Area Forecast Discussion
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000 FXUS61 KPBZ 011738 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 1238 PM EST SUN MAR 1 2015 .SYNOPSIS... SIGNIFICANT SNOW ACCUMULATIONS ARE EXPECTED ACROSS THE REGION TODAY INTO THIS EVENING...WITH SNOW MIXING WITH AND CHANGING TO RAIN FOR A PERIOD SOUTH OF I-70. A SECOND STORM...ACCOMPANIED BY MILDER TEMPERATURES...WILL BRING MOSTLY RAIN TO THE REGION TUESDAY AND TUESDAY NIGHT...POSSIBLY BEGINNING AS A PERIOD OF SNOW OR FREEZING RAIN EARLIER IN THE DAY. TEMPERATURES WILL GRADUALLY TREND WARMER THROUGH WEDNESDAY...BEFORE COLDER AIR RETURNS LATER IN THE WEEK. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... WIDESPREAD PRECIPITATION ENVELOPE EXTENDS FROM THE PENNSYLVANIA COMMONWEALTH ALL THE WAY BACK TO MISSOURI THIS MORNING...SHOWING THE VERY LARGE PRESENCE OF THIS WINTER EVENT. WIDESPREAD 2-3" SNOW AMOUNTS HAVE ALREADY BEEN REPORTED ACROSS MANY AREAS...GIVING ME SOME CONCERN. 12Z KPBZ SOUNDING SHOWS A SATURATED PROFILE...WITH THE WARMEST LAYER (950-900MB) STILL A COUPLE DEGREES CELSIUS BELOW FREEZING. TO THAT END...GIVEN THE VAST VOLUME OF PRECIPITATION ON REGIONAL RADAR IMAGERY...MOST OF THE MODEST WARM ADVECTION IS BEING REALIZED AS VERTICAL ASCENT. SEE LITTLE REASON TO JUSTIFY THE DEGREE OF MID LEVEL WARMING INDICATED IN PREVIOUS FORECASTS. THIS SHOULD ULTIMATELY YIELD A NEARLY ISOTHERMAL PROFILE JUST BELOW FREEZING...WITH THE EXCEPTION OF THE BOUNDARY LAYER IN THE LOWER ELEVATIONS. SO THE QUESTION IS JUST HOW MUCH BOUNDARY LAYER WARMING CAN WE EXPECT...AND IS THERE ENOUGH VERTICAL DEPTH GREATER THAN 0C TO MIX/CHANGE TO RAIN? IT IS QUITE POSSIBLE THAT PRECIPITATION COULD REMAIN AS SNOW AND/OR A MIX UP TO MAYBE 35-36F SURFACE TEMPERATURES. PITTSBURGH-INDIANA SEEMS LIKE A ROUGH DEMARCATION OF THE NORTHERN EXTENT OF THIS DIURNAL WARMING AS IT IS MARCH 1ST...WITH THE GREATEST CHANCE FOR A COMPLETE TEMPORARY CHANGEOVER LIKELY SOUTH OF I-70 AND WEST OF THE RIDGES. IF MY HUNCH IS CORRECT...THIS ALSO THROWS A WRENCH INTO THE LAUREL RIDGES INTO WV/MD...WHERE ITS CERTAINLY POSSIBLE THAT LOCATIONS WITH ELEVATIONS OF 2-4KFT MSL ARE ACTUALLY /ABOVE/ THE WARM LAYER AND COULD REMAIN SNOW. HAVE MADE UPWARD SNOW ADJUSTMENTS IN THESE AREAS AS WELL. WITH THAT SAID...THIS WILL BE AN EXTREMELY HEAVY...WET SNOW THAT WILL BE TOUGH TO MANAGE. PERSONS OUT SHOVELING NEED TO EXERCISE EXTREME CAUTION...TAKING FREQUENT BREAKS. ADDITIONALLY...WITH PAVEMENT TEMPERATURES SO COLD FROM THE PREVIOUS ARCTIC OUTBREAK(S)...A GLAZE OF SURFACE ICE WILL LIKELY DEVELOP ON UNTREATED...EXPOSED SURFACES WHERE SNOW MELT AND/OR RAIN MAKES CONTACT. AS FOR SNOW AMOUNTS...THIS IS AN EVENT WHERE PROPER MEASURING IS KEY. IF ONE WAITS UNTIL THE END OF THE EVENT TO STICK A RULER INTO THE SNOW...YOU MAY ONLY SEE 1/3 TO 1/2 OF WHAT ACTUALLY FELL DUE TO THE COMBINATION OF RAIN OVER THE SOUTH AND THE COMPACTION/SETTLING/MELTING OF HEAVY...WET SNOW ACROSS THE ENTIRE REGION. GIVEN 2-3" OF SNOWFALL ALREADY...TOTAL AMOUNTS OF 5-8" SEEM REASONABLE ACROSS MOST AREAS NORTH OF I-70 AS WELL AS THE RIDGES. HOWEVER...DUE TO THE LONG DURATION OF THE EVENT...MIXING OF RAIN...AND SETTLING THERE MAY NEVER BE A SNOW /DEPTH/ GREATER THAN 4-6". FOR THESE REASONS...AND THE MAINLY LIGHT NATURE TO PERIODICALLY MODERATE OF THE SNOW...WILL MAINTAIN THE UPPER END ADVISORY HEADLINE AT THIS TIME. BOOKBINDER && .SHORT TERM /6 PM THIS EVENING THROUGH TUESDAY/... BUILDING SURFACE HIGH PRESSURE WILL RESULT IN MAINLY DRY CONDITIONS ON MONDAY...HOWEVER...HOWEVER...A SOUTH-SOUTHWESTERLY 850MB JET ON THE EASTERN FLANK OF MIDWESTERN LOW PRESSURE IS PROJECTED TO STRENGTHEN ON MONDAY NIGHT AND FUEL ANOTHER ROUND OF WARM...MOIST ADVECTION WITH LIGHT PRECIPITATION AGAIN DEVELOPING OVER THE REGION. THAT PRECIPITATION LIKELY WILL BEGIN AS LIGHT SNOW...BUT WITH RAPID WARMING ALOFT...A PERIOD OF FREEZING RAIN IS LIKELY IN THE ENTRENCHED SURFACE COLD. THAT PERIOD IS EXPECTED TO BE RELATIVELY BRIEF WITH THE SURFACE LOW PROJECTED TO PASS NORTHWEST OF THE FORECAST AREA...LEAVING THE OHIO VALLEY WELL WITHIN THE WARM...HENCE THE RAIN SECTOR UNTIL COLD FRONTAL PASSAGE ON WEDNESDAY. AS MODELS TEND TO OVERDO QPF IN WARM AIR ADVECTION PATTERNS...AND GIVEN THAT THIS PROJECTED SYSTEM IS AN OPEN WAVE...QPF ON TUESDAY WAS TONED DOWN SLIGHTLY FROM THE MORE ASSERTIVE GFS VALUES. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... COLD FRONT CROSSES THE REGION TUESDAY NIGHT...REACHING THE MID- ATLANTIC REGION AROUND DAWN WEDNESDAY. RAIN WILL CONTINUE TO FALL AS THE FRONT PASSES THROUGH. WILL DECREASE POPS FROM NORTHWEST TO SOUTHEAST WEDNESDAY WITH COLDER AND DRIER AIR ADVECTING IN. ANY LINGERING PRECIPIATION WEDNESDAY AFTERNOON...WILL CHANGE TO SNOW SHOWERS AS COLDER AIR RUSHES IN FROM THE NORTHWEST. SURFACE HIGH MOVES IN THURSDAY...KEEPING THE REMAINDER OF THE LONG TERM DRY AND COLD. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/...
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IFR/OCCASIONAL LIFR CONDITIONS WILL CONTINUE INTO THE EARLY EVENING IN LOW CIG/VIS FROM SN. RAIN WILL MIX IN AT SEVERAL TERMINALS...ESPECIALLY SOUTH OF I-70...WHICH COULD ALLOW FOR TEMPORARY IMPROVEMENT TO MVFR. NORTH OF PIT...PRECIP REMAINS ALL SNOW WHICH WILL LOCK IN IFR. CIGS AT IFR/MVFR WILL BE MAINTAINED THROUGH THE NIGHT AS ANY MIXED PRECIP CHANGES BACK OVER TO SNOW. SLOW IMPROVEMENT BEGINS AFTER MIDNIGHT AS SNOW TAPERS FROM WEST TO EAST...WITH MVFR CIGS MAINTAINING THROUGH THE REST OF THE TAF PERIOD. SW WINDS THIS AFTERNOON AROUND 10 KNOTS WILL SETTLE TOWARDS WEST WITH TIME. CL .OUTLOOK.../SUNDAY NIGHT THROUGH THURSDAY/... CEILING RESTRICTIONS LIKELY WILL PERSIST THROUGH MUCH OF MONDAY. LOW PRESSURE CROSSING THE GREAT LAKES IS LIKELY TO SPAWN WIDESPREAD RESTRICTIONS ONCE AGAIN BY LATE TUESDAY.
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&& .HYDROLOGY... MANY OF THE AREA RIVERS AND STREAMS ARE ICE COVERED. AN INCREASE IN FLOW AND STAGE IS EXPECTED TO CAUSE ICE MOVEMENT STARTING TUESDAY...BEGINNING ON THE SOUTHERNMOST RIVER BASINS. THE CURRENT FORECAST CONTINUES TO HAVE A HIGH LEVEL OF UNCERTAINTY ABOUT PRECIPITATION PHASE AND AMOUNTS AS WELL AS THE DEGREE OF SNOW MELT. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...WINTER WEATHER ADVISORY UNTIL 7 AM EST MONDAY FOR MDZ001. OH...WINTER WEATHER ADVISORY UNTIL 7 AM EST MONDAY FOR OHZ039>041- 048>050-057>059. PA...WINTER WEATHER ADVISORY UNTIL 7 AM EST MONDAY FOR PAZ007>009- 013>016-020>023-029-073>076. WV...WINTER WEATHER ADVISORY UNTIL 7 AM EST MONDAY FOR WVZ001>003- 023-041. && $$

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