Area Forecast Discussion
Issued by NWS

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000 FXUS61 KPBZ 220240 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 940 PM EST FRI NOV 21 2014 .SYNOPSIS... HIGH PRESSURE WILL DOMINATE TONIGHT. A COUPLE OF WEAK DISTURBANCES WILL CROSS THE REGION OVER THE WEEKEND UNTIL LOW PRESSURE RETURNS WIDESPREAD SHOWERS SUNDAY NIGHT. && .NEAR TERM /THROUGH SATURDAY/... ...FREEZING RAIN CHANCES INCREASING FROM ZANESVILLE TO BEAVER TO DUBOIS AND NORTHWARD FOR SATURDAY MORNING AND EARLY AFTERNOON... TEMPERATURES ARE ALREADY IN FREE FALL ACROSS THE AREA THIS EVENING AS HIGH PRESSURE MAINTAINS SWAY FOR THE NIGHT TONIGHT AS WINDS QUICKLY SUBSIDE TO BARELY A SOUTHERLY DRIFT. DEWPOINTS OVER THE REGION ARE LARGELY IN THE SINGLE DIGITS...AND WHILE A BIT MORE MOIST AIR IS POISED TO ADVECT TOWARD THE REGION GOING TOWARD SUNRISE...THIS WILL DO LITTLE TO DECREASE THE DOWNWARD POTENTIAL OF TEMPERATURES OVERNIGHT...PARTICULARLY IN AREAS WITH SNOW ON THE GROUND. THAT SAID...TEENS SEEM TO BE IN STORE FOR MOST LOCATIONS EXCEPT THE SCATTERED SINGLE DIGITS IN THE COLD SPOTS WITH SNOW COVER. TEMPERATURES MAY START TO EDGE UPWARD TOWARD MORNING AS SOUTHERLY FLOW STARTS TO INCREASE AND CLOUD INCREASE FROM THE WEST AS WELL AHEAD OF THE NEXT SYSTEM. LIFT IN THE 290-300K LAYER QUICKLY INCREASES FROM THE SOUTHWEST AROUND 12Z ON SATURDAY. CONDENSATION PRESSURE DEFICITS IN THE LAYER GENERALLY BOTTOM OUT AROUND 10 MB IN A CORRIDOR FROM ZANESVILLE TO BEAVER TO DUBOIS AND NORTHWARD GOING INTO THE LATTER HALF OF THE MORNING HOURS. ADDITIONALLY...THE BOUNDARY LAYER BELOW THE LIFTED LAYER SEEMS TO SATURATE SUFFICIENT. WARM ADVECTION IN THE LIFTED LAYER SEEMS LIKELY TO BRING TEMPERATURES IN THE WARM LAYER ALOFT INTO THE +2 TO +5C RANGE OVER A DEPTH OF ABOUT 5 KFT. THIS SHOULD BE SUFFICIENT TO MELT ALL FALLING HYDROMETEORS AS THEY FALL. GIVEN THE EXTREMELY COLD START TO THE DAY AND WEAK SURFACE LAYER ADVECTION UNDER THE INVERSION...ALONG WITH THE RECENT VERY COLD WEATHER...FROZEN GROUND...AND SNOW COVER IN THE NORTHERN REACHES OF THE FORECAST AREA...IT DOES SEEM THAT LIGHT FREEZING RAIN WILL BE LIKELY DURING THE MORNING AND EVEN EARLY AFTERNOON HOURS FROM ZANESVILLE NORTHEASTWARD TO THE I-80 CORRIDOR. PRECIPITATION RATES LOOK TO BE VERY LIGHT...HOWEVER RESTRICTED UPWARD MOBILITY OF TEMPERATURES DUE TO WET BULB EFFECTS AND A COLD START MEAN SOME ICE ACCUMULATION WILL BE POSSIBLE. DUE TO THE FACT THAT THE ATMOSPHERE IS LIKELY TO BE VERY DRY AT THE ONSET OF THE EVENT...AS WELL AS THE FACT THAT LIFT AND SATURATION IS NOT PARTICULARLY STRONG WHATSOEVER...CONFIDENCE ON WIDESPREAD ICE ACCUMULATION IS NOT REALLY HIGH AT THE MOMENT. HOWEVER...CONFIDENCE IN AT LEAST SOME FREEZING RAIN NORTH OF THE AFOREMENTIONED AREAS IS SUFFICIENT TO RAISE THE PROBABILITY OF FREEZING RAIN TOWARD 60 PERCENT...AND ABOVE 80 PERCENT NEAR THE DEEPER SATURATION ALONG AND NORTH OF I-80. IT IS ONLY IN THE LATTER AREA WHERE CONFIDENCE IS SUFFICIENT TO ISSUE A FREEZING RAIN ADVISORY. HOWEVER...HOWEVER THE REMAINDER OF THAT CORRIDOR WILL NEED TO BE LOOKED AT MORE CLOSELY AS THE PRECIPITATION DEVELOPS. TEMPERATURES WILL INCREASE BY LATE AFTERNOON AT ALL SITES ENOUGH THAT ANY FALLING PRECIPITATION BY THAT JUNCTURE SHOULD BE PLAIN RAIN. FRIES && .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/... AN UPR TROF IS PROGGED TO MOVE INTO THE CNTRL CONUS THRU THE WKEND. SVRL WK SHRTWVS WL ROTATE ARND THE BASE OF THE TROF AND ADVN ACRS THE OH VLY AND GT LKS RGN IN SW FLOW. THE FIRST OF THESE IS PROGGED FOR A SAT PASSAGE. THE BEST MSTR AND UPR SPPRT IS PROGGED TO STAY ALG I 80 AND NWD...SO MAINTAINED SHWR CHCS IN THIS RGN. DID MENTION JUST A SLGT CHC OF FREEZING RAIN IN THIS RGN AS CRITICAL THICKNESSES INDICATE LIQUID PCPN...AND SFC TEMPS MAY STILL BE COLD ENOUGH IF PCPN WOULD OCCUR IN THE MRNG. AFTER A COUPLE MORE WK WAVES SAT NGT AND SUN...A STRONGER SHRTWV WITH DEEP MOISTURE AND UPR SPPRT IS PROGGED FOR A SUN NGT PASSAGE. MAINTAINED CAT SHWR POPS WITH THIS FEATURE. AS THE MAIN TROF ADVNS TWD THE GT LKS MON...A CDFNT IS EXPD TO CROSS THE RGN. WITH LTD MSTR KEPT POPS IN THE CHC CATEGORY FOR NOW. WITH WRM ADVCTN THRU MUCH OF THE PD...TEMPS SHOULD GRDLY WRM TO SVRL DEG ABV SEASONAL LVLS BY LT IN THE WKEND. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... WIDESPREAD SHOWERS END MONDAY NIGHT WITH COLDER AIR MOVING IN THROUGH THE LONG RANGE. CLOSE TO WPC PROGS. FAST MOVING SHORTWAVE WILL BRING A CHANCE OF SNOW SHOWERS THURSDAY. && .AVIATION /03Z SATURDAY THROUGH WEDNESDAY/... VFR OVERNIGHT WITH SKC AND LIGHT WINDS THE RULE. WARM ADVECTION SATURDAY MORNING WILL BRING A RETURN OF CLOUDS...ALTHOUGH CIGS WILL INITIALLY REMAIN VFR. NOT INCLUDED YET BUT LLWS IS A POSSIBILITY AS A SW LLJ CRANKS UP. AS NOTED IN NEAR TERM SECTION ABOVE...FZRA IS A POSSIBILITY ACROSS THE NW PORTION OF THE FORECAST AREA. FOR NOW...HANDLING VIA PROB30/TEMPO GROUPS FOR ZZV/FKL/DUJ. CONFIDENCE STILL A BIT LOW FOR INCLUSION FURTHER SOUTH BUT BVI/PIT/AGC WILL NEED WATCHING. CIGS WILL LOWER A BIT TOWARDS THE MVFR/VFR THRESHOLD DURING THE AFTERNOON. TEMPERATURES SHOULD WARM SUFFICIENTLY TO ALLOW FOR REMAINING FZRA TO TURN TO PLAIN RAIN TOWARDS MIDAFTERNOON. WIND GUSTS UP TO 20 KNOTS FROM THE SOUTHWEST CAN BE ANTICIPATED. CL OUTLOOK.../SATURDAY NIGHT THROUGH WEDNESDAY/... POSSIBLE MVFR TO IFR CONDITIONS SUNDAY NIGHT INTO MONDAY AS THE NEXT STORM SYSTEM APPROACHES. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...FREEZING RAIN ADVISORY FROM 8 AM TO 2 PM EST SATURDAY FOR PAZ007>009-015-016. WV...NONE. && $$

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