Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 180222 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 922 PM EST WED DEC 17 2014 .SYNOPSIS... HIGH PRESSURE WILL BUILD INTO THE AREA THROUGH THURSDAY AND PERSIST THROUGH FRIDAY NIGHT..EXCEPT FOR A WEAK DISTURBANCE THAT WILL CROSS THE AREA THURSDAY NIGHT. LOW PRESSURE WILL TRACK SOUTH OF THE AREA SATURDAY THROUGH SUNDAY. A SECONDARY LOW IS EXPECTED TO MOVE UP FROM THE SOUTHEAST COAST EARLY NEXT WEEK. A LARGE AREA OF LOW PRESSURE LOOKS TO DEVELOP IN THE OHIO VALLEY DURING THE MIDDLE OF NEXT WEEK. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... AS OF 02Z...999MB SFC LOW OVER SRN NOVA SCOTIA AND 1031MB SFC HIGH OVER FAR WRN ONTARIO. 4MB SFC PRESSURE GRADIENT PERSISTS ACROSS THE CWA...ALLOWING OCCASIONAL 20 MPH NW GUSTS. MIXING PERSISTS OVER NIGHT...SO MINS LIMITED IN SPITE OF RATHER CLEAR CONDITIONS SOUTH OF THE FIRST TIER OF COUNTIES FROM THE MASON-DIXON LINE. WILL RAISE MIN TEMPS A COUPLE DEGREES FOR ALL BUT SHELTERED VALLEYS. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/... SUNNY START TO THURSDAY WITH MID-LEVEL TROUGH ENTERING THE AREA IN THE AFTERNOON. COULD SQUEEZE OUT SOME SNOW FLAKES FOR THE ALLEGHENIES...BUT JUST HIGHER CLOUDS ELSEWHERE. DOWNSLOPING WLY FLOW WITH GUSTS TO AROUND 20 MPH...BUT COLDER AIR MASS IN PLACE...ONLY MID 40S FOR MAX TEMPS AT LOWER ELEVATIONS. && .LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/... VERTICALLY STACKED LOW PRESSURE WILL DRIFT TOWARD NEWFOUNDLAND THURSDAY NIGHT WHILE HIGH PRESSURE BUILDS ACROSS THE GREAT LAKES. A DAMPENING SHORTWAVE WILL APPROACH IN THE FAST SOUTHERN STREAM. DESPITE A FEW MODELS TRYING TO PRODUCE QPF IN UPSLOPE AREAS...THINK THE MOISTURE PROFILES ONLY SUPPORT AN INCREASE IN MID LEVEL CLOUDS. GOOD GUIDANCE AGREEMENT WITH TEMPERATURES RANGING FROM THE MID 20S IN THE MOUNTAINS TO LOWER 30S METROS/EAST. DRY AND TRANQUIL WEATHER FOR FRIDAY AND FRIDAY NIGHT AS THE SURFACE RIDGE BUILDS IN FULLY. HOWEVER...LOW LEVEL WINDS TAKE ON A BIT MORE OF A NW DIRECTION BEHIND THE DEPARTING TROUGH...LEADING TO WEAK CAA. HIGHS GENERALLY IN THE 40S. HIGH/MID CLOUDS INCREASE FRIDAY NIGHT AHEAD OF THE APPROACHING SOUTHERN STREAM SYSTEM. SPEED/THICKNESS OF CLOUDS MAY DETERMINE HOW LOW TEMPS DROP SINCE DEW POINTS REMAIN LOW WITH LIGHT WINDS. TRENDED TOWARD SLIGHTLY WARMER GFS/ECMWF RAW TEMPS WITH LOWS NEAR OR JUST BELOW FREEZING. MODELS CONTINUE TO TREND DOWN THE INTENSITY OF LOW PRESSURE AFFECTING THE MID-ATLANTIC OVER THE WEEKEND AND TAKE THE HIGHEST QPF OVER THE CAROLINAS. IN THE LAST 3 DAYS GUIDANCE HAS TAKEN THE SYSTEM FROM A POTENT CLOSED LOW OFF NORFOLK AT 06Z SUNDAY TO AN OPEN WAVE WITH THE MAJORITY OF ITS ENERGY WELL TO OUR SOUTH. CONFIDENCE IS GROWING IN THE CURRENT SOLUTION THAT THE MAJORITY OF PRECIP WITH THE SYSTEM...OUTSIDE OF THE HIGHER ELEVATIONS...SHOULD BE RAIN...AND QPF WILL BE FAIRLY LOW OVER THE HIGHER ELEVATIONS WHERE THE TEMPS ARE LOWEST. ANY ACCUMULATIONS SHOULD BE FOCUSED ALONG AND WEST OF THE BLUE RIDGE...THOUGH THERE IS STILL THE POSSIBILITY FOR MUCH OF THE AREA TO SEE AT LEAST A COUPLE SNOW FLAKES. PRECIP SHOULD BE OUT OF THE AREA BY MIDDAY SUNDAY. HIGH PRESSURE WILL BUILD IN SUNDAY EVENING THROUGH MIDDAY MONDAY. A LARGE UPPER LEVEL TROUGH DEVELOPING OVER THE CENTRAL CONUS MONDAY WILL KEEP WEATHER ACTIVE THROUGH THE MIDDLE OF NEXT WORKWEEK. BROAD SURFACE LOW PRESSURE PROGRESSING ACROSS THE NORTHERN GREAT PLAINS COULD HELP LIFT A STALLED COASTAL FRONT ACROSS THE AREA AS A WARM FRONT SOMETIME MONDAY NIGHT OR TUESDAY. HAVE INCLUDED LOW END CHANCE POPS IN THIS TIME FRAME TO ACCOUNT FOR THIS. A WAVE OF LOW PRESSURE MAY THEN FORM WITHIN THE COLD FRONT OF THE LARGER PARENT LOW AND MOVE THROUGH OUR AREA TUESDAY NIGHT AND WEDNESDAY BRINGING HIGH END CHANCE POPS INTO THE FORECAST. EARLY IMPRESSIONS ARE THAT P-TYPE WILL BE LARGELY ELEVATION DEPENDENT WILL LOWER ELEVATIONS MOSTLY SEEING RAIN. OVERALL CONFIDENCE IS LOW IN THE TIMING AND DETAILS OF THIS SYSTEM. TEMPS SHOULD REMAIN AROUND NORMAL THROUGH THE LONG TERM WITH THE EXCEPTION OF TUESDAY NIGHT AND WEDNESDAY/POST WARM FRONT...WHEN TEMPS WILL BE 5 TO 10 DEGREES ABOVE NORMAL. && .AVIATION /02Z THURSDAY THROUGH MONDAY/... VFR CONDS XPCTD THROUGH FRIDAY NIGHT. NW GUSTS TO AROUND 20 KT ON OCCASION TONIGHT AND MORE FREQUENTLY THURSDAY. FLOW WEAKENS A BIT BUT REMAINS NWLY WITH PRESSURE GRADIENT THURSDAY NIGHT AND FRIDAY. MVFR AND IFR CONDITIONS ARE POSSIBLE IN SHOWERS AS A WAVE OF LOW PRESSURE PASSES WELL TO OUR SOUTH SATURDAY NIGHT AND SUNDAY MORNING. && .MARINE... NWLY 18 TO 20 KT SURGE CURRENTLY CROSSING THE WATERS LATE THIS EVENING...WITH GUSTS RETURNING TO SRN MD WATERS EXPECTED FOR THE FIRST TIME IN SEVERAL HOURS. SCA FOR ALL THE WATERS INTO THURSDAY AFTERNOON. WINDS WILL DIMINISH THURSDAY EVENING. NW WIND GUSTS THURSDAY AFTERNOON WILL BE MARGINAL FOR A SCA...BUT ONE MAY BE NEEDED FOR PORTIONS OF THE WATERS DEPENDING ON THE EFFICIENCY OF ATMOSPHERIC MIXING. LIGHT WINDS FRIDAY NIGHT. CONFIDENCE IS LOW IN THE OCCURRENCE OF ANY MARINE HAZARDS IN THE LONG TERM. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EST THURSDAY FOR ANZ530>534- 537>543. SMALL CRAFT ADVISORY UNTIL 1 PM EST THURSDAY FOR ANZ535-536. && $$ UPDATE...JACKSON PREVIOUS...WOODY!/ADS/CEB

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