Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 030855 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 355 AM EST TUE MAR 3 2015 .SYNOPSIS...
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HIGH PRESSURE WILL PERSIST OVER THE AREA THIS MORNING. A WARM FRONT WILL LIFT THROUGH THE AREA THIS AFTERNOON AND EVENING. A COLD FRONT WILL MOVE INTO THE REGION WEDNESDAY FOLLOWED BY HIGH PRESSURE FOR THURSDAY LASTING INTO THE WEEKEND.
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&& .NEAR TERM /THROUGH TONIGHT/...
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AS OF 08Z...1031MB SFC HIGH CENTERED OVER E-CNTRL PA WITH 1030MB PRESSURE OVER MOST OF LWX. SFC WINDS EITHER DECOUPLED OR LIGHT OUT OF THE NORTH. TRANSLUCENT CI HAS OVERSPREAD THE AREA... WILL THICKEN REST OF THE NIGHT...LIMITING MIN TEMPS A DEGREE OR TWO. MOST AREAS TO START THE MORNING IN THE LOW TO MID 20S. PRECIP FOR TODAY/TONIGHT IS ADVANCING EAST OVER IL/IN...AHEAD OF AN UPR TROUGH MOVING EAST FROM THE NRN PLAINS. CLOUDS SHOWING UP ON RADAR WEST FROM SRN SHEN VLY. WITH DRY SFC CONDITIONS...NO PRECIP IS EXPECTED OUT THERE FOR A FEW MORE HOURS. TODAY...PRECIP ONSET CONSENSUS TO BE LATE MORNING FOR WRN/NWRN SECTION OF THE CWA...AFTER NOON FOR MUCH OF THE REST OF THE AREA INCLUDING DC. THEREFORE...PUSHED BACK THE WINTER WEATHER ADVISORY BEGINNING TIMES TO 10 AM FOR SHEN VLY AND N-CNTRL VA AND NOON FOR GREATER BALT-WASH AND SRN MD. WITH WARM AIR RETURN NOT DELAYED... THE WINDOW FOR FROZEN/FREEZING PRECIP IS SHORTER FOR AREAS LIKE SRN MD. HOWEVER... THE NRN TIER SHOULD SEE SNOW/SLEET ACCUMS OF PERHAPS HALF AN INCH BEFORE GETTING ICE ACCRETION. LEFT HEADLINES UP FOR ALL AREAS CONSIDERING THE FREEZING RAIN THRESHOLD IS JUST A TRACE. THIS EVENING...TYPICAL AREAS IN THE NRN SHEN VLY/WRN MD AND NRN MD SEE FREEZING RAIN THE LONGEST. MAY NEED TO EXTEND UNTIL MIDNIGHT OR SO FOR NRN TIER OF MD COUNTIES ALONG THE MASON-DIXON LINE FOR TEMPS LINGERING NEAR FREEZING. TEMPERATURES RISE OVERNIGHT WITH PLAIN RAIN BY MIDNIGHT FOR THE ENTIRE AREA. RAIN RATES INCREASE OVER ALLEGHENIES LATE...WILL NEED TO BE ON THE LOOKOUT FOR FLOODING CONCERNS GIVEN EXPECTED SNOWPACK MELT WITH HIGHLANDS TEMPERATURES IN THE 40S. ONE TO TWO TENTHS QPF EAST OF THE ALLEGHENY FRONT AND HALF INCH OR MORE WEST.
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&& .SHORT TERM /WEDNESDAY THROUGH THURSDAY/...
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WEDNESDAY...COLD FRONT ENTERS CWA FROM THE WEST IN THE MORNING AND DRIFTS EAST. WARMEST AIR IN NEARLY A MONTH (60F AT KIAD ON FEB 8) AHEAD OF THE FRONT WITH LOW 50S (A LITTLE LOWER THAN PREVIOUS FORECASTS) EXPECTED GIVEN WIDESPREAD RAIN OVER THE AREA AT THE TIME. QPF QUARTER TO HALF INCH OF RAIN OVER THE AREA WEDNESDAY. MOST OF THE AREA LOOKS TO BE BETWEEN SHORTWAVES IN THE AFTERNOON...REDUCING RAIN RATES. WEATHER IMPACTS WILL INCREASE WEDNESDAY NIGHT. SFC BOUNDARY MAY HAVE PUSHED A GOOD PART OF THE WAY THROUGH DURING THE EVENING...AS A WEAK SFC WAVE IS PROJECTED TO CROSS THE CAROLINAS OVERNIGHT. HOWEVER... COLDER TEMPS...ESPECIALLY ALOFT...WILL BE SLOW TO WORK SOUTHWARD. PER COORDINATION WITH WPC...A GFS/ECMWF SOLUTION IS FAVORED...WHICH ALLOWS THERMAL PROFILES TO COOL A BIT MORE QUICKLY AMONGST THE MODEL SUITE. THIS ALSO GIVES A MORE DEFINITIVE RAIN-TO-SNOW TRANSITION VS A MORE PRONOUNCED WARM NOSE IN THE NAM (LIKELY DUE TO A STRONGER SSW LLJ IM THE 850-600MB LAYER) AND MORE MIXED PRECIP. CANNOT RULE OUT A PERIOD OF IP/FZRA...BUT DID NOT HAVE ENOUGH CONFIDENCE ON TIMING/PLACEMENT TO INCLUDE IN THE FORECAST AT THIS TIME. ON THE WHOLE THOUGH...THERE WAS A SLIGHT SLOWING TREND OVERALL IN THE TIMING OF PRECIP THROUGHOUT THE EVENT. ALL AREAS ARE FORECAST TO BE SNOW BY THURSDAY MORNING...WITH PRECIP ENDED NW-SE DURING THE DAY. TEMPERATURES WILL HOLD STEADY OR FALL. SNOWFALL AMOUNT FORECASTS WILL BE CHALLENGING GIVEN THE UNCERTAINTIES WITH PTYPES...TIMING...AND HOW MUCH MOISTURE FALLS IN THE COLD AIR. THERE WILL BE TREMENDOUS MOISTURE TRANSPORT WITH THE LLJ AS WELL AS LIFT ASSOCIATED WITH UPPER JET...BUT THE AXIS OF HIGHEST QPF WILL LIKELY BE VERY NEAR THE TRANSITION ZONE...WITH POTENTIAL FOR COLDER BUT DRIER AIR TO BEGIN WORKING INTO THE BACK SIDE. NOT MUCH CHANGE TO CURRENT FORECAST OVER PREVIOUS. IF THE QPF INDEED FALLS AFTER THE TRANSITION TO SNOW...OUR CURRENT FORECAST IS ON THE CONSERVATIVE SIDE. HOWEVER FEEL THERE IS STILL TOO WIDE OF A SPREAD IN SOLUTIONS TO GO HIGHER. SEE OUR WEBPAGE FOR THE PROB RANGES. WILL ALLOW DAYSHIFT TO DECIDE ON POTENTIAL FOR WATCHES. HIGHEST CONFIDENCE IN LARGER SNOW TOTALS ARE OVER THE HIGHLANDS AT THIS TIME.
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&& .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
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ARCTIC HIGH PRESSURE WILL QUICKLY BUILD IN THURSDAY NIGHT. THERE MAY BE A PERIOD OF UPSLOPE SNOW SHOWERS IN THE EVENING. NAM INDICATES SNOW SHOWERS WILL BE POSSIBLE EAST OF THE MOUNTAINS AS WELL AS A VORT MAX PASSES...BUT HAVE NOT INCLUDED THIS IN THE FORECAST NOW. TEMPERATURES HAVE TRENDED COLDER...SINGLE DIGITS EXCEPT IN THE METROS/NEAR THE BAY AND BELOW ZERO IN THE HIGHLANDS. IF GRADIENT DOES NOT RELAX...WIND CHILL ADVISORIES MAY BE NEEDED IN THE HIGHLANDS. THE HIGH WILL SLIDE EAST ACROSS THE AREA THROUGH SATURDAY. FRIDAY WILL STILL BE QUITE COLD BUT TEMPERATURES BEGIN TO MODERATE SATURDAY. MOISTURE STARVED COLD FRONTS TRAILING LOW PRESSURE CENTERS WELL TO THE NORTH WILL MAKE RUNS AT THE AREA SATURDAY NIGHT AND AGAIN MONDAY. FOR NOW HAVE ONLY INCLUDED POPS IN THE UPSLOPE AREAS. THERE ALSO WILL BE LITTLE EFFECT ON TEMPERATURES...WITH READINGS SLIGHTLY BELOW NORMAL EXPECTED.
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&& .AVIATION /09Z TUESDAY THROUGH SATURDAY/...
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VFR THIS MORNING UNDER HIGH PRESSURE. LIGHT WINTRY MIX OVERSPREADS THE TERMINALS LATE THIS MORNING (KMRB AND KCHO) THROUGH THE AFTERNOON (DC METROS) AS A WARM FRONT APPROACHES. HIGH CLOUDS THICKEN AND LOWER TO MVFR CIGS BY MIDDAY...IFR CIGS EXPECTED LATE THIS AFTERNOON INTO THE OVERNIGHT. LIGHT SLEET/SNOW AT ONSET CHANGING QUICKLY OVER TO FREEZING RAIN. PLAIN RAIN SPREADS NORTH OVER THE AREA THIS AFTERNOON AND EVENING. RAIN INTENSITY PICKS UP LATE TONIGHT WITH IFR CONDS POSSIBLE AND PARTICULARLY FOR WEDNESDAY MORNING WHEN IFR CONDS ARE MORE LIKELY IN MODERATE RAIN. RAIN IS FORECAST TO CHANGE TO SNOW THURSDAY NIGHT. VSBY/CIG REDUCTIONS WILL CONTINUE AND MAY DROP TO LIFR IF MODERATE/HEAVY SNOW DEVELOPS. THE SNOW WILL END ON THURSDAY. NO AVIATION HAZARDS EXPECTED THEREAFTER.
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&& .MARINE...
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LIGHT NLY FLOW UNTIL SUNRISE WHEN HIGH PRESSURE CENTERS OVER THE CHESAPEAKE BAY REGION. WARM FRONT APPROACHES THIS MORNING...LIFTING NORTH OVER THE MD PART OF THE BAY THIS AFTERNOON AND EVENING. SLY FLOW THIS EVENING EXPECTED TO GET TO 15 KT...HELD OFF ON SCA FOR NOW THOUGH SOME 18 KT GUSTS POSSIBLE. COLD FRONT APPROACHES WEDNESDAY WITH WIDESPREAD RAIN. A COLD FRONT WILL PASS THROUGH THE WATERS WEDNESDAY NIGHT. RAIN WILL CHANGE TO SNOW BY THURSDAY MORNING. SCA CONDITIONS ARE POSSIBLE FROM LATE WEDNESDAY NIGHT THROUGH THURSDAY NIGHT BEHIND THE FRONT. WINDS WILL SUBSIDE THEREAFTER UNDER HIGH PRESSURE.
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&& .HYDROLOGY...
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LIQUID PRECIP FCST FROM WPC WEDNESDAY AND WEDNESDAY NIGHT AREA ONE TO ONE AND A HALF INCHES. WITH TEMPERATURES EXPECTED TO RISE INTO THE 50S ON WEDNESDAY...THERE WILL BE SOME...POSSIBLY A LOT OF...MELTING OF THE EXISTING SNOWPACK...WHICH COMPUTER MODELS AND OBSERVATIONS INDICATE CONTAINS ANYWHERE FROM 3/4 INCH TO 2 INCHES OF SNOW WATER EQUIVALENT. THIS COMBINATION MAY LEAD TO MINOR FLOODING AS THE RAIN FALLS ON WEDNESDAY. FURTHER COMPLICATING THIS FORECAST IS AN EXPECTED CHANGEOVER TO SNOW WEDNESDAY NIGHT FOR MUCH OF THE AREA. ALTHOUGH RIVER ICE IS NOT ESPECIALLY THICK...IT WILL HAVE TO BE MONITORED FOR POTENTIAL ROLE IN AFFECTING RUNOFF. ALSO...PLOWED SNOW IS LIKELY COVERING SOME OF THE DRAINS OUT THERE...WHICH COULD CAUSE MORE POOR DRAINAGE FLOODING THAN WOULD OTHERWISE USUALLY BE EXPECTED.
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...WINTER WEATHER ADVISORY FROM NOON TODAY TO 10 PM EST THIS EVENING FOR DCZ001. MD...WINTER WEATHER ADVISORY FROM 7 AM THIS MORNING TO 7 PM EST THIS EVENING FOR MDZ501-502. WINTER WEATHER ADVISORY FROM NOON TODAY TO 10 PM EST THIS EVENING FOR MDZ004>006-011-013-014-503>508. WINTER WEATHER ADVISORY FROM 10 AM THIS MORNING TO 10 PM EST THIS EVENING FOR MDZ003. WINTER WEATHER ADVISORY FROM NOON TODAY TO 7 PM EST THIS EVENING FOR MDZ016>018. VA...WINTER WEATHER ADVISORY FROM 7 AM THIS MORNING TO 7 PM EST THIS EVENING FOR VAZ503-504. WINTER WEATHER ADVISORY FROM 10 AM THIS MORNING TO 7 PM EST THIS EVENING FOR VAZ025>031-036>040-050-051-501-502-507- 508. WINTER WEATHER ADVISORY FROM NOON TODAY TO 10 PM EST THIS EVENING FOR VAZ053-054-505-506. WINTER WEATHER ADVISORY FROM NOON TODAY TO 7 PM EST THIS EVENING FOR VAZ052-055>057. WV...WINTER WEATHER ADVISORY FROM 7 AM THIS MORNING TO 7 PM EST THIS EVENING FOR WVZ050-055-501>506. WINTER WEATHER ADVISORY FROM 10 AM THIS MORNING TO 10 PM EST THIS EVENING FOR WVZ051>053. MARINE...NONE. && $$ SYNOPSIS...BAJ/ADS NEAR TERM...BAJ SHORT TERM...BAJ/ADS LONG TERM...ADS AVIATION...BAJ/ADS MARINE...BAJ/ADS HYDROLOGY...LWX

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