Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 230504 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 1204 AM EST TUE DEC 23 2014 .SYNOPSIS... WEAK LOW PRESSURE WILL TRACK UP THE MID-ATLANTIC COAST TONIGHT INTO TUESDAY. 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 TUESDAY/... STILL HAVE POCKETS OF FREEZING OR NEAR FREEZING TEMPERATURES IN PARTS OF WESTERN/CENTRAL MD...EASTERN WV AND INTO NORTHERN SHENANDOAH VALLEY. WITH WAVES OF VERY LIGHT RAIN OR DRIZZLE POISED TO MOVE NORTHWARD DURING THE OVERNIGHT...HAVE EXTENDED THE FREEZING RAIN ADVISORY TIL 6 AM TUESDAY MORNING. PREV... RDR SHOWS BANDS OF RA MOVG INTO CENTRAL MD. THAT COMBINED W/ SFC TEMPS AOA FRZG HV LET THE ADSRY XPIRE IN NRN VA. ADDED THE NEW ZN BRK OF WRN HOWARD TO THE ADVSRY BASED ON RDR RETURN OVR AN OB SITE REPORTING 31 DEGS. THIS IS PART OF THE MDT RAIN BAND THAT PASSED THRU IAD 1/2 HR PRIOR. HVR RAFL DOES NOT AUTOMATICALLY LEAD TO GREATER FZRA ACCRETION - MUCH OF THAT LIQUID WL DRAIN OFF INTO STERAMS ETC. A WARM FNT WILL MOVE UP THE MID-ATLANTIC COAST TONIGHT. WARM MOIST AIR WILL CONTINUE TO OVERRUN THE SURFACE COLD AIR IN PLACE...RESULTING IN PLENTY OF CLOUDS ALONG WITH LIGHT RAIN AND DRIZZLE. FOR LOCATIONS ALONG AND WEST OF THE BLUE RIDGE MOUNTAINS AS WELL AS ALONG THE MASON-DIXON LINE...TEMPERATURES ARE A BIT COLDER ESPECIALLY IN THE HIGHER ELEVATIONS ABOVE 1500 FEET. PRECIPITATION WILL NOT BE AS WIDESPREAD ACROSS THESE AREAS...BUT THERE SHOULD BE AT LEAST SOME LIGHT RAIN THAT FREEZES ON CONTACT...CAUSING THE POTENTIAL FOR SLIPPERY ROADWAYS AND HAZARDOUS TRAVEL. THE FREEZING RAIN ADVISORY CONTINUES UNTIL MIDNIGHT FOR LOCATIONS NEAR THE MASON-DIXON LINE AND ACROSS PORTIONS OF EASTERN WEST VIRGINIA. WARMER AIR IS EXPECTED TO WORK ITS WAY INTO THE AREA TONIGHT...ALLOWING FOR PRECIPITATION ACROSS MOST AREAS TO CHANGE TO RAIN. HOWEVER...THAT PROCESS WILL BE SLOW WITH LITTLE TO NO WARM ADVECTION AT THE SURFACE. THEREFORE...TEMPS WILL HAVE TO BE MONITORED BECAUSE ICING MAY PERSIST INTO LATE TONIGHT...ESPECIALLY ACROSS THE HIGHER ELEVATIONS ALONG AND WEST OF THE BLUE RIDGE MOUNTAINS. LOW PRESSURE OFF THE MID-ATLANTIC COAST WILL CONTINUE TO MOVE NORTHEAST AWAY FROM THE AREA TUESDAY. HIGH PRESSURE WILL CONTINUE TO WEDGE ITSELF INTO THE MID-ATLANTIC WHILE LOW PRESSURE DEVELOPS ALONG THE GULF COAST. LOW CLOUDS ALONG WITH AREAS OF LIGHT RAIN...DRIZZLE AND FOG ARE EXPECTED ACROSS MOST LOCATIONS. HOWEVER...TEMPS WILL BE WELL ABOVE FREEZING WITH MAX TEMPS RANGING FROM THE LOWER TO MIDDLE 40S ACROSS MOST AREAS TO THE LOWER 50S IN PORTIONS OF THE POTOMAC HIGHLANDS WHERE THE MARINE LAYER MAY MIX OUT. && .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/... RELATIVE LULL IN ACTIVITY WILL COME TO AN END TUE EVNG AS LOPRES EMERGES FM GLFMEX INTO THE MS/TN RVR VLYS. THERE WL BE PLENTY OF ISENT LIFT AHD OF THE SYSTEM...WHICH WL BE THE PRIMARY FACTOR IN PCPN GENERATION. THE SFC LOW WL HEAD TO THE GRTLKS WED...KEEPING ENTIRE CWFA ON THE WARM /WET/ SIDE OF THE SYSTEM. A 40-50 KT LLJ WL PASS OVHD WED...BUT VERT MIXING QUITE POOR. INSTEAD...WIND FIELD WL BE DEDICATED TO UPGLIDE/MSTR TRANSPORT. PWAT INCR TO 1.25-1.50 INCHES...WHICH IS CLOSE TO 2SD ABV NRML FOR DATE. AM RUNNING CAT POPS W/ MDT RAFL ATTM. WUDNT BE SURPRISED IF ELEMENTS OF HVY RAIN PRESENT. WL WITHHOLD MENTION OF FLOODING BASED ON UNCERTAINTIES OF EVOLUTION... BUT ITS NOT OUT OF THE REALM OF PSBLTYS. THERES DECENT CLUSTERING OF TEMP GDNC. HV SETTLED ON A MEAN SOLN...MID 30S-MID 40S FOR MIN-T AND 50S TO ARND 60F FOR MAXT. ATTENDENT CDFNT WL BE DRAGGED THRU WED NGT. SMALL TIMING DIFFS BTWN NAM/GFS...BUT EVEN THE QUICKER SOLN SUGGESTS A LT NGT /XMAS EVE/ FROPA. AHD OF FNT MARGINAL INSTBY RESIDES. GIVEN KINEMATICS...CANNOT RULE OUT AN ISOLTD RUMBLE OR TWO OF THUNDER. CERTAINLY NOT PRIMARY ORDER THREAT...NOR IS ANY SVR WX ANTICIPATED...BUT ENUF FOR A SCHC THUNDER FCST. HV OPTED TO PLACE NEARER CORE OF INSTBY...WHICH IS E OF BLURDG AND S OF DCA/NAK. CAT POPS EVERYWHERE...SPCLY IN THE EVNG. AFTER CFP...THINK THERE WL BE A SHARP CUTOFF TO PCPN. A KEY QSTN WL BE ON WHAT SIDE OF 11Z IT WL OCCUR. HV INCL A CHC OF SHRA E OF I-95 THU /XMAS/ MRNG DUE TO THESE TIMING CONCERNS. OTRW...W/ HV AN UPTICK IN CAA WHICH WL FACILITATE BETTER MIXING. USED MEAN MIXED LYR FOR 20-30 KT GUSTS. DID NOT GO FOR HIER MIXING DUE TO H5 PVA WHICH WL INHIBIT CLRG. TRAJECTORY THU NOT THAT GREAT FOR UPSLP SHSN GENERATION...FLOW A BIT TOO SHEARED...AND LLVL TEMPS ONLY MARGINALLY SUPPORTIVE. HV HIGH END CHC POPS FOR AFTN SHSNRA. DRY ELSW. FLLWD MOS FOR TEMPS...WHICH WL BE COOLER THAN WED...BUT STILL NOT BLO AVG. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... HIGH PRESSURE WILL BUILD INTO THE REGION THURSDAY NIGHT. DRY CONDITIONS FRIDAY AND FRIDAY NIGHT WITH HIGH PRESSURE MOVING TO THE SOUTH AND OFFSHORE. HIGH TEMPERATURES MAY STILL BE SLIGHTLY ABOVE NORMAL. A COLD FRONT WILL MOVE ACROSS THE REGION SATURDAY AND SATURDAY NIGHT...BRINGING A CHANCE OF RAIN AND SNOW SHOWERS...MAINLY SATURDAY NIGHT AND INTO SUNDAY. HIGH PRESSURE WILL BUILD INTO THE REGION SUNDAY NIGHT AND MONDAY. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/... CIGS VSBYS WILL DROP TO IFR LEVELS TNGT. LIFR CONDITIONS ARE POSSIBLE LATE TONIGHT INTO TUESDAY. CIGS AND VSBYS MAY NOT IMPROVE ABOVE IFR LEVELS TUESDAY. AREAS OF LIGHT RAIN AND DRIZZLE WILL AFFECT THE TERMINALS DURING THIS TIME. RAIN MAY FREEZE ON SOME SURFACES...ESPECIALLY ACROSS KMRB THIS EVENING. FLGT RESTRICTIONS WL BE PREVALENT THRU WED NGT...MOSTLY AOB IFR. IN ADDITION...THE WIND FIELD JUST OFF THE DECK WL INCR WED NGT...FOR LKLY LLWS CONCERNS. SFC WNDS SHUD MOSTLY BE SLY. CFP WL COME WED NGT...AOA MIDNGT FOR TERMINALS. WHILE FLGT CATS WL IMPRV AT THAT TIME...SO WL WND GUSTS AT THE GRND. WNDS WL BECOME WNWLY...W/ SOME GUSTS UP TO 30 KT. FRI WL BE A MORE TRANQUIL WX DAY...W/ NO CIG OR WIND ISSUES ANTICIPATED ATTM. && .MARINE... LOW PRESSURE WILL MOVE UP THE MID-ATLANTIC COAST TONIGHT. THE GRADIENT SHOULD SUBSIDE TONIGHT AS THE LOW MOVES TOWARD THE DELMARVA PENINSULA. NO MARINE HEADLINES ARE FORECAST TONIGHT THROUGH TUESDAY. PATCHY FOG ALONG WITH AREAS OF LIGHT RAIN AND DRIZZLE ARE EXPECTED DURING THIS TIME. LGT SLY WNDS TUE NGT WL INCR WED. SCA LKLY WED-WED NGT. GLW NOT TTLY OUT FO THE QSTN WED NGT...BUT IT WUD REQUIRE BETTER MIXING THAT THINK WL BE PRESENT. HWVR...THERE MAY BE A FEW STRONGER SHRA THAT CUD BRING DOWN LCLLY HIER WND GUSTS. CDFNT WL CROSS WATERS ELY THU MRNG. NW FLOW BHD FRNT WL MIX MORE EFFECTIVELY. AGAIN...SCA LKLY AND GLW PSBL. WL CAP AT SCA LVL FOR THE FCST. WNDS WL SUBSIDE THU NGT AS HIPRES BLDS. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...FREEZING RAIN ADVISORY UNTIL 6 AM EST TUESDAY FOR MDZ003>005- 501-502-505. VA...FREEZING RAIN ADVISORY UNTIL 6 AM EST TUESDAY FOR VAZ027-028- 030-031. WV...FREEZING RAIN ADVISORY UNTIL 6 AM EST TUESDAY FOR WVZ050>053- 055-501>504. MARINE...NONE. && $$ BPP/WOODY!/BJL/HTS/KLW

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