Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 232247 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 547 PM EST TUE DEC 23 2014 .SYNOPSIS... WEAK LOW PRESSURE WILL TRACK UP THE MID-ATLANTIC COAST TONIGHT. STRONGER LOW PRESSURE WILL PUSH NORTH ALONG THE APPALACHIANS ON WEDNESDAY...SENDING A COLD FRONT EASTWARD WEDNESDAY NIGHT. BREEZY CONDITIONS WILL FOLLOW THE FRONT ON THURSDAY...THEN HIGH PRESSURE WILL BUILD BACK INTO THE REGION TO CLOSE OUT THE WEEK. && .NEAR TERM /THROUGH WEDNESDAY/...
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HV UPDATED THE DENSE FOG ADVSRY TO INCLUDE NRN BALT/HARFORD AND WRN LOUDOUN AND XTND THE END TIME UNTIL 1 AM. CLOUDY AND COOL...INTERMITTENT DRIZZLE THRU THE EVE HRS...WHILE SEVERAL REGIONAL-SIZED SLUGS OF RAIN GATHER THEMSELVES OVER THE GULF COAST. LITTLE CHANGE WILL OCCUR OVER OUR AREA UNTIL THESE ARRIVE LATE TONIGHT. WHILE ONE UPPER WAVE EXITS OFF TO THE NE...IT LEAVES BEHIND A TRAIL OF DEEP LOW LEVEL MOISTURE AND LITTLE/IF ANY SYNOPTIC FORCE TO REMOVE IT. THIS IS EVIDENCED BY THE LOW CLOUDS...W/ CEILINGS ONLY 100-200` ABOVE THE SFC AND W/ SOME RIDGES AND AREA HILLS WELL ABOVE THAT ELEVATION DIFFERENCE...AREAS OF FOG AND LOCALLY DENSE FOG HAVE BEEN APPEARING ACROSS THE REGION SINCE EARLY THIS MRNG. ALL RAIN AND NO CONVECTIVE EXPECTED OVERNIGHT...AS THE RAIN BATCHES MAKE THEIR WAY NORTH AND ENCOUNTER THE EDGE OF THE CAD WEDGE. LOCALLY HEAVY EMBEDDED SHOWERS POSSIBLE AT TIMES...ESPEC ACROSS THE I-95 CORRIDOR AND EAST W/ SOME OF THE ACTIVITY ORIGINATING AS DEEP CONVECTION WELL TO THE SOUTH. WEDNESDAY... BATCHES OF LIGHT/MODERATE RAIN WILL CONTINUE TO SPREAD FROM SW-TO-NE ACROSS THE AREA...AIDED BY A STRENGTHENING AND POTENT LOW LEVEL JET MAX. GLOBAL MODELS AND EVEN NEAR-TERM DERIVATIVES ARE IN GOOD AGREEMENT ON THE INITIAL PHASES OF THE INCOMING STORM SYSTEM. A COUPLE OF KEY FEATURES THAT HAVE HAD MANY DIFFERENT LOOKS AND EFFECTS IN THESE RECENT RUNS ARE GRADUALLY BEING RESOLVED. AN INTENSE SFC LOW WILL BE THE MAIN FEATURE OUT OF ALL THIS ENERGY INTERACTION IN THE UPPER LEVELS OVER THE ERN HALF OF THE CONUS. THE LOW WILL ORIGINATE DOWN OVER THE LA GULF COAST AND MAKE A PATH STRAIGHT TOWARD THE UPPER MIDWEST/GREAT LAKES FROM LATE TODAY INTO LATE WED EVE. THE WARM FRONT OUT AHEAD OF THE SFC LOW WILL HAVE PASSED OVER THE AREA BY EARLY WED MRNG...ALLOWING WARMER THAN AVG TEMPS TO FOLLOW UP THE ERN SEABOARD. WHILE RAINING FOR A BETTER PART OF THE DAY...WE WILL STILL SEE TEMPS CLIMB WELL INTO THE 50S...W/ SOME L60S APPEARING OVER THE SERN SECTIONS OF THE CWA WED AFTN. TOTAL QPF RANGES FOR THE 24-30 HR RAIN EVENT ARE EXPECTED TO BE IN THE 1-1.5" RANGE ALONG AND E OF I-95...TAPERING OFF TO ABOUT 0.5-1.0 FROM THE PIEDMONT WEST TO THE MTNS. ANOMALOUSLY HIGH PWATS WILL BE ASSOCIATED W/ THIS SYSTEM CLOSE TO THE COAST...AS THE CONVECTIVE AND MODIFIED TROPICAL CHARACTERISTICS CARRY AMPLE MOISTURE UP THE COAST.
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&& .SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/...
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CDFNT WL BE ON THE WRN EDGE OF CWFA AT START OF PD...AND SHUD BE MARCHING ACRS AREA THRU THE EVNG INTO THE ELY OVNGT HRS. THIS TIMING HASNT CHGD MUCH PAST CPL CYCLES...PERHAPS A PINCH FASTER THAN YDA. FNT WL BE MARKED BY STRONG THERMAL GRADIENT AND BE W/IN ZONE OF DP SLY FLOW AHD OF AMPLIFIED H5 TROF AXIS. THEREFORE...THERE WL BE PLENTY OF WARM MOIST AIR TO BE TRANSPORTED NWD...W/ UPGLIDE STILL PRESENT FOR ADDED LIFT. AHD OF FNT...AMS UNCHARACTERISTICALLY WARM AND UNSTBL FOR LT DEC... W/ DEWPTS IN THE 50S/PWAT 1.50-1.75 INCH/SVRL INSTBY PARAMETERS STARTING TO REGISTER-- SUCH AS NONZERO MUCAPE...LIS NEAR 0...TQ 15-20...K APPCHG 30. WHILE AM DOUBTING HOW MUCH ACTUAL LTNG THERE WL BE...SCOPE OF DYNAMICS/WIND FIELD SUGGESTS THAT FNT MAY BE MARKED BY BKN LINE OF LOW TOPPED CNVCTN ALONG OR JUST AHD OF IT. THIS CUD BRING DOWN SOME OF THE 40-50 KT KT WINDS PRESENT H9-7. THEREFORE... HV EXPANDED AREA OF SCHC THUNDER TO JUST ABT ENTIRE CWFA IN THE EVNG...AND WLL TRIM AS FROPA APPROACHES. PWAT WELL ABV 2SD NOW... AND INCRSG...SO WL BE ADDING LCL FLOODING TO HWO. THINK THERE WL BE RAPID DRYING BHD FNT WED NGT AS FLOW VEERS WLY. AM STILL A LTL HESITANT TO BE TOO SHARP ON BACK SIDE OF POP FIELD IN CASE LATER GDNC TIMING CHGS AGN...BUT FOR NOW HV MOST OF THE PCPN ENDING BEFORE 12Z THU. MIXING POTL WL BE MUCH BETTER THU...STILL W/ A GOOD WIND FIELD. MEAN LYR MIXING WL YIELD 20-30 KT...W/ SOME GUSTS UP TO 40 KT PSBL ACRS THE HIER TRRN. THIS WL BE A TIME PD TO MONITOR...AS GRAIDENT MAY JUSTIFY WND ADVY FOR SOME WRN/NWRN CNTYS W/ AN UPCOMING FCST CYCLE. WL HOLD THAT IN THE HWO FOR NOW. EVEN W/ RELATIVELY STRONG CAA...TEMPS IN THE APLCNS WL ONLY MARGINALLY SUPPORT SHSN...AND THE WLY TRAJ DOESNT HELP MUCH. WL BE KEEPING CHC POPS FOR WRN UPSLP AREAS THRU THU...BUT WX TYPE SHRASN. DRY ELSW. MAXT BASED ON MOS MEAN. WL BE ABT 10 DEGF COOLER THAN WED...WHICH IS STILL ABV CLIMO. AFTR AN ACTV PD...WX THU NGT THRU FRI NGT WL BE BENIGN AS HIPRES BLDS. WL EVEN GET TO SEE THE SUN. TEMPS STILL AOA CLIMO.
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&& .LONG TERM /SATURDAY THROUGH TUESDAY/... A COLD FRONT WILL MOVE ACROSS THE REGION SATURDAY BEFORE SLIDING OFF TO THE SOUTH AND ACROSS NORTH CAROLINA SATURDAY NIGHT. MUCH OF THE DAY SATURDAY SHOULD BE DRY. THERE IS A SLIGHT CHANCE OF A FEW RAIN OR SNOW SHOWERS DEVELOPING POST-FRONTAL LATE SATURDAY AND SATURDAY NIGHT. MOST OF ANY ENERGY APPEARS TO TAFFY-OUT WELL TO OUR NORTH. THE SLIGHT CHANCE OF LIGHT STRATIFORM RAIN LINGERS ON SUNDAY AS ADDITIONAL UPPER LEVEL ENERGY TRIES TO SCOOT SOUTHWARD FROM THE LOWER GREAT LAKES TO BEHIND THE FRONT WHICH MAY STALL ACROSS THE CAROLINAS. AS TEMPERATURES DECREASE INTO SUNDAY NIGHT...THERE EXISTS A SLIGHT CHANCE OF LIGHT SNOW. MODERATE LEVELS OF UNCERTAINTY LATE SUNDAY THROUGH MONDAY LIES WITH THE EUROPEAN AND GFS MODELS TRYING TO DEVELOP A LOW ALONG THE STALLED FRONT OVER THE CAROLINAS AND SPREADING SNOW NORTH INTO OUR REGION. COLDER AIR FUNNELING IN BEHIND THE COLD FRONT ON A NORTHERLY WIND AND SEVERAL WAVES OF UPPER ENERGY FROM THE OHIO VALLEY WOULD PROBABLY SUPPORT THIS. HOWEVER...THE POSITION OF THE POSSIBLE DEVELOPING LOW ALONG THE FRONT APPEARS TO BE TOO FAR SOUTH TO PRODUCE A NOTICABLE THREAT OF SNOW. FOR NOW...WENT WITH SLIGHT CHANCE OF SNOW SUNDAY NIGHT AND A SLIGHT CHANCE TO CHANCE OF LIGHT RAIN OR LIGHT SNOW MONDAY NIGHT. AS FOR TUESDAY...WE HAVE A SLIGHT CHANCE OF LIGHT RAIN OR LIGHT SNOW SHOULD A LOW DEVELOP ALONG THE FRONT. IT ISN`T UNTIL THE MAIN TROUGH OF LOW PRESSURE PIVOTS ACROSS THE REGION LATE TUESDAY WILL CONDITIONS IMPROVE. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
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LOW CLOUDS AND FOG CONTINUE ACROSS MUCH OF THE REGION THIS EVE. NOT UNTIL OVERNIGHT W/ THE ONSET OF STEADY PRECIP WILL WE LOSE THE SUB-IFR CONDITIONS. CIGS WILL REMAIN LOW THROUGHOUT THE NEXT 24-36 HRS UNTIL A COLD FRONT MOVES THRU WED NIGHT. RAIN WILL BE FAIRLY STEADY FROM LATE TONIGHT AND THRU MUCH OF THE DAYTIME HRS ON WED. ONLY BRIEF AND INTERMITTENT BREAKS EXPECTED...W/ IFR CIGS OR LOWER. AOB IFR WL BE PREVALENT WED NGT. LLWS CONCERNS FM THE AFTN WL CARRY INTO THE EVNG HRS. CFP EITHER LT EVNG OR JUST AFTR MIDNGT. ENUF UNSEASONABLE WARMTH AND INSTBY FOR LOW TOPPED CNVCTN...MEANING BRIEF HIER WND GUSTS EMBEDDED W/IN AREAS OF RA. G30-35 KT W/IN REASON. WORST CASE SCENARIO WUD BE HIER THAN THAT. SLY WNDS WL BECOME WLY BHD FNT. MIXING BETTER THU...W/ A WIND FIELD THAT WUD SUPPORT W15G30KT. CIGS WL LIFT. WL EITHER HV VFR OR MVFR THRU THE DAY. VFR THU NGT-SAT UNDER HIPRES.
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&& .MARINE... LIGHT WINDS OVER THE WATERS...THOUGH VSBYS ARE LOW - ESPEC OVER THE MIDDLE/LOWER MD BAY. WINDS WILL STAY LIGHT UNTIL WAVES OF LIGHT/MODERATE RAIN MOVE IN OVERNIGHT AND INTO EARLY WED. BY MIDDAY WED...SCA CONDITIONS WILL BECOME APPARENT FROM SOUTH TO NORTH. SLY SFC FLOW WL INCR WED NGT...TO ARND 15 KT. MOMENTUM TRANSFER CHALLENGED...BUT 20-25 KT JUST OFF THE DECK...SO CANT RULE OUT THAT IT WUD COME DOWN IN SHRA. HIER GUSTS THAT THAT NOT TTLY OUT OF THE QSTN EITHER...BUT THINK THE ENVIRONMENT WUD MORE LKLY JUSTIFY SMW VS GLW. CDFNT WL CROSS WATERS ELY THU MRNG. NW FLOW BHD FRNT WL MIX MORE EFFECTIVELY. SCA LKLY AND GLW PSBL. SINCE ITS BYD 36 HRS...WL KEEP IN SYNOPSIS. WL CAP AT SCA LVL FOR THE FCST. WNDS WL SUBSIDE THU NGT AS HIPRES BLDS. && .TIDES/COASTAL FLOODING... WATER LVLS RUNNING A HALF-FT TO 1 FT ABV ASTRO NORMS. THESE DEPARTURES WILL STAY ABOUT THE SAME THROUGH THE TIDE CYCLE WED MRNG. AFTER THAT...XPCT ANOMALIES TO INCREASE...DRIVEN BY AN UPTICK IN SLY WINDS. THAT MAY PUT A FEW SITES ALONG THE WESTERN SHORE OF THE BAY ON THE CUSP OF MINOR FLOODING. A COLD FRONT WILL PASS EAST OF WATERS BEFORE THE THU MRNG TIDE. DEPARTURES SHOULD DECREASE A LTL AS A CONSEQUENCE...BUT AM NOT SURE HOW QUICKLY BLOWOUT CONDS WILL ENSUE. && .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE. MD...DENSE FOG ADVISORY UNTIL 1 AM EST WEDNESDAY FOR MDZ003>006-013- 014-016>018-503>507. VA...DENSE FOG ADVISORY UNTIL 1 AM EST WEDNESDAY FOR VAZ505. WV...NONE. MARINE...SMALL CRAFT ADVISORY FROM 9 PM WEDNESDAY TO 5 AM EST THURSDAY FOR ANZ535-536. SMALL CRAFT ADVISORY FROM 1 PM WEDNESDAY TO 5 AM EST THURSDAY FOR ANZ530>534-537>543.
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&& $$ UPDATE...WOODY! PTVS...GMS/HTS/KLW

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