Special Weather Statement, NWS Pittsburgh, PA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
241 PM EDT SUN AUG 14 2011

.SYNOPSIS...
A LARGE LOW PRESSURE SYSTEM, MOVING SLOWLY EASTWARD THROUGH THE
UPPER OHIO VALLEY, WILL BRING SHOWERS AND SCATTERED THUNDERSTORMS
AT TIMES INTO MONDAY NIGHT. HIGH PRESSURE, COMING EAST FROM IOWA,
WILL FOLLOW WITH DRY SEASONABLE CONDITIONS TUESDAY AND WEDNESDAY.

&&

.NEAR TERM /THROUGH MONDAY/...
STILL SHOWERS WILL BECOME MORE NUMEROUS THROUGH EARLY EVENING AND
SCATTERED THUNDERSTORMS CAN DEVELOP, BASED ON RECENT RADAR DATA
AND HRRR MODEL OUTPUT, WHICH SHOWED A BAND OF SHOWERS ORGANIZING
OVER CENTRAL OHIO. THIS SHOWER BAND, ASSOCIATED WITH THE UPPER
LEVEL/H5/ COLD POOL, SHOULD EXPAND AS IT MOVES EAST INTO WESTERN
PENNSYLVANIA.

CONCUR WITH SPC THAT THREAT OF SEVERE THUNDERSTORMS IS DIMINISHING
NOW THAT CLOUDS HAVE FILLED IN EAST OF THE MONONGAHELA RIVER
VALLEY, HENCE REDUCING POTENTIAL OF LARGE INSTABILITY. EFFECTIVE BULK
VERTICAL SHEAR, PROJECTED TO GO NO HIGHER THAN 25 KTS, HAS ALSO
BEEN A LIMITING FACTOR.

SO FLOODING POTENTIAL FROM HEAVY RAIN APPEARS TO BE THE MAIN
CONCERN IF ANY. A FEW SPOTS HAVE HAD MORE THAN 2 INCHES WITH NO
PROBLEMS. SO IT WILL TAKE AT LEAST 2.5 INCHES, IF NOT 3 INCHES, IN
LESS THAN 3 HOURS TO CAUSE FLOODING PROBLEMS. THE EXCEPTION, OF
COURSE, WOULD BE URBAN AREAS.

HAVE FORECASTED HIGH TEMPERATURES TO BE NO MORE THAN 2-3 DEGREES
HIGHER THAN 2 PM READINGS, WHICH YIELDED VALUES 2-5 DEGREES COOLER
THAN NORMAL DUE TO CLOUDS AND SHOWER PROSPECTS.

EXPECT COVERAGE OF SHOWERS AND POTENTIAL FOR THUNDERSTORMS TO
DECREASE AFTER MIDNIGHT AS SURFACE LAYER COOLS NOCTURNALLY,
NEGATING INSTABILITY GENERATION OF THE PASSING UPPER LEVEL COLD
POOL.

DO NOT HAVE YET SUFFICIENT CONFIDENCE TO INCLUDE MENTION OF FOG.
ALTHOUGH RAINFALL WILL MOISTEN THE SURFACE LAYER, LOW CLOUDS MAY
BE ENOUGH TO NEGATE THE COOLING NEEDED TO CAUSE FOG WITH LOW
VISIBILITY TO FORM.

FORECASTED LOWS TONIGHT TO BE NEAR NORMAL PER RECENT GFS AND NAM
MOS.

REGARDING MONDAY, EXPECT THE H5 COLD POOL TO CAUSE A DIURNAL INCREASE
IN INSTABILITY BEFORE EXITING EAST PAST THE MOUNTAINS BY EVENING.
HENCE HAVE FORECASTED A CHANCE OF SHOWERS IN THE MORNING FOLLOWED
BY LIKELY SHOWERS AND A CHANCE OF THUNDERSTORMS IN THE AFTERNOON.

FORECASTED HIGHS MONDAY CLOSER TO WARMER GFS MOS, WHICH STILL
YIELDED VALUES ABOUT 5 DEGREES COOLER THAN NORMAL.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
CONCUR WITH RECENT SREF AND NAEFS MODEL OUTPUT THAT HIGH PRESSURE
COMING EAST FROM IOWA, AND PASSING EAST WEDNESDAY, WILL PROVIDE DRY
CONDITIONS AND MAINLY ONLY SCATTERED CLOUDS THIS PERIOD.

EXPECT CONDITIONS TO BE FAIRLY COMFORTABLE AS FORECASTED
EARLY MORNING LOW TEMPERATURES TO BE UP TO 5 DEGREES COOLER THAN
NORMAL. HIGHS TUESDAY MAY STILL BE SLIGHTLY COOLER THAN NORMAL,
BUT HIGHS WEDNESDAY CAN GO UP TO 3 DEGREES WARMER THAN NORMAL PER
RECENT GFS MOS AND NAEFS MEDIAN VALUES. SURFACE DEW POINTS SHOULD
BE MAINLY IN THE 55 TO 62 RANGE, WHICH IS CLOSE TO NORMAL.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
LITTLE CHANGES MADE TO EXTENDED FORECAST...AS MODELS SHOW GENERAL
CONSENSUS FOR THIS TIME PERIOD. LOW PRESSURE PASSING OVER EASTERN
CANADA WILL DRAG A COLD FRONT ACROSS THE GREAT LAKES THURSDAY INTO
FRIDAY. HAVE BROUGHT IN CHANCE POPS BY THURSDAY AFTERNOON...WITH
POPS PERSISTING THURSDAY NIGHT AND FRIDAY. CONDITIONS MAY BEGIN TO
DRY OUT FRIDAY NIGHT INTO SATURDAY...WITH WEAK HIGH PRESSURE
BUILDING IN FROM THE WEST. TEMPERATURES WILL BE NEAR NORMAL.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
LOW TO MEDIUM CONFIDENCE THIS AFTERNOON WITH HEIGHT OF BKN/OVC
CEILING. MODELS INSIST ALL SITES WILL GO VFR...ALTHOUGH OBSERVATIONS
HAVE SHOWN VARIATION BETWEEN LOW MVFR AND VFR. WILL TRY TO SPLIT THE
DIFFERENCE USING TEMPO GROUPS TO SHOW VARIABILITY. HAVE ALSO REMOVED
PREVAILING THUNDERSTORMS FROM TAFS...WITH THE WIDESPREAD CLOUDS
REDUCING THE CHANCES FOR THUNDERSTORMS. HOWEVER...ISOLATED
THUNDERSTORMS ARE EXPECTED INTO THE EVENING HOURS...WITH SCATTERED
SHOWERS CONTINUING OVERNIGHT. HIGH CONFIDENCE THAT RESTRICTIONS WILL
OCCUR OVERNIGHT...ALTHOUGH WIND SPEED WILL HELP DETERMINE WHETHER
LOW MVFR/IFR CONDITIONS ARE DUE TO FOG OR STRATUS. CONDITIONS SHOULD
SLOWLY LIFT TO VFR BY EARLY MONDAY AFTERNOON...ALTHOUGH SCATTERED
SHOWERS WILL CONTINUE.

OUTLOOK /MONDAY THROUGH FRIDAY/...
SHOWERS AND RESTRICTIONS WILL FINALLY DIMINISH MONDAY NIGHT. HIGH
PRESSURE WILL ALLOW FOR VFR CONDITIONS FOR TUESDAY AND WEDNESDAY. A
COLD FRONT WILL APPROACH THE REGION THURSDAY INTO FRIDAY...BRINGING
POSSIBLE RESTRICTIONS.

&&

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

&&

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE PITTSBURGH PA
1258 PM EDT SUN AUG 14 2011

OHZ039>041-048>050-057>059-068-069-PAZ007>009-013>016-020>023-029-
031-073-074-WVZ001>004-012-151700-
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-GREENE-WESTMORELAND-WESTMORELAND RIDGES-HANCOCK-
BROOKE-OHIO-MARSHALL-WETZEL-
1258 PM EDT SUN AUG 14 2011

THIS HAZARDOUS WEATHER OUTLOOK IS FOR 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.

THUNDERSTORMS THIS AFTERNOON AND EVENING MAY ALSO PRODUCE LOCALLY
HEAVY RAIN. RAIN AMOUNTS OF MORE THAN 2 INCHES IN LESS THAN 3
HOURS MAY CAUSE FLOODING.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY.

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.

MDZ001-PAZ075-076-WVZ021>023-041-151700-
GARRETT-FAYETTE-FAYETTE RIDGES-MARION-MONONGALIA-PRESTON-TUCKER-
1258 PM EDT SUN AUG 14 2011

THIS HAZARDOUS WEATHER OUTLOOK IS FOR WESTERN MARYLAND...SOUTHWEST
PENNSYLVANIA AND NORTHERN WEST VIRGINIA.

.DAY ONE...THIS AFTERNOON AND TONIGHT.

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON AND
EVENING. THE PRIME THREATS WILL BE LARGE HAIL AND DAMAGING WINDS.

THUNDERSTORMS THIS AFTERNOON AND EVENING MAY ALSO PRODUCE LOCALLY
HEAVY RAIN. RAIN AMOUNTS OF MORE THAN 2 INCHES IN LESS THAN 3
HOURS MAY CAUSE FLOODING.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY.

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.

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE PITTSBURGH PA
308 PM EDT SUN AUG 14 2011

OHZ041-PAZ013-020-141945-
BEAVER PA-COLUMBIANA OH-LAWRENCE PA-
308 PM EDT SUN AUG 14 2011

...HEAVY RAIN...

THUNDERSTORMS WITH HEAVY RAIN TO MOVE THROUGH THE FOLLOWING
COUNTIES...
COLUMBIANA...BEAVER AND LAWRENCE...

AT 259 PM EDT NATIONAL WEATHER SERVICE DOPPLER RADAR IN PITTSBURGH
SHOWED THUNDERSTORMS WITH HEAVY RAIN OVER BLACKHAWK...MOVING
NORTHEAST AT 10 MPH.

SOME OF THESE STORMS WILL BE ACCOMPANIED BY DANGEROUS LIGHTNING AND
WIND GUSTS TO 35 MPH. THESE THUNDERSTORMS CAN PRODUCE HEAVY RAIN
THAT MAY CAUSE PONDED WATER ON ROADS AND IN LOW LYING AREAS.
VISIBILITY CAN BE REDUCED.

SOME LOCATIONS THAT WILL BE IMPACTED BY THESE THUNDERSTORMS
INCLUDE...
  SHIPPINGPORT...       BLACKHAWK...          EAST PALESTINE...
  BEAVER...             DARLINGTON...         BEAVER FALLS...
  NEW CASTLE...         HARLANSBURG...        FOMBELL...
  ELLWOOD CITY...       BESSEMER...

DO NOT DRIVE YOUR VEHICLE INTO AREAS WHERE THE WATER COVERS THE
ROADWAY. THE WATER DEPTH MAY BE TOO GREAT TO ALLOW YOUR CAR TO CROSS
SAFELY. MOVE TO HIGHER GROUND.

PLEASE REPORT HEAVY RAIN AND FLOODING PROBLEMS TO THE NATIONAL
WEATHER SERVICE BY CALLING TOLL FREE...1-877-633-6772.

LAT...LON 4106 8018 4073 8016 4058 8048 4087 8063
      4091 8058 4091 8053 4095 8053 4107 8038