Severe Thunderstorm Warning 157, NWS Pittsburgh, PA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
314 PM EDT SAT JUL 26 2008

.SYNOPSIS...
A WEAK COLD FRONT PASSING THROUGH THE UPPER OHIO VALLEY WILL CAUSE
SCATTERED SCATTERED SHOWERS AND THUNDERSTORMS THROUGH EARLY
TONIGHT. ENSUING MIDWEST HIGH PRESSURE WILL BRING DRY CONDITIONS
SUNDAY. A WARM FRONT DEVELOPING ACROSS THE OHIO VALLEY MONDAY WILL
SPELL MORE HUMID CONDITIONS STARTING MONDAY AND PERHAPS ISOLATED
SHOWERS AND THUNDERSTORMS LATE TUESDAY INTO WEDNESDAY.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
WITH RADAR DATA SHOWING SCATTERED THUNDERSTORMS DEVELOPING OVER THE
UPPER OHIO VALLEY PARTICULARLY WITHIN THE ERIE LAKE SHORE
CORRIDOR...WILL KEEP MENTION OF SCATTERED THUNDERSTORMS THROUGH
ABOUT MIDNIGHT BUT INTO SUNDAY MORNING ALONG THE APPALACHIAN
MOUNTAINS AS SUGGESTED BY RECENT SREF MODEL RUNS.

ALTHOUGH RECENT BROKEN CLOUD COVER HAS SLOWED INCREASE IN SOLAR
HEATING AND DEEP LAYER INSTABILITY...CONCUR WITH SREF VALUES THAT
CAPE CAN STILL GO OVER 1000 J/KG. FORTUNATELY DEEP LAYER SHEAR
SHOULD BE LIMITED TO 25 KTS...SO CONCUR WITH SPC THAT SEVERE
POTENTIAL REMAINS LOW WITH THE MORE FAVORABLE DEVELOPMENT CONDITIONS
FROM THE I-80 CORRIDOR NORTH.

BY LATE TONIGHT...HAVE FORECASTED PATCHY FOG SUGGESTED BY GFS AND
NAM MOS...AS LOW TEMPERATURES WILL BE IN RANGE OF EXPECTED SURFACE
DEW POINTS PARTICULARLY IN THOSE SCATTERED LOCATIONS GETTING RAIN
THIS EVENING.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
HIGH PRESSURE FROM THE MIDWEST WILL BRING SOME SURFACE LAYER DRYING
AND HENCE MORE STABLE CONDITIONS TO MUCH OF THE UPPER OHIO VALLEY
SUNDAY INTO SUNDAY NIGHT. HOWEVER RECENT SREF MODEL RUNS INDICATE
THERE CAN BE ISOLATED THUNDERSTORM DEVELOPMENT SUNDAY BEFORE THERE
IS SUFFICIENT SURFACE DRYING TO STABILIZE CONDITIONS EVEN THERE.

FORECASTED TEMPERATURES CLOSE TO BLEND OF CLOSELY AGREEING SREF
VALUES AND GFS AND NAM MOS.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
GFS ENSEMBLE MEAN CONTINUES TO SHOW HIGH PRESSURE COVERING OUR
AREA MONDAY AND ON INTO TUESDAY. TUESDAY NIGHT HIGH PRESSURE MOVES
OFF TO OUR EAST. DURING THE DAY ON WEDNESDAY LOW LEVEL MOISTURE
INCREASES WITH THE APPROACH OF LOW PRESSURE SYSTEM. CHANCE OF PCPN
WEDNESDAY AND WEDNESDAY NIGHT WITH LOW PRESSURE MOVING THROUGH.
HIGH PRESSURE BUILDS BACK INTO OUR AREA FROM THE WEST ON THURSDAY
AND HOLDS THROUGH SATURDAY. TEMPERATURES WILL AVERAGE NEAR
SEASONAL NORMS.

&&

.AVIATION /19Z SATURDAY THROUGH THURSDAY/...
EXPECT PREVALENT VFR THIS ENTIRE PERIOD ALBEIT ISOLATED MVFR
POSSIBLE TONIGHT WITH SCATTERED SHOWERS AND THUNDERSTORMS. CONCUR
WITH SPC THAT SEVERE THUNDERSTORM POTENTIAL ACROSS THE UPPER OHIO
VALLEY WILL BE LIMITED DUE TO WEAK SHEAR AND INSTABILITY
VALUES...ALTHOUGH THUNDERSTORMS WITHIN THE I-80 CORRIDOR HAVE MORE
POTENTIAL THAN STORMS FARTHER SOUTH. WINDS WILL BE FROM THE
SOUTHWEST 10 KTS THIS EVENING AND THEN DECREASE TO 2-5 KTS LATE
TONIGHT.

HAVE INCLUDED MVFR TO IFR VISIBILITIES IN FOG SUNDAY MORNING AROUND
DAYBREAK AS SUGGESTED BY NAM AND GFS LAMP MOS...AS LOW TEMPERATURES
WILL BE IN RANGE OF EXPECTED SURFACE DEW POINTS PARTICULARLY IN
THOSE SCATTERED LOCATIONS GETTING RAIN THIS EVENING SUCH AS KFKL AND
KDUJ.

JUDGING FROM RECENT NAM MODEL PROFILES EXPECT MAINLY SCATTERED
CUMULUS SUNDAY.

BASED ON RECENT SREF MODEL RUNS AND NAM PROFILES...EXPECT BUILD UP
IN SURFACE LAYER MOISTURE STARTING MONDAY SHOULD SPELL EARLY MORNING
FOG AND HAZE WITH A COUPLE HOURS MVFR AND ISOLATED IFR. ISOLATED
SHOWERS AND THUNDERSTORMS WITH MVFR CAN ALSO DEVELOP...MAINLY
TUESDAY INTO WEDNESDAY.

&&

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

&&

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE PITTSBURGH PA
502 AM EDT SAT JUL 26 2008

MDZ001-OHZ039>041-048>050-057>059-068-069-PAZ007>009-013>016-020>023-
029>032-WVZ001>004-012-021>023-041-270915-
GARRETT-TUSCARAWAS-CARROLL-COLUMBIANA-COSHOCTON-HARRISON-
JEFFERSON OH-MUSKINGUM-GUERNSEY-BELMONT-NOBLE-MONROE-MERCER-VENANGO-
FOREST-LAWRENCE-BUTLER-CLARION-JEFFERSON PA-BEAVER-ALLEGHENY-
ARMSTRONG-INDIANA-WASHINGTON-WESTMORELAND-GREENE-FAYETTE-HANCOCK-
BROOKE-OHIO-MARSHALL-WETZEL-MARION-MONONGALIA-PRESTON-TUCKER-
502 AM EDT SAT JUL 26 2008

THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN MARYLAND...EAST
CENTRAL OHIO...NORTHWEST PENNSYLVANIA...SOUTHWEST
PENNSYLVANIA...WEST CENTRAL PENNSYLVANIA...NORTHERN WEST VIRGINIA
AND NORTHERN PANHANDLE OF WEST VIRGINIA.

.DAY ONE...TODAY AND TONIGHT

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.

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