Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 271427 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 1027 AM EDT MON APR 27 2015 .SYNOPSIS... AN UPPER LEVEL TROUGH TO THE NORTH WILL MOVE THROUGH THE AREA TODAY. HIGH PRESSURE WILL MOVE INTO THE AREA TUESDAY. LOW PRESSURE IS EXPECTED TO TRACK ACROSS THE SOUTHEASTERN U.S. DURING THE SECOND HALF OF THE WEEK. && .NEAR TERM /THROUGH TONIGHT/... UPPER LVL LOW REMAINS POSITIONED OVER CANADIAN MARITIMES...EXTENDING WEST INTO THE GREAT LAKES AND SOUTH ACROSS THE MID ATLANTIC. EMBEDDED SHORTWAVE ROUNDING THE LOW IS BRINGING INCREASED CLOUD COVER THIS MORNING ALONG THE MASON-DIXON. CLOUDS WILL SPREAD TO THE SOUTH AND EAST THROUGH THIS AFTN. TEMPS HAVE WARMED QUICKLY THIS MORNING OUTSIDE THE CLOUDY REGION...THOUGH STILL EXPECTING HIGHS INTO THE UPPER 50S-MID 60S WITH THE INCREASING CLOUD COVER THIS AFTN. SHORTWAVE CURRENTLY OVER THE GREAT LAKES AS NOTED ON 14Z WATER VAPOR IMAGERY WILL DIVE SOUTH THIS AFTN. THIS FORCING COMBININGWITH WEAK INSTABILITY COULD RESULT IN ISO-SCT RAIN SHOWERS. ANY SHOWER WILL BE LIGHT IN NATURE. COULD SEE LIGHT SNOW MIXING IN AT THE HIGHEST ELEVATIONS OF THE POTOMAC HIGHLANDS THIS EVENING BEFORE THE PCPN TAPERS OFF. AS HAS FRQNTLY BEEN THE CASE LATELY TEMPS XPCTD TO BE BLO NRML. W/ THE CENTRAL SHEN VLLY BEING THE LAST TO CLD OVR TEMPS SHOULD RISE TO THE M60S...BUT MUCH OF THE RMDR OF THE FCST AREA WL TOP OUT IN THE U50S/L60S. && .SHORT TERM /TUESDAY/... THE SYNOPTIC PTTN IS GOING TO BE SLOW TO CHG THRU TUE: THE AFOREMENTIONED UPR LOW LOOKS TO SPIN SLOWLY OUT TO SEA. HIGH PRES WL WORK ITS WAY INTO THE MID ATLC DURG TUE. LOWS TNGT WL BE IN THE L40S. W/ MORE INSOLATION TUE TEMPS SHOULD CLIMB BACK INTO THE U60S - STILL A FEW DEGS BLO NRML. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... AN ACTIVE AND COMPLEX STORM SYSTEM APPROACHING FROM THE GULF COAST REGION IS CERTAIN FOR THE SECOND HALF OF THE WORK WEEK. MODEL DIVERGENCE FOR THE SYSTEM AS IT NEARS THE AREA TOWARD MID WEEK ADDS UNCERTAINTY. THE 00Z VERSION OF THE ECM KEEPS A MORE SRN-STREAM SYSTEM AND KEEPS IT AS MORE OF AN OPEN WAVE UPON ARRIVING OVER THE ATLC COAST WED INTO THU. INSTEAD OF AN INTENSIFICATION OF THE SYSTEM FROM A BACK SIDE UPPER VORT DIVING DOWN FROM THE GREAT LAKES REGION...IT PUSHES THE SYSTEM OFF THE COAST. THE GFS HOWEVER HAS QUITE THE AGGRESSIVE DEPICTION IN ITS 00Z RUN...TAKING A DEEPENING UPPER CUT OFF LOW OVER THE OHIO VLY AND SLIDING IT INTO THE BACK SIDE OF THE PRECIP SHIELD OVER THE CAROLINAS AT ABOUT THE SAME TIME. THE ADDITION OF THIS POTENT UPPER VORT DIVING DOWN OUT OF SRN CANADA ADDS THE ENERGY THE SYSTEM WOULD NEED TO DO AN INTENSE PHASING...SIMILAR TO SYSTEM IN THE MIDDLE OF WINTER OVER THE MID- ATLC. THIS AGGRESSIVE SOLN BRINGS AN INTENSE SFC LOW HUGGING THE DELMARVA COAST LATE THU INTO FRI. GUSTY WINDS OVER THE BAY AND A COLD RAIN OVER THE REST OF THE MID-ATLC. RAISED POPS INTO THE MED CHANCE CATEGORIES FROM LATE WED INTO EARLY FRI...BUT STILL NOT CONFIDENT IN GFS SOLN W/ THE INTENSITY/DURATION AND ALL THE PROPER FACTORS COMING TOGETHER FOR SUCH AN INTENSE STORM SYSTEM. BLENDED SOME OF THE BIAS-CORRECTED VALUES AND LEANED ON THE EURO IN A LONG- TERM BLEND OF VARIOUS WX ELEMENTS FOR THIS TIME PERIOD. WILL MONITOR TRENDS. THE MORE AGGRESSIVE AND RECENT GFS RUN KEEPS THE SYSTEM OVER THE AREA FOR MUCH OF THE DAY FRI WHILE THE EURO HAS A BULK OF THE FEATURE WELL OFF THE COAST BY THEN. EITHER WAY...A MULTI-DAY PERIOD OF HIGH PRESSURE WILL RETURN FROM THE WEEKEND AND LIKELY INTO EARLY NEXT WEEK. && .AVIATION /14Z MONDAY THROUGH FRIDAY/... VFR CONDITIONS THRU THE TAF PERIOD. BRIEF RAIN SHOWER PSBL THIS AFTN...MAINLY 19-22Z...WITH MINIMAL CATEGORICAL IMPACTS. NW WINDS INCREASING WITH GUSTS MIXING IN BETWEEN 15-17Z. GUSTS END TIME 22-00Z THIS EVENING. LOW CONFIDENCE IN THE POSSIBLE EFFECTS OF A LOW PRESSURE SYSTEM THAT WILL APPROACH THE AREA DURING THE MIDDLE OF THE WEEK. POSSIBLY A COUPLE OF DAYS OF RAIN AND GUSTY WINDS...BUT A LESS INTENSE SOLN WOULD BE FOR THE SYSTEM TO PASS JUST SOUTH OF THE AREA AND SLIDE OFF THE ATLC COAST. && .MARINE... SCA HAS BEEN XTND FOR THE MAJORITY OF THE WATERS THRU TUE. LOW PRES IN THE GULF OF ME TDA WL TRACK SLOWLY E...BUT W/ HIGH PRES MOVG INTO THE RGN TUE THE PRES GRAD WL RMN IN PLACE AND G20 XPCTD THRU MID AFTN TUE. A POTENT LOW PRESSURE SYSTEM OVER THE DEEP SOUTH EARLY THIS WEEK WILL HAVE THE POTENTIAL TO BRING SMALL CRAFT AND POSSIBLY GALE CONDITIONS TO THE WATERS FROM LATE WED INTO FRI. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 4 PM EDT TUESDAY FOR ANZ530>534- 537>543. SMALL CRAFT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR ANZ535- 536. && $$

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