Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 231745 AAD AFDLWX AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 1245 PM EST TUE DEC 23 2014 .SYNOPSIS... WEAK LOW PRESSURE WILL TRACK UP THE MID-ATLANTIC COAST TODAY. 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/... EARLY AFTN UPDATE - ISSUED A NEW DENSE FOG ADVISORY FOR A GOOD PORTION OF MD/WEST OF THE BAY...EXCLUDES BALT/NRN METRO AND EXTREME WRN MD - THRU 6PM THIS EVE. MORE DENSE FOG OBS...WEBCAM AND SPOTTER REPORTS PAINTING AN AXIS OF LOWER VSBYS ORIENTED ALONG AN NW-TO-SE BOUNDARY JUST NE OF THE POTOMAC RIVER. HRRR/LAV/LAMP- AVIATION AND OTHER NEAR TERM LOCAL GUIDANCE SUGGESTS THIS WILL CONTINUE INTO THE LATE AFTN/EARLY EVE. EVEN A BRIEF MIXING OF THIS LAYER ALONG THIS AXIS IN THE MID AFTN WILL AGAIN REBOUND TO LOWER CIG/VSBY VALUES - MORE DENSE FOG FOR THESE AREAS AND MAY NEED TO BE EXPANDED/EXTENDED IF CONDITIONS PERSIST. FROM PREV DISC... AMPLE MOISTURE IN THE LOWER HALF OF THE TROPOSPHERE ACROSS THE ENTIRE EAST COAST. BROADENING THE SCOPE EVEN FURTHER...SEVERAL LARGE AND SMALL SCALE FEATURES ARE ROTATING AND INTERACTING W/ EACH OTHER ATTM - WHICH WILL EVENTUALLY DRAW-UP ONE LARGE SYSTEM FOR THE ERN SEABOARD LATER TODAY INTO WED. THE FIRST WAVE OF ACTIVITY MOVED THRU YESTERDAY AND IT NOW DISSIPATING OVER NEW ENGLAND. A LARGER AND MUCH MORE POTENT SYSTEM WILL BE GEARING UP THRU THE REST OF THE DAY DOWN ACROSS THE SOUTHEAST. IN BETWEEN THESE TWO FEATURES...QUITE A STAGNANT AND MOIST ENVIRONMENT. AFTER THE EARLY MORNING CONCERNS W/ FREEZING TEMPS STILL STREWN ABOUT THE SHEN VLY AND APLCNS...THE CONCERN HAS NOW SHIFTED TO LOCALLY DENSE FOG AND LOW CLOUDS OVER MUCH OF THE REGION. AREAS OF DENSE FOG OVER THE POTOMAC HIGHLANDS HAS LIFTED A BIT...THOUGH PATCHY DENSE OBS STILL APPEARING ACROSS THESE AREAS AND FURTHER EAST. DENSE FOG OVER THE LOWER BAY WATERS HAS CREPT ONTO COASTAL AREAS AND COMBINED FURTHER INLAND W/ STRATUS DECK CEILINGS AT 100-200` AND LOWERING. NOT MUCH LIMITING FACTORS FOR THIS... OUTSIDE OF MORE AND ENHANCED PRECIP COMING UP FROM THE SOUTH BUT THIS ACTIVITY MAY HOLD OFF UNTIL OVERNIGHT. OTHER THE OVERCAST SKIES AND INTERMITTENT SHOWERS/DRIZZLE...TEMPS WILL CONTINUE TO SLOWLY RISE INTO THE U40S OVER THE I-95 CORRIDOR/...WHILE AREAS CLOSER TO THE BLUE RIDGE AND ESPEC OVER THE SHEN VLY WILL BE MORE WEDGED-IN W/ TEMPS BARELY CROSSING THE 40 DEG MARK. WITH ALL THE MOISTURE IN THE AIR AND THE INSULATING CLOUD COVER...OUR TEMPS OVERNIGHT WON`T DROP MUCH FURTHER - ONLY IN THE L-M40S...U30S OVER THE POTOMAC HIGHLANDS...AS A RAIN SHIELD APPROACHES FROM THE SOUTH. LOW LEVEL JET STRENGTHENS ON WEDNESDAY...PUSHING A PLUME OF NEAR 1.5 INCH PW/S INTO THE MID-ATLANTIC. PERIODS OF MODERATE RAIN MAY BE HEAVY AT TIMES. DESPITE DECENT WIND NOT TOO FAR OFF THE DECK...INSTABILITY IS EXPECTED TO RESIDE SOUTH OF THE CWA AND THUS SEVERE WX IS NOT EXPECTED. CONTINUED TO LEAN TOWARD THE LOWER SUITE OF GUIDANCE /MET/ FOR MAXIMA WEDNESDAY GIVEN THE EROSION OF THE WEDGE AND THEN PERIODS OF RAIN. THIS BRINGS 50S THROUGH THE CWA...BUT CONFIDENCE IN 60 OR ABOVE IS LOW. && .SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/... DEEPENING SFC LOW /PRESSURES FALLING THROUGH THE 980S MB/ AND VIGOROUS UPPER LEVEL TROUGH WILL BE LIFTING THROUGH THE GREAT LAKES THURSDAY NIGHT. THE TRAILING COLD FRONT WILL CROSS THE CWA. USED A BLEND OF THE 00Z ECMWF AND GFS FOR MOST OF THE WX ELEMENTS AS THEY MIRROR THE MODEL CONSENSUS. THIS PUSHES THE FRONT OFF THE DELMARVA BY 12Z. SHOULD SEE A SHARP CUT OFF IN PRECIP BEHIND THE FRONT...BUT LINGERED SOME POPS IN THE EAST AFTER DAYBREAK IN CASE A SLOWER SOLUTION TAKES PLACE. MODELS ARE INDICATING A HUNDRED OR TWO J/KG OF MUCAPE AHEAD OF THE FRONT...ALTHOUGH IT MAY NOT BE DEEP ENOUGH TO CONSISTENTLY PRODUCE THUNDER. THEREFORE KEPT THE SLIGHT CHANCE OF THUNDER IN THE EAST WHERE A SLIGHTLY MORE UNSTABLE PROFILE WILL EXIST. NONETHELESS...PRECIP WILL BE A MORE SHOWERY DURING THIS TIME FRAME...AND WITH UNSEASONABLY HIGH PWAT VALUES...SOME MODERATE TO HEAVY ELEMENTS OF RAIN COULD EXIST. FOR AN AREAL AVERAGE THOUGH...IT APPEARS AMOUNTS WILL BE UNDER A HALF INCH. 40-50 KT WINDS WILL BE LOCATED A FEW THOUSAND FEET ABOVE MSL...BUT THE TEMP PROFILE WILL NOT BE SUPPORTIVE OF THESE MIXING DOWN CONSISTENTLY. HOWEVER...WILL HAVE TO MONITOR THE WIND FORECAST FOR THE PEAKS...AS IT MAY BE CLOSE TO ADVISORY CRITERIA. EVEN THOUGH TEMPERATURES WILL BE FALLING IN THE WEST BEHIND THE FRONT...ONLY THE HIGHEST ELEVATIONS HAVE A CHANCE OF SEEING A CHANGEOVER TO SNOW ONCE THE UPSLOPE ENVIRONMENT TAKES OVER. TIGHT PRESSURE GRADIENT WILL BE IN PLACE THURSDAY...SO EXPECT BREEZY CONDITIONS IN A CAA/DOWNSLOPE ENVIRONMENT. GOOD CONSENSUS ON 20-30 KT GUSTS. SCT/BKN STRATOCU MAY BE MORE PREVALENT IN THE NORTHERN PART OF THE CWA. THE MOST FAVORABLE TIME FOR UPSLOPE RAIN/SNOW SHOWERS WILL BE IN THE MORNING...WITH MOISTURE PROFILES THINNING DURING THE AFTERNOON AS HIGH PRESSURE BUILDS IN FARTHER. WHILE HIGH TEMPERATURES WILL BE COOLER THAN WEDNESDAY...THEY WILL STILL BE ABOVE NORMAL. HIGH PRESSURE WILL BE CENTERED OVER THE CAROLINAS BY LATE THURSDAY NIGHT. WINDS WILL DIMINISH AND LOWS WILL DROP TO EITHER SIDE OF FREEZING. && .LONG TERM /FRIDAY THROUGH MONDAY/... HIGH PRESSURE WILL DRIFT OFF THE MID ATLANTIC COAST FRIDAY AND SATURDAY. TEMPERATURES WILL BE ABOVE NORMAL. A COLD FRONT WILL APPROACH FROM THE WEST SATURDAY NIGHT...BUT IT WILL BE MOISTURE STARVED WITH A THE HIGHEST CHANCE OF LIGHT PRECIP IN THE MOUNTAINS. MODEL SOLUTIONS THEN DIVERGE WITH HOW TO HANDLE UPPER LEVEL ENERGY EMERGING FROM THE DESERT SOUTHWEST AND HOW IT INTERACTS WITH THE FRONT WHICH BECOME MORE PARALLEL TO THE UPPER FLOW. WHILE THE FORECAST WILL SHOW A HIGHER CHANCE OF PRECIP SUNDAY...THE LATEST 00Z GUIDANCE SUGGESTS IT MAY BLEED OVER INTO MONDAY. TEMPERATURES WILL BE COOLER BEHIND THE FRONT AND THUS THERE COULD BE SOME PTYPE CONCERNS...BUT THERE WILL BE A LACK OF A TRUE ARCTIC AIR SOURCE. && .AVIATION /17Z TUESDAY THROUGH SATURDAY/... GIVEN THE WEDGE/CAD SCENARIO...FLIGHT RESTRICTIONS ARE EXPECTED DURING THE TAF VALID PERIOD DUE TO PERSIST FOG/DRIZZLE AND ALSO PERIODS OF RAIN. IFR IS LIKELY WITH THE POTENTIAL FOR LIFR PARTICULARLY TONIGHT. IFR IS LIKELY TO CONTINUE INTO WEDNESDAY AS EVEN IF THE WEDGE STARTS TO ERODE PERIODS OF MODERATE TO HEAVY RAIN WILL BRING POOR CONDITIONS. CAN/T RULE OUT THE POSSIBILITY OF LLWS ON WEDNESDAY AS WELL WITH STRENGTHENING SOUTHERLY LOW LEVEL JET. IFR OR LOWER CIGS REMAIN POSSIBLE INTO WEDNESDAY NIGHT UNTIL A COLD FRONT PASSES AROUND MIDNIGHT. PRIOR TO THE FRONT...SHOWERS MAY REDUCE VSBY AT TIMES AND LLWS MAY BE A CONCERN. THE FRONT WILL SHIFT WINDS TO THE WEST AND GUSTS WILL INCREASE ABOVE 20 KT. SOME WESTERLY WIND GUSTS UP TO 30 KT POSSIBLE THROUGH THURSDAY. WINDS DIMINISH THURSDAY EVENING WITH HIGH PRESSURE/VFR TO FOLLOW. && .MARINE... HIGH PRESSURE EXTENDS FROM NEW ENGLAND INTO THE MID-ATLANTIC. CURRENT WINDS ARE GENERALLY FROM THE NORTH...10 TO 15 KT DOWN THE BAY. SHIFT TO THE SOUTH IS EXPECTED OCCUR TONIGHT INTO WEDNESDAY. WINDS WILL INCREASE DURING THE AFTERNOON. BEST SOUTHERLY PUSH LOOKS LIKE EVENING...BUT GUIDANCE SUGGESTS 20 KT OCCURRING UP THE BAY IN THE AFTERNOON AND WILL RAISE SCA. SCA CONDITIONS LIKELY TO CONTINUE THROUGH WEDNESDAY NIGHT. SHOWERS WILL CONTINUE AND MAY MIX DOWN HIGHER GUSTS. A COLD FRONT WILL PASS LATE AT NIGHT OR JUST AFTER DAYBREAK THURSDAY. SCA CONDITIONS WILL CONTINUE AND SUSTAINED WINDS WILL INCREASE A BIT. MAY BE CLOSE TO GALES...BUT FORECAST AT THIS TIME WILL KEEP IT JUST SHY. WILL DEPEND ON HOW EFFECTIVE MIXING IS. HIGH PRESSURE WILL BUILD IN THURSDAY NIGHT WITH LIGHTER WINDS THROUGH FRIDAY NIGHT. GUSTS MAY APPROACH SCA CRITERIA SATURDAY AFTERNOON. && .TIDES/COASTAL FLOODING... WATER LEVELS WERE RUNNING 1/2 TO 3/4 FT ABOVE NORMAL. AS WINDS TURN TO THE SOUTH BY WEDNESDAY...ANOMALIES ARE EXPECTED TO INCREASE. AM NOT EXPECTING ANY MINOR TIDAL FLOODING ISSUES THROUGH WEDNESDAY MORNING...BUT WILL HAVE TO WATCH TIDES WEDNESDAY AFTERNOON/EVENING AS WATER LEVELS COULD GET CLOSE TO THOSE LEVELS IF ANOMALIES INCREASE OVER 1 FT. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...DENSE FOG ADVISORY UNTIL 6 PM EST THIS EVENING FOR MDZ003>005- 013-014-016>018-503>506. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY FROM 1 PM TO 6 PM EST WEDNESDAY FOR ANZ530>534-537>543. && $$ UPDATE...GMS PREV DISCUSSION...BPP/ADS

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