Area Forecast Discussion
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000 FXUS61 KPBZ 272345 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 645 PM EST TUE JAN 27 2015 .SYNOPSIS... HIGH PRESSURE WILL BUILD AND DECREASE CLOUDS TONIGHT. A COLD WEDNESDAY WILL FOLLOW. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... COVERAGE OF LIGHT SNOW HAS BEEN EXPANDING RAPIDLY OVER THE PAST HOUR OR SO AS THE LAST DEFORMATION ZONE HAS BEEN SHIFTING WEST AND SOUTHWESTWARD FROM CENTRAL PENNSYLVANIA BACK INTO WESTERN PENNSYLVANIA. THIS HAS ALLOWED FOR EXTREMELY EFFICIENT SNOW TO DEVELOP WITH RATIOS LIKELY IN EXCESS OF 25 TO 1. THIS COUPLED WITH UNIDIRECTIONAL UPSLOPE FLOW FROM THE NORTHWEST IN THE BOUNDARY LAYER INTO THE RIDGES HAS ALLOWED FOR AN INTENSIFYING TREND FOR SNOW SHOWERS IN THE RIDGES AS WELL. MODEL SOUNDINGS SUGGEST A 3 KFT SATURATED LAYER ENTIRELY BISECTING THE DENDRITIC GROWTH LAYER WITH AN UNSTABLE...OROGRAPHIC...AND NOW LARGE SCALE LIFTING MECHANISM ALL OVERLAYING THE RIDGES FOR THE NEXT ROUGHLY 10 HOURS OR SO. GIVEN GROUND TRUTH REPORTS FROM GARRETT COUNTY OF NEAR ADVISORY LEVEL ACCUMULATIONS TODAY ALONG WITH AN INCREASINGLY FAVORABLE ENVIRONMENT FOR SNOW SHOWER DEVELOPMENT THROUGH MUCH OF THE EVENING...WINTER WEATHER ADVISORIES WERE HOISTED FOR THE RIDGES THROUGH 1 AM. ELSEWHERE...LIGHT SNOW WILL LARGELY BE GENERATED BY THE SOUTHWESTWARD DRIFTING DEFORMATION ZONE. ACCUMULATIONS OUTSIDE OF THE OROGRAPHIC LIFTING AREAS WILL LIKELY BE MINIMAL...DUE LARGELY TO MEAGER QPF...THOUGH THE SNOW TO LIQUID RATIOS THAT COME OUT OF IT WILL LIKELY BE LARGE. THAT SAID...IT WOULD NOT BE SHOCKING TO GET AN INCH ANYWHERE IN PARTICULAR GENERALLY FROM STEUBENVILLE EASTWARD. OTHERWISE...DRIER ARCTIC AIR WILL START TO ENCROACH FROM THE NORTHEAST OVERNIGHT...WHICH SHOULD WIND SNOW SHOWER ACTIVITY DOWN BY MORNING...AND ALLOW FOR TEMPERATURE FREE FALL LATE TONIGHT. IT SEEMS THE SNOW GLOBE WILL CONTINUE TO BE SHAKEN OUTSIDE UNTIL THAT TIME. FRIES && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/... WEDNESDAY HIGHS WERE LIMITED TO ROUGHLY 10 DEGREES UNDR THE AVGS WITH SFC HIGH PRES SLIDING ACRS THE UPR OH REGION. SHRTWV RIDGING WL MAINTAIN DRY CONDITIONS THROUGH WEDNESDAY NIGHT...BUT STRENGTHENING WARM ADVCTN IN ADVN OF TROUGH DIGGING RAPIDLY TWD THE WRN LAKES WL IMPROVE THE THURSDAY MRNG LOWS. THE NAM...GFS...ECMWF FORECASTED CENTER TRACK OF THAT SYSTEM RMNS N OF THE REGION...HENCE CONTD WARM ADVCTN ON THE ERN FLANK IS EXPECTED TO LIMIT SNOW ACCUMULATION POTENTIAL. HOWEVER...THE SCENARIO WL FAVOR A WINTRY MIX COMPLICATED BY COLD SURFACES LEFTOVER OVR FM THE PREVIOUS TWO NGTS. ANY PCPN THAT DOES TURN TO RAIN WL STILL HAVE THE POTENTIAL TO FREEZE ON CONTACT. IN ADDITION...THE DRY LAYER WHICH IS PROGGED TO LIMIT PCPN ONSET IN THE MRNG MAY OFFSET A WEAKER WARM ADVCTN REGIME VIA WET BULBING. BOTTOM LINE IS THAT FORECAST WL FEATURE A WINTRY MIX WITH A CHANGE TO SNOW WITH PASSAGE OF THE SYSTEMS COLD FRONT ON THURSDAY EVENING. A HAZARDOUS WEATHER OUTLOOK WAS ALSO INCLUDED FOR THE FREEZING RAIN POTENTIAL. QPF WAS COMPLETED USING WPC GUIDANCE TRIMMED FOR LOCAL POP TRENDS WITH SNOW TOTALS ADJUSTED FOR SFC TEMP EXPECTATIONS. IN THE WAKE OF THE FRONT...COLD TEMPS WL AGAIN VISIT THE REGION. DEPTH OF COLD AT MOMENT LKS SUFFICIENT TO SPPRT SNOW SHWRS...SO LIKELY POPS WERE MAINTAINED OVR THE RIDGES PAST DAYBREAK DESPITE DRY ADVCTN AND LACK OF ANY REINFORCING LAKE ERIE MSTR DUE TO ICE. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... COLD ARCTIC HIGH SHIFTS EAST INTO SATURDAY WITH SNOW SHOWERS IN NORTHWEST FLOW FRIDAY ENDING FRIDAY NIGHT. WITH 850MB TEMPS PROGGED NEAR -20C BY 00Z SATURDAY TEMPERATURES FRIDAY WILL BE STEADY OR FALL. CLOUDS SHOULD BEGIN TO BREAK AS CENTER OF HIGH MOVES INTO REGION FRIDAY NIGHT...WITH LOWS BELOW ZERO NORTH AND SINGLE DIGITS SOUTH. IF CONDITIONS GO CLEAR AND CALM FRIDAY NIGHT MAY GO BELOW ZERO ACROSS THE ENTIRE REGION. TEMPERATURES RECOVER TO MAINLY THE 20S SATURDAY. A SIGNIFICANT STORM LOOKS POSSIBLE FOR SUNDAY INTO EARLY MONDAY BEFORE ARCTIC AIR RETURNS TO START THE WORK WEEK. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/... ONGOING SNOW SHOWERS WILL BEGIN TO WANE FROM NORTH TO SOUTH AS DRIER AIR ARRIVES TO CHOKE OFF THE MOISTURE. EXPECTING MVFR CIGS/VSBY TO CONTINUE IN THE LIGHT SNOW BEFORE FINALLY TAPERING OFF LAST NEAR KMGW/KLBE AFTER MIDNIGHT. CLOUDS WILL BEGIN TO SCATTER OUT AS THE DRIER AIR ARRIVES FROM THE NORTH. ALREADY BEGINNING TO SEE THIS IN DUJ WHERE THE LLVL MOISTURE EVACUATED LEAVING A MID-DECK LINGERING. CLEARING IS EXPECTED FOR MOST TERMINALS BY ABOUT DAYBREAK WEDS MORNING...ALTHOUGH SOME SCT LOW CLOUDS COULD REMAIN NEAR KMGW. WINDS WILL BEGIN TO DISSIPATE TONIGHT AND THROUGH THE DAY WEDS AS RIDGE OF HIGH PRESSURE BUILDS IN FROM THE WEST. TAX .OUTLOOK.../WEDNESDAY THROUGH SUNDAY/... WIDESPREAD RESTRICTIONS ARE EXPECTED ON THURSDAY WITH CROSSING LOW PRESSURE. FREEZING PRECIPITATION IS POSSIBLE AT ALL TERMINALS THURSDAY WITH PRECIPITATION CHANGING OVER TO SNOW BY MIDNIGHT FRIDAY. RESTRICTIONS WILL CONTINUE INTO FRIDAY. VFR CONDITIONS ARE EXPECTED SATURDAY...WITH ANOTHER SET OF RESTRICTIONS POSSIBLE SUNDAY. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...WINTER WEATHER ADVISORY UNTIL 1 AM EST WEDNESDAY FOR MDZ001. OH...NONE. PA...WINTER WEATHER ADVISORY UNTIL 1 AM EST WEDNESDAY FOR PAZ074- 076. WV...WINTER WEATHER ADVISORY UNTIL 1 AM EST WEDNESDAY FOR WVZ023- 041. && $$

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