Severe Thunderstorm Warning 145, NWS Pittsburgh, PA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
204 PM EDT TUE JUL 22 2008

.SYNOPSIS...
AN APPROACHING COLD FRONT WILL RESULT IN SCATTERED TO NUMEROUS
SHOWERS AND THUNDERSTORMS INTO WEDNESDAY. HIGH PRESSURE WILL
BUILD INTO THE REGION FOR LATE IN THE WEEK...BRINGING DRY AND
SEASONABLY COOL CONDITIONS. THE NEXT FRONTAL SYSTEM WILL IMPACT
THE AREA OVER THE WEEKEND.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
SCATTERED SHOWERS/ISOLATED TSTMS ARE DEVELOPING ACROSS NORTHEAST
OH/NORTHWEST PA ALONG A LAKE INDUCED BOUNDARY...OTHERWISE THE
NEXT WAVE IS APPROACHING FROM THE WESTERN GREAT LAKES. THIS
WAVE WILL ROTATE ACROSS THE AREA EARLY THIS EVENING ACROSS
EASTERN OHIO...AND ACROSS WESTERN PA EASTWARD LATE THIS
EVENING/OVERNIGHT. AS HAS BEEN THE CASE THE LATE COUPLE OF
DAYS...THE POTENTIAL FOR STORMS TO PRODUCE LOCALLY STRONG WINDS
WILL CONTINUE. NAM/GFS/SREF ALL DEPICT A SLOWER EXIT OF THE
FORCING...ESPECIALLY ALONG THE SE RIDGES...THUS WILL KEEP HIGH
END CHC POPS THROUGH MOST OF WEDNESDAY THERE...WITH DIMINISHING
PRECIP COVERAGE FURTHER NORTH AND WEST. NOTICEABLY COOLER AND
DRIER CONDITIONS WILL WORK IN ACROSS NORTHERN SECTIONS WEDNESDAY
WITH HIGHS IN THE MID 70S WITH DEWPOINTS FALLING INTO THE 50S.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/...
RESIDUAL ISOLATED SHWRS WILL END WEDNESDAY EVENING ACROSS THE
RIDGES AS THE UPPER LOW EXITS TO THE EAST. HIGH PRESSURE WILL
BUILD IN FOR THE REMAINDER OF THE WORK WEEK...BRINGING DRY AND
COOLER CONDITIONS...WITH MOST LOCATIONS IN THE 50S WEDNESDAY NIGHT
AND THURSDAY NIGHT.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
MEDIUM RANGE MODELS CONTINUE TO BE IN DECENT AGREEMENT BRINGING
THE NEXT FRONTAL BOUNDARY ACROSS THE REGION SATURDAY...WITH
PERHAPS A SECONDARY FEATURE FOR SUNDAY. WILL KEEP CHANCE POPS
FOR SAT/SUN. SOME DIFFERENCES FOR EARLY NEXT WEEK...WITH THE GFS
SHOWING YET ANOTHER WAVE CROSSING THE AREA...AND THE ECMWF SHOWING
THE FEATURE DEPARTING TO THE SOUTH. WILL KEEP MINIMAL RESIDUAL
CHANCES FOR MONDAY...WITH DRY CONDITIONS FOR TUESDAY. NEAR NORMAL
TEMPERATURES WILL PREVAIL FOR THE LONG TERM.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
BLEND OF MOST RECENT RUC NAM AND SREF MODEL RUNS SUGGEST A BAND OF
SCATTERED TO NUMEROUS THUNDERSTORMS CAN MOVE THROUGH THE UPPER OHIO
VALLEY BETWEEN 19Z AND 02Z. A SECOND BAND OF SHOWERS AND SCATTERED
THUNDERSTORMS CAN MOVE THROUGH THIS AREA LATE TONIGHT.

RECENT RADAR DATA SHOWING ISOLATED THUNDERSTORMS SPROUTING WITHIN
THE LAKE ERIE BREEZE ZONE TO THE VICINITY OF THE I-80 CORRIDOR
SUPPORTS THE CONTENTION OF THE INITIAL THUNDERSTORM BAND. SREF DEEP
LAYER BULK SHEAR AND CAPE VALUES SUPPORT SPC THINKING THE STORMS MAY
DEVELOP SEVERE CHARACTERISTICS. SO THUNDERSTORM GUSTS NEAR 30 KTS
INCLUDED WITH 3-HOUR WINDOW OF THUNDERSTORM ONSET ALONG WITH MVFR.
THIS WILL BE MONITORED FOR UPWARD ADJUSTMENT AS NEEDED.

THE DEGREE OF DESTABILIZATION WITH THE FRONTAL BAND OF SHOWERS AND
THUNDERSTORMS WILL DEPEND ON SEVERAL FACTORS THAT INCLUDE HOW MUCH
CAPE IS USED TO SUPPORT PROPOSED INITIAL BAND AND EXACT TIMING OF
SLOW COLD FRONTAL PASSAGE. SO AT THIS TIME HAVE FORECASTED A PERIOD
OF SHOWERS LATE TONIGHT ALBEIT THERE CAN ALSO BE SUFFICIENT RESIDUAL
LIFT AND INSTABILITY TO GENERATE SCATTERED THUNDERSTORMS AND MVFR.

WITH THE EXPECTED RAIN MOISTENING OF THE SURFACE LAYER...HAVE
FORECASTED LATE NIGHT FOG WITH WIDESPREAD MVFR AND SCATTERED IFR.

BY WEDNESDAY NIGHT...EXPECT THE SURFACE LAYER TO SUFFICIENTLY DRY TO
END SHOWER CHANCES TO INDUCE WIDESPREAD VFR. BASED ON BLEND OF SREF
AND GEFS MODEL RUNS EXPECT VFR TO BE PREVALENT THURSDAY AND FRIDAY
WITH ONLY IFR POSSIBILITY IN ISOLATED EARLY MORNING FOG PATCHES.

LATEST GEFS MODEL RUN SHOWS ANOTHER FRONT AFFECTING THE UPPER OHIO
VALLEY SATURDAY AND SUNDAY RAISING THE CHANCES OF SHOWERS AND
THUNDERSTORMS AND AT LEAST MVFR CONDITIONS.

&&

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

&&

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE PITTSBURGH PA
915 AM EDT TUE JUL 22 2008

MDZ001-OHZ039>041-048>050-057>059-068-069-PAZ007>009-013>016-020>023-
029>032-WVZ001>004-012-021>023-041-231315-
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-
915 AM EDT TUE JUL 22 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

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS TODAY AND TONIGHT.
THE BEST CHANCE OF SUCH STORMS WILL BE LATE THIS AFTERNOON AND
TONIGHT. THE MAIN HAZARD WILL BE DAMAGING WIND. LARGE HAIL IS
ALSO POSSIBLE.

THUNDERSTORMS CAN ALSO HAVE HEAVY RAIN. LOCATIONS GETTING MORE
THAN 1.5 INCHES IN LESS THAN 2 HOURS MAY SEE FLOODING WHERE
DRAINAGE IS POOR AND ALONG SMALL STREAMS.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER
CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES.

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SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE PITTSBURGH PA
326 PM EDT TUE JUL 22 2008

PAZ007-008-013-014-222030-
BUTLER PA-LAWRENCE PA-MERCER PA-VENANGO PA-
326 PM EDT TUE JUL 22 2008

...THUNDERSTORMS...

THUNDERSTORMS TO MOVE THROUGH THE FOLLOWING COUNTIES...
BUTLER...VENANGO...MERCER AND LAWRENCE...

AT 323 PM EDT NATIONAL WEATHER SERVICE DOPPLER RADAR IN PITTSBURGH
INDICATED STRONG THUNDERSTORMS 10 MILES SOUTHWEST OF FARRELL...MOVING
EAST AT 36 MPH.

SOME LOCATIONS THAT WILL BE IMPACTED BY THESE STORMS INCLUDE...
  CLINTONVILLE...EAU CLAIRE...ENTERPRISE...FARRELL...GROVE CITY...
  HERMITAGE...KENNERDELL...MERCER...MOUNT PLEASANT...NEW
  WILMINGTON...OAKLAND...SHARON...AMSTERDAM...ARMSTRONG AND ATWELLS
  CROSSING

THESE STORMS ARE CAPABLE OF PRODUCING HALF INCH HAIL...WIND GUSTS TO
40 MPH...AND INTENSE LIGHTNING.

KEEP AN EYE TO THE SKY AND MOVE TO A SAFE PLACE IF THUNDERSTORMS
APPROACH.

PLEASE REPORT HAIL...STRONG WINDS OR WIND DAMAGE TO THE NATIONAL
WEATHER SERVICE BY CALLING TOLL FREE...1-877-633-6772.