Area Forecast Discussion
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000 FXUS61 KPBZ 222323 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 723 PM EDT FRI MAY 22 2015 .SYNOPSIS... AFTER WELL BELOW NORMAL VALUES TONIGHT...TEMPERATURES SHOULD REBOUND TO ABOVE NORMAL VALUES BY SUNDAY. OTHER THAN A PASSING SHOWER THIS AFTERNOON...CONDITIONS SHOULD BE DRY UNTIL MEMORIAL DAY. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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RAPIDLY DECREASING DEWPOINTS HAVE ALREADY BEGUN THEIR DESCENT INTO THE AREA AS EVIDENCED BY KPIT FALLING 7 DEGREES IN THE PAST HOUR. LOOKING UPSTREAM...DEWPOINTS QUICKLY FALL OFF INTO THE 20S AND EVEN MID TEENS AS CLOSE AS CENTRAL LOWER MICHIGAN. BRISK NORTHWESTERLY FLOW WILL BRING THESE VALUES OVER THE AREA THIS EVENING...ALLOWING FOR RAPID CLEARING BEHIND THE FRONTAL BOUNDARY CURRENTLY EXITING THE SOUTHERN END OF THE AREA...EXCEPT FOR A FEW HIGH CIRRUS CLOUDS FROM CONVECTIVE BLOW OFF WAY UPSTREAM THAT MAY WANDER THROUGH OHIO LATE THIS EVENING. HIGH RESOLUTION MODEL GUIDANCE HAS A GOOD HANDLE ON THE DEWPOINT FALLS OVERNIGHT...HOWEVER COARSER MODEL GRIDS AS WELL AS STATISTICAL GUIDANCE REALLY HAS NO HANDLE ON IT WHATSOEVER. AS SURFACE HIGH PRESSURE SETTLES SMACK OVER THE AREA IN THE 09-12Z TIME FRAME TONIGHT...SUBSEQUENT TO RAPIDLY CLEARING AND DRIER AIR ARRIVING...DECOUPLING SHOULD OCCUR VERY STRONGLY. STRONG RADIATIONAL COOLING WILL RESULT...AND TEMPERATURES WILL GO INTO FREE FALL FOR SEVERAL HOURS. EVEN WITH MOS GUIDANCE FAILING TO HANDLE THE DRYING EVIDENT...AND EVEN THOUGH MODEL GUIDANCE IS LIKELY KEEPING DEWPOINTS TOO HIGH OVERNIGHT...MAV/MET NUMBERS SUGGEST WIDESPREAD UPPER 20S AND LOWER 30S ACROSS THE NORTH...WITH WIDESPREAD MID 30S JUST SOUTH OF THERE. GIVEN HISTORIC OBSERVED TRENDS...IT WOULD SEEM THAT THE TEMPERATURE SPREAD WOULD FAVOR TEMPERATURES APPROACHING THE LOW TO MID 30S ALL THE WAY DOWN INTO WASHINGTON AND GREENE COUNTY. HOWEVER...THE URBAN HEAT ISLAND WILL LIKELY BE RESPONSIBLE FOR 6-10 DEGREES LESS TEMPERATURE DECLINE IN PITTSBURGH AND ITS IMMEDIATE ENVIRONS. THIS WILL MEAN FROST IN THE CITY ITSELF IS FAR LESS LIKELY THAN ALL SURROUNDING AREAS. TO ACCOUNT FOR THIS...LOWS WERE REDUCED OVER LARGE TRACTS OF OHIO AND SOUTHWESTERN PENNSYLVANIA...HOWEVER WERE INCREASED IN THE URBAN CORE. TO ACCOUNT FOR THE ABOVE LOGIC...THE FROST ADVISORIES WERE EXPANDED TO INCLUDE TUSCARAWAS AND CARROLL COUNTIES IN OHIO...AS WELL AS WASHINGTON AND GREENE IN PENNSYLVANIA. FRIES
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&& .SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/... ALTHOUGH WINDS SHOULD REMAIN NEARLY CALM SATURDAY NIGHT AS WELL...HIGH CLOUDS MOVING INTO THE AREA SHOULD PREVENT AS MUCH RADIATIONAL COOLING AND KEEP OVERNIGHT LOWS IN THE 40S. MODEL TRENDS FOR THE SYSTEM DEVELOPING ACROSS THE CENTRAL UNITED STATES CONTINUE TO BE SLOWER IN MOVING THE STORM TO THE EAST. THE DELAYED TIMING SHOULD NOT ONLY KEEP ANY SHOWERS/STORMS TO THE WEST OF THE REGION ON SUNDAY...BUT SHOULD ALSO KEEP SUNDAY NIGHT RELATIVELY DRY WITH THE WARM FRONT MOVING ACROSS THE AREA DURING THE OVERNIGHT HOURS. AS THE COLD FRONT INCHES EAST ON MONDAY...MOST OF THE AREA SHOULD HAVE A CHANCE FOR SHOWERS/STORMS ON MEMORIAL DAY...BUT STORMS SHOULD BE SCATTERED IN NATURE. SOUTHWESTERLY WINDS BOTH SUNDAY AND MONDAY WILL ALLOW TEMPERATURES TO WARM BACK ABOVE NORMAL...ESPECIALLY AFTER THE WARM FRONT PASSES SUNDAY NIGHT. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... SOUTHWEST FLOW IS PROGGED TO DEVELOP THROUGH MOST OF THE PERIOD. WEAK CROSSING SHORTWAVES EMBEDDED IN THE FLOW ARE EXPECTED TO KEEP PERIODIC CHANCES FOR SHOWERS/STORMS IN THE FORECAST. AN UPPER TROUGH IS PROGGED FOR A LATE WEEK PASSAGE WITH BETTER FOCUS FOR PRECIP. USED TWEAKED WPC ENSEMBLE BASED GUIDANCE TO SMOOTH OUT SOME MODEL DIFFERENCES. TEMPERATURES SHOULD AVERAGE 10 TO 15 DEGREES ABOVE SEASONAL LEVELS. && .AVIATION /23Z FRIDAY THROUGH WEDNESDAY/... DRY HIGH PRESSURE WILL BUILD IN THE WAKE OF TODAYS COLD FRONT AND SUPPORT VFR FOR THE TAF PERIOD. .OUTLOOK.../SATURDAY THROUGH WEDNESDAY/... DISTURBANCES IN SOUTHWEST FLOW ALOFT WILL INCREASE THE CHANCE FOR RESTRICTIONS BY TUESDAY. && .CLIMATE... PITTSBURGH RECORD LOW TEMPERATURE FOR SATURDAY MAY 23...32 DEGREES IN 1963. ZANESVILLE RECORD LOW TEMPERATURE FOR SATURDAY MAY 23...32 DEGREES IN 1963. MORGANTOWN RECORD LOW TEMPERATURE FOR SATURDAY MAY 23...34 DEGREES IN 2006. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...FROST ADVISORY FROM MIDNIGHT TONIGHT TO 9 AM EDT SATURDAY FOR MDZ001. OH...FROST ADVISORY FROM MIDNIGHT TONIGHT TO 9 AM EDT SATURDAY FOR OHZ039>041. PA...FROST ADVISORY FROM MIDNIGHT TONIGHT TO 9 AM EDT SATURDAY FOR PAZ013-014-020>023-029-031-073>076. FREEZE WARNING FROM MIDNIGHT TONIGHT TO 9 AM EDT SATURDAY FOR PAZ007>009-015-016. WV...FROST ADVISORY FROM MIDNIGHT TONIGHT TO 9 AM EDT SATURDAY FOR WVZ001-002-023-041. && $$

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