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Area Forecast Discussion
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000
FXUS61 KPBZ 011834
AFDPBZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
234 PM EDT MON SEP 1 2014

.SYNOPSIS...
SCATTERED SHOWERS AND STORMS WILL DIMINISH IN COVERAGE GOING INTO
THE EVENING...WITH HUMID AND SOMEWHAT UNSTABLE CONDITIONS
CONTINUING THROUGH EARLY TUESDAY. A COLD FRONT WILL ADVANCE ACROSS
THE AREA TUESDAY...WIDESPREAD SHOWERS AND STORMS.

&&

.NEAR TERM /THROUGH TUESDAY/...
THE 12Z KPBZ RAOB INDICATED A NEARLY SATURATED ATMOSPHERE BELOW
700 MB...AND WHILE SOME OF THE MOISTURE HAS LIKELY MIXED OUT A BIT
AS STRATUS HAS BROKEN UP ACROSS THE AREA...THE SOURCE REGION AIR
MASS FOR THE LARGE SCALE FLOW CONTINUES TO HAVE DEWPOINTS LARGELY
IN THE LOWER 70S THIS AFTERNOON. AS SUCH...RATHER DEEP INSTABILITY
WAS NOTED ON THE 12Z SOUNDING...AND IT LIKELY STILL EXISTS OVER
THE AREA THIS AFTERNOON. WHILE FORCING FOR ASCENT IS RATHER
NEBULOUS TO FIND AT THE MOMENT...A COUPLE OF WEAK EMBEDDED
VORTEXES SEEM TO BE MORE THAN ENOUGH TO HARNESS THIS INSTABILITY
AND TRANSLATE IT INTO RATHER EFFICIENT HEAVY RAIN PRODUCING
SHOWERS AND THUNDERSTORMS GIVEN PWAT VALUES OF AROUND OR ABOVE 2
INCHES. THE FIRST OF THESE HAS ALREADY BASICALLY EXITED THE AREA
TO THE NORTHEAST. THE SECOND IS CURRENTLY MOVING INTO EASTERN OHIO
AND SHOULD TRANSLATE ACROSS THE BULK OF THE REST OF THE AREA SOUTH
OF A NEW PHILADELPHIA TO INDIANA LINE THIS EVENING. BRIEF HEAVY
RAINFALL WILL BE LIKELY WITH THESE CELLS. HOWEVER...THEY ARE
RATHER TRANSIENT...SO FLOODING CONCERNS ARE MINIMIZED AS A RESULT.

DEEP INSTABILITY AND A VERY HUMID AIR MASS REMAIN BEHIND THE
ACTIVITY THIS EVENING...SO WHILE SHOWERS AND A STORM OR TWO CANNOT
BE RULED OUT...THE CHANCES DO LOOK TO DWINDLE OWING TO A LACK OF
FORCING OTHER THAN ANOTHER TRANSIENT WAVE THAT MAY BRING SOME
SHOWERS THROUGH AROUND MIDNIGHT. THE REAL FOCUS BY TONIGHT LOOKS
TO BE TURNING TO THE DAYTIME ON TUESDAY...WHEN THE MID-LEVEL
SYSTEM APPROACHES FROM THE GREAT LAKES ALONG WITH THE ASSOCIATED
COLD FRONT.

MODEL SOLUTIONS SEEM TO BE KEYING IN ON A LATE MORNING/EARLY
AFTERNOON ARRIVAL INTO NORTHWEST PORTIONS OF THE AREA...WITH A
MID-AFTERNOON CROSSING OF THE PITTSBURGH AREA...AND A LATE
AFTERNOON/EARLY EVENING EXIT OF THE CWA FOR THE FRONTAL BOUNDARY.
INSTABILITY ALONG THE FRONT WHILE LIKELY CONTINUING TO BE RATHER
DEEP...SHOULD ALSO BE RATHER UNIMPRESSIVE OWING IN LARGE PART TO A
LACK OF INSOLATION AHEAD OF THE FRONT THROUGH THE EARLY PORTIONS
OF THE DAY. THIS SHOULD LIMIT ADDITIONAL DESTABILIZATION.
ADDITIONALLY...OWING TO THE FACT THAT THE MID-LEVEL WAVE LARGELY
SHEARS OFF TO OUR NORTH...0-6 KM BULK SHEAR VALUES REALLY ONLY RUN
UP TOWARD 35 KTS OF WEAKLY VEERED FLOW AS THE BOUNDARY IMPINGES
UPON THE AREA. AGAIN WITH THIS VARIABLE...THOSE VALUES DO NOT
EXACTLY MAKE THIS FORECASTER PARTICULARLY JUMPY.
FURTHERMORE...WITH SHEAR VALUES THAT HIGH AND A FAIRLY QUICK
MOVING WAVE PASSAGE...WHILE THE CELLS THAT DO MOVE THROUGH ARE
LIKELY TO BE HEAVY RAIN PRODUCERS...PROLONGED HEAVY RAINFALL IN
ANY PARTICULAR LOCATION AS WELL AS TRAINING OF ECHOES SEEMS
UNLIKELY. THIS SHOULD MINIMIZE THE RISK OF FLASH FLOODING AS WELL.
IT IS WORTH NOTING THAT SPC HAS PLACED THE AREA IN A SLIGHT RISK
FOR TOMORROW...HOWEVER OWING TO LESS THAN STELLAR INSTABILITY
VALUES...MODERATE SHEAR...A LACK OF INSOLATION...FORCING THAT
FOCUSES HEIGHT FALLS LARGELY TO THE NORTH OF THE AREA ALONG WITH
THE HIGHEST SHEAR VALUES...IT SEEMS LIKE THIS SLIGHT RISK IS A
LESS CONFIDENT SLIGHT RISK THAN NORMAL.  FRIES



&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
THE NEXT SHORTWAVE TROUGH WILL MOVE THROUGH TUESDAY WITH A WEAK
FRONTAL BOUNDARY. MODELS CONTINUE TO SHOW AN UNSTABLE ATMOSPHERE
AS THE HIGH SURFACE DEWPOINTS REMAIN ENTRENCHED. TIMING ON THE
BOUNDARY APPEARS TO BE IN THE AFTERNOON VIEWABLE WITH A LINE OF
LOW LEVEL FORCING. TUESDAY LOOKS LIKE A GOOD BET TO SEE WIDESPREAD
SHOWERS WITH THE RISK FOR STORMS. SHOULD BE PLENTY OF CLOUD COVER
TUESDAY WHICH WILL LIMIT THE STRENGTH OF CONVECTION. WOULD THINK
THE GREATER THREAT WOULD BE HEAVY DOWNPOURS AS PWATS WILL RISE TO
NEAR 2 INCHES RIGHT AHEAD OF THE CROSSING BOUNDARY. UPPER LEVEL
SUPPORT WILL QUICKLY MOVE TO THE EAST IN THE EVENING...CARRYING
THE BOUNDARY WITH IT. THIS WILL BRING AN END TO THE THREAT FOR
PRECIPITATION.

DRIER AIR WILL EVENTUALLY SETTLE IN OVER THE REGION ON WEDNESDAY.
TEMPS WILL STILL BE WARM BUT CONDITIONS WILL BE NOTICEABLY MORE
COMFORTABLE.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
HIGH PRESSURE WILL REMAIN ALONG THE EAST COAST THROUGH FRIDAY...
ALLOWING CONDITIONS TO REMAIN DRY. COLD FRONT WILL BRING SHOWERS
AND STORMS FOR THE BEGINNING OF THE WEEKEND...WITH COOLER DRIER
AIR FOR THE END OF THE LONG TERM.

&&

.AVIATION /18Z MONDAY THROUGH SATURDAY/...
VFR CONDITIONS WILL LIKELY BE LOCALLY MARRED BY CONVECTION THROUGH
THE AFTERNOON HOURS...THOUGH TIMINIG IS DUBIOUS AT BEST AT THE
MOMENT FOR ANY PARTICULAR TERMINAL. MVFR VIS ARE LIKELY TO RETURN
OVERNIGHT AS CONVECTION DWINDLES AND ABUNDANT LOW LEVEL MOISTURE
AGAIN RETURNS. HOWEVER...A COLD FRONT WILL ADVANCE ON THE AREA ON
TUESDAY...BRINGING A BETTER RISK OF SHOWERS/STORMS AT ALL SITES
NEAR/AFTER THE END OF THE CURRENT FORECAST VALID PERIOD. FRIES

OUTLOOK.../TONIGHT THROUGH FRIDAY/...
SHOWERS AND STORMS WILL BE LIKELY AT ALL SITES TUESDAY AFTERNOON. 

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...NONE.
OH...NONE.
PA...NONE.
WV...NONE.

&&

$$






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