Severe Thunderstorm Warning 142, NWS Pittsburgh, PA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
305 PM EDT THU JUL 4 2013

.SYNOPSIS...
MOIST SOUTHERLY FLOW WILL CONTINUE HUMID WEATHER AND DAILY CHANCES
FOR THUNDERSTORMS THROUGH THE WEEKEND.

&&

.NEAR TERM /THROUGH FRIDAY/...
GULF MOISTURE WILL CONTINUE TO BE FUNNELED NORTHWARD TOWARDS THE
REGION HELPING TO PROVIDE FOR VERY HUMID CONDITIONS AND PERIODS OF
HEAVIER RAINFALL IN SHOWERS AND THUNDERSTORMS THROUGH THE PERIOD.

A BRIEF BREAK IN THE PRECIPITATION LOOKS TO BE DUE TO THE DRIER
AIR BEING PUSHED WESTWARD FROM THE BUILDING COASTAL HIGH...AS IS
APPARENT IN THE WATER VAPOR SATELLITE LOOP. THIS HAS ALLOWED FOR
SOME BREAKS IN THE CLOUD COVER OVER WESTERN/CENTRAL PA. IF THIS
CONTINUES...EXPECT THAT DAYTIME HEATING AND DESTABILIZATION SHOULD
ALLOW FOR MORE WIDELY SCATTERED SHOWERS/THUNDERSTORMS TO DEVELOP
IN THESE AREAS. FURTHER WEST...MUCH OF THE PRECIPITATION MAY BE
ENHANCED FROM UPPER LEVEL SHORTWAVES MOVING THROUGH THE SOUTHERLY
FLOW.

BETWEEN PRECIPITABLE WATER VALUES APPROACHING 2 INCHES AND WARM
RAIN PROCESSES...RAINFALL RATES COULD BE HIGHER THAN HAS BEEN
SEEN IN PREVIOUS DAYS. MODEL CONSENSUS SUGGESTS THE BULK OF THE
HEAVIEST RAINFALL WILL REMAIN WEST OF THE FORECAST AREA OVER
SOUTHWESTERN OHIO...WHERE THE GREATEST DYNAMICS WILL BE PRESENT.
WHILE THIS WILL NOT COMPLETELY RULE OUT FLOODING
CONCERNS...ESPECIALLY IN AREAS THAT EXPERIENCE TRAINING
THUNDERSTORMS...THINK THAT THIS WILL BE MORE OR LESS A LOCALIZED
PROBLEM. THUS...NO FLOOD WATCHES HAVE BEEN ISSUED FOR THE AREA.

TEMPERATURES WILL BE VIRTUALLY THE SAME AS THEY HAVE BEEN FOR THE
LAST WEEK.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
A CONTINUED VERY SLOW EVOLUTION OF THE LARGE SCALE PATTERN OVER
THE EASTERN HALF OF THE CONUS LOOKS TO TAKE PLACE THROUGH THE
WEEKEND AND THE UPPER LOW TO OUR WEST GETS PROGRESSIVELY SQUEEZED
BY SPRAWLING UPPER ANTI-CYCLONES OVER BERMUDA AND THE FOUR CORNERS
AREA. THIS SHOULD ACTUALLY SLOWLY SQUEEZE THE UPPER LOW OVER THE
MID-MISSISSIPPI VALLEY NORTHWARD AND GRADUALLY OPEN IT UP AS IT
NEARS THE POLAR JET OVER THE NORTHERN GREAT LAKES. HOWEVER...MODEL
TIMING FOR THE PROGRESSION OF SAID EVOLUTION HAS REALLY STARTED TO
BECOME A BIT SCATTER SHOT. THE 12Z NAM TREMENDOUSLY SLOWED THE
EVOLUTION OF THE UPPER LOW AS DID THE 12Z GFS TO A LESSER DEGREE.
HOWEVER...THE 12Z CANADIAN GLOBAL REMAINED IN LOCK STEP WITH THE
00Z ECMWF FROM LAST NIGHT IN BRINGING THE ENTIRETY OF THE UPPER
LOW THROUGH THE FORECAST AREA AND PUSHING IT TO OUR EAST BY LATE
SUNDAY.

BECAUSE OF AT LEAST SOME SLOWING OF THE CONSENSUS RELATIVE
TO THE PREVIOUS RUNS...THE FORECAST TIMING FOR THE PROGRESSION OF
THE UPPER WAVE THROUGH THE AREA WAS SLOWED BY ROUGHLY 12 HOURS IN
THE GRIDS. AS SUCH...DEEP SOUTHERLY FLOW WITH THE MAIN UPPER JET
STREAK FOCUSING LARGE SCALE LIFT PREFERENTIALLY OVER THE WESTERN
HALF OF THE CWA LOOKS TO CONTINUE THROUGH THE FIRST HALF OF THE
WEEKEND. AFTER THAT TIME...THE SPEED OF THE NORTHEASTWARD
PROGRESSION OF THE LOW OVER THE MID-MISSISSIPPI VALLEY BECOMES
KEY. IN FAVORING A PASSAGE CLOSE TO THE GFS GIVEN ITS COMPROMISE
SOLUTION BETWEEN THE NAM AND ECMWF...HIGH DEWPOINTS AND UNSTABLE
CONDITIONS LOOK TO CONTINUE UNTIL SUNDAY. AFTER THAT TIME...BETTER
SYNOPTIC LIFT IS LIKELY TO TRACK ACROSS THE AREA.
ADDITIONALLY...SHEAR VALUES INCREASE MARKEDLY WITH ABUNDANT
INSTABILITY. AS SUCH...THE BEST CHANCE FOR ORGANIZED CONVECTION
LOOKS TO HOLD OFF UNTIL SUNDAY. THIS WAS WHEN POPS WERE REALLY
FOCUSED IN ON IN THE SHORT TERM.

TEMPERATURES THROUGH THE SHORT TERM LOOK TO BE RANGE BOUND BY
SIGNIFICANT CLOUD COVER. CONVECTIVE DEBRIS CLOUDS AS WELL AS
CONVECTIVE CUMULUS CLOUDS WILL LIKELY KEEP A LID ON THE WARMING OF
THE LOWER BOUNDARY LAYER. AS SUCH...WARMING THE AIR WILL MORE
LIKELY TAKE PLACE DUE TO MIXING. WITH THAT SAID...A LACK OF
INSOLATION REALLY LOOKS TO KEEP HIGHS DOWN...WHILE CLOUDS WILL
KEEP LOWS UP...AT LEAST UNTIL SUNDAY NIGHT. FRIES

&&

.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
THE UPPER LOW WILL SLOWLY DEPART TO THE EAST BY MONDAY NIGHT WITH A
MORE ZONAL FLOW ALOFT DEVELOPING BY MID WEEK. HARD TO DEFINE A 24 HR
PERIOD WHICH WOULD BE RAIN FREE AS AT LEAST 2 SEPARATE SHORTWAVES IN
THE ZONAL FLOW WILL MOVE ACROSS THE OHIO VALLEY THIS PERIOD. HIGH
CHANCE POPS WERE USED AS TIMING WILL AGAIN BE A PROBLEM ESPECIALLY
IN ZONAL FLOW. TEMPERATURES WILL TREND TOWARD SEASONAL NORMS.

&&

.AVIATION /19Z THURSDAY THROUGH TUESDAY/...
ABUNDANT MOISTURE WILL MOVE NORTHWARD WITH UPPER LEVEL
DISTURBANCES CONTINUING TO HELP SPAWN SCATTERED SHOWERS AND
THUNDERSTORMS TODAY. TEMPORARY RESTRICTIONS WILL BE
EXPECTED...ESPECIALLY IN THOSE LOCATIONS THAT EXPERIENCE HEAVIER
RAINFALL THROUGH THE AFTERNOON. HOWEVER...FOR NOW JUST MAINTAINED
THE VFR CONDITIONS AND WILL ADD TEMPOS AS NEEDED TO REFLECT ANY
BRIEF PERIODS OF MVFR/IFR.

OUTLOOK.../THURSDAY NIGHT THROUGH MONDAY/...
BRIEF IFR VIS RESTRICTIONS ARE POSSIBLE THROUGH THE WEEKEND IN
SHOWERS AND THUNDERSTORMS. IN ADDITION...IFR CONDITIONS ARE POSSIBLE
IN PREDAWN FG EACH MORNING...ESPECIALLY IF AN AIRPORT EXPERIENCES A
STORM IN THE AFTN/EVNG.

&&

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

&&

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE PITTSBURGH PA
325 AM EDT THU JUL 4 2013

MDZ001-OHZ039>041-048>050-057>059-068-069-PAZ007>009-013>016-020>023-
029-031-073>076-WVZ001>004-012-021>023-041-051200-
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-GREENE-WESTMORELAND-WESTMORELAND RIDGES-
FAYETTE-FAYETTE RIDGES-HANCOCK-BROOKE-OHIO-MARSHALL-WETZEL-MARION-
MONONGALIA-PRESTON-TUCKER-
325 AM EDT THU JUL 4 2013

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.

LOCALLY HEAVY RAIN IN SCATTERED THUNDERSTORMS MAY CAUSE FLOODING
IN AREAS THAT HAVE RECEIVED HEAVY RAINFALL DURING THE PAST SEVERAL
DAYS.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY.

LOCALLY HEAVY RAIN IN SCATTERED THUNDERSTORMS FRIDAY MAY CAUSE
FLOODING IN AREAS THAT HAVE RECEIVED HEAVY RAINFALL DURING THE
PAST SEVERAL DAYS.

.SPOTTER INFORMATION STATEMENT...

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

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