Severe Thunderstorm Warning 137, NWS State College, PA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
400 PM EDT TUE AUG 18 2009

.SYNOPSIS...
AN UPPER LEVEL RIDGE OVER THE EASTERN US AND WESTERN ATLANTIC
WILL DOMINATE OUR WEATHER FOR THE NEXT FEW DAYS. THE FIRST IN
SERIES OF FRONTS WORKING TO WEAKEN THE RIDGE WILL TRIGGER
THUNDERSTORMS THIS AFTERNOON. A STRONGER TROUGH TO OUR NORTHWEST
SHOULD PUSH A STRONGER FRONT INTO THE REGION LATER THIS WEEK AND
EARLY THIS WEEKEND TRIGGERING MORE SHOWERS. IT WILL ALSO KEEP THE
TROPICAL ACTIVITY TO OUR EAST. SUNDAY THROUGH PERHAPS TUESDAY
SHOULD BE COOLER AND DRIER.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
A LINE OF THUNDERSTORMS HAS DEVELOPED ALONG THE LAKE BREEZE AND
SHOULD MOVE STEADILY WESTWARD INTO WARREN COUNTY THIS AFTERNOON.
UPPED POPS AND QPF IN NW PA TO ACCOUNT FOR THIS. THIS LINE SHOULD
MOVE EASTWARD SPREADING STORMS INTO NORTH-CENTRAL AREAS THIS
AFTERNOON AND POSSIBLY INTO THE EARLY EVENING HOURS.

TO THE SOUTHWEST THE S/W ON WAVER VAPOR HAS TRIGGERED A LINE OF
THUNDERSTORMS IN SW PA. THIS LINE IS MOVING ACROSS SOMERSET COUNTY
AND SHOULD MOVE EAST-NORTHEAST UPPED POPS IN SW TO 90 PERCENT AND
TAPERED OFF TO ENE. LOOKS LIKE MOST AREAS OF WESTERN PA HAVE A
GOOD SHOT FOR THUNDER THIS AFTERNOON AND EARLY EVENING AS THIS
SYSTEM TRACKS TO THE EAST.

EVEN A FEW STORMS IN THE LOWER SUSQUEHANNA VALLEY WHERE SOME
STATIONS...MOSTLY SECONDARY STATIONS...ARE IN THE LOWER 90S. MOST
AIRPORTS ARE STILL ONLY IN THE UPPER 80S. BUT DEW POINTS ARE IN
THE 70S. ANY SHOWERS DOWN IN THE SOUTH/SOUTHEAST CAN PRODUCE SOME
LOCALLY HEAVY RAINFALL.

MOST ACTIVITY SHOULD TAIL OFF SHORTLY AFTER SUNSET ESPECIALLY IN
THE WEST.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/...
THE FRONT TO OUR WEST IS FORECAST TO DRY IT OUT IN WEST AND SAG
SOUTHWARD. THUS AN EAST-WEST BOUNDARY IS FORECAST TO BE STALLED
OVER SOUTHERN PA/MD REGION WEDNESDAY. THIS COULD SERVE AS BOUNDARY
FOR SHOWERS AND STORMS ON WEDNESDAY AFTERNOON. THE SREF/SUPER
ENSEMBLE SHOW HIGHER POPS IN SOUTH. MADE GRIDS REFLECT THIS WITH
LOWER POPS AS ONE MOVE SOUTH TO NORTH. FARTHER NORTH IN PA
TOMORROW THE BETTER. IT SHOULD BE COOLER AND DRIER WEDNESDAY OVER
MOST REGIONS. CHANGED GRIDS TO REFLECT THIS.

THE BOUNDARY IS FORECAST TO SURGE BACK TO THE NORTH AND BRING AN
INCREASE IN HUMIDITY OVERNIGHT WED INTO THURSDAY. SHOWERS AND
THUNDERSTORMS ARE POTENTIALLY A PROBLEM ON THURSDAY. WITH ABOVE
NORMAL PW VALUES...SOME LOCALLY HEAVY RAINS ARE POSSIBLE WITH
THESE STORMS.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
EXTENDED PORTION OF THE FORECAST STARTS OFF ACTIVE AND VERY MILD
BEFORE TURNING DRIER AND COOLER OVER THE WEEKEND.

A STRONG TROUGH TO OUR NORTHWEST WILL PUSH A STRONG FRONT ACROSS
THE REGION FRI INTO SAT...TRIGGERING MORE SHOWERS/THUNDERSTORMS.
IT WILL ALSO KEEP THE TROPICAL ACTIVITY OFF TO OUR EAST AND
OFFSHORE. WITH PLENTY OF MOISTURE REMAINING ACROSS PA AHEAD OF THE
FRONT AND INCREASING DYNAMICS ASSOCIATED WITH THE APPROACH OF THE
COLD FRONT...ANTICIPATE THAT THE STORMS ON FRI MAY BE STRONG TO
POTENTIALLY SEVERE...AND WILL HAVE TO MONITOR FOR POTENTIAL FOR
HEAVIER RAINFALL...ALTHOUGH FRONT LOOKS TO REMAIN FAIRLY
PROGRESSIVE.

ONCE THE FRONT PASSES THROUGH TO THE EAST...SURFACE HIGH WILL
BUILD IN AND SAT NIGHT THROUGH TUESDAY SHOULD BE COOLER AND DRIER
WITH HIGH TEMPS 5-10F COOLER AND NIGHTTIME LOWS 10-15F COOLER.

MODEL DIFFERENCES BETWEEN GFS AND ECMFW COME INTO PLAY BY MIDWEEK
AS THEY HANDLE PROGRESSION OF NEXT TROUGH DIFFERENTLY...WITH THE
GFS FASTER. FOR NOW HANDLED WITH LOW CHANCE POPS ACROSS THE NORTH.

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
NMRS SHRA/TSRA HAVE DEVELOPED IN THE PAST FEW HOURS ACROSS THE
CWA. HENCE EXPECT WIDELY VARYING FLYING CONDITIONS THIS
AFTERNOON...WITH VFR CONDITIONS TURNING TO MVFR/IFR IN THESE
STORMS.

SHRA/TSRA WILL TAPER THIS EVENING AS CONVECTION SHUTS DOWN...AND A
RETURN TO WIDESPREAD VFR IS EXPECTED. THERE IS ONCE AGAIN A CHANCE
FOR FOG DEVELOPMENT...ALTHOUGH IT APPEARS THE WINDS MAY BE STRONG
ENOUGH...ESPECIALLY ACROSS THE LAUEL HIGHLANDS...TO PREVENT FOG
FROM SETTLING IN.

ANOTHER ROUND OF MVFR SHOWERS IS EXPECTED WEDNESDAY AS A COLD
FRONT MOVES THROUGH.

OUTLOOK...

THUR-FRI...MAINLY MVFR IN SHRA/TSRA...FOG...AHD HZ.
SAT/SUN...MORNING FOG...THEN MAINLY VFR.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

SYNOPSIS...GRUMM/RXR
NEAR TERM...GRUMM
SHORT TERM...GRUMM
LONG TERM...RXR
AVIATION...DICKEY

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE STATE COLLEGE PA
527 AM EDT TUE AUG 18 2009

PAZ004>006-010>012-017>019-024>028-033>037-041-042-045-046-049>053-
056>059-063>066-190930-
WARREN-MCKEAN-POTTER-ELK-CAMERON-NORTHERN CLINTON-CLEARFIELD-
NORTHERN CENTRE-SOUTHERN CENTRE-CAMBRIA-BLAIR-HUNTINGDON-MIFFLIN-
JUNIATA-SOMERSET-BEDFORD-FULTON-FRANKLIN-TIOGA-NORTHERN LYCOMING-
SULLIVAN-SOUTHERN CLINTON-SOUTHERN LYCOMING-UNION-SNYDER-MONTOUR-
NORTHUMBERLAND-COLUMBIA-PERRY-DAUPHIN-SCHUYLKILL-LEBANON-CUMBERLAND-
ADAMS-YORK-LANCASTER-
527 AM EDT TUE AUG 18 2009

THIS HAZARDOUS WEATHER OUTLOOK IS FOR CENTRAL PENNSYLVANIA.

.DAY ONE...TODAY AND TONIGHT.

THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY.

THE PROBABILITY FOR WIDESPREAD HAZARDOUS WEATHER IS LOW.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT EXPECTED AT THIS TIME.

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE STATE COLLEGE PA
244 PM EDT TUE AUG 18 2009

PAZ066-181915-
LANCASTER PA-
244 PM EDT TUE AUG 18 2009

...A STRONG THUNDERSTORM WILL AFFECT CENTRAL LANCASTER COUNTY...

AT 243 PM EDT...A STRONG THUNDERSTORM WAS LOCATED OVER LEOLA...MOVING
EAST AT 25 MPH.

WIND GUSTS TO 30 MPH AND SMALL HAIL ARE POSSIBLE WITH THIS STORM.

THIS STORM WILL BE NEAR LEOLA AROUND 250 PM...NEW HOLLAND AROUND 300
PM...TERRE HILL AROUND 305 PM AND CHURCHTOWN AROUND 315 PM.

THIS WILL IMPACT THE PENNSYLVANIA TURNPIKE BETWEEN MILE MARKERS 286
AND 295.

THIS WILL ALSO IMPACT THE FOLLOWING MAJOR ROADS...ROUTE 30...ROUTE
222...ROUTE 322...STATE ROAD 501.

LAT...LON 4013 7590 4011 7593 4005 7594 4002 7595
      4000 7632 4018 7636 4023 7601 4015 7589
      4014 7589

EXPERIMENTAL

FORECASTER: GRUMM

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE STATE COLLEGE PA
309 PM EDT TUE AUG 18 2009

PAZ026>028-035-036-056-063-181945-
CUMBERLAND PA-FRANKLIN PA-FULTON PA-HUNTINGDON PA-JUNIATA PA-
MIFFLIN PA-PERRY PA-
309 PM EDT TUE AUG 18 2009

...A CLUSTER OF THUNDERSTORMS WILL AFFECT NORTHEASTERN FULTON...
NORTHERN FRANKLIN...SOUTHERN HUNTINGDON...SOUTHWESTERN JUNIATA...
SOUTHWESTERN MIFFLIN...SOUTHWESTERN PERRY AND WESTERN CUMBERLAND
COUNTIES...

AT 308 PM EDT...STRONG THUNDERSTORMS WERE ALONG A LINE FROM 14 MILES
SOUTH OF HUNTINGDON TO 17 MILES NORTHEAST OF BREEZEWOOD TO 10 MILES
EAST OF BREEZEWOOD...MOVING EAST AT 25 MPH.

WIND GUSTS TO 30 MPH ARE POSSIBLE WITH THESE STORMS.

THESE STORMS WILL BE NEAR CASSVILLE AROUND 315 PM...FORT LITTLETON
AROUND 320 PM...SHADE GAP...AND ORBISONIA AROUND 325 PM...MAPLETON...
AND SHIRLEYSBURG AROUND 330 PM...MOUNT UNION...AND FANNETTSBURG
AROUND 335 PM...NEWTON HAMILTON AND WILLOW HILL AROUND 340 PM.

THIS WILL IMPACT THE FOLLOWING CENTRAL PENNSYLVANIA INTERSTATES...THE
PENNSYLVANIA TURNPIKE BETWEEN MILE MARKERS 168 AND 216...I-81 BETWEEN
MILE MARKERS 24 AND 34.

THIS WILL ALSO IMPACT THE FOLLOWING MAJOR ROADS...ROUTE 11...ROUTE
22...ROUTE 22/522...ROUTE 30...ROUTE 522.

LAT...LON 4015 7811 4033 7824 4037 7820 4045 7748
      4024 7733 4002 7743 3993 7820

EXPERIMENTAL

FORECASTER: DEVOIR

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE STATE COLLEGE PA
339 PM EDT TUE AUG 18 2009

PAZ012-017>019-026-027-045-049-050-182045-
CLEARFIELD PA-HUNTINGDON PA-MIFFLIN PA-NORTHERN CENTRE PA-
NORTHERN CLINTON PA-SNYDER PA-SOUTHERN CENTRE PA-SOUTHERN CLINTON PA-
UNION PA-
339 PM EDT TUE AUG 18 2009

...A LINE OF THUNDERSTORMS WILL AFFECT CENTRE...EAST CENTRAL
CLEARFIELD...NORTHEASTERN HUNTINGDON...NORTHERN MIFFLIN...
SOUTHEASTERN CLINTON...SOUTHWESTERN UNION AND WEST CENTRAL SNYDER
COUNTIES...

AT 338 PM EDT...THUNDERSTORMS WERE ALONG A LINE FROM 15 MILES
WEST OF BELLEFONTE TO STATE COLLEGE TO 9 MILES SOUTH OF STATE
COLLEGE...MOVING NORTHEAST AT 25 MPH.

WIND GUSTS TO 40 MPH ARE POSSIBLE WITH THESE STORMS.

THESE STORMS WILL BE NEAR BOALSBURG...AND BELLEVILLE AROUND 345 PM...
SNOW SHOE...AND UNIONVILLE AROUND 350 PM...PLEASANT GAP...
MILESBURG...BELLEFONTE...AND REEDSVILLE AROUND 400 PM...POTTERS MILLS
AND CENTRE HALL AROUND 405 PM.

THIS WILL IMPACT THE FOLLOWING CENTRAL PENNSYLVANIA INTERSTATES...
I-80 BETWEEN MILE MARKERS 131 AND 185...I-99 BETWEEN MILE MARKERS 64
AND 85.

THIS WILL ALSO IMPACT THE FOLLOWING MAJOR ROADS...ROUTE 220...
ALTERNATE ROUTE 220...ROUTE 322...STATE ROAD 26...STATE ROAD 45...
STATE ROAD 120.

LAT...LON 4127 7751 4104 7729 4080 7716 4054 7786
      4078 7799 4100 7821

EXPERIMENTAL

FORECASTER: DEVOIR

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SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE STATE COLLEGE PA
437 PM EDT TUE AUG 18 2009

PAZ064-065-182130-
ADAMS PA-YORK PA-
437 PM EDT TUE AUG 18 2009

...A STRONG THUNDERSTORM WILL AFFECT SOUTHEASTERN ADAMS AND WEST
CENTRAL YORK COUNTIES...

AT 435 PM EDT...A STRONG THUNDERSTORM WAS LOCATED 4 MILES NORTHEAST
OF EMMITSBURG...MOVING NORTHEAST AT 25 MPH.

WIND GUSTS UP TO 50 MPH AND HAIL UP TO DIME SIZE ARE POSSIBLE WITH
THIS STORM. EXPECT FREQUENT...DANGEROUS...CLOUD TO GROUND LIGHTNING
FROM THIS STORM. DO NOT STAY IN THE OPEN NOR SEEK SHELTER UNDER
TREES WHEN LIGHTNING THREATENS...MOVE INDOORS WHEN A THUNDERSTORM
APPROACHES.

THIS STORM WILL BE NEAR GERMANTOWN AROUND 450 PM...BONNEAUVILLE
AROUND 500 PM...NEW OXFORD AROUND 510 PM...ABBOTTSTOWN AROUND 520 PM
AND SPRING GROVE AROUND 530 PM.

THIS WILL IMPACT THE FOLLOWING MAJOR ROADS...ROUTE 15...ROUTE 30...
STATE ROAD 94...STATE ROAD 97.

LAT...LON 3975 7736 4003 7696 3987 7684 3972 7713
      3972 7734

EXPERIMENTAL

FORECASTER: LAMBERT