Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 251621 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 1121 AM EST SUN JAN 25 2015 .SYNOPSIS... HIGH PRESSURE BUILDS INTO THE MID ATLANTIC STATES BRIEFLY TODAY. LOW PRESSURE OVER IOWA WILL TRACK ACROSS SOUTHERN VIRGINIA TONIGHT...STRENGTHENING AS IT MOVES UP THE COAST MONDAY AND TUESDAY. HIGH PRESSURE IS THEN EXPECTED THROUGH MIDWEEK. && .NEAR TERM /THROUGH TONIGHT/... A COUPLE OF CHANGES TO THE HEADLINES IN EFFECT FOR THE WINTER STORM TONIGHT-MONDAY. THE WINTER STORM WARNING REMAINS IN EFFECT FOR NORTH CENTRAL MD...AND PORTIONS OF SHENANDOAH VALLEY. HAVE CHANGED THE AREAS UNDER A WINTER STORM WATCH TO A WINTER WEATHER ADVISORY...WHILE ALSO EXTENDING THE ADVISORY SOUTH TO INCLUDE DC METRO AND SOUTHWEST DOWN TO ORANGE COUNTY. ALL PRODUCTS IN EFFECT UNTIL 23Z MON. HAVE ALSO ISSUED A WINTER STORM WATCH FOR THE COUNTIES BORDERING THE CHESAPEAKE BAY FOR MONDAY NIGHT THRU TUESDAY TO ACCOUNT FOR ADDITIONAL SNOW ON THE BACK SIDE OF THE LOW AS IT DEEPENS AND PUSHES TO THE NORTHEAST. BRIEF HIGH PRESSURE BRINGS A QUIET FIRST HALF OF THE DAY TO THE AREA. SOUTHERLY FLOW WILL PUSH TEMPS INTO THE 40S AND INTO THE LOWER 50S AROUND DC METRO. UPR LOW WL BE TRACKING SWD IN THE SOMEWHAT PERSISTENT WRN RDG/ERN TROF THAT N AMERICA HAS BEEN SEEING THIS WINTER. THIS IS PROGGED TO TRACK NEAR THE VA/NC BORDER OVRNGT AND THEN DEEPEN QUICKLY OFFSHORE MON. THIS KEEPS THE MID ATLC IN THE COLD AIR. WHILE THE SFC TEMPS WL NOT BE MUCH COLDER THAN NRML THE ATMOSPHERIC COLUMN WL BE SUBFRZG SO PCPN WL REACH THE GRND AS SNOW. EVERY MDL WE`VE LOOKED AT HAS A BULLSEYE OF HVIEST SNOWFALL OVR THE NWNRN PART OF THE FCST AREA. BLV AFTR MDNGT THE SNOW COULD COME DOWN AT A RATE OF OVR AN INCH/HR ACROSS WRN MD/ERN WV. THIS IS XPCTD TO CONT INTO MON MRNG B4 THE MOISTURE/ENERGY TRANSLATE TOWARD NJ/NY. && .SHORT TERM /MONDAY/... THIS MULTI-FACETED LOW PRESSURE SYSTEM PASSAGE WILL BE UNDERGOING THE FIRST TRANSITIONAL PHASE LATE SUN INTO THE PREDAWN HRS MON. WHILE THE FIRST PHASE WILL HAVE BROUGHT A FAIRLY SOLID BATCH OF PRECIP TO THE WRN SECTIONS OF THE AREA...THE PARENT UPPER LOW WILL BE SWINGING AROUND THE MIDDLE TENN VLY TOWARD THE SRN APLCNS. THE TROUGH AXIS PHASE SHIFT FROM POSITIVE TO NEUTRAL...THEN TO NEGATIVE - ALL OCCURRING ON MONDAY AND SOUTH OF OUR AREA WILL CHANGE THE DYNAMICS OF THE PRECIP POTENTIAL ACROSS THE MID-ATLC REGION. WHILE UNDERGOING THIS DRAMATIC SHIFT DURING THE DAYTIME HRS ON MON...THE FORCING FOR SNOW BANDS ACROSS THE CWA WILL BE OF A MUCH SMALLER SCALE AND DURATION THAN THE CLIPPER-LIKE PHASE LATE SUN NIGHT. WIDESPREAD LIGHT SNOW SHOWERS WILL LIKELY CONTINUE THROUGHOUT THE DAY...W/ POCKETS OF MODERATE TO HEAVY BATCHES THAT MOVE AND PIVOT ACROSS THE AREA THAT ADD AN EXTRA CHALLENGE TO FORECASTING MORE PRECISE STORM TOTAL AMOUNTS. THE MORE CONFIDENT LOCATIONS FOR THE HEAVIEST SNOWS WILL BE THE POTOMAC HIGHLANDS OVER THRU THE NRN SHEN VLY INTO THE MIDDAY HRS ON MON. THE NEXT TIER OF COUNTIES TO THE SOUTH AND EAST ARE COMING TO LIGHT W/ RECENT MODEL GUIDANCE AS THE POSSIBLE LOCATIONS FOR WARNING CRITERIA SNOW DURATION A PORTION OF THIS EVENT. ONE OF THE ISSUES IS THAT THE DIFFERENT TRANSITIONS OF THIS STORM WILL CAUSE THE EVENT TO LAST WELL INTO TUE AFTN - ALBEIT DISSIPATING BY THEN. VECTOR ANALYSIS SHOWS BRIEF AND SUBTLE BANDING POTENTIAL IN DIFFERENT LOCATIONS ACROSS THE REGION...SO WHILE EXACT LOCATIONS ARE UNCERTAIN - THE POTENTIAL WILL BE THERE FOR LOCALLY HEAVY SNOW BANDS AND QUICK ADDITIONAL ACCUMULATIONS. ANOTHER POTENTIAL LIMITING FACTOR - ALBEIT A RELATIVELY MINOR ONE - WILL BE SFC TEMPS ACROSS THE SRN MD/LOWER TIER COUNTIES OF THE AREA MON AFTN AS THE COASTAL LOW GEARS-UP AND PULLS IN SOME WARMER AIR JUST INLAND. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... THE NEXT AND LARGER IMPACTING PHASE FOR THE ATLC COAST WILL BE THE DEVELOPING AND QUICKLY STRENGTHENING COASTAL LOW AS THE PARENT UPPER LOW APPROACHES THE CAROLINA COAST. THIS WILL EFFECTIVELY CUT OFF A LARGE MEASURE OF THE FORCING FOR THE SNOWS AND RAIN /TO OUR SOUTH/ FOR THE INLAND PORTIONS OF THE EASTERN SEABOARD STATES /OUTSIDE THE HIGHER TERRAIN/ AND WRAP-UP THE PRECIP LOCALLY AROUND THE COASTAL LOW. THE WRN EXITING EDGE OF THE COMMA HEAD OF PRECIP WILL BE A SHARP CUT OFF CENTERED OVER DELMARVA AND UNCERTAINTY EXISTS TO HOW FAR BACK INLAND IT WILL RESIDE INTO MD FOR ADDITIONAL ACCUMULATIONS LATE MON/EARLY TUE. THE NEXT WX CONCERN FOR THE EXTENDED IS THE COLD...AS A COUPLE OF REINFORCING WAVES OF CAA SWING OVER THE AREA DURING THE MIDDLE OF THE WEEK. DAILY HIGHS WILL MAX-OUT NEAR THE FREEZING MARK AND OVERNIGHT LOWS WILL DROP WELL INTO THE TEENS AND 20S ACROSS THE REGION...SOME SINGLE DIGITS OVER THE APLCNS. HIGH PRES BRIEFLY BUILDS IN FROM LATE WED INTO THU AND A RELATIVE WARM-UP BUT ONLY INTO THE U30S ON THU AFTN. ANOTHER CLIPPER WILL BE WELL ON ITS WAY TOWARD THE AREA DURING LATTER HALF OF THE WEEK...MOVING ACROSS THE REGION LIKELY LATE THU INTO FRI ACCORDING TO THE RECENT GFS AND EURO RUNS. NOT A COMPLETELY SIMILAR SOLN BETWEEN THEM BUT ELEMENTS OF THE SAME LOOK...EXCEPT THE GFS HOLDS A MORE COMPACT UPPER WAVE THAT SLIDES OVER THE AREA BUT KEEPS A LARGE PORTION OF THE PRECIP NORTH OF THE MASON-DIXON LINE W/ THE POTENTIAL FOR SOME BANDS OF LIGHT SNOW OVER THE NRN HALF OF THE CWA THU AFTN/EVE. YET ANOTHER CLIPPER WILL BE ON THE WAY AFTER THAT...BUT MAY HOLD OFF UNTIL EARLY NEXT WEEK. HIGH PRES IN BETWEEN SYSTEMS WHICH MAY BE LITTLE CONSOLATION AS BREEZY AND COLD AIR CONDITIONS WILL MARK THESE DAYS AS WELL. && .AVIATION /15Z SUNDAY THROUGH THURSDAY/... VFR CONDITIONS TODAY WITH LOWERIGN CIGS HEADING INTO THIS EVENING. WINDS LIGHT FROM THE SOUTH BCMG LIGHT/VRB IN THE AFTN AS THEY BACK TO THE EAST. SUB-VFR CONDITIONS FIRST HALF OF THE NIGHT...WITH IFR BCMG LIKELY AFTR 06Z AS THE PCPN OVERSPREADS THE REGION. LIFR CONDITIIONS PSBL AS EARLY AS 09Z...AND LASTING THRU MON MORNING WITH PERIODS OF HEAVIER SNOW. PCPN TYPE QUESTIONABLE AS PSBL RAIN/SNOW MIX OR ALL RAIN AT KDCA/KBWI/KCHO AT FIRST...THEN BCMG ALL SNOW AFTR 12Z. OTHER TERMINALS MORE LIKELY ONLY A BRIEF PERIOD OF RAIN/SNOW MIX BCMG ALL SNOW OVERNIGHT. ONGOING PCPN MONDAY WITH SNOW...IFR OR LOWER CONDITIONS LIKELY. ANOTHER ROUND OF HEAVIER PCPN (ALL SNOW) MON NIGHT INTO TUES KEEPS IFR OR LOWER CONDITIONS IN PLACE. && .MARINE... WINDS BLO SCA LVLS TDA BUT WINDS WL BE INCRSG TNGT AS A LOW APRHS THE AREA. SCA IN EFFECT FOR THE WATERS TNGT. SAC WINDS XPCTD MON...PSBLY REACHING GALE LVL ON THE BAY MON NGT. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...WINTER WEATHER ADVISORY FROM 2 AM TO 6 PM EST MONDAY FOR DCZ001. MD...WINTER STORM WARNING FROM 9 PM THIS EVENING TO 6 PM EST MONDAY FOR MDZ003. WINTER WEATHER ADVISORY FROM 2 AM TO 6 PM EST MONDAY FOR MDZ013-014. WINTER WEATHER ADVISORY FROM 10 PM THIS EVENING TO 6 PM EST MONDAY FOR MDZ004>006-011-503>508. WINTER STORM WARNING FROM 6 PM THIS EVENING TO 6 PM EST MONDAY FOR MDZ501-502. VA...WINTER STORM WARNING FROM 9 PM THIS EVENING TO 6 PM EST MONDAY FOR VAZ028. WINTER WEATHER ADVISORY FROM 2 AM TO 6 PM EST MONDAY FOR VAZ039-051>054-502. WINTER WEATHER ADVISORY FROM 10 PM THIS EVENING TO 6 PM EST MONDAY FOR VAZ026-027-029>031-040-501-503>507. WV...WINTER STORM WARNING FROM 9 PM THIS EVENING TO 6 PM EST MONDAY FOR WVZ051>053. WINTER WEATHER ADVISORY FROM 10 PM THIS EVENING TO 6 PM EST MONDAY FOR WVZ505-506. WINTER STORM WARNING FROM 6 PM THIS EVENING TO 6 PM EST MONDAY FOR WVZ050-055-501>504. MARINE...SMALL CRAFT ADVISORY FROM 9 PM THIS EVENING TO 6 PM EST MONDAY FOR ANZ530>543. && $$

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