Area Forecast Discussion
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000 FXUS61 KPBZ 310238 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 938 PM EST FRI JAN 30 2015 .SYNOPSIS... HIGH PRESSURE WILL BUILD IN THROUGH SATURDAY. LOW PRESSURE WILL BRING WINTRY WEATHER SUNDAY INTO MONDAY. && .NEAR TERM /THROUGH SATURDAY/...
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THE FAA TERMINAL DOPPLER RADAR INDICATES ONLY A COUPLE OF MICROSCALE SNOW BANDS REMAIN...ONE OVER MOSTLY WASHINGTON COUNTY...AND ANOTHER MUCH WEAKER ONE OVER SOUTHWESTERN ALLEGHENY COUNTY. MODEL SOUNDINGS FROM BOTH THE RAP AND HRRR SHOW A SCENARIO WHEREBY INVERSION HEIGHTS ARE FALLING SIMULTANEOUSLY WITH BOUNDARY LAYER MOISTURE DEPTH DECREASING AS WELL. LIKEWISE...UPSTREAM ACTIVITY OFF OF LAKE HURON IS QUICKLY FALLING APART...AND THE TREND TOWARD ANY ADDITIONAL INPUT FROM THE SLIVER OF LAKE ERIE THAT IS OPEN WILL NOT BE PARTICULARLY HELPFUL TO REGENERATION OF ANY OF THE BANDS. THAT SAID...ACTIVITY WILL LIKELY TAKE A FEW HOURS TO WANE WITH THE UPSLOPE AREAS TAKING THE LONGEST TO FULLY HALT THEIR SNOW SHOWER AND FLURRY ACTION. NORTHWESTERLY FLOW CONTINUES THROUGH MUCH OF THE EVENING HOURS BEFORE SLOWLY TURNING WEST OVERNIGHT AS A SURFACE HIGH BUILDS GENERALLY JUST TO THE SOUTH OF THE REGION. WITH AT THE VERY LEAST PARTIAL CLEARING...IF NOT FULL CLEARING AT TIMES...TEMPERATURES SHOULD DROP RAPIDLY WITH NEW SNOW COVER. THIS COMBINED WITH DECREASING YET STILL BRISK SURFACE FLOW WILL ALLOW FOR WIND CHILL ADVISORY CRITERIA WIND CHILL INDEX VALUES BY MORNING OVER THE HIGHER TERRAIN AND NORTHEASTERN CWA. THIS IS IN LINE WITH CURRENT HEADLINES...AND NO ADDITIONAL EXPANSION OF THESE HEADLINES ARE ANTICIPATED AT THIS TIME. HOWEVER...WITH RAPID CLEARING AND NEW SNOW ON THE GROUND...ALL AREAS WILL LIKELY BE VERY COLD BY MORNING...WITH MANY PORTIONS OF THE CWA CHALLENGING OR EVEN DROPPING BELOW ZERO BY THAT JUNCTURE. SOME WARMER AIR DOES START TO FLOW NORTHWARD ON SATURDAY AS THE SURFACE HIGH AXIS MOVES TO THE EAST OF THE AREA AND SOUTHWESTERLY FLOW PREVAILS FOR A TIME. EXPECTATIONS SHOULD BE MUTED...THOUGH...AS SUCH A COLD START AND WEAK VERTICAL MIXING WILL LIKELY KEEP MOST OF THE AREA IN THE 20S. FRIES
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&& .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/... HIGH PRES SHOULD CONT DRY WEA INTO SAT EVE. A DIGGING UPR TROF IS PROGGED TO ADVN OUT OF THE PLAINS AND TRACK ACRS THE GT LKS AND OH VLY RGN SUN INTO MON. ASSOCIATED SFC LOW PRES IS PROGGED TO DEEPEN AS IT MOVES ACRS THE TN AND OH VLY RGNS ALSO. THIS WL SPREAD SNW INTO THE RGN LT SAT NGT THRU MON MRNG WITH DEEP AVAILABLE MSTR AND OMEGA. WITH A CLOSED 850MB LOW...A MORE PROLONGED PCPN EVENT IS EXPD AS OPPOSED TO THE OPEN SYSTEM EARLIER IN THE WK. WITH ENOUGH POTENTIAL FOR HEAVY SNW OR A SNW/ICE MIX...ISSUED A WINTER STORM WATCH FOR MUCH OF THE AREA. LEFT AREAS GENLY S OF I 70 OUT OF THE WATCH...EXCEPT FOR THE WV/MD RIDGES...AS ENOUGH WRM AIR IS EXPD TO WRAP IN AHD OF THE LOW TO ALLOW FOR A RAIN/SNW MIX OR EVEN A PD OF ALL RAIN. AREAS BETWEEN I 70- AND I 80 COULD SEE ENOUGH WRM AIR ALOFT FOR FRZG RAIN TO MIX IN AT TIMES AS WELL. GENLY FOLLOWED A SREF/GFS/ECMWF MDL BLEND TO WORK OUT THE DETAILS...AND USED CRITICAL THICKNESSES/MDL SOUNDING PROFILES FOR PCPN TYPE. BEST POTENTIAL FOR GREATER THAN 6 INCHES OF SNW EXISTS N OF PIT BASED ON LATEST MDL GUIDANCE...THOUGH THIS WL BE REFINED OVR THE NXT COUPLE OF DAYS. SNW SHOULD CONT MON UNTIL THE UPR TROF AXIS SHIFTS E IN THE AFTN. NUDGED TEMPS TO THE LATEST COLDER THAN SEASONAL AVG SREF GUIDANCE. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... A COLD...WINTER PATTERN WILL CONTINUE FOR THE REST OF THE LONG TERM. THE NEXT BEST CHANCE FOR SNOW SHOWERS WILL ARRIVE LATE IN THE PERIOD. && .AVIATION /03Z SATURDAY THROUGH WEDNESDAY/... LINGERING MVFR STRATOCUMULUS AND SNOW SHOWERS CONTINUE TO PLAGUE SEVERAL OF THE TAF SITES EARLY TONIGHT. THIS IS IN PART DUE TO WHAT LOOKS TO BE AN UPSTREAM CONNECTION WITH MOISTURE FROM LAKE HURON. SUBSIDENCE FROM THE BUILDING RIDGE AND A WESTERLY WIND SHIFT WILL HELP TO DIMINISH THE CLOUD COVER AND IMPROVE CONDITIONS OVER NEXT FEW HOURS...WITH THE HRRR AND RUC SUGGESTING VFR CONDITIONS BY 03Z. IN ADDITION...WINDS WILL WEAKEN WITH THE BUILDING HIGH PRESSURE....WITH NEARLY CALM WIND ANTICIPATED OVERNIGHT. VFR CONDITIONS WILL REMAIN THROUGH THE REST OF THE TAF PERIOD...WITH HIGH CLOUDS AND SOME DIURNAL CU DEVELOPING SATURDAY AFTERNOON AHEAD OF THE SYSTEM PROGGED FOR SUNDAY. .OUTLOOK.../SATURDAY NIGHT THROUGH WEDNESDAY/... WIDESPREAD RESTRICTIONS CAN BE EXPECTED SUNDAY AND MONDAY AS A LOW PRESSURE SYSTEM CROSSES THE REGION. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...WINTER STORM WATCH FROM LATE SATURDAY NIGHT THROUGH MONDAY MORNING FOR MDZ001. WIND CHILL ADVISORY UNTIL 10 AM EST SATURDAY FOR MDZ001. OH...WINTER STORM WATCH FROM LATE SATURDAY NIGHT THROUGH MONDAY MORNING FOR OHZ039>041-048>050-057>059. PA...WINTER STORM WATCH FROM LATE SATURDAY NIGHT THROUGH MONDAY MORNING FOR PAZ007>009-013>016-020>023-029-073>076. WIND CHILL ADVISORY UNTIL 10 AM EST SATURDAY FOR PAZ008-009- 015-016-023-074-076. WV...WINTER STORM WATCH FROM LATE SATURDAY NIGHT THROUGH MONDAY MORNING FOR WVZ001>003-023-041. WIND CHILL ADVISORY UNTIL 10 AM EST SATURDAY FOR WVZ023-041. && $$

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