Area Forecast Discussion
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000 FXUS61 KPBZ 261135 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 635 AM EST THU FEB 26 2015 .SYNOPSIS...
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A DISTURBANCE WILL BRING CHANCES FOR SNOW TODAY. DRY AND FRIGID CONDITIONS WILL END THE WEEK.
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&& .NEAR TERM /THROUGH TONIGHT/...
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UPDATE TO INCREASE POPS N OF I 80 WHERE SURFACE OBSERVATIONS AND RADAR SHOWED SNOW REACHING THE GROUND. PREVIOUS...CURRENT RADAR IMAGERY SHOWS WEAK ECHOES ASSOCIATED WITH VIRGA BEGINNING TO ENCROACH THE AREA...SEEMINGLY FROM ALL SIDES. CURRENT DEWPOINT SPREADS OF 10 TO 15 DEGREES AND A SIGNIFICANT LAYER OF DRY AIR RECORDED ON THE 00Z UPPER AIR SOUNDING WILL CONTINUE TO HAMPER FURTHER DEVELOPMENT OF SNOW THIS MORNING. AS THE SOUTHERN STREAM LOW PRESSURE SYSTEM GETS EJECTED FROM THE REGION BY THE UPPER LEVEL TROF THIS MORNING...DEEPER MOISTURE WILL SKIRT THE SOUTHEAST RIDGE ZONES. THIS WILL RESULT IN ENHANCED CLOUD COVER AND LIGHT SNOW BANDS ENTERING THE SOUTHEASTERN PART OF THE FORECAST AREA. BEST CHANCE OF THIS HAPPENING WILL BE FROM ABOUT SUNRISE THROUGH MIDDAY. CLOUDS OVERSPREADING THE AREA WILL KEEP TODAYS HIGHS IN CHECK. AT THE SAME TIME...A RELATIVELY DRY UPPER LEVEL TROF WILL SWING THROUGH THE SOUTHERN GREAT LAKES AND DEEPEN THE MOISTURE OVER THE EASTERN OH AND NORTHWEST PA. ALTHOUGH THERE IS A GENERAL LACK OF FORCING WITH THIS SYSTEM...THE MODEST LIFT WITH THE APPROACHING 700MB TROF AND DEEPER MOISTURE SHOULD BE ENOUGH TO GENERATE LIGHT SNOW. BY EVENING THE 850MB TROF IS CLEARING THE AREA AND WIND WILL SHIFT TO THE NORTHWEST. THIS WILL BRING IN MUCH COLDER AIR AS THE NIGHT PROGRESSES. A COMBINATION OF THE STRONG COLD AIR ADVECTION AND THE PASSAGE OF THE MID-LEVEL TROF WILL GENERATE POSSIBLY THE BEST CHANCES OF SNOW AREA WIDE FROM LATE EVENING TO MIDNIGHT. MODEL SOUNDINGS SHOW LOW LEVEL LAPSE RATES STEEPENING AS 850MB TEMPERATURES DROP BELOW -15C. CONVECTIVELY DRIVEN SNOW SHOWERS WILL GENERALLY BE LIGHT...BUT SNOW RATIOS SHOULD INCREASE AS THE COLDER AIR INVADES THE MOISTURE SOURCE LAYER. ALL TOLD A QUICK COATING COULD FALL THROUGH THE NIGHT...MAINLY EAST OF THE OH/WV BORDER...1-2" COULD OCCUR IN THE MOUNTAINS OF WV/PA/MD AS RESIDENCE TIME WILL BE LONGER. TAX
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&& .SHORT TERM /FRIDAY THROUGH SATURDAY/... INCREASED LOWS A DEGREE OR TWO THURS NIGHT...AS THE COLDER AIR IS A BIT SLOWER TO MOVE IN. A NORTHWEST TO SOUTHEAST GRADIENT WILL BE PRESENT IN LOW TEMPERATURES THROUGH FRI MORNING. LOWS SHOULD BE IN THE SINGLE DIGITS BELOW ZERO ACROSS OUR FAR NORTHWESTERN ZONES IN OH/PA. WINDS WILL BE DIMINISHING...BUT MARGINAL ADVISORY LEVEL WIND CHILL VALUES MAY OCCUR. CONFIDENCE IN KEEPING WIND ABOVE 5KTS IS NOT HIGH ENOUGH AT THIS TIME...PRECLUDING THE NEED FOR AN ADVISORY. FRIDAY WILL FEATURE CLEARING SKIES...BUT TEMPERATURES ARE EXPECTED TO REMAIN WELL BELOW AVERAGE...TOPPING OUT IN THE TEENS. THIS IS DUE TO THE MUCH COLDER AIR MASS IN PLACE IN THE WAKE OF THE LATEST FRONT. SUNSHINE FRIDAY AFTERNOON WILL CHALLENGE THE COLD AIR AND MAY BUMP HIGHS UP A FEW DEGREES...BUT OVERALL A COLD DAY IS ON TAP. WITH HIGH PRESSURE OVERHEAD FRI NIGHT/SAT MORNING THE BOTTOM WILL ONCE AGAIN FALL OUT ON THE TEMPERATURES AS IDEAL RADIATIONAL COOLING WILL SET UP. DESPITE WARM AIR ADVECTION TAKING PLACE IN THE LOW- TO MID-LEVELS...THE ATMOSPHERE SHOULD DECOUPLE AND WONT ALLOW THE WARMER AIR TO MIX DOWN. WITH THE REMAINING SNOWPACK IN PLACE...TEMPERATURES ARE EXPECTED TO ONCE AGAIN DIP BELOW ZERO...POSSIBLY CHALLENGING SOME DAILY LOW RECORDS. ONCE AGAIN...LACK OF SURFACE FLOW WILL PRECLUDE THE NEED FOR A WIND CHILL ADVISORY...BUT IT WILL BE COLD NEVERTHELESS. SATURDAY OFFERS A QUICK WARM UP WITH MIXING OF THE WARMER AIR ALOFT AND ABUNDANT SUNSHINE. HIGH CLOUDS WILL BEGIN STREAMING IN FROM THE SOUTHWEST LATER IN THE DAY...BUT THE DRY TREND WILL HOLD THROUGH SATURDAY. TAX && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... A SHORTWAVE AND ITS ASSOCIATED COLD FRONT IS PROGGED APPROACH AND CROSS THE GREAT LAKES AND UPPER OHIO VALLEY REGION LATE SATURDAY NIGHT THROUGH SUNDAY NIGHT. WARM ADVECTION AHEAD OF THE WAVE SHOULD ALLOW FOR A MIX OF RAIN AND SNOW SOUTH OF I 80...WITH MAINLY SNOW TO THE NORTH. A BRIEF PERIOD OF FREEZING RAIN IS POSSIBLE BUT NOT ENOUGH CONFIDENCE IN THE DETAILS TO INCLUDE AT THIS TIME. A PATTERN CHANGE AND RELATIVE WARM UP THEN SETS UP THROUGH MUCH OF NEXT WEEK AS WESTERN CONUS TROUGHING DEVELOPS. SHORTWAVES ARE PROGGED TO EJECT OUT OF THE TROUGH AND MOVE ACROSS THE OHIO VALLEY REGION IN SOUTHWEST FLOW...KEEPING PERIODIC RAIN AND SNOW CHANCES THROUGH LATE WEEK. THE BEST CHANCE APPEARS TO BE WITH A TUESDAY/TUESDAY NIGHT WAVE. MODEL QPF AMOUNTS APPEAR TO BE OVERDONE IN THE WARM ADVECTION REGIME...BUT WILL MONITOR AS A DECENT SNOWPACK REMAINS. ENSEMBLE BASED WPC GUIDANCE OFFERED A REASONABLE START TO THE FORECAST...THOUGH MADE ADJUSTMENTS TO THE LATEST GFS TO WARM SOME TEMPS...WITH ADJUSTMENTS FOR PRECIP TYPE BASED ON GFS CRITICAL THICKNESSES. && .AVIATION /12Z THURSDAY THROUGH MONDAY/...
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VFR CONDITIONS ARE EXPECTED FOR MOST PORTS INTO EARLY MORNING AS CLOUDS INCREASE WITH A COUPLE OF APPROACHING SHORTWAVES. ANY SNOW FROM A WAVE CROSSING THE MID ATLANTIC REGION SHOULD STAY TO OUR SOUTH. THE SECOND SHORTWAVE PROGGED TO ADVANCE ACROSS THE GREAT LAKES TODAY SHOULD SPREAD MVFR CONDITIONS WITH SCATTERED SNOW SHOWERS ACROSS AREA PORTS...AND THIS WAS ALREADY AFFECTING FKL THIS MORNING. PATCHY IFR CONDITIONS ARE EXPECTED ALSO THIS AFTERNOON...ESPECIALLY FROM PIT NORTH. SNOW SHOWERS SHOULD DECREASE AS SUPPORT EXITS TONIGHT...THOUGH MVFR CEILINGS SHOULD REMAIN. OUTLOOK.../FRIDAY THROUGH MONDAY/... RESTRICTIONS ARE LIKELY WITH CROSSING LOW PRESSURE SUNDAY INTO MONDAY.
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&& .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...NONE. WV...NONE. && $$

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