Area Forecast Discussion
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000 FXUS61 KPBZ 010742 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 323 AM EDT SAT NOV 1 2014 .SYNOPSIS...
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LOW PRESSURE WILL REDEVELOP SOUTHEAST OF THE AREA ON SATURDAY WITH GUSTY NORTHERLY FLOW BECOMING ESTABLISHED. SCATTERED SHOWERS WILL CONTINUE THROUGH THE DAY AND BECOME MIXED WITH AND CHANGE TO SNOW IN THE HIGHER ELEVATIONS. HIGH PRESSURE RETURNS EARLY NEXT WEEK.
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&& .NEAR TERM /THROUGH TONIGHT/...
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THE SURFACE AND 850 MB LOWS ARE QUICKLY TRANSITIONING TO THE CAROLINAS EARLY THIS MORNING AS THE UPPER JET CARVES A VERY SHARP UPPER TROUGH WITH A BASE WELL DOWN INTO DIXIE. LOW LEVEL COLD AIR LAGS THE SYSTEM QUITE A GREAT DEAL...HOWEVER AS THE SURFACE LOW DEEPENS RAPIDLY THIS MORNING OVER THE CAROLINA COAST...THE PRESSURE GRADIENT OVER THE UPPER OHIO VALLEY WILL SHARPEN UP QUITE CONSIDERABLY RATHER QUICKLY. AS THIS OCCURS...ISALLOBARIC FLOW WILL RAPIDLY INCREASE FROM THE NORTH...WHICH SHOULD WORK TO ERADICATE THE LOW LEVEL INDUCED DRIZZLE FROM THE AREA. AS THE FLOW QUICKLY BACKS TO THE NORTH IN THE LOWEST 5 KFT OF THE COLUMN...COLD ADVECTION THROUGHOUT THE COLUMN ALSO RAPIDLY INCREASES. THIS IS EVIDENCED BY 850 MB TEMPERATURES FALLING FROM ROUGHLY -2 TO ABOUT -6 TO -8C BY THIS AFTERNOON. MODEL SOUNDINGS SUGGEST THE RESULT WILL BE VERY STEEP LAPSE RATES UP TO ALMOST THE BASE OF THE DENDRITIC GROWTH LAYER. HOWEVER...BOUNDARY LAYER TEMPERATURES BELOW THIS HEIGHT WILL BE PROBLEMATIC FOR SNOW FALL AT THE SURFACE OUTSIDE THE RIDGES UNTIL LATE AFTERNOON. THAT SAID...LAKE ERIE SURFACE TEMPERATURES RUNNING ROUGHLY 54F PER MID- LAKE BUOYS GENERATE A LAKE INDUCED CAPE OF AROUND 500 J/KG...WITH A LAKE INDUCED POSITIVE AREA THAT BISECTS FULLY THE DENDRITIC GROWTH LAYER. AS SUCH...EVEN THOUGH THE INVERSION HEIGHTS FAIL TO REACH VERY IMPRESSIVE HEIGHTS THIS AFTERNOON AND EVENING AS THE FLOW FINALLY TURNS NORTHERLY ENOUGH TO AFFECT THE NORTHER TIER OF THE FORECAST AREA...THE MAGNITUDE OF INSTABILITY SEEMS LIKELY TO BE SUFFICIENT TO ALLOW FOR LAKE EFFECT SHOWERS TO MOVE INLAND ENOUGH WITH COLD ADVECTION TO ALLOW FOR SOME CHANGEOVER FROM RAIN TO SNOW SHOWERS NORTH OF I-80. A SIMILAR SCENARIO HOLDS TRUE FOR THE RIDGES. WHILE SOME LIGHT SNOW WAS REPORTED GENERALLY AROUND 2900 FEET AND HIGHER OVERNIGHT...A LACK OF FORCING FOR ASCENT WILL KEEP A LID ON FURTHER SNOW DEVELOPMENT UNTIL LOW LEVEL FLOW BACKS SIGNIFICANTLY AND THE OVER LAKE FETCH IMPROVES. THIS WILL LIKELY TAKE UNTIL THIS EVENING. WHILE VERTICAL SHEAR MAY BE PROBLEMATIC IN THE RIDGES AS WELL...SIGNIFICANT UPSLOPE WITH COLDER PROFILES AND IMPRESSIVE LAKE INDUCED INSTABILITY PARAMETERS SHOULD ALLOW FOR SNOW SHOWERS TO DEVELOP BY LATE AFTERNOON/EVENING AND CONTINUE INTO TONIGHT. QPF VALUES DO NOT LOOK IMPRESSIVE...HOWEVER INSTABILITY PROFILES DO MANAGE TO BISECT THE LOWER HALF OF THE DENDRITIC LAYER...AND GIVEN POOR DIURNAL TEMPERATURE RISES...ACCUMULATIONS MAY BE EASIER TO MUSTER IN THE HIGHER ELEVATIONS DUE TO A BIT COOLER GROUND. THAT SAID...MODEL TIME-HEIGHT SECTIONS DO NOT FAVOR SNOW TO LIQUID RATIOS IN EXCESS OF 10 TO 1 ANYWHERE...AND OWING TO STILL MARGINAL BOUNDARY LAYER TEMPERATURES AND GROUND TEMPERATURES...EVEN THESE VALUES SEEM HARD TO SWALLOW. AS SUCH...MODEST QPF WITH UPSLOPE ENHANCEMENT WOULD STILL SUGGEST AS MUCH AS AROUND 2 INCHES IN THE HIGHER ELEVATIONS OF TUCKER/GARRETT AND UP TO AN INCH IN THE HIGHER ELEVATIONS OF PRESTON/FAYETTE/WESTMORELAND. THIS DOES NOT SEEM SUFFICIENT TO WARRANT WINTER WEATHER HEADLINES...HOWEVER IT WILL CERTAINLY BE A HARSH REMINDER THAT THE CALENDAR HAS NOW SWITCHED TO NOVEMBER. TEMPERATURES ACROSS THE AREA SEEM LIKELY TO BE STUCK IN THE MUD THROUGH THE EARLY PORTION OF THE DAY...MAINLY IN THE MID 30S TO LOWER 40S BEFORE LIKELY FALLING BACK A BIT BY AFTERNOON AS COLD ADVECTION GETS PRIMED UP. A CONTINUATION OF NORTHERLY FLOW AND COLD ADVECTION INTO TONIGHT WILL ALLOW FOR WIDESPREAD FREEZING CONDITIONS...HOWEVER DRASTIC TEMPERATURE FALLS SEEM UNLIKELY GIVEN WIDESPREAD LAKE-INDUCED STRATOCUMULUS. FRIES
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&& .SHORT TERM /SUNDAY THROUGH TUESDAY/...
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&& .LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
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STRONG HIGH PRESSURE AT THE BEGINNING OF THE EXTENDED PERIOD WILL SLOW THE EASTWARD PROPAGATION OF A COLD FRONT. BY THE TIME THE ASSOCIATED LOW PRESSURE SYSTEM PASSES NORTH OF THE GREAT LAKES TUES NIGHT INTO WEDS...THE FRONT BEGINS TO STAGNATE IN OUR REGION AS THE FLOW IS ORIENTED MORE PARALLEL TO THE BOUNDARY. THIS WILL BRING RAIN CHANCES BACK INTO THE FORECAST FOR MIDDLE OF NEXT WEEK. FROM THIS POINT ON...MODEL SOLNS DIVERGE AS A RE-ENFORCING LOW APPROACHES THE GREAT LAKES AND WILL EVENTUALLY PUSH THE FRONT THROUGH OUR AREA. ANOTHER SHOT OF COLD AIR WILL ACCOMPANY THIS LOW...DRIVING TEMPS BELOW AVG AGAIN TOWARDS NEXT WEEKEND. TAX
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&& .AVIATION /07Z SATURDAY THROUGH WEDNESDAY/...
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RAIN AND DRIZZLE ARE LIKELY TO CONTINUE THROUGH DAYBREAK AT MOST SITES. WIDESPREAD IFR/MVFR CONDITIONS WILL LIKEWISE CONTINUE. WINDS WILL TURN MORE NORTHERLY ON SATURDAY AND BECOME GUSTY. THIS SHOULD INCREASE VIS/CIG A BIT...HOWEVER LAKE EFFECT SHOWERS AND STRATOCUMULUS WILL CONTINUE THROUGH THE DAY...SO CONDITIONS BETTER THAN MVFR ARE UNLIKELY. FRIES OUTLOOK.../SATURDAY NIGHT THROUGH WEDNESDAY/... RESTRICTIONS FROM LAKE INDUCED STRATOCUMULUS WILL CONTINUE INTO SUNDAY. MORE RESTRICTIONS WILL BE POSSIBLE WITH A SYSTEM THAT MOVES THROUGH THE AREA ON WEDNESDAY.
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&& .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...NONE. WV...NONE. && $$

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