Area Forecast Discussion
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000
FXUS61 KPBZ 222042
AFDPBZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
442 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/...
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. 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

&&

.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 /21Z 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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