Area Forecast Discussion
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000 FXUS61 KPBZ 270811 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 311 AM EST FRI FEB 27 2015 .SYNOPSIS... A DISTURBANCE WILL BRING CHANCES FOR LIGHT SNOW THROUGH THIS EVENING. DRY AND FRIGID CONDITIONS WILL END THE WEEK. && .NEAR TERM /THROUGH TONIGHT/... SNOW QUICKLY TAPERING OFF WEST TO EAST ACROSS THE RIDGES AT THIS HOUR...WILL COMPLETELY EXIT BY 12Z. CURRENT 11-3.9 MICRON FOG CHANNEL SATELLITE IMAGERY SHOWING SKIES CLEARING QUICKLY BEHIND THE EXITING SNOW. MID- AND HIGH-LEVEL MOISTURE HAS ALREADY EVACUATED THE AREA...LEAVING ONLY THE LOW-LEVEL MOISTURE ASSOCIATED WITH THE DWINDLING SNOW. THE RATE OF CLEARING IS A BIT FASTER THAN PREVIOUS GUIDANCE INDICATED...BUT THE LATEST HI-RES MODELS HAVE A GOOD HANDLE ON THIS. ULTIMATELY CUT BACK ON CLOUD COVER THIS MORNING THROUGH MIDDAY WHERE AT LEAST MOSTLY SUNNY CONDITIONS ARE EXPECTED. DESPITE THE MORE POTENT LATE FEBRUARY SUNSHINE...TEMPERATURES WILL REMAIN COLD THROUGH THE DAY AS COLD AIR CONTINUES TO ADVECT IN. COLDEST 850MB TEMPERATURES NEAR -22C WILL BE DIRECTLY OVERHEAD THIS AFTERNOON AS HIGH PRESSURE BUILDS. AS THE SUN SETS TONIGHT...TEMPERATURES WILL FALL QUICKLY UNDER CALM...DRY AND MOSTLY CLEAR CONDITIONS. THIS SHOULD OPTIMIZE RADIATIONAL COOLING FOR MOST LOCATIONS...ESPECIALLY THOSE LOCATIONS THAT RECEIVED A FRESH COATING OF SNOW. SFC HIGH PRESSURE WILL BE DIRECTLY OVER THE FORECAST AREA PRE-DAWN SATURDAY. MODELS CONTINUE TO SHOW WARMING OF THE MID-LEVELS TO THE TUNE OF 6 TO 8 DEGREES C ABOVE THE 00Z MINIMUMS. WITH A LACK OF FLOW BETWEEN THE SFC AND 750MB...A NEAR SFC INVERSION WILL DECOUPLE THE ATMOSPHERE AND DROP TEMPERATURES BELOW ZERO FOR MOST LOCATIONS...WELL BELOW ZERO ACROSS THE NORTHERN ZONES. AT THIS POINT...THE ONLY FLY IN THE OINTMENT FOR TEMPERATURES AS LOW AS FORECAST IS POSSIBILITY OF HIGH CLOUDS SHIELDING THE OUTGOING LONGWAVE RADIATION. THE 00Z NAM IS A LITTLE BIT FASTER IN INTRODUCING HIGH CLOUDS IN RESPONSE TO A WEAK UPPER LEVEL WAVE. ULTIMATELY TWEAKED SAT MORNING LOWS...WHICH INCLUDES BUMPING UP TEMPERATURES ACROSS THE SRN 1/2 OF THE CWA BY A DEGREE OR TWO. AFTER DAYBREAK SATURDAY...THE NEAR SFC TEMPERATURE INVERSION SHOULD MIX OUT AND ALLOW FOR A QUICK WARM-UP UNDER MOSTLY SUNNY CONDITIONS. TAX && .SHORT TERM /SATURDAY/... WITH HIGH PRESSURE OVERHEAD FRI NIGHT/SAT MORNING TEMPERATURES SHOULD DROP SIGNIFICANTLY ONCE AGAIN...WITH THE HELP OF STRONG RADIATIONAL COOLING AND SNOWPACK. TEMPERATURES SHOULD MODERATE ON SATURDAY HOWEVER...AS WINDS SHIFT TO THE SOUTHWEST AND WARM ADVECTION ENSUES. NEXT SYSTEM WILL MAKE ITS APPROACH ON SUNDAY. AS OF NOW...THE SURFACE LOW LOOKS TO MOVE RIGHT ACROSS THE FORECAST AREA...WITH WARM ADVECTION AND 850 TEMPERATURES WARM ENOUGH TO BRING A MIX TO AREAS 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. HAVE HIGHLIGHTED THIS FEATURE IN THE HWO AS SOME ACCUMULATING SNOW MAY BE POSSIBLE...DEPENDING ON THE TRACK AND WARM AIR ALOFT. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... 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 /07Z FRIDAY THROUGH TUESDAY/... SNOW AND ASSOCIATED MVFR CLOUD COVER IS CONTINUING TO WANE THIS MORNING. THE LATEST SATELLITE IMAGERY REVEALS CLEARING SKIES WEST TO EAST. MVFR CEILINGS MAY HOLD IN MGW AND LBE THIS MORNING FOR A FEW MORE HOURS...BUT ALL SITES ARE EXPECTED TO BE VFR WITH MOSTLY CLEAR SKIES BY DAYBREAK. HIGH PRESSURE WILL ENSURE VFR CONDITIONS WITH WEAK SURFACE FLOW THROUGH THE BALANCE OF THE TAF PERIOD. TAX OUTLOOK.../FRIDAY NIGHT THROUGH TUESDAY/... RESTRICTIONS ARE LIKELY WITH CROSSING LOW PRESSURE SUNDAY INTO MONDAY. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...NONE. WV...NONE. && $$

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