Area Forecast Discussion
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000 FXUS61 KPBZ 290137 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 836 PM EST WED JAN 28 2015 .SYNOPSIS... CROSSING LOW PRESSURE WILL BRING A WINTRY MIX OF PRECIPITATION TO THE UPPER OHIO REGION ON THURSDAY AND SNOW EARLY ON FRIDAY. && .NEAR TERM /THROUGH THURSDAY/...
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OVERNIGHT CONDITIONS LOOK TO REMAIN RATHER QUIET AS DECOUPLING HAS ALREADY OCCURRED RAPIDLY THIS EVENING. SOME TRANSLUCENT CIRRUS COVER IS ADVANCING SOUTHEASTWARD AT THIS HOUR AHEAD OF THE NEXT SYSTEM...HOWEVER IT SEEMS TO BE HAVING LITTLE EFFECT ON TEMPERATURE FALLS AT THE MOMENT. DEWPOINTS FROM WALL TO WALL ACROSS THE CWA ARE NO HIGHER THAN THE LOWER TEENS...WITH MOST OF THE NORTHEASTERN HALF OF THE CWA GENERALLY IN THE SINGLE DIGITS. THIS COMBINED WITH NEW SNOW COVER WILL ALLOW FOR FAIRLY DECENT BOUNDARY LAYER TEMPERATURE FALLS UNDER THE INVERSION LEVELS EVEN WHILE FAIRLY RAPID WARM ADVECTION IS LIKELY TO CONTINUE TO OCCUR ALOFT. MODEL 850 MB TEMPERATURES GENERALLY SURPASS 0C OVER THE MAJORITY OF THE CWA EXCEPT THE NORTHEASTERN FRINGE ON THE CONSENSUS BY 12Z THURSDAY. THIS IS EVIDENT IN SOUNDINGS ACROSS THE CWA...HOWEVER THE MODELS LIKELY ARE FAR TOO RAPID MIXING OUT THE INVERSIONS AS THE ADVECTION KICKS IN ALOFT. LIKEWISE...DYNAMICAL MODEL DEWPOINT VALUES START OFF FAR TOO MOIST ACROSS THE CWA...AND WILL LIKELY AGAIN AFFECT THE WET BULB TEMPERATURE PROFILES GOING INTO THE MORNING ACROSS THE AREA. AS SUCH...THE FORECAST WAS ADJUSTED TOWARD THE COLDER END OF GUIDANCE THROUGH THE NIGHT...EVEN WITH EASTWARD ADVANCING CLOUDS AND WARM ADVECTION ALOFT BUILDING IN. THE REAL FUN BEGINS SHORTLY AFTER SUNRISE IN OHIO...AND SPREADS EASTWARD ACROSS THE CWA THROUGH THE REST OF THE MORNING AND EARLY AFTERNOON. A FAIRLY POTENT 500 MB SHORT WAVE TROUGH FIRMLY ENTRENCHED IN THE LEFT EXIT OF A 120 KT JET STREAK BLISTERS THROUGH THE AREA ON THURSDAY. AN UNSEASONABLY STRONG LLJ DEVELOPS AHEAD OF THIS...WITH LOW LEVEL CONVERGENCE MAXIMIZED ON ITS NOSE...WHICH COINCIDENTALLY RUNS ALONG THE OHIO VALLEY THROUGH EARLY AFTERNOON ON THURSDAY. THIS POINTS TOWARD WARM ADVECTION BEING VERY EFFICIENT ACROSS THE AREA BY THAT JUNCTURE...AND SHOULD ALLOW MUCH OF THE AREA TO RUN UP ABOVE FREEZING ON THURSDAY. HOWEVER...BEFORE THAT OCCURS...COLD AIR WILL NEED TO BE DISPLACED...AND WET BULB EFFECTS WILL NEED TO BE OVERCOME. IN THE INTERIM...THIS MEANS A PERIOD OF FREEZING RAIN WILL BE POSSIBLE AS WARM AIR WORKS IN OFF THE SURFACE BEFORE IN THE BOUNDARY LAYER. MODEL SOUNDINGS ACROSS OHIO SUGGEST THE BEST CHANCE OF FREEZING RAIN WILL BE OVER OUR FAR WESTERN COUNTIES AS THE PRECIPITATION ONSET WILL BE CLOSEST TO SUNRISE THERE. AS A RESULT...OVERNIGHT INVERSIONS ARE UNLIKELY TO HAVE BEEN WIPED OUT BY THAT JUNCTURE...RESULTING IN A PERIOD OF ICING BEING LIKELY. FARTHER EAST...THE DETAILS GET A LITTLE BIT MURKY. THE RACE BETWEEN ONSET...WET BULBING...BOUNDARY LAYER MIX OUT...AND WARM ADVECTION WILL BE A CLOSE RACE VIRTUALLY EVERYWHERE. AT THE MOMENT...IT SEEMS AT LEAST FOR A TIME...THAT NORTH OF THE TURNPIKE...AT LEAST A PERIOD OF SNOW/ICE WILL BE POSSIBLE...WITH REALLY ONLY ACCUMULATING SNOW LIKELY BY AFTERNOON ALONG I-80 AND IN THE RIDGES OF PA AND MD. ELSEWHERE...A LATE ONSET SHOULD ALLOW FOR GROUND TEMPERATURES TO RISE ENOUGH SUCH THAT PLAIN RAIN WILL DOMINATE AND PRECLUDE MUCH IN THE WAY OF ICING. FRIES
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&& .SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
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WHILE WARM ADVECTION LOOKS RAPID AHEAD OF THE FIRST WAVE ON THURSDAY AFTERNOON...THERMAL PROFILES QUICKLY BECOME MUCH MORE UNSTABLE BY THURSDAY EVENING. COLD ADVECTION BEGINS IN EARNEST ALOFT AS TWO MORE SHORT WAVE TROUGHS ARE SET TO CROSS THE AREA THROUGH FRIDAY MORNING. THIS WILL OCCUR SIMULTANEOUSLY TO THE SOME DRIER AIR COMING IN...HOWEVER THE DENDRITIC GROWTH LAYER LOOKS TO ABSOLUTELY CRASH TOWARD THE SURFACE ON THURSDAY NIGHT 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 LIKELY 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. FRIES
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&& .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... 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 /01Z THURSDAY THROUGH MONDAY/...
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HIGH PRESSURE WILL KEEP WINDS LIGHT OVERNIGHT WITH ONLY HIGH CLOUDS. LOW PRESSURE MOVING OVER THE EASTERN GREAT LAKES WILL BRING PRECIPITATION TO ALL SITES FROM LATE MORNING TO EARLY AFTERNOON. PRECIPITATION TYPE WILL BE TRICKY...WITH MGW THE ONLY SITE WITH HIGH CONFIDENCE THAT WILL NOT HAVE FREEZING RAIN. HAVE ONLY MENTIONED FZRA EXPLICITLY IN THE TAFS FOR FKL/DUJ FOR A COUPLE HOUR TIME PERIOD...BUT A BRIEF 1-3 HOUR PERIOD OF FREEZING RAIN CANNOT BE RULED OUT AT OTHER TERMINALS. SIMILIARLY...WHILE LOW LEVEL WIND SHEAR IS ONLY INCLUDED IN THE ZZV TAF...CANNOT RULE OUT A BRIEF 1-3 HOUR PERIOD OF LLWS AT OTHER TERMINALS BEFORE PRECIPITATION STARTS AND HIGHER WINDS ALOFT ARE ABLE TO MIX OUT AS GUSTS. OVERALL TREND WILL BE FOR VFR CONDITIONS TO QUICKLY DROP TO IFR IN PRECIPITATION AS LOWER CEILINGS MOVE IN FROM THE NORTHWEST. .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.
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&& .PBZ WATCHES/WARNINGS/ADVISORIES...
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MD...WINTER WEATHER ADVISORY FROM 11 AM THURSDAY TO 10 AM EST FRIDAY FOR MDZ001. OH...FREEZING RAIN ADVISORY FROM 8 AM TO NOON EST THURSDAY FOR OHZ048-057. PA...WINTER WEATHER ADVISORY FROM 11 AM THURSDAY TO 10 AM EST FRIDAY FOR PAZ007>009-015-016-023-074-076. WV...WINTER WEATHER ADVISORY FROM 7 PM THURSDAY TO 10 AM EST FRIDAY FOR WVZ023-041.
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&& $$

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