Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 280800 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 400 AM EDT SAT MAR 28 2015 .SYNOPSIS... AN UPPER-LEVEL TROUGH WILL MOVE ACROSS THE EASTERN UNITED STATES TODAY AND TONIGHT. HIGH PRESSURE WILL BUILD OVERHEAD ON SUNDAY. A SERIES OF WEAK SYSTEMS WILL AFFECT THE AREA THROUGHOUT THE UPCOMING WORK WEEK. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... WATER VAPOR IMAGERY SHOWS A DEEPENING TROUGH OVER THE EASTERN CONUS THIS MORNING WITH CONNECTIONS TO GREENLAND. A FRONT WITH DEVELOPING LOW PRESSURE IS OFFSHORE...WHILE A SECONDARY ARCTIC FRONT IS PUSHING INTO THE AREA AHEAD OF THE UPPER TROUGH AXIS...NOTABLE IN THE DEW POINT GRADIENT OVER THE REGION. SOME LIFT HAS BROUGHT VERY LIGHT PRECIP TO CENTRAL VA...WHICH SHOULD CONTINUE TO DRIFT SE. BASED ON REGIONAL RADAR AND OBS IN WV/PA...THE POTOMAC HIGHLANDS HAVE THE BEST CHANCE AT ACCUMULATING SNOWFALL THROUGH DAYBREAK...ALTHOUGH THE BEST RETURNS HAVE LIKELY ALREADY OCCURRED. AREAS NEAR THE PA BORDER MAY ALSO SEE A FLURRY. BASED ON THE LATEST TRENDS IN HI-RES GUIDANCE AND PROJECTED FORCING MECHANISMS...MADE SOME MINOR ADJUSTMENTS TO THE POPS THROUGH TODAY. WHILE ROGUE FLURRIES ARE POSSIBLE JUST ABOUT ANYWHERE AT ANYTIME...MAIN CHANCES WILL TAKE PLACE ONCE CONVECTIVE MIXING OCCURS. EVEN THEN...THINK A COMPACT VORT MAX WITHIN THE TROUGH AXIS MAY BE THE MAIN PLAYER IN PRODUCING SHOWERS. THIS IS FORECAST TO SKIRT INTO NORTHERN MD DURING THE MIDDAY/AFTERNOON HOURS. COVERAGE IS STILL EXPECTED TO BE SCATTERED AT BEST SO HAVE MAINTAINED THE CHANCE POPS...BUT TAPERED THEM OFF LATER IN THE AFTERNOON. DEPENDING ON NEAR-SFC TEMPS AND THE INTENSITY OF THE SHOWERS...RAIN...SNOW...AND GRAUPEL COULD OCCUR (MORE LIKELY THE LATTER TWO IN THE FAVORED AREA). DESPITE GOOD MIXING...DOWNSLOPE FLOW AND AT LEAST SOME BREAKS OF SUN...HIGHS WILL BE LIMITED BY 850 MB TEMPS BELOW -10C. ONLY MINOR TWEAKS TO GOING FORECAST...WITH 40S IN PIEDMONT/COASTAL AREA...30S WEST...AND BELOW FREEZING AT HIGHER ELEVATIONS. WIND GUSTS UP TO 30 MPH WILL ADD A BITE TO THE AIR. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/... MID/UPPER TROUGH AXIS BEGINS TO SLIDE EAST TONIGHT AS SFC HIGH PRESSURE BUILDS INTO THE OHIO VALLEY...ALLOWING SKIES TO CLEAR. GRADIENT WILL PREVENT WINDS FROM DIMINISHING...BUT THE AIR WILL BE DRY AND ANOMALOUSLY COLD. ALL LOCATIONS EXPECTED TO DROP BELOW 30F...WITH TEENS WEST OF THE BLUE RIDGE AND PERHAPS SOME SINGLE DIGITS ON THE RIDGETOPS. SEE CLIMATE SECTION BELOW FOR RECORDS. THE SFC HIGH WILL QUICKLY DRIFT SE ACROSS THE AREA SUNDAY AS THE NEXT UPPER TROUGH PUSHES INTO THE UPPER MS VALLEY. SKIES WILL BE MAINLY SUNNY BUT RETURN FLOW WILL BE MODEST AND TEMPS WILL REMAIN BELOW NORMAL. EXPECT HIGHS IN THE UPPER 40S TO LOWER 50S. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... AN UPPER TROUGH...NOT NEARLY AS AMPLIFIED OR STRONG AS THE CURRENT ONE...WILL CLIP ACROSS THE REGION SUNDAY NIGHT INTO MONDAY...SENDING AN ASSOCIATED COLD FRONT THROUGH THE REGION. MOISTURE RETURN IS LIMITED AND H8/H9 FLOW QUICKLY SHIFTS TO WESTERLY EVEN AHEAD OF THE FRONT. THE OPERATIONAL SUITE OF MODELS IS QUITE DRY EAST OF THE ALLEGHENY FRONT...BUT ENSEMBLE DATA HINTS AT A BRIEF WINDOW OF LIGHT PRECIPITATION OVERNIGHT FURTHER EAST. KEPT MENTION IN GENERALLY ALONG/WEST OF THE BLUE RIDGE...AND SOME LIGHT SNOW IS POSSIBLE IN THE COLD POCKETS. DESPITE FROPA...THE WESTERLY WINDS WILL PROMOTE QUICK WARMING ON MONDAY...WITH HIGHS SOARING INTO THE 60S EAST OF THE BLUE RIDGE AND PERHAPS CLOSE TO 70 IN THE PIEDMONT. A SECOND SHORTWAVE WILL PASS MAINLY TO THE NORTH ON TUESDAY. MOST LIKELY THE PRECIPITATION STAYS NORTH OF THE MASON-DIXON LINE BUT I DID KEEP SLIGHT CHANCES IN ALMOST THE ENTIRE FORECAST AREA ON TUESDAY AND ROUGHLY NORTH OF US 48/50 ON TUESDAY NIGHT. HIGH PRESSURE QUICKLY SHIFTS OFFSHORE BY WEDNESDAY AFTERNOON WITH RETURN FLOW COMMENCING AND WARM MOIST AIR QUICKLY SPREADING NORTH FOR THE END OF THE WORK WEEK. A WEAK SOUTHERN STREAM IMPULSE IS EXPECTED TO PASS ACROSS THE CAROLINAS AND MID-ATLANTIC ON THURSDAY...WITH SCATTERED SHOWERS AND PERHAPS A THUNDERSTORM. HIGHS NEAR 70 ARE LIKELY IN VALLEYS WEST AND SOUTH OF DC. MODEL SOLUTIONS DIVERGE BEYOND THURSDAY...WITH THE 00Z GFS PUSHING A COLD FRONT THROUGH ON FRIDAY. THE ECMWF IS SLOWER...AND IN THESE SCENARIOS I TEND TO FAVOR A SLOWER SOLUTION RATHER THAN BARRELING A FRONT THROUGH. SO FRIDAY WAS KEPT SEASONABLY WARM WITH RAIN CHANCES. && .AVIATION /08Z SATURDAY THROUGH WEDNESDAY/... VFR CONDITIONS WILL PREVAIL THROUGH THE TAF PERIOD. THE ONLY EXCEPTION COULD BE A CHANCE OF SHOWERS TODAY. THESE COULD CONTAIN A MIXTURE OF RA/SN AND GRAUPEL. HOWEVER DUE TO ISOLATED/SCATTERED NATURE...PROBABILITY OF REDUCED CONDITIONS AT A TERMINAL IS LOW. THE MOST FAVORED LOCATIONS MAY BE BWI/MTN FROM THE MIDDAY INTO EARLY AFTERNOON HOURS. CAN/T RULE OUT STRAY FLURRIES AT OTHER TIMES...BUT LITTLE TO NO IMPACTS. NW WINDS WILL BE SUSTAINED GREATER THAN 10 KT. SPORADIC GUSTS THROUGH DAYBREAK...BECOMING COMMON UP TO 25 KT DURING THE DAYLIGHT HOURS. WINDS ONLY GRADUALLY DIMINISH TONIGHT. VFR SUNDAY WITH WINDS BECOMING LIGHT AND SOUTHERLY BY LATE AFTERNOON. LOW CIGS POSSIBLE SUNDAY NIGHT AHEAD OF A COLD FRONT. ONCE THAT FRONT PASSES...GUSTY WEST WINDS UP TO 30 KTS ARE POSSIBLE MONDAY AFTERNOON. SHRA ARE POSSIBLE ON TUESDAY AND TUESDAY NIGHT...BUT SHOULD REMAIN LIGHT SO RESTRICTIONS TO VSBY/LOW CIGS ARE NOT LIKELY. && .MARINE... OCCASIONAL TO FREQUENT GUST OF 20 KT OR GREATER THIS MORNING ON ALL WATERS AS SECONDARY ARCTIC FRONT SURGES INTO THE AREA. EXPECT THESE GUST TO BECOME EVEN MORE COMMONPLACE AFTER THE SUN RISES. MIXED LAYER WINDS REMAIN BELOW 30 KT...SO THAT SHOULD REPRESENT AN UPPER LIMIT TO GUSTS. SCATTERED RAIN/SNOW SHOWERS POSSIBLE OVER THE NORTHERN BAY TOWARD THE MIDDAY HOURS. HIGH PRESSURE BEGINS TO BUILD IN TONIGHT BUT WILL REMAIN TO THE WEST...ALLOWING SCA CONDITIONS TO CONTINUE. WINDS WILL DIMINISH SOME ON SUNDAY...BUT LAST VESTIGES OF NORTHERLY WINDS WILL ALLOW SCA LEVEL GUSTS TO CONTINUE ON THE MAIN STEM OF THE BAY THROUGH THE MORNING. SOUTHERLY CHANNELING AHEAD OF A COLD FRONT WILL RAISE THE POTENTIAL FOR GUSTS ABOVE SMALL CRAFT ADVISORY CRITERIA SUNDAY NIGHT...MAINLY AFTER MIDNIGHT. ONCE THE FRONT PASSES...WINDS TURN OUT OF THE WEST BUT BECOME STRONGER AND GUSTIER WITH WINDS/GUSTS SOLIDLY ABOVE SCA LEVELS. CARRYING SOME GUSTS IN THE UPPER BAY OVER 30 KTS...SO WILL NEED TO WATCH FOR GALE POTENTIAL ON MONDAY. WINDS BEGIN TO SETTLE BY TUESDAY MORNING AS HIGH PRESSURE BRIEFLY BUILDS IN. && .CLIMATE... TEMPERATURES SUNDAY MORNING MAY APPROACH THE RECORD LOWS FOR THE DATE. CURRENTLY THE FORECAST LOWS ARE ABOVE THESE RECORDS. HOWEVER...IF THE LOW DROPS TO 21 OR LESS AT DULLES IT WOULD BE THE COLDEST SO LATE IN THE SEASON SINCE 1987...AND IF THE LOW DROPS TO 24 OR LESS AT BWI IT WOULD BE THE COLDEST SO LATE IN THE SEASON SINCE 1985. SITE...3/29 RECORD MIN T... DCA......18 (1923)......... BWI......18 (1923)......... IAD......20 (1982)......... && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EDT SUNDAY FOR ANZ530>543. && $$ SYNOPSIS...JE NEAR TERM...ADS SHORT TERM...ADS LONG TERM...JE AVIATION...ADS/JE MARINE...ADS/JE CLIMATE...DFH/JE

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