Area Forecast Discussion
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000 FXUS61 KPBZ 211859 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 259 PM EDT THU MAY 21 2015 .SYNOPSIS... COOL TEMPERATURES WILL REMAIN THROUGH LATE WEEK. A WEAK DISTURBANCE WILL BRING SHOWERS MAINLY FROM PITTSBURGH SOUTH THIS MORNING. && .NEAR TERM /THROUGH FRIDAY/...
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A WEAK PRESSURE GRADIENT CONTINUES OVER THE FORECAST AREA INTO THE EARLY AFTERNOON AS WEAK NORTHEASTERLY FLOW HAS FAILED TO ALLOW FOR A PROMPT EROSION OF THE INVERTED TROUGH WEST OF THE RIDGES. AS HIGH PRESSURE ARCS UP INTO THE OHIO VALLEY BY THIS EVENING...A STRONGER GRADIENT SHOULD ALLOW NORTHWEST FLOW TO BE AT LEAST BRIEFLY MANIFEST ACROSS THE AREA. THIS SHOULD START TO ERODE THE LOW CLOUDS ACROSS THE CWA. THIS SHOULD OCCUR AS THE MEAN H5 AND H7 WAVE PASSES EAST OF THE AREA THROUGH THE 00Z HOUR. MUCH DRIER AIR FLOWS IN AS THIS OCCURS...WHICH SHOULD ALLOW ALL PORTIONS OF THE AREA TO CLEAR OVERNIGHT. TEMPERATURES WILL LIKELY TUMBLE AS A RESULT...BUT SOME AMOUNT OF MIXING AS WELL AS LINGERING BOUNDARY LAYER MOISTURE WILL LIKELY PRECLUDE TEMPERATURE FALLS FROM GETTING OUT OF HAND TONIGHT. A WEAKER PIECE OF MID-LEVEL MOISTURE ALONG A 925-700 MB THERMAL GRADIENT SEEMS TO WORK ITS WAY SOUTHWARD ACROSS THE AREA IN THE NORTHWESTERLY FLOW THROUGH FRIDAY MORNING AND EARLY AFTERNOON. MODEL SATURATION OF THE UNSTABLE LOWER FRONTOGENETICAL LAYER IS NOT VERY CONVINCING...NOR IS LIFT PARTICULARLY DEEP WITH THIS FEATURE. IT WOULD SEEM ISOLATED SHOWERS WILL BE THE BEST THAT WILL LIKELY BE MUSTERED...SO POPS WERE MAINTAINED IN THIS CATEGORY. LIKEWISE...WITH LESS THAN CONVINCING SATURATION ALONG THE BOUNDARY...AND A GIGANTIC SLUG OF DRY AIR WITH LAYER MEAN RH VALUES AROUND 15 PERCENT IN ITS WAKE...SKIES SHOULD RAPIDLY CLEAR BY EVENING. FRIES
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&& .SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
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WITH SKIES CLEARING OUT QUICKLY FRIDAY EVENING AND HIGH PRESSURE RESIDING OVER WESTERN PENNSYLVANIA BY SUNRISE SATURDAY...CONDITIONS WILL BE PRIME FOR A NIGHT OF RADIATIONAL COOLING. RAW MODEL GUIDANCE FROM THE 12Z GFS IS NEARLY 10 DEGREES COLDER THAN THE NAM/SREF...ALTHOUGH MOS LOWS BETWEEN THE NAM AND GFS ARE RELATIVELY SIMILAR. WITH THE IDEAL RADIATIONAL COOLING CONDITIONS...HAVE NUDGED THE FORECAST IN THE DIRECTION OF THE RAW GFS FORECAST. OVERALL...THIS GENERALLY BROUGHT FRIDAY NIGHT LOWS DOWN 2-3 DEGREES...BUT DID NOT NEED TO EXPAND MENTION OF FROST TOO MUCH FROM PREVIOUS FORECAST. CONSIDERING LOW TEMPERATURE FORECAST ALONG THE INTERSTATE 80 CORRIDOR IS RIGHT AROUND FREEZING...DECIDED TO ISSUE A FREEZE WATCH FOR SEVERAL COUNTIES. HIGH PRESSURE WILL MOVE OFFSHORE SATURDAY NIGHT...AND LOW PRESSURE DEVELOPING ACROSS THE CENTRAL PLAINS WILL SPREAD A WIDE SWATH OF SHOWERS AND THUNDERSTORMS ACROSS THE CENTRAL UNITED STATES. HIGH CLOUDS WILL MOVE INTO THE AREA SATURDAY AND SATURDAY NIGHT...WITH LOWER CLOUDS MOVING IN FOR SUNDAY. HOWEVER...APPEARS THAT ANY LIFTING MECHANISM WILL REMAIN TOO FAR WEST TO PRODUCE ANY SHOWERS LOCALLY. SUNSHINE ON SATURDAY WILL ALLOW HIGHS TO RISE A FEW DEGREES WARMER THAN FRIDAY...WITH SOUTHERLY WINDS ON SUNDAY BRINGING ANOTHER INCREASE TO HIGHS.
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&& .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... UPPER RIDGING OVER THE SOUTHEAST CONUS IS EXPECTED TO DEVELOP BY EARLY NEXT WEEK...AS SHORTWAVES ADVANCE ALONG THE NORTHERN PERIPHERY OF THE RIDGE. MAINTAINED CHANCE POPS FOR THE HOLIDAY FORECAST AS THE STRENGTH OF RIDGING AND PLACEMENT OF A SURFACE BOUNDARY ACROSS THE AREA REMAIN IN QUESTION. SOUTHWEST FLOW IS PROGGED TO DEVELOP THEREAFTER WITH OCCASIONAL WEAK EMBEDDED CROSSING SHORTWAVES. THIS WILL CONTINUE PERIODIC CHANCES FOR SHOWERS/STORMS. USED WPC BASED ENSEMBLE MEAN GUIDANCE WITH DOWNWARD ADJUSTMENTS TO POPS TO HELP SMOOTH OUT INDIVIDUAL MODEL DIFFERENCES...ESPECIALLY FOR MONDAY. TEMPERATURES SHOULD AVERAGE ABOVE SEASONAL LEVELS. && .AVIATION /19Z THURSDAY THROUGH TUESDAY/...
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HIGH PRESSURE SHOULD START TO NOSE UP THE OHIO VALLEY THIS EVENING...ALLOWING FOR SOME MIXING OUT OF LOW CLOUDS AND AN INCREASE IN NORTHWESTERLY FLOW. THIS SHOULD BRING ALL SITES BACK TO VFR BY TONIGHT. ANOTHER SYSTEM QUICKLY SAGS INTO THE AREA ON FRIDAY...HOWEVER SHOWERS AND MVFR RESTRICTIONS WILL LIKELY BE SPOTTY ALONG THE ASSOCIATED FRONT AND QUICKLY DEPART THE AREA BY LATE AFTERNOON. GUSTY NORTHWEST WINDS WILL FOLLOW THIS SYSTEM BY LATER FRIDAY. FRIES .OUTLOOK.../FRIDAY THROUGH TUESDAY/... RESTRICTIONS ARE POSSIBLE WITH A LATE SUNDAY AND MONDAY WARM FRONT.
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&& .PBZ WATCHES/WARNINGS/ADVISORIES...
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MD...NONE. OH...NONE. PA...FREEZE WATCH FROM LATE FRIDAY NIGHT THROUGH SATURDAY MORNING FOR PAZ007>009-015-016. WV...NONE.
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&& $$

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