Area Forecast Discussion
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000 FXUS61 KPBZ 300013 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 713 PM EST THU JAN 29 2015 .SYNOPSIS... A COLD FRONT WILL CROSS THE AREA TONIGHT...FOLLOWED BY BUILDING HIGH PRESSURE FRIDAY AND SATURDAY. LOW PRESSURE MAY BRING MORE WINTRY WEATHER SUNDAY. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
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THE KITCHEN SINK AND POTPOURRI OF GOODNESS THAT HAS BEEN FALLING FROM THE SKY OVER THE PAST ROUGHLY 12 HOURS IS ALREADY SHOWING SIGNS OF TRANSITIONING TOWARD ALL SNOW TO OUR IMMEDIATE NORTH AND WEST. SURFACE OBSERVATIONS AND DUAL POL SIGNATURES SUGGEST THIS IS OCCURRING...AND MODEL SOUNDINGS INDICATE RAPIDLY STEEPENING LAPSE RATES THROUGH THE EVENING...EVEN THOUGH SURFACE TEMPERATURES MAY TAKE A FEW HOURS TO FALL OFF PRECIPITOUSLY. AS SUCH...WHILE ALL BUT THE NORTHERN TIER OF THE CWA IS LIKELY RAINING AT THE MOMENT...THE TREND TOWARD FROZEN PRECIPITATION WILL BE RAPID THROUGH THE EVENING HOURS. THAT SAID...FREEZING SURFACE TEMPERATURES ARE ONLY REALLY NOTED IN SURFACE OBSERVATIONS FROM CLEVELAND TO THE NORTH AND WEST. AS SUCH...SEVERAL HOURS OF SNOW ARE LIKELY DURING THE EVENING WITH MARGINAL TEMPERATURES FOR ACCUMULATION AT BEST. AS SUCH...THE INITIAL ONSLAUGHT OF SNOW THAT WILL BE LIKELY DURING THE EVENING IS FAIRLY UNLIKELY TO BE AN EFFICIENT ACCUMULATOR. HOWEVER...THINGS WILL DRASTICALLY CHANGE OVERNIGHT. A DEEPER AND MUCH MORE THERMODYNAMICALLY ABRUPT SHORT WAVE AND LOW LEVEL FRONTAL BOUNDARY COMBO WILL MOVE THROUGH THE AREA BETWEEN 06 AND 12Z TONIGHT. AS THIS OCCURS...THE DENDRITIC GROWTH ZONE WILL TANK DOWN INTO THE SATURATED LAYER AND GIVEN FRONTOGENETICAL LIFTING...THIS WILL LIKELY LEAD TO A PERIOD OF FAIRLY EFFICIENT SNOW SHOWERS FOR ALL LOCATIONS GIVEN STEEP LAPSE RATES AND LARGE SCALE FORCING FOR ASCENT. IN THE RIDGES...THIS LARGE SCALE ASCENT WILL BE OVERLAID WITH UNIDIRECTIONAL NORTHWESTERLY UPSLOPE FLOW WORKING ON VERY UNSTABLE LOW LEVEL LAPSE RATES. WHILE MOISTURE FLUX INTO THE UNSTABLE LAYER FROM LAKE ERIE WILL LIKELY BE MINIMAL DUE TO ABUNDANT ICE COVER...SATURATION BELOW THE INVERSION LEVEL WILL NOT BE DEPENDENT UPON THIS...AND WITH INSTABILITY...UPSLOPE...AND LARGE SCALE ASCENT ALL OVERLAYING EACH OTHER IN THE OVERNIGHT HOURS...SNOW SHOWERS WILL LIKELY BE HEAVY EFFICIENT DENDRITE PRODUCERS. AS SUCH...WHILE MOST LOCATIONS WILL ONLY SEE 1-3 INCHES OF SNOW OVERNIGHT OUTSIDE THE RIDGES...LOCATIONS IN THE HIGHER ELEVATIONS SEEM MORE LIKELY TO END UP WITH 4 TO 8 GIVEN RATIOS SURGING TOWARD 25 TO 1 OVERNIGHT. ALL ADVISORIES WILL REMAIN IN EFFECT FOR THE OVERNIGHT AND INTO FRIDAY. HEAVY SNOW SHOWERS WILL LIKELY BE HANDLED INDIVIDUALLY WITH SPS STATEMENTS THROUGH THE NIGHT. FRIES
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&& .SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY/... EXTENDED THE WINTER WEA ADVY THRU THE DAY FRI FOR THE RIDGES...THOUGH WITH A FROZEN LAKE ERIE WL ALLOW FOR THE NW PA PORTION EXPIRE AT FRI MRNG. UPSLOPE SNW SHWRS SHOULD CONT THRU THE DAY IN THE RIDGES BEFORE THINNING MSTR IN THE SNW GROWTH RGN AND LWRG TEMP INVERSIONS END THE PCPN. A CROSSING UPR TROF SHOULD ALLOW FOR SOME SCT SNW SHWRS OUTSIDE OF THIS AREA AS WELL. BLDG HIGH PRES SHOULD BRING DRY WEA FRI NGT INTO SAT. BELOW SEASONAL AVG TEMPS WERE FCST USING THE LATEST SREF NMBRS. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... MODELS CONT TO JOUST IN HANDLING OF LOW PRES PROJECTED TWD THE MID ATLANTIC REGION FM SATURDAY NGT INTO MONDAY. PERSISTENCE RMNS PRUDENT WITH LATEST GFS IN GENL LINE WITH CURRENT THINKING OUTSIDE OF TIMING ISSUES. MEANWHILE...ECMWF IS FORECASTING A SOUTHWARD TRACK TO SFC SLOW CENTER AND PCPN SHIELD. BOTH MDLS CONT TO DEPICT AN OPEN MID LVL WAVE. BOTTOM LINE IS THAT AN EXTENDED PERIOD OF LGT...TO MODERATE...BUT ACCUMULATING SNOW IS LIKELY...WITH CONFIDENCE BUILDING FOR AREAS ALNG THE INTERSTATE 70 CORRIDOR. COLDER WEATHER WL FOLLOW AS A SERIES OF SHRTWVS AGAIN DIG AN ERN CONUS UPR TROUGH...DETAILS FOR WHICH WL BE REFINED WITH TIME. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/... CONDITION DETERIORATION IS UNDERWAY AND DEGRADATIONS CAN BE EXPECTED INTO FRIDAY AS MIXED PCPN SPREADS OVR UPR OH TERMINALS AND CHANGES TO SNOW WITH CDFNT PASSAGE THIS EVE. IFR CAN BE EXPECTED IN SNOW SHWRS THIS EVE...AND IN WIDESPREAD STRATUS WHICH WL ACCOMPANY THE COLD SURGE OVR THE REGION. .OUTLOOK.../FRIDAY NIGHT THROUGH TUESDAY/... IMPROVEMENTS CAN BE EXPECTED AS HIGH PRES BLDS LTR ON SATURDAY...HOWEVER...SNOW AND RESTRICTIONS ARE LIKELY WITH SUNDAY LOW PRES. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...WINTER WEATHER ADVISORY UNTIL 7 PM EST FRIDAY FOR MDZ001. OH...NONE. PA...WINTER WEATHER ADVISORY UNTIL 10 AM EST FRIDAY FOR PAZ007>009- 015-016-023. WINTER WEATHER ADVISORY UNTIL 7 PM EST FRIDAY FOR PAZ074-076. WV...WINTER WEATHER ADVISORY UNTIL 7 PM EST FRIDAY FOR WVZ023-041. && $$

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