Area Forecast Discussion
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000 FXUS61 KPBZ 211733 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 133 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/... A WEAK PRESSURE GRADIENT CONTINUE 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 && .SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/... CLOSED LOW OVER EASTERN CANADA WILL WOBBLE SOUTH FRIDAY...DEEPENING UPPER TROUGH AND PUSHING A MOISTURE STARVED COLD FRONT ACROSS THE REGION. ONLY SLIGHT CHANCE POPS WITH THE FRONT AS IT CROSSES THE REGION DURING THE DAY FRIDAY AND EXITS THE RIDGES BY EVENING. A GOOD COLD PUNCH BEHIND FRONT WITH DRY SURFACE HIGH BUILDING OVER THE REGION FRIDAY NIGHT. WITH CLEAR SKIES AND LIGHT WINDS...TEMPERATURES WILL FALL INTO THE LOWER AND MID 30S NORTH AND RIDGES WITH AREAS OF FROST EXPECTED. ELSEWHERE LOOKS TO BE BORDERLINE FOR FROST AND ADDED PATCHY FROST EXCEPT FOR THE ZANESVILLE AREA FOR NOW. LATER SHIFTS WILL BE BETTER ABLE TO DEFINE. SUNSHINE AND A RETURN TOWARD SEASONAL TEMPERATURES SATURDAY. AS SURFACE RIDGE SHIFTS EAST SUNDAY CLOUDS WILL INCREASE AHEAD OF A WARM FRONT WITH HIGHS IN THE 70S. && .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 /17Z THURSDAY THROUGH MONDAY/... 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 MONDAY/... RESTRICTIONS ARE POSSIBLE WITH A LATE SUNDAY AND MONDAY WARM FRONT. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...NONE. WV...NONE. && $$

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