Flood and Hail in Pennsylvania, September 9, 2013

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
303 PM EDT MON SEP 9 2013

.SYNOPSIS...
HEAT AND HUMIDITY WILL BUILD THIS WEEK BEFORE A STRONG COLD FRONT
ON THURSDAY USHERS IN MUCH COOLER TEMPERATURES.

&&

.NEAR TERM /THROUGH TUESDAY/...
QUICK UPDATE MADE TO ACCOUNT FOR CURRENT SHWRS/TSTMS SLGTLY
EARLIER THAN IN GOING FCST. PREV DISCUSSION FOLLOWS...

A WARM FRONT IS STILL PROGGED TO LIFT NORTH ACROSS THE REGION
LATER THIS AFTERNOON BUT QUESTION REMAINS ON HOW MUCH CONVECTION
WE WILL SEE WITH IT. DEWPOINTS HAVE ALREADY BEGUN TO REBOUND INTO
THE MID 60S OVER EASTERN OHIO AND NORTHERN WEST VIRGINIA BUT
INSTABILITY REMAINS ELEVATED PER THE MOST RECENT MESOANALYSIS.
STILL THINK THAT...WITH THE HELP OF A PASSING UPPER- LEVEL
SHORTWAVE THAT HAS SUPPORTED SOME SHOWERS AND STORMS OVER
MICHIGAN...THERE COULD BE AT LEAST SCATTERED SHOWERS AND STORMS
OVER OUR REGION TODAY. WHILE THERE ARE A FEW DIFFERENCES IN THE
DETERMINISTIC SOLUTIONS...THE RAP AND HRRR SEEM TO SUGGEST THAT
THE NORTHERN ZONES MAY HAVE THE BEST CHANCE FOR PRECIP. WITH THIS
IN MIND...KEPT THE CHANCE POPS FOCUSED IN THIS AREA AND CONTINUED
A SLIGHT CHANCE EVERYWHERE ELSE. OF COURSE...THIS DOES NOT
COMPLETELY RULE OUT THE CHANCE FOR THUNDERSTORMS FARTHER
SOUTH...SINCE THOSE COUNTIES ARE EXPERIENCING MORE-RAPID SURFACE
HEATING DUE TO LESS CLOUD COVER.

HIGH PRESSURE WILL BUILD EASTWARD TONIGHT...AND WITH IT WILL RETURN
VERY WARM AND MUGGY WEATHER. HIGHS ARE FORECAST TO BE WELL ABOVE
SEASONAL AVERAGES TOMORROW...WITH MOST PLACES SEEING MID 80S TO
EVEN 90. WHILE THIS COULD LEAD TO PLENTY OF SURFACE
INSTABILITY...THERE DOES NOT SEEM TO BE ANY FOCUS FOR CONVECTION.
THE ONLY CONSIDERATION IS THE HIGHER ELEVATIONS...WHERE A FEW
THUNDERSTORMS COULD DEVELOP WITH THE HELP OF OROGRAPHIC LIFT. AT
THIS TIME THOUGH...MAINTAINED A DRY FORECAST FOR ALL OF TUESDAY.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/...
A VERY MOIST AND UNSTABLE AMS WILL RMN IN PLACE THRU THU OWING TO
PERSISTENT SWLY LOW-LVL FLOW. TUE NGT AND WED NGT WILL BOTH SEE
MINIMA IN THE 60S...WITH MINIMA APRCHG 70 TUE NGT.

SHWRS AND TSTMS WILL INCR IN CVRG ON WED AS A LOW-AMPLITUDE SHRTWV
TROF APRCHS AND UPR RDG FLATTENS. CLD CVR XPCD TO BE SUBSTANTIAL
OWING TO UNSTABLE AMS...WHICH MAY LMT MAXIMA SLGTLY COMPARED TO
TUE. HOWEVER...MAXIMA STILL XPCD TO REACH MID-UPR 80S.

LACK OF STRONG MID-LVL FLOW ON WED WILL YIELD RATHER ANEMIC SHEAR
DESPITE MDT INSTBY. WITH PWATS FCSTD IN EXCESS OF 1.8 IN...MAIN
CONCERN WILL BE FOR FLOODING FROM SLOW-MOVG TSTMS PRODUCING VERY
HVY RAIN.

BECAUSE THE FLY ALWAYS FINDS ITS OINTMENT...THE 12Z/09 NAM12 HAS
OFFERED A MUCH SLOWER ARRRIVAL OF THE CDFNT THAT WAS XPCD TO
ARRIVE ON THU. GFS/ECMWF STILL AGREE ON A MID-LATE DAY FROPA WHILE
NAM SUGGESTS AN ARRIVAL OVNGT THU NGT.

GIVEN CONSISTENCY OF GFS ENSEMBLE WITH GFS/ECMWF SOLUTIONS...THE
NAM12 SOLUTION WILL BE DEEMED AN OUTLIER...AND FCST TIMING WILL BE
MAINTAINED WITH FROPA DURG THU. WITH FAVORABLE TIMING OF FROPA AND
MINIMAL OVNGT CNVCTN XPCD...THU APPEARS QUITE FAVORABLE FOR WDSPRD
TSTMS ALONG THE ADVCG BNDRY. THUS...POPS WERE INCRD TO LKLY AS THE
BNDRY CROSSES AND MAXIMA WERE INCRD SLGTLY FOLLOWING THE TREND OF
LATEST GUIDANCE.

GUIDANCE ALSO SUGGESTS POST-FRONTAL CLDS WILL INVADE THU NGT AHD
OF SECONDARY PRES SURGE. CLD CVR WAS INCRD SGFNTLY LATE THU NGT...
WHICH WILL SLOW THE XPCD COOLING. THUS...THU NGT MINIMA WERE INCRD
A FEW DEG F.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
A STG CDFNT WL CROSS THE RGN THU CONTG THE SHWR/TSTM CHCS. HIGH
PRES IS THEN EXPD TO BLD IN THRU THE WKEND. AFT FROPA...850MB
TEMPS DROP INTO THE SINGLE DIGITS...BOTTOMING OUT ARND 2 DEG C FRI
NGT. THIS WL BRING WELL BLO AVG TEMP FRI THRU SUN...ALTHOUGH SOME
MODERATION CAN BE EXPD SUN AS THE FLOW TURNS SRLY AND THE HIGH
SHIFTS EWD.

&&

.AVIATION /19Z MONDAY THROUGH SATURDAY/...
GENERAL VFR IS EXPECTED TO CONTINUE THROUGH MUCH OF THE PERIOD. A
LIFTING WARM FRONT WILL STILL PROVIDE THE CHANCE FOR SHOWERS AND
THUNDERSTORMS THIS AFTERNOON BUT AT THIS POINT COVERAGE IS
EXPECTED TO REMAIN SMALL. WILL MENTION VCTS IN THE SITES NORTH OF
PIT WHERE THE MODEL GUIDANCE CONTINUES TO SUGGEST THE GREATEST
PROBABILITY AND WILL MAINTAIN SCATTERED/BROKEN MID DECK EVERYWHERE
ELSE. ONE THING TO NOTE IS ANY TAF SITE THAT DOES EXPERIENCE A
SHOWER OR STORM WILL LIKELY EXPERIENCE IFR VISIBILITIES WITH
INCREASING LOW LEVEL MOISTURE.

WIND WILL GRADUALLY SHIFT TO SOUTHWESTERLY THROUGH THE AFTERNOON.

HIGH PRESSURE WILL BUILD OVERHEAD TONIGHT...ENDING THE THREAT FOR
PRECIPITATION. WITH THE LOW LEVELS REMAINING MOIST...DO ANTICIPATE
SOME FOG IN SPOTS BUT LINGERING CLOUDS AND ELEVATED WIND MAY KEEP
IT MINIMAL.

.OUTLOOK.../MONDAY NIGHT THROUGH SATURDAY/...
GENERAL VFR IS EXPECTED UNTIL A COLD FRONT APPROACHES FRIDAY.

&&

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

&&

UPDATE...KRAMAR

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE PITTSBURGH PA
158 PM EDT MON SEP 9 2013

MDZ001-OHZ039>041-048>050-057>059-068-069-PAZ007>009-013>016-020>023-
029-031-073>076-WVZ001>004-012-021>023-041-101800-
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-
158 PM EDT MON SEP 9 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...THIS AFTERNOON AND TONIGHT.

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY.

SLOW-MOVING THUNDERSTORMS CAPABLE OF LOCALIZED FLASH FLOODING WILL
BE POSSIBLE ON WEDNESDAY.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.

KRAMAR