FXUS61 KLWX 261505 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 1005 AM EST TUE FEB 26 2013 .SYNOPSIS... A COMPLEX LOW PRESSURE SYSTEM WILL ARRIVE LATER THIS MORNING... MOVING ACROSS THE REGION OVER THE COURSE OF THE DAY. A SURFACE LOW WILL SLIDE OVER THE AREA LATE TONIGHT...BRINGING MORE RAIN AND GUSTY WINDS BEFORE MOVING OFF TO THE NORTHEAST WEDNESDAY MORNING. A TROUGH OF LOW PRESSURE WILL FOLLOW AND WILL PASS SLOWLY EAST ACROSS THE REGION WEDNESDAY NIGHT AND THURSDAY. FOR THE WEEKEND...LOW PRESSURE WILL REMAIN OFF THE COAST WHILE HIGH PRESSURE SLOWLY PUSHES IN FROM THE CENTRAL STATES. && .NEAR TERM /THROUGH TONIGHT/... LEADING EDGE OF LIGHT PRECIP WAS MOVING INTO THE CENTRAL VA FOOTHILLS AND CENTRAL SHENANDOAH VALLEY AREA AT 9 AM. MORE SIGNIFICANT PRECIP WAS LOCATED ACROSS SOUTHWEST VIRGINIA AND WILL SHIFT NORTHEAST THROUGHOUT THE DAY AS A LOW LEVEL JET/ISENTROPIC LIFT STRENGTHEN. ONSET OF PRECIP HAS BEEN A LITTLE SLOWER THAN PREVIOUSLY FORECAST...AND GRIDS HAVE BEEN ADJUSTED TO REFLECT THIS SLIGHTLY SLOWER PROGRESSION. EAST OF THE BLUE RIDGE...WHILE A BRIEF PERIOD OF SLEET CAN/T BE RULED OUT AT THE ONSET IT LOOKS LIKE RAIN WILL BE THE PREDOMINANT P-TYPE. FURTHER WEST PARTICULARLY OVER THE HIGHER ELEVATIONS ABOVE 1000 OR SO FT...SLEET AND FREEZING RAIN IS MORE LIKELY IN A LAYER OF COLDER AIR AND THIS IS WHERE HEADLINES ARE IN EFFECT. WILL CONTINUE HEADLINES AS IS FOR NOW...WARNING ACROSS THE EXTREME WEST AND THEN ADVISORY AREAS THE REMAINDER OF THE AREA WEST OF THE BLUE RIDGE AND THE CENTRAL VIRGINIA COUNTIES ALONG THE BLUE RIDGE. FOR THESE AREAS...THIS WOULD BE FOR ICING DUE TO FREEZING RAIN ACROSS THE HIGHER ELEVATIONS. THE ADVISORY MAY BE ABLE TO BE CANCELLED EARLY OVER THE EASTERN TIER IF TEMPERATURE WARMING TRENDS CONTINUE. THE PARENT LOW MOVES TOWARD THE GREAT LAKES TONIGHT...AS ANOTHER LOW PUSHES THROUGH THE MID-ATLANTIC. EXPECT PRECIPITATION TO END FROM SOUTH TO NORTH DURING THE NIGHTTIME HOURS. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY/... WEDNESDAY MORNING THE SECONDARY LOW WILL BE PULLING NORTHEAST OF THE AREA...LEAVING JUST THE LARGE 500MB CUTOFF OVER THE MIDWEST. IN BETWEEN THE TWO...TEMPS ON SW FLOW WILL WARM INTO THE 50S AND LOWS 60S ACROSS THE FORECAST AREA ON WED. LATER...THE CENTER OF THAT 500 MB LOW WILL SLIDE SLOWLY EAST OVER SOUTHERN PA AND NORTHERN MD WED NIGHT INTO THURSDAY. WITH THE STEEP LAPSE RATES ASSOC WITH THAT...THERE WILL BE SCATTERED SHOWERS AROUND WED NIGHT INTO THU...LIKELY WILL BE A MIX OF RAIN AND SNOW SHOWERS DEPENDING ON THE TIME OF DAY AND ELEVATION OF REPORT. PRECIP AMOUNTS WILL BE LIGHT...AND WITH TEMPS STAYING ABOVE FREEZING THRU THE TIME...IMPACT OF ANY SNOW SHOWERS SHOULD BE MINIMIZED. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... AFTER THAT FOR THE END OF THE WEEK INTO EARLY NEXT WEEK...ANY PRECIP SHOULD BE LIMITED TO MOUNTAIN SNOW SHOWERS. THE OPERATIONAL GFS HAS A STRONGER UPPER LOW FORECAST OVER THE AREA ON SUNDAY...BUT IS DISCOUNTED FOR NOW. AFTER WED...TEMPS WILL BE NEAR OR BELOW NORMAL INTO EARLY NEXT WEEK. && .AVIATION /15Z TUESDAY THROUGH SATURDAY/... DELAYED ONSET OF PRECIP BY A COUPLE OF HOURS PER LATEST RADAR TRENDS. WHILE A BRIEF PERIOD OF SLEET CAN/T BE RULED OUT AT THE ONSET AT THE HUBS...IT LOOKS MORE LIKELY THAT PRECIP WILL BE RAIN. WILL TRANSITION TO MVFR CONDITIONS FOR THE AFTERNOON...THEN IFR APPEARS LIKELY BEGINNING LATE IN THE AFTERNOON OR EARLY EVENING AS PERIODS OF MODERATE TO HEAVY RAIN MOVE THROUGH. CONDITIONS WILL GRADUALLY IMPROVE BEGINNING WEDNESDAY MORNING AS LOW PRESSURE SLOWLY PULLS AWAY TO THE NORTH AND EAST. SCATTERED RAIN AND SNOW SHOWERS WILL BRING LOCALLY LOWER VSBYS AND CIGS WITH SHOWERS WED NIGHT THRU THU. AREAS OF FOG COULD DEVELOP DURING THE OVERNIGHT PERIODS WITH MOIST GROUND IN PLACE. && .MARINE... QUIET ON THE WATERS BUT ONLY FOR A FEW MORE HRS. AN INTENSE STORM SYSTEM AFFECTING AREAS FROM THE PLAINS TO THE SOUTHEAST WILL SWEEP ACROSS THE REGION TODAY. WINDS WILL PICK UP OUT OF THE EAST DURING THE MID-LATE MRNG HRS. A SFC LOW COMING OUT OF THE CAROLINAS WILL SLIDE UP TOWARD THE AREA LATER TODAY...BRINGING WIDESPREAD RAIN AND GUSTY WINDS TO THE MARINE AREAS. NEAR-GALE GUSTS WILL BE POSSIBLE LATE TONIGHT AS THE LOW MOVES OVER THE NRN CHESAPEAKE BAY. SMALL CRAFT CONDITIONS WILL ARRIVE EARLIER IN THE DAY...BUT ALSO END QUICKLY DURING THE OVERNIGHT HRS. BREEZY CONDITIONS COULD DEVELOP ON THE BACKSIDE OF THE LOW THU AND FRI. A SMALL CRAFT ADVISORY MAY BE NEEDED. WINDS ARE EXPECTED TO REMAIN BELOW ADVISORY LEVELS FRIDAY NIGHT AND SATURDAY. && .TIDES/COASTAL FLOODING... LOPRES MVG THRU THE OHVLY TUE WL PROMOTE INCRSG E/SELY FLOW. THEREFORE...WUD XPCT POS WATER ANOMOLIES TO INCR DURING THE DAY. A SECONDARY AREA OF LOPRES WIL CROSS THE WATERS WED MRNG. HOWEVER... WNDS DONT TURN W/NWLY TIL LATE DAY THU. THAT WUD SUGGEST THAT WHATEVER EXCESS WATER IS DRIVEN INTO THE ESTUARY MAY BE THERE FOR A WHILE. IN SPITE OF A FULL MOON...ETSS MDL GDNC YIELDS WATER LVLS THAT WOULDNT YIELD ADVY LVL WATER HGTS. THE 1ST TIDE OF CONSEQUENCE WOULD BE THE WED MRNG TIDE CYCLE. THE TWO TIDES ASTRONOMICALLY ARE PRACTICALLY THE SAME...SO THE SEMI-DIURNAL CYCLE WONT FACTOR CONSIDERABLY THIS TIME. ESTOFS...CBOFS AND HEC-RAS GDNC SOLNS DO RESULT IN MINOR FLOODING... EITHER BEGINNING WED MRNG /CBOFS/ OR TUE NGT /ESTOFS FOR THE WRN SHORE OF THE CHSPK BAY AS WELL AS HEC-RAS AT WASD2/. BASED ON THE PTTN...THESE RESULTS SEEM MORE REALISTIC. SINCE WE/RE AT LEAST 24 HRS OUT...WL CONT HAZARDOUS WEATHER OUTLOOK WORDING AT THIS TIME. WOULD BE MINDFUL OF BOTH TIDE CYCLES FOR STARTERS. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...FLOOD WATCH FROM 3 PM EST THIS AFTERNOON THROUGH THIS EVENING FOR DCZ001. MD...WINTER STORM WARNING UNTIL MIDNIGHT EST TONIGHT FOR MDZ501. FLOOD WATCH FROM 3 PM EST THIS AFTERNOON THROUGH THIS EVENING FOR MDZ004>006-009>011-013-014. WINTER WEATHER ADVISORY UNTIL 6 PM EST THIS EVENING FOR MDZ003- 502. VA...WINTER STORM WARNING UNTIL MIDNIGHT EST TONIGHT FOR VAZ503-504. FLOOD WATCH FROM 3 PM EST THIS AFTERNOON THROUGH THIS EVENING FOR VAZ042-053-054-501. WINTER WEATHER ADVISORY UNTIL 6 PM EST THIS EVENING FOR VAZ025>031-036>040. WV...WINTER STORM WARNING UNTIL MIDNIGHT EST TONIGHT FOR WVZ501-503- 505-506. WINTER WEATHER ADVISORY UNTIL 6 PM EST THIS EVENING FOR WVZ050>053-055-502-504. MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EST WEDNESDAY FOR ANZ530>543. && $$ BPP/CAS/GMS