SYNOPSIS... MULTIPLE LOW PRESSURES IMPACT THE REGION THROUGH WEDNESDAY BEFORE PUSHING OFF TO THE NORTHEAST. HIGH PRESSURE BUILDS IN THE WAKE THROUGH FRIDAY. A QUICK MOVING COLD FRONT SWINGS THROUGH FRIDAY NIGHT WITH CANADIAN HIGH PRESSURE BUILDING IN FOR THE WEEKEND. && .NEAR TERM /THROUGH TONIGHT/... A FEW ADJUSTMENTS BEING MADE THIS MORNING WITH THE LATEST MODEL RUNS CONVERGING ON DCRSG POTENTIAL OF THE HIGHER SNOW TOTALS. OVERALL...HAVE DROPPED SNOW TOTALS ANYWHERE BETWEEN 1-3 INCHES ACROSS THE AREA. AS SUCH...HAVE ENOUGH CONFIDENCE TO CANCEL THE WINTER STORM WARNING...REPLACING WITH A WINTER WX ADVISORY THRU THIS EVENING. THE WINTER WX ADVISORY ALREADY IN PLACE REMAINS THE SAME EXCEPT HAVE CANCELLED FOR DC/ARLINGTON/FAIRFAX AND PRINCE WILLIAM WITH THE INCREASED CONFIDENCE NOW OF LESS THAN 2 INCHES... ADVISORY CRITERIA. COASTAL FLOOD ADVISORIES ARE IN EFFECT TODAY AS WELL...PLEASE REFER TO THE COASTAL FLOOD SECTION FOR MORE DETAILS. THE LIGHT RAIN HAS BEEN SLOW TO TRANSITION TO SNOW OR EVEN A RAIN/SNOW MIX TONIGHT OUTSIDE OF THE POTOMAC HIGHLANDS. UPPER LVL TROUGH ACROSS A GOOD PORTION OF THE EASTERN US THE MAIN PLAYER IN PCPN DEVELOPMENT EARLY THIS MORNING WITH ONE SFC LOW WELL NORTH OVER THE EASTERN GREAT LAKES...AND A SECOND LOW ORGANIZING OFF THE COAST OF VA. AS THIS SECOND LOW DEEPENS...PUSHING OFF TO THE NE... EXPECTING AN INVERTED TROUGH EXTENDING BACK ACROSS MD INTO PA TO ACT AS A TRIGGER FOR FURTHER PCPN DEVELOPMENT OVER THE EASTERN HALF OF THE CWA THIS MORNING AND THE AFTN. WITH THE UPPER LVL TROUGH IN PLACE...A POTENT SHORTWAVE MOVES INTO WESTERN VA...WHICH WILL ACT AS THE TRIGGER FOR SNOW SHOWERS FOR THE WESTERN HALF OF THE CWA. AS IT MOVES OVER DELMARVA THIS EVENING...THE PCPN AREA WILL TRANSITION...LEADING TO DRYING OVER CENTRAL VA. WHILE THERE IS HIGHER CONFIDENCE FOR THE PCPN LOCATION/TIMING... THERE IS NOW LESS CONFIDENCE OF THE HIGHER QPF AMTS...AND THE SNOW POTENTIAL LEADING TO HIGHER SNOW AMTS. AS PREVIOUSLY MENTIONED... BACKED OFF OF SNOW TOTALS BETWEEN 1-3 INCHES FOR A COUPLE OF REASONS. THE PCPN WAS SLOW TO TRANSITION TO SNOW TONIGHT WITH A LACK OF HEAVIER BANDS SETTING UP. QPF TOTALS ON THE 00Z RUN ARE ALSO LOWER. A QUESTION THAT WE HAD BEEN DISCUSSING FOR THE PAST FEW DAYS WAS THE THERMAL PROFILES AND THE RESULTING PCPN. WHILE THERE IS PLENTY OF COLD AIR ALOFT...THE LOWEST LAYERS WERE STRUGGLING TO DROP BELOW FREEZING. HAD THERE BEEN HEAVIER PCPN... HAD THOUGHT WET BULBING WOULD OCCUR...TRANSITIONING TO THE RAIN TO SNOW. HOWEVER...TEMPS ARE STILL HOVERING IN THE MID TO UPPER 30S...AND EVEN DEW PTS ARE ABV FREEZING...SUGGESTING IT MAY STILL BE SOME TIME BEFORE MOST OF THE CWA CHANGES OVER. THINKING THIS SHOULD OCCUR BETWEEN 10-15Z AS WINDS BECOME MORE NLY...INJECTING IN LOWER DEW PTS. BUFKIT PROFILES SHOW BOTH WITH THE NAM AND GFS THAT SOUTHERN MD AND AREAS OF THE PIEDMONT MAY HAVE A SNOWFLAKE OR TWO...BUT NO ACCUM. MVG NORTH...CULPEPER TO DC AND SOUTH WILL BE NO MORE THAN AN INCH. THE HIGHEST AMTS ARE STILL THE NORTHEAST CORNER OF MD...TOPPING OFF UNDER 5 INCHES...BUT THESE MAY STILL BE OVERDONE...WITH 3-5 INCHES BEING MORE SPARSE THAN WIDESPREAD. ALSO TO NOTE...THAT WITH THE WARMER TEMPS...THE SNOW MAY FALL FOR A GOOD WHILE BEFORE ACTUALLY ACCUMULATING. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... HIGHER CONFIDENCE IN THE MIDDLE OF THE WEEK FORECAST AS THE FOCUS TURNS FROM PCPN THREAT AND MORE INTO THE MUCH COLDER TEMPS. WITH THE DEPARTING LOW...EXPECTING NW FLOW TO PERSIST THRU THIS TIME...KEEPING UPSLOPE SNOW SHOWERS IN THE FORECAST THRU THURSDAY. THE WINTER WX ADVISORY FOR THE ALLEGHENY FRONT IS IN EFFECT THRU THURS WITH BETWEEN 6 AND 10 INCHES PSBL FROM NOW TILL THEN. OUTSIDE OF THE UPSLOPE SNOW...AS THE UPPER LVL TROUGH PIVOTS EAST...ENOUGH ENERGY ALOFT COULD TRIGGER AN ISO SNOW SHOWER ALONG THE MASON-DIXON...THOUGH WITH THE MUCH DRIER AIRMASS IN PLACE...IT WILL BE DIFFICULT AND IT MAY END UP BEING MORE JUST FLURRIES. FOR THE TEMPS...WED WILL BE SLIGHTLY COOLER THAN TODAY...WITH THE FIRST SURGE OF CAA COMING IN DURING THE DAY...DROPPING LOWS WED NIGHT INTO THE SINGLE DIGITS AND TEENS. WIND CHILL ADVISORIES MAY BE NEEDED FOR THE ALLEGHENY FRONT WITH WIND CHILLS DROPPING TO BELOW -10 DEGREES. THE THREAT WILL BE PSBL AGAIN THURS NIGHT. && .LONG TERM /FRIDAY THROUGH MONDAY/... ARCTIC AIR WILL BE REINFORCED FRI-SAT BY ANOTHER DISTURBANCE WITHIN H5 TROF. GDNC SUGGESTING THAT THE LEADING EDGE WL TRACK NORTH OF THE AREA FRI...ALLOWING SHSN TO BE CAUGHT IN THE MTNS...FOLLOWED BY A GREATER PUSH LATE FRI NGT/ELY SAT MRNG. NW WINDS AND SGFNT CAA WL FOLLOW THAT. LTST GDNC SUGGESTING THAT MAXT SAT WL BE IN THE TEENS PTMC HIGHLANDS/20S ELSW. WIND CHILLS WILL BE A CONCERN THEN...AND WL ONLY BE AMPLIFIED SAT NGT AS TEMPS FALL INTO THE SINGLE DIGITS--EVEN IN THE CITIES OF DC/BALT. SUBZERO TEMPS FCST IN THE MTNS. WL HV A GRADUAL MODERATING TRENDS BY THE START OF THE NEW WEEK...PERHAPS WITH ANOTHER ROUND OF POTL PCPN. && .AVIATION /09Z TUESDAY THROUGH SATURDAY/... IFR/MVFR CIGS CURRENTLY BEING OBSERVED ACROSS THE TAF SITES WITH LIGHT RAIN IMPACTING ALL BUT KCHO. AS THE PCPN TRANSITIONS TO ALL SNOW...EXPECTING CIGS TO BECOME IFR OR LIFR AND VIS TO DIMINISH TO 1SM OR LESS. THE TIME FRAME FOR TRANSITIONING IS STILL LOW-MOD CONFIDENCE...GENERALLY 11-14Z. SNOW PERSISTS THIS MORNING BEFORE TRANSITIONING BACK TO RAIN AT KDCA AND RAIN/SNOW MIX AT KIAD/KBWI/KMTN. CIGS/VIS WILL IMPROVE TO MVFR THIS AFTN WITH THIS TRANSITION. SNOW AMTS WILL BE LESS THAN ONE INCH KCHO/KDCA...1-3 KIAD/KBWI...AND 2-4 KMRB/KMTN. THE PCPN WILL TAPER OFF COMPLETELY BY TONIGHT WITH VFR CONDITIONS THEN EXPECTED TONIGHT THRU THURSDAY. WINDS DURING THE TAF PERIOD WILL BE NE LESS THAN 10 KTS...BCMG NW AND INCRSG THIS AFTN...WITH GUSTS PSBL TONIGHT. GUSTY NW WINDS WILL CONTINUE WED-THURS. VFR MOST LKLY FRI-SAT. WINDS SAT CUD GUST NW 20-25 KT. && .MARINE... SUB-SCA CONDITIONS ON ALL WATERS THROUGH TODAY. INCRSG NW WINDS TONIGHT WILL PRODUCE OCNL SCA GUSTS ON THE CHESAPEAKE BAY...BCMG MORE PERSISTENT AND WIDESPREAD THURSDAY AND THURSDAY NIGHT. WINDS FRIDAY WL BE ON THE LGT SIDE...AS WE/LL BE IN A WK HIPRES RDG AHD OF ANOTHER TROF AXIS. THAT AXIS/REINFORCING FNT WL CROSS WATERS BEFORE SAT AM. SCA CONDS XPCTD DURING THE DAY...AND MOST LKLY LINGERING THRU THE NGT. && .TIDES/COASTAL FLOODING... WATER LEVELS SHOT UP TO 2.5 FEET ABOVE ASTRO NORMALS OVERNIGHT... WHICH IS SIGNIFICANTLY ABOVE ANY GUIDANCE FORECAST...EXCEPT PERHAPS CBOFS. ITS ON PACE TO EXCEED MINOR FLOOD THRESHOLDS AT JUST ABOUT ALL TIDE SITES ON THE WESTERN SHORE OF THE BAY. HAVRE DE GRACE WILL BE TOUGH TO ACHIEVE...BUT CORRELATIONS SUGGEST THAT MINOR FLOODING SHOULD OCCUR SOUTH OF THERE NEAR EDGEWOOD. THEREFORE...HV EXPANDED CF ADVISORY TO THE ENTIRE SHORELINE. HAVE ALSO ADDED CHARLES CO TO ACCOUNT FOR POTENTIAL EFFECTS ON/NEAR COBB ISLAND. PINEY POINT AND ANNAPOLIS MAY EACH COME CLOSE TO MDT /WRNG/ LVL...BUT WILL HOLD OFF FOR NOW. WINDS WILL GRADUALLY BE SWINGING AROUND TO THE NW THIS AFTN AND EVENTUALLY WEST TONIGHT. HOWEVER AM NOT SURE HOW STRONG THEY WILL BE...AND ITS THEREFORE IN DOUBT WHETHER THEY WILL HAVE A BLOWOUT EFFECT. IN ADDITION...THE PM TIDE CYCLE IS THE HIGHER OF THE TWO ASTRONOMICALLY...SO EVEN IF THERE IS A PINCH OF RELIEF...IT WILL BE COMPENSATED. FOR THAT REASON...HAVE EXTENDED THESE ADVISORIES FOR A 2ND TIDE CYCLE. LATEST HEC-RAS GUIDANCE SUGGESTS THAT MINOR THRESHOLD WILL BE ACHIEVED AT SW DC/ALEXANDRIA AS WELL. ITS UNCLEAR WHETHER THE BIG SLUG WILL MAKE IT ALL THE WAY UP. WASD2 SEEMS TO BE TRACKING WELL SO FAR...BUT THERE ARE THE FIRST INDICATIONS AT ALEXANDRIA THAT THE LOW TIDE WONT BE NEARLY AS LOW AS MODELED. THAT COULD PLAY INTO THE REST OF THE POTOMAC SHORELINE...WHICH IS SOMETHING THAT WILL BE MONITORED. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...COASTAL FLOOD ADVISORY UNTIL 10 AM EST THIS MORNING FOR DCZ001. MD...WINTER WEATHER ADVISORY UNTIL 6 PM EST WEDNESDAY FOR MDZ501. WINTER WEATHER ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR MDZ003>006-011-013-014-502>508. COASTAL FLOOD ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR MDZ011- 014-016>018-508. VA...WINTER WEATHER ADVISORY UNTIL 6 PM EST WEDNESDAY FOR VAZ503. WINTER WEATHER ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR VAZ027- 028-030-031-501-504>507. COASTAL FLOOD ADVISORY UNTIL 10 AM EST THIS MORNING FOR VAZ054. WV...WINTER WEATHER ADVISORY UNTIL 6 PM EST WEDNESDAY FOR WVZ501- 503-505. WINTER WEATHER ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR WVZ050>053-055-502-504-506. MARINE...SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO 6 AM EST WEDNESDAY FOR ANZ533-534-537-541-543. && $$ SYNOPSIS...SEARS NEAR TERM...SEARS SHORT TERM...SEARS LONG TERM...HTS AVIATION...SEARS/HTS MARINE...SEARS/HTS TIDES/COASTAL FLOODING...HTS

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