Area Forecast Discussion
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000 FXUS61 KPBZ 290731 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 231 AM EST THU JAN 29 2015 .SYNOPSIS... CROSSING LOW PRESSURE WILL BRING A WINTRY MIX OF PRECIPITATION TO THE UPPER OHIO REGION TODAY AND SNOW EARLY ON FRIDAY. && .NEAR TERM /THROUGH TODAY/...
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MODELS ARE COMING INTO GOOD AGREEMENT WITH TIMING OF PRECIPITATION AHEAD OF FRONT AND THE STRONG WAA AS WELL. THE KEY IS WHAT WILL THE SURFACE TEMPS DO. MODELS ARE INDICATING A SLOW RESPONSE TO THE WAA AT THE SURFACE BUT I HAVE MY DOUBTS THAT IT WILL BE FAST ENOUGH TO PREVENT SOME ICING AT THE BEGINNING OF THE EVENT. BECAUSE OF THIS...HAVE EXTENDED THE FREEZING RAIN ADVISORY TO COVER MOST OF MY OHIO ZONES. THERE ARE A LOT OF FACTORS AT PLAY HERE WHICH MAKES THIS A VERY DIFFICULT FORECAST. FIRST ALOFT. ALL THE MODELS ARE SHOWING A STRONG SURGE OF WARMER AIR ENVELOPING MY ENTIRE CWA TODAY. THIS SHOWS UP QUIET WELL IN THE THERMAL PATTERN AT 850MB AND IN THE LOW AND MID-LEVEL THICKNESS PATTERNS. I HAVE DECIDED TO CHANGE VERY LITTLE FROM PREVIOUS THINKING ON PRECIP TYPES. THE THING TO WATCH WILL BE HOW THE ATMOSPHERE RESPONDS ONCE THE PRECIP BEGINS AND THE WET BULBING EFFECTS COME INTO PLAY. MODEL SOUNDINGS SHOW A PROFILE VERY CLOSE TO THE 0 DEGREE LINE WHICH WILL KEEP THE DIFFERENCE BETWEEN LIQUID OR FROZEN VERY CLOSE. AT THE SURFACE. MODELS DO SHOW SURFACE TEMPS RISING QUICKLY AS THE PRECIP APPROACHES. HOWEVER...MY CONCERN IS THAT WITH SUCH COLD DEWPOINTS AT THE SURFACE...WET BULBING WILL ALLOW FOR A PERIOD OF FREEZING RAIN...AT LEAST IN OHIO AT THE ONSET OF THE EVENT. OTHER FACTORS THAT NEED TO BE CONSIDERED ARE THE WIDESPREAD SNOW PACK AND LOCALIZED EFFECTS...MAINLY SHELTERED AREAS WHERE TEMPS WILL TAKE LONGER TO RECOVER. MAIN AREA OF PRECIPITATION WILL EXIT THIS AFTERNOON AS THE SURFACE FRONT SWINGS INTO CENTRAL PA. THE ONSET OF CAA WILL BE RIGHT BEHIND THE EXITING FRONT.
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&& .SHORT TERM /TONIGHT THROUGH SATURDAY/... THERMAL PROFILES QUICKLY BECOME MORE UNSTABLE TONIGHT. COLD ADVECTION BEGINS IN EARNEST ALOFT AS TWO SHORT WAVE TROUGHS ARE SET TO CROSS THE AREA THROUGH FRIDAY MORNING. THIS WILL OCCUR SIMULTANEOUSLY TO THE DRIER AIR COMING IN...HOWEVER THE DENDRITIC GROWTH LAYER LOOKS TO CRASH TOWARD THE SURFACE TONIGHT IN THE RIDGES...WELL BEFORE THE MOISTURE PEELS OFF. CONSENSUS SNOW TO LIQUID RATIOS FROM THE NAM AND GFS VIA BUFKIT SUGGEST AROUND 25 TO 1 BEGIN OVERNIGHT. GIVEN INSTABILITY AND UNIDIRECTIONAL UPSLOPE...THIS SHOULD RESULT IN VERY EFFICIENT SNOW GROWTH. MODEL QPF IS GENERALLY ONLY A COUPLE OF TENTHS...AND GIVEN ICE COVER UPSTREAM ON LAKE ERIE...A TON OF QPF IS VERY UNLIKELY. HOWEVER...EVEN LIGHT QPF IN THIS CASE IS LIKELY TO ADD UP TO SEVERAL INCHES OF SNOW. GIVEN THAT AHEAD OF THE SYSTEM ON THURSDAY THERE COULD BE AN INCH OR SO IN SOME OF THE SHELTERED HIGHER ELEVATIONS...AND ANOTHER 2 TO 5 SEEM LIKELY IN THE UPSLOPE THROUGH FRIDAY WITH ADDITIONAL SYNOPTIC HELP VIA TWO ADDITIONAL WAVES CROSSING THE AREA...3 TO 6 INCH TOTALS SEEM REASONABLE IN THE RIDGES BY FRIDAY MORNING. WINTER WEATHER ADVISORIES WERE EXPANDED TO ACCOMMODATE THIS. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... HIGH LEVELS OF UNCERTAINTY IN THE LONG TERM PARTICULARLY WITH THE SYSTEM THAT COULD AFFECT THE AREA DURING THE SUNDAY/MONDAY TIME FRAME. FOR NOW...CONSISTENCY WILL BE THE NAME OF THE GAME UNTIL THE MODELS PROVIDE A BETTER PICTURE. COLD PATTERN WILL CONTINUE THROUGH THE REMAINDER OF THE LONG TERM. && .AVIATION /08Z THURSDAY THROUGH MONDAY/... VFR OVERNIGHT THROUGH SUNRISE WITH THICKENING MID/HI CLOUDS. PRECIPITATION RETURNS AFTER 14Z WITH LOW PRESSURE TRACKING TO THE NORTH. EXPECT A DROP TO MVFR SOON AFTER PRECIP ONSET...WITH IFR CIGS TO FOLLOW AT MOST TERMINALS DURING THE AFTERNOON AND EVENING. PRECIP TYPES ARE THE MAIN DIFFICULTY. STILL THINK BEST CHANCES OF FZRA WILL LIE IN OHIO AND AT FKL/DUJ DURING THE FIRST FEW HOURS OF PRECIPITATION. CANNOT RULE OUT AT LEAST A BRIEF PERIOD OF FZRA ANYWHERE SAVE PERHAPS MGW. CHANGOVER TO SNOW WILL OCCUR AFTER 00Z AS A COLD FRONT SWEEPS THROUGH. WINDS WILL STRENGTHEN OUT OF THE SOUTH AROUND MIDDAY AND REMAIN GUSTY AS THEY VEER TOWARDS SW/W WITH TIME. WILL CONTINUE TO MONITOR FOR LLWS POSSIBILITIES. CL .OUTLOOK.../THURSDAY NIGHT THROUGH MONDAY/... RSTRNS ARE LIKELY THRU ERLY FRI AS A CDFNT EXITS. WDSRPD RSTRNS ARE LIKELY AGAIN WITH ADVNG LOW PRES SUN AND MON. && .PBZ WATCHES/WARNINGS/ADVISORIES...
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MD...WINTER WEATHER ADVISORY FROM 11 AM THIS MORNING TO 10 AM EST FRIDAY FOR MDZ001. OH...FREEZING RAIN ADVISORY FROM 8 AM THIS MORNING TO NOON EST TODAY FOR OHZ039>041-048>050-057>059. PA...WINTER WEATHER ADVISORY FROM 11 AM THIS MORNING TO 10 AM EST FRIDAY FOR PAZ007>009-015-016-023-074-076. WV...WINTER WEATHER ADVISORY FROM 7 PM THIS EVENING TO 10 AM EST FRIDAY FOR WVZ023-041.
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