Severe Thunderstorm Warning 73, NWS Pittsburgh, PA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
249 PM EDT THU JUN 26 2008

.SYNOPSIS...
A STALLED WARM FRONT WILL KEEP WARM AND HUMID CONDITIONS ACROSS
THE UPPER OHIO VALLEY INTO THE WEEKEND. SCATTERED THUNDERSTORMS
CAN BE EXPECTED TONIGHT AND FRIDAY. A CANADIAN COLD FRONT WILL
BRING MORE WIDESPREAD THUNDERSTORMS SATURDAY INTO SUNDAY FOLLOWED
BY MORE COMFORTABLE CONDITIONS STARTING MONDAY.

&&

.NEAR TERM /THROUGH FRIDAY/...
SCATTERED STORMS ARE A POSSIBILITY FOR THIS AFTERNOON AND
EVENING...RESULTING FROM DIFFERENTIAL SOLAR HEATING ALONG THE
CLOUD BOUNDARIES DEPICTED IN RECENT SATELLITE DATA. WITH THE
RECENT SREF MODEL RUN SHOWING A UPPER LEVEL SHORT WAVE TROUGH
MOVING EASTWARD THROUGH THE UPPER OHIO VALLEY TONIGHT...A FEW
STORMS COULD BE TRIGGERED LATE. THE AIRMASS WILL REMAIN UNSTABLE INTO
FRIDAY...WITH ADDITIONAL WEAK WAVES ALOFT HELPING TO INITIATE
CONVECTION. THERE IS A SLIGHT RISK OF STORMS REACHING SEVERE
POTENTIAL AS INDICATED BY SPC CONVECTIVE OUTLOOK. INSTABILITY CAN BE
LARGE DUE TO THE HUMID SURFACE LAYER BUT VERTICAL WIND SHEAR
APPEARS MARGINAL.

TEMPERATURES WILL BE AT OR ABOVE NORMAL FOR THE
PERIOD AS INDICATED BY RECENT SREF AND NAM AND GFS MOS.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/...
JUDGING FROM BLEND OF RECENT SREF MODEL RUNS...EXPECT
THUNDERSTORM POTENTIAL TO SHOW LITTLE CHANGE LATE FRIDAY INTO
EARLY SATURDAY...THAT IS SCATTERED IN COVERAGE WITH POTENTIAL TO
BRIEFLY PULSE INTO THE SEVERE RANGE.

HOWEVER AS THE CANADIAN COLD FRONT AND ASSOCIATED COLD UPPER
LEVEL LOW CENTER ADVANCE THROUGH THE GREAT LAKES SATURDAY...THE
THUNDERSTORMS WILL BECOME MORE NUMEROUS AND POTENTIALLY ORGANIZED
INTO LINES ACROSS THE UPPER OHIO VALLEY.  THIS IS DUE TO THE
INCREASED WINDS ALOFT AND HENCE INCREASED VERTICAL WIND SHEAR. THE
INSTABILITY WILL REMAIN LARGE DUE TO THE HUMID SURFACE LAYER. THE
PRIME SEVERE THREAT SHOULD BE DAMAGING WIND...WHILE LARGE HAIL AND HEAVY
RAIN POSE SECONDARY THREATS. THE SPECIFIC TIME OF DAY SUCH A
PREFRONTAL LINE OF THUNDERSTORMS MOVES THROUGH THE UPPER OHIO
VALLEY WILL EFFECT THE SEVERITY...WITH LATE AFTERNOON AND EARLY
EVENING THE MOST HAZARDOUS TIME FRAME. SEVERAL SREF MODEL MEMBERS
INDICATE THIS POSSIBLE SCENARIO.

FORECASTED TEMPERATURES WERE BASED ON A CONSENSUS OF SREF VALUES
AND NAM AND GFS MOS.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
BLEND OF RECENT GEFS/GFS ENSEMBLE/ AND ECMWF MODEL RUNS SHOW THE
COLD UPPER LOW SLOWING AS IT MOVES THROUGH THE GREAT LAKES AND
NORTHEASTERN U.S. SUNDAY INTO WEDNESDAY. THIS WILL MAINTAIN
INSTABILITY SHOWERS AND THUNDERSTORMS ACROSS THE UPPER OHIO VALLEY
INTO MONDAY AS THE COOL DOWN ALOFT WILL BE LARGER THAN THE COOL
DOWN IN THE SURFACE LAYER.

EXPECT THAT BY AROUND TUESDAY...THE SURFACE LAYER WILL
SUFFICIENTLY DRIED AND THE COLD TEMPERATURES ALOFT SUFFICIENTLY
MODERATED TO DISSIPATE THE PROSPECTS OF SHOWER DEVELOPMENT.

BASED ON A CONSENSUS OF HPC GUIDANCE AND GFS MOS...FORECASTED HIGH
TEMPERATURES MONDAY AND TUESDAY TO BE NEARLY 10 DEGREES COOLER
THAN NORMAL BEFORE MODERATING WEDNESDAY AND THURSDAY. SURFACE DEW
POINTS WILL LIKEWISE BE IN THE COMFORTABLE RANGE.

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
GENERALLY VFR CONDITIONS CAN BE EXPECTED THROUGH FRIDAY...WITH
CONDITIONS LOWERING TO MVFR AT TIMES THIS EVENING IN SCATTERED
STORMS. SOME MVFR VISIBILITIES IN FOG ARE POSSIBLE OVERNIGHT TOWARD
DAWN. A PERIOD OF VERY UNSETTLED WEATHER IS EXPECTED FOR FRIDAY THROUGH
TUESDAY...AS A SERIES OF FRONTS AND UPPER WAVES PASS EASTWARD ACROSS
THE REGION. WHILE CONDITIONS WILL PREVAIL DURING THE PERIOD AT
VFR...IFR WILL BE POSSIBLE AT TIMES IN STORMS. THERE IS ALSO SOME
SEVERE POTENTIAL...MAINLY ISOLATED INTO FRIDAY BUT POTENTIALLY
MORE WIDESPREAD SATURDAY.

&&

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

&&

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE PITTSBURGH PA
302 PM EDT THU JUN 26 2008

MDZ001-OHZ039>041-048>050-057>059-068-069-PAZ007>009-013>016-020>023-
029>032-WVZ001>004-012-021>023-041-271915-
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-
302 PM EDT THU JUN 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...THIS AFTERNOON AND TONIGHT

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS TONIGHT. THE
PRIMARY SEVERE WEATHER HAZARD IS DAMAGING THUNDERSTORM WINDS. THE
SECONDARY HAZARD IS LARGE HAIL. HEAVY RAIN CAN POSE A FLOOD HAZARD
IN LOCATIONS THAT GET MORE THAN 1.5 INCHES IN LESS THAN 3 HOURS.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR FRIDAY...
SATURDAY...AND SUNDAY...THE SEVERE POTENTIAL CAN BE MORE
WIDESPREAD SATURDAY. THE PRIMARY SEVERE WEATHER HAZARD IS DAMAGING
THUNDERSTORM WINDS. THE SECONDARY HAZARD IS LARGE HAIL. HEAVY RAIN
CAN POSE A FLOOD HAZARD IN LOCATIONS THAT GET MORE THAN 1.5 INCHES
IN LESS THAN 3 HOURS.

.SPOTTER INFORMATION STATEMENT...

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

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