Severe Thunderstorm Warning 143, 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
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

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

PAZ052-057-058-182215-
DAUPHIN PA-NORTHUMBERLAND PA-SCHUYLKILL PA-
519 PM EDT TUE AUG 18 2009

...A LINE OF STRONG THUNDERSTORMS WILL AFFECT NORTHEASTERN
DAUPHIN...SOUTHEASTERN NORTHUMBERLAND AND SOUTHWESTERN SCHUYLKILL
COUNTIES THROUGH 615 PM EDT...

AT 515 PM EDT...STRONG THUNDERSTORMS WERE ALONG A LINE FROM 15 MILES
SOUTH OF SELINSGROVE TO 6 MILES NORTH OF LINGLESTOWN...MOVING
NORTHEAST AT 25 MPH. THESE THUNDERSTORMS WERE OCCURRING BETWEEN TWO
AREAS OF SEVERE THUNDERSTORMS...ONE NORTH OF PILLOW AN LECK
KILL...AND THE SECOND TO THE SOUTH OF ELLENDALE FORGE AND DEHART
DAM.

WIND GUSTS TO 45 MPH AND PEA-SIZED HAIL ARE POSSIBLE WITH THESE
STORMS. EXPECT INTENSE LIGHTNING FROM THESE STORMS. DO NOT STAY IN
THE OPEN NOR SEEK SHELTER UNDER TREES WHEN LIGHTNING THREATENS...MOVE
INDOORS WHEN A THUNDERSTORM APPROACHES.

THESE STORMS WILL BE NEAR LYKENS AROUND 530 PM...ROUGH AND READY
AROUND 545 PM AND MOUNT CARMEL AROUND 600 PM.

THIS WILL IMPACT I-81 BETWEEN MILE MARKERS 105 AND 110.

THIS WILL ALSO IMPACT THE FOLLOWING MAJOR ROADS...ROUTE 209...STATE
ROAD 61.

LAT...LON 4060 7640 4055 7653 4056 7654 4052 7660
      4040 7687 4060 7684 4082 7641 4080 7640

EXPERIMENTAL

FORECASTER: LAMBERT

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

PAZ037-182215-
TIOGA PA-
545 PM EDT TUE AUG 18 2009

...SCATTERED STRONG THUNDERSTORMS WILL AFFECT TIOGA COUNTY...

AT 543 PM EDT...THUNDERSTORMS WERE SCATTERED ABOUT THE NORTHERN HALF
OF TIOGA COUNTY. A STRONG THUNDERSTORM WAS LOCATED 6 MILES NORTH OF
MANSFIELD...MOVING NORTHEAST AT 20 MPH.

WIND GUSTS TO 40 MPH ARE POSSIBLE WITH THIS STORMS...ALONG WITH
BRIEF HEAVY RAINFALL.

TAKE SHELTER WHEN THREATENING WEATHER APPROACHES.

THIS WILL IMPACT THE FOLLOWING MAJOR ROADS...ROUTE 6...ROUTE 15.

LAT...LON 4200 7693 4176 7690 4166 7734 4162 7761
      4199 7760 4201 7739 4201 7694

EXPERIMENTAL

FORECASTER: DEVOIR

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

PAZ006-037-182245-
POTTER PA-TIOGA PA-
546 PM EDT TUE AUG 18 2009

...STRONG THUNDERSTORMS WILL AFFECT CENTRAL POTTER AND NORTHWESTERN
TIOGA COUNTIES THROUGH 645 PM EDT...

AT 543 PM EDT...STRONG THUNDERSTORMS WERE ALONG A LINE FROM 4 MILES
WEST OF ELKLAND...TO 5 MILES NORTHEAST OF GALETON...TO 4 MILES
NORTHEAST OF WHARTON...MOVING EAST NORTHEAST AT 20 MPH.

WIND GUSTS TO 50 MPH AND PEA-SIZED HAIL ARE POSSIBLE WITH THESE
STORMS. VERY HEAVY RAIN WILL FALL FROM THESE STORMS...AND WILL CAUSE
WATER TO POND ON ROADS AND FILL POOR DRAINAGE AREAS. THE RAIN WILL
CAUSE RAPID RISES ON SMALL STREAMS AND CREEKS. EXPECT
FREQUENT...DANGEROUS CLOUD TO GROUND LIGHTNING FROM THESE
STORMS. DO NOT STAY IN THE OPEN NOR SEEK SHELTER UNDER TREES WHEN
LIGHTNING THREATENS...MOVE INDOORS WHEN A THUNDERSTORM APPROACHES.

THESE STORMS WILL BE NEAR GALETON AROUND 550 PM...GALETON AROUND 555
PM...GAINES AROUND 600 PM...KEENEYVILLE AROUND 630 PM AND LEONARD
HARRISON STATE PARK AROUND 645 PM.

THIS WILL IMPACT ROUTE 6.

LAT...LON 4200 7713 4168 7735 4154 7802 4169 7792
      4183 7767 4201 7751

EXPERIMENTAL

FORECASTER: LAMBERT