Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 231507 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 1007 AM EST SUN NOV 23 2014 .SYNOPSIS... HIGH PRESSURE EAST OF CAPE HATTERAS WILL CONTINUE TO DRIFT OFFSHORE. A WARM FRONT WILL PUSH NORTH THROUGH THE AREA TONIGHT. LOW PRESSURE INTENSIFYING OVER THE GREAT LAKES WILL BRING AN ASSOCIATED COLD FRONT THROUGH THE MID ATLANTIC MONDAY EVENING. LOW PRESSURE IS EXPECTED TO TRACK NORTHEAST OFF THE COAST WEDNESDAY. HIGH PRESSURE WILL RETURN FOR THURSDAY AND FRIDAY. && .NEAR TERM /THIS AFTERNOON/... THE AREA OF HIGH PRES OFF NERN N CAROLINA HAS DONE A VALIANT JOB OF HOLDING THE AREA OF RA AT BAY AS IT ATTEMPTS TO PROGRESS N. BUT THE HIGH WL BE MOVG OUT TO SEA...AND MID ATLC CAN EXPECT TO SEE INCRSG CLDS THIS AFTN. A FAIRLY COMFORTABLE LATE NOV AFTN - HIGHS XPCTD TO REACH THE M50S OVR MUCH OF THE AREA. IT IS INTERESTING TO LOOK AT THE PWATS FM THE 12Z IAD SNDGS OVR THE PAST 3 DAYS: FRI 0.11" SAT 0.17" SUN 0.57". AFTR THE COLD MRNG FRI 24 HR TEMP CHGS OF THE ATOMOSPHERE HV SHOWN LARGE INCREASES THE PAST 2 MRNGS. THERE ARE TWO RGNS OF S/WV ENERGY IN THE SRN STREAM... ONE MVG ONSHORE INVOF NWRN FL AND A HEALTHY VORT EMERGING INTO THE GLFMEX FM CSTL TX. AS THESE S/WVS LIFT/DIG...H5 FLOW PTTN WL BECOME MORE AMPLIFIED. THAT WL ALLOW A WMFNT TO APPRCH THE CWFA TDA. FOR THE FIRST PD...AM CONFINING LKLY POPS TO SWRN CWFA...GNLY SHD SWD. GFS/ECMWF HV A BETTER HANDLE THAN NAM ON EVOLUTION... AS EVIDENCED BY COOL BIAS IN YDA FCST. && .SHORT TERM /TONIGHT THROUGH 6 PM MONDAY/... WMFNT WL LIFT ACRS CWFA TNGT...AIDED BY 60-70 KT LLJ BRINGING PWAT VALUES UP TO ARND 1.5 IN. THUS...CAT POPS AREAWIDE FOR MOST OF THE NGT...REACHING METRO BALT BY MID EVNG AND ENDING IN THE MTNS PRE-DAWN. AM XPCTG A PD OF MDT RAFL IN THE MIDDLE OF THIS TIMEFRAME...SPCLY FOR THE BLURDG EWD...WHICH WL HV THE ASSISTANCE OF THE RDG LINE FOR ENHANCED LIFT. STORM TTL QPF BTWN 0.50-1.00 INCH... BUT LOCALLY HIER CERTAINLY PSBL. CANT RULE OUT A RUMBLE OF THUNDER EITHER GIVEN SHEAR AND MODEST INSTBY /BEST LI SUBZERO SRN MD 06-09Z/. HV CONFINED SCHC SE OF I-95 FOR JUST A CPL HRS AFTR MIDNGT. THE WNDS WL CAUSE ANOTHER ISSUE FOR THE HILLS...AS THE JET MAY BE DOWN AS LOW AS 1500-2000 FT. HWVR...MIXING SHUD BE RATHER POOR. CONFIDENCE IN POSITION/HGT/STRENGTH FOR THE JET PRECLUDE AN ADVY ATTM...HWVR THE THREAT ADEQUATE ENUF TO JUSTIFY INCLUSION IN HWO. THE WMFNT SHUD LIFT N OF CWFA BY DAYBREAK...TAKING ANY PCPN ACRS THE DELMARVA. HV KEPT A CHC OF PCPN INTO MID-MRNG TO ACCT FOR ANY TIMING DIFFS. OTRW...THERE/S NOT A LOT OF FORCING FOR SVRL HRS TIL THE ATTENDENT CDFNT ARRIVES. THEREFORE...HV WHITTLED OUT A BREEZY BUT DRY PD DURING THE MIDDAY. EVEN WHEN THE CDFNT DOES MAKE IT HERE /LATE DAY/...THERES BAROCLINICITY BUT VIRTUALLY NO ULVL FORCING. AM KEEPING ACCOMPANYING POPS IN THE 20-30 PCT RANGE. H8 TEMPS PEAK ARND 14C AT 12Z MON MRNG. THEREFORE...WUDNT BE SURPRISED TO SEE MIN-T BE LESS THAN DIURNAL. HV TAKEN THE WARMER END OF MOS TO COMPOSE MIN-T GRID...MID 40S TO LWR 50S. HV SIDED SIMILARLY WARM FOR MAXT MON. TEMPS 70+ SHUD PREVAIL E OF THE BLURDG MON. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... A COLD FRONT WILL RAPIDLY SWING THROUGH THE AREA MONDAY NIGHT... USHERING IN A DRYING WEST WIND...BUT STILL SOME UPSLOPE SHOWERS... PROBABLY MAINLY IN THE FORM OF RAIN GIVEN THE WARM STARTING CONDITIONS. IF THE UPSLOPE OPPORTUNITY LINGERS LATER INTO THE NIGHT...A FEW SNOW SHOWERS WILL BE POSSIBLE. DESPITE A PARTLY CLOUDY SKY...TEMPERATURES WILL NOT REBOUND MUCH ON TUESDAY...REACHING JUST THE UPPER 40S/LOWER 50S. THE ALLEGHENY FRONT REMAINS IN THE 30S ALL DAY DUE TO MORE CLOUD COVER. HOWEVER...EVERY DAY AFTER TUESDAY THIS WEEK WILL BE EVEN COLDER. THE COLD FRONT THAT MOVES THROUGH MONDAY NIGHT WILL GET HELD UP IN THE WESTERN ATLANTIC BY A STRONG UPPER RIDGE AND ASSOCIATED SFC HIGH. MODELS THEN INDICATE DEVELOPMENT OF LOW PRESSURE ALONG THE FRONT AS UPPER ENERGY DIGS INTO THE DEEP SOUTH. FROM THERE...UNCERTAINTY RAPIDLY INCREASES. DEPENDING ON HOW CLOSE THE LOW IS TO THE COAST...PART OR ALL OF THE AREA WILL SEE PRECIPITATION SPREAD IN TUESDAY NIGHT AND CONTINUE THROUGH WEDNESDAY. AND OF COURSE...SFC TEMPS ARE RIGHT AROUND FREEZING PART OF THE TIME...AND POTENTIAL SOLUTIONS ALOFT RUN A WIDE RANGE. THERE ARE TIMING DIFFERENCES ON TOP OF ALL OF THAT TOO. WPC NOTES...AS DO WE...THAT THE DIFFERENCES HAVE A LINK TO AN UPSTREAM CLIPPER SYSTEM AND HOW IT PLAYS INTO THE MOTION/EVOLUTION OF THE COASTAL STORM. THE BOTTOM LINE IS THAT ALL SOLUTIONS ARE STILL ON THE TABLE...FROM NOT MUCH OF ANYTHING TO ACCUMULATING SNOW. THE CURRENT FORECAST HAS A GENERIC RAIN-OR-SNOW MENTION BUT WITH INCREASED POPS. LATER TODAY...OUR PROBABILISTIC SNOW FORECASTS WILL GO THROUGH THIS TIMEFRAME...SO WE WILL AT LEAST HAVE A GOALPOST AND PROBABILISTIC REFERENCES OF CERTAINTY THEN. THE SYSTEM WILL QUICKLY PULL AWAY...LEAVING A SMALL CHANCE FOR LIGHT SNOW OR FLURRIES WEDNESDAY NIGHT. WESTERLIES BEHIND THE SYSTEM WILL FAVOR UPSLOPE SNOW ON THE ALLEGHENY FRONT FOR THANKSGIVING DAY...BUT THE AFOREMENTIONED UNCERTAINTIES KEEP THINGS TRICKY ELSEWHERE. IF UPPER ENERGY DIGS FURTHER SOUTH...A FEW LIGHT SHOWERS /PROBABLY RAIN GIVEN A BIT OF A WARMUP/ WOULD BE POSSIBLE JUST ABOUT ANYWHERE WITH THE CLIPPER PASSAGE. AFTER THAT...HIGH PRESSURE FINALLY BUILDS IN AND THINGS ARE QUIET...BUT COLD...FOR THE REST OF THE HOLIDAY WEEKEND. SOME OF THE GUIDANCE HINTS AT YET ANOTHER CLIPPER FRIDAY NIGHT AND EARLY SATURDAY. FOR NOW...I DID NOT PUT ANY PRECIP EAST OF THE ALLEGHENY FRONT...BUT I DID BRING IN ANOTHER PERIOD OF UPSLOPE SNOW OUT WEST. HIGHS ARE EXPECTED TO BE IN THE 30S AND 40S...WITH LOWS IN THE 20S. && .AVIATION /15Z SUNDAY THROUGH THURSDAY/... VFR CONDS ACRS TERMINALS TDA. PCPN /LGT-MDT RA/ SHUD ENVELOP AREA BY LT AFTN/EVE PUSH...PROGRESSING FM SW TO NE-- 21-23Z CHO TO 02-04Z BWI/MTN. FLGT CONDS SHUD RAPIDLY DECLINE THRU MVFR TO IFR. XPCT IFR CONDS OVNGT INTO THE BGNG OF MON MRNG PUSH...BEFORE GRDL IMPRVMNT COMES. VFR SHUD RTN BY NOON MON. WNDS WL ALSO BE A CONCERN...AS A 60-70 KT LOW LVL JET WL RESIDE AS LOW AS 2K FT. THESE CONDS SUFFICIENT TO TRIGGER LLWS MENTION FOR ALL TAFS ELY MON MRNG. THINK SHEAR SHUD LESSEN BY SUNRISE MON. HWVR... 15-20 KT SUSTAINED SSWLY WNDS WL REMAIN THRU MOST OF DAY MON BEFORE VEERING LT IN THE DAY. WINDS BECOME LIGHT AND SHIFT FROM WESTERLY TO NORTHERLY TUESDAY AFTERNOON/EVENING. LOW PRESSURE EXPECTED TO MOVE UP/OFF THE COAST ON WEDNESDAY. DEPENDING ON HOW CLOSE IT IS...WINDS COULD STRENGTHEN. GOOD CHANCE OF -RA AND/OR -SN WEDNESDAY. IF SNOW FALLS...LOW CIGS/VSBY WOULD RESULT. CONDITIONS IMPROVE BY THURSDAY TO VFR. && .MARINE... NO PROBS ON WATERS ATTM. THE P-GRAD WL INCREASE SUN AFTN AS A WMFNT APPROACHES. HV EXPANDED SCA FOR THE EVNG HRS TO INCL MOST OF THE BAY. A 60-70 LLJ WL PASS OVER WATERS LT AT NGT. HWVR MIXING WL BE POOR...ASSISTED BY 50+ DEGF AIR TEMPS OVER WATER TEMPS IN THE LWR- MID 40S. HV CAPPED WINDS AT 30 KT...HOLDING OFF GLW MENTION. DAYSHIFT WL BE GIVING THIS MORE ATTN...AS THERE WL BE A LOT OF WND NOT FAR OFF THE WATERS EDGE. THE JET...AND THE WMFNT...WL PASS N OF THE WATERS MON MRNG BUT WNDS WL INCR AGN MON AFTN AS THE CDFNT APPROACHES. THERE MAY BE A BRIEF LULL /RELATIVELY SPEAKING/...BUT THE GRADIENT WL SUPPORT 20-25 KT WINDS MON AFTN. HV XTNDD SCA FOR ALL WATERS INTO MON. LIGHT WINDS EXPECTED MONDAY NIGHT THROUGH TUESDAY NIGHT. DEPENDING ON TRACK OF LOW UP THE ATLANTIC SEABOARD...SOME GUSTS TO SCA LEVEL ARE POSSIBLE...ESPECIALLY IN THE LOWER MARYLAND BAY...ON WEDNESDAY. MORE SCA-LEVEL GUSTS ARE LIKELY THURSDAY NIGHT AND FRIDAY BEHIND A CLIPPER SYSTEM. && .TIDES/COASTAL FLOODING... WINDS ON THE MID CHESAPEAKE BAY WILL INCREASE TO 20-30 MPH BY SUN NIGHT. HOWEVER...DUE TO THE TEMP CONTRAST BETWEEN THE AIR AND WATER...MUCH BETTER WINDS WILL BE CONFINED ALOFT. EVEN THE TYPICALLY AGGRESSIVE CBOFS GUIDANCE SUGGESTS THAT THERE WL BE NO WATER LVL RISE WITH TIDES TODAY OR TONIGHT. THIS WILL NEED TO BE MONITORED OF COURSE...BUT EVEN IF THERE WERE MODEL ERRORS STILL DO NOT ANTICIPATE ANY ISSUES. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY FROM 9 PM THIS EVENING TO 6 PM EST MONDAY FOR ANZ531>534-536-537-539>543. SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO 6 PM EST MONDAY FOR ANZ530-535-538. && $$ UPDATE..WOODY! PRVS...HTS/JCE

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