Flooding in Pennsylvania, December 1 to 3, 2010

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
1107 PM EST TUE NOV 30 2010

.SYNOPSIS...
A STRONG FRONTAL SYSTEM ASSOCIATED WITH A DEEP AREA OF LOW
PRESSURE LIFTING NORTHEAST THROUGH THE WESTERN GREAT LAKES WILL
PUSH SLOWLY EAST AND CROSS CENTRAL PENNSYLVANIA TONIGHT INTO
EARLY WEDNESDAY. THIS SYSTEM WILL BE ACCOMPANIED BY HEAVY RAIN AND
GUSTY WINDS. COLDER AIR WILL SWEEP INTO THE AREA BEHIND THE FRONT
AND WILL CHANGE RAIN TO SNOW SHOWERS OVER THE WESTERN HIGHLANDS.
UNSEASONABLY MILD TEMPERATURES ARE FORECAST AHEAD OF THE FRONT
WITH MUCH COLDER POST-FRONTAL WEATHER LASTING INTO THE WEEKEND
WITH SNOW SHOWERS LIKELY CONTINUING OVER THE ALLEGHENY PLATEAU.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
AN ACTIVE OVERNIGHT IN STORE FOR CENTRAL PA. SIGNIFICANT STORM SYSTEM
THAT HAS ALREADY PRODUCED 1-3 INCHES OF RAIN IN WARM SECTOR DRIVEN
PRECIP ACROSS MUCH OF NW HALF OF CWA WILL SEE ANOTHER ROUND - THIS
TIME FRONTOGENETICALLY FORCED - WITH ADDITIONAL TOTALS AROUND
ANOTHER INCH OVERNIGHT AS PRECIP SHIELD SLOWLY SHIFTS EASTWARD
ACROSS PA. EXPECT FLOODING ISSUES TO SPREAD AND SEVERAL RIVER
FLOOD WARNINGS HAVE BEEN ISSUED THIS WEEKEND.

UPPER TROF AND JET STREAK NOW BEGINNING TO TAKE ON A STRONG
NEGATIVE TILT CONFIGURATION AS IT MOVES THROUGH THE NERN
US...RESULTING IN THE RIGHT JET ENTRANCE REGION ENTICING A SERIES
OF WAVES ALONG THE TRAILING COLD FRONT. CROSS SECTIONS SHOW THE
POTENT AGEOSTROPHIC RESPONSE OF THE THERMALLY DIRECT TRANSVERSE
JET CIRCULATION...WITH THE ACCOMPANYING INTENSE FRONTOGENESIS AND
UPWARD VERTICAL MOTION DEVELOPING ALONG AND JUST BEHIND THE
SURFACE WAVES/FRONT. IT ALL POINTS TO A HIGH CONFIDENCE OF A
WIDESPREAD HEAVY RAINFALL ALONG WITH THE POTENTIAL OF LOCALLY
DAMAGING WIND GUSTS ASSOCIATED WITH THE POSSIBLE FORMATION OF A
NARROW COLD FRONTAL RAIN-BAND FEATURE AS THE FRONTAL SYSTEM SWINGS
THROUGH THE FORECAST AREA LATE TONIGHT AND EARLY WED.

WHILE SURFACE BASED INSTABILITY IS FCST TO BE MARGINAL WITH
MODELS CONFINING CAPES WELL TO THE SOUTH OF THE REGION...THE
STRONG UPPER JET DYNAMICS RESULT IN THE DEVELOPMENT OF WIDESPREAD
ELEVATED CONVECTIVE AND INERTIAL INSTABILITY. SO WHILE IT WILL
LIKELY BE HARD TO GENERATE DEEP UPRIGHT CONVECTION...ANY LOW
TOPPED ORGANIZED SHOWERS WILL HAVE THE POTENTIAL TO TAP THE HIGH
SPEED AIR JUST OFF THE SURFACE CAUSING STRONG WIND GUSTS. THIS IS
MOST PROBABLE OVER THE LWR SUSQ VLY WHICH OFTEN BREAKS INTO THE
MINI WARM SECTOR SOUTH OF NWD MOVING WARM FRONT AND EAST OF TRIPLE
POINT LOW. IF THE NARROW COLD FRONTAL RAIN-BAND CAN BECOME WELL
DEVELOPED...AN ISOLATED TORNADO CANNOT BE RULED OUT IN WHAT WILL
BE AN INTENSELY SHEARED ENVIRONMENT.

NON-DIURNAL TEMPERATURE CURVE CAN BE EXPECTED TONIGHT WITH
FALLING TEMPERATURES BEHIND FROPA IN THE WEST AFT 06Z AND AN
OVERNIGHT MAX/STEADY TEMPS BETWEEN 55-60F IN THE SOUTHEAST ZONES.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/...
SHORT RANGE OPERATIONAL MODEL TIMING SUGGESTS THE WAVY FRONT WILL
CLEAR OF ALL BUT MY FAR EASTERN ZONES BY 12Z WED...AND BE INTO NJ
BY 18Z. THIS SHOULD MEAN A RATHER RAPID TRANSITION FROM STEADY
HEAVY RAINS TO MORE SPOTTY AND SHOWERY TYPE PRECIP THAT MAY MIX
WITH OR CHANGE TO SNOW SHOWERS...ESPECIALLY IN THE WEST. THIS SHUD
RESULT IN HIGH TEMPS BEING REACHED EARLY IN THE DAY OVER MOST OF
THE AREA...WITH FALLING TEMPS THROUGHOUT THE DAY ON A DEVELOPING
GUSTY WEST WIND.

AWIPS PRECIP ALGORITHMS SHOW THE POTENTIAL FOR SOME GROUND
WHITENING SNOWS IN THE WAKE OF THE DEPARTING RAINS. BUFKIT
PROFILES SHOW AROUND AN INCH OVER CENTRAL AREAS...WITH PERHAPS A
FEW INCHES FURTHER WEST OVER THE LAUREL HIGHLANDS AND NORTHERN
MOUNTAINS.

ALL THIS WILL BE BEFORE WE TRANSITION INTO A MORE NORMAL FOR THE
TIME OF YEAR POST COLD FRONTAL WEST-NORTHWEST FLOW REGIME THAT
TYPICALLY FEATURES WIDESPREAD STRATO-CUMULUS CEILINGS AND SNOW
SHOWER ACTIVITY OVER WESTERN AND NORTHERN HIGH TERRAIN.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
MEDIUM RANGE MODELS SEEM IN FAIRLY GOOD AGREEMENT IN LARGE SCALE
FEATURES THROUGH THE LONG TERM PERIOD. SHARP UPPER TROUGH SWINGING
THROUGH THE MID ATLC ON WED WILL TRANSITION INTO A BROADER TROUGH
WHICH SETTLES INTO PLACE OVER THE EASTERN THIRD/HALF OF NORTH
AMERICA. THIS WILL LEAD TO NW FLOW DOMINATING PA THROUGH THIS
COMING WEEKEND AND INTO EARLY NEXT WEEK.

ACCORDINGLY CHANCE POPS FOR SNOW ARE IN ORDER FOR MOST OF THE EXTENDED
PERIODS IN THE NW DUE TO THE ALMOST CONSTANT FAVORABLE FLOW OVER
THE LAKES. OVER THE REST OF THE AREA...THE HIGHER /BUT STILL IN
CHANCE OR SLIGHT CHANCE RANGE/ POPS WOULD BE CENTERED OVER SAT/SUN
DUE TO THE POSSIBILITY OF THE CLIPPER PASSING SOMEWHERE CLOSE. THE
COLD AIR SETTLES IN FOR THE LONG HAUL KEEPING TEMPS BELOW NORMALS
THROUGH THE ENTIRE PERIOD. THUS...ANY PRECIP WOULD BE SNOW AND
SNOW TO WATER RATIOS COULD BE A LITTLE FLUFFY FOR EARLY DEC.

&&

.AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
WIDESPREAD MODERATE TO HEAVY RAIN HAS BEEN FOCUSED SO FAR ACROSS
THE NORTHWEST HALF OF PENNSYLVANIA. MVFR/IFR CONDITIONS WITH
SIGNIFICANT LLWS WILL CONTINUE INTO WEDNESDAY AT ALL TAF SITES
AHEAD OF THE APPROACHING STRONG COLD FRONTAL SYSTEM. WARMER AND
MORE UNSTABLE AIR STREAMING INTO SOUTHERN PENN LATE TONIGHT
THROUGH DAYBREAK WEDNESDAY WILL ENHANCE BANDS OF HEAVY RAIN AND
INCREASE THE AREAL COVERAGE OF IFR CIGS AND VSBYS ACROSS THE
SUSQUEHANNA VALLEY. THERE COULD EVEN BE A NARROW BAND OF TSRA
/FROM NEAR KIPT TO KSEG AND KMDT/ MOVING THROUGH THE LARGER SHIELD
OF RAIN. LOCALLY STRONG WIND GUSTS ARE POSSIBLE WITH THIS
ORGANIZED/DEEPER CONVECTION ALONG AND JUST AHEAD OF THE COLD FRONT
LATER TONIGHT INTO WED MORNING.

COLDER AIR WRAPPING INTO THE AREA IN THE WAKE OF THE
FROPA/WIND SHIFT WILL CHANGE RAIN TO SNOW SHOWERS OVER THE WESTERN
HIGHLANDS AND CENTRAL MOUNTAINS DURING THE MID TO LATE
MORNING...WITH SOME WET SNOWFLAKES MIXING IN AT THE TAIL END OF
THE RAIN ACROSS THE MIDDLE SUSQUEHANNA VALLEY AROUND OR SHORTLY
AFTER 17Z.

A MORE TYPICAL COLD SEASON POST- FRONTAL WEATHER PATTERN WILL
THEN DEVELOP AND BRING LAKE EFFECT AND UPSLOPE SNOW SHOWERS AND
ASSOCIATED MVFR/IFR CIGS AND VSBYS INTO BFD AND JST WED NIGHT INTO
THURSDAY...WHILE AREAS SOUTH AND EAST OF THE ALLEGHENY PLATEAU
IMPROVE TO HIGH MVFR/VFR.

OUTLOOK...
THUR-SAT...MVFR/IFR WESTERN SXNS WITH OCNL LAKE EFFECT/UPSLOPE SNOW
SHOWERS. MAINLY VFR CENTRAL AND EASTERN AIRFIELDS WITH A BRIEF
SNOW SHOWER POSSIBLE MAINLY WEST OF IPT-MDT.

&&

.HYDROLOGY...
WIDESPREAD 2-3 INCH STORM TOTAL RAINFALL IS EXPECTED THROUGH EARLY
WEDNESDAY AFTERNOON...WITH THE POTENTIAL FOR LOCALIZED 3-4
INCH AMOUNTS. THIS WILL RESULT IN SIGNIFICANT RISES ALONG AREA
WATERWAYS WITH MINOR FLOODING POSSIBLE ALONG MANY SMALLER STREAMS
AND CREEKS. A FLOOD WATCH CONTINUES FOR THE ENTIRE AREA THROUGH
THE DAY WEDNESDAY...WITH NUMEROUS RIVER FLOOD WARNINGS IN EFFECT
ALONG WITH AN URBAN AND SMALL STREAM FLOOD ADVISORY FOR THE NW.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
FLOOD WATCH THROUGH WEDNESDAY EVENING FOR PAZ004>006-010>012-
017>019-024>028-033>037-041-042-045-046-049>053-056>059-
063>066.
WIND ADVISORY UNTIL 10 PM EST THIS EVENING FOR PAZ024-033.

&&

SYNOPSIS...LA CORTE/RXR
NEAR TERM...LA CORTE/RXR
SHORT TERM...LA CORTE
LONG TERM...DANGELO/GARTNER
AVIATION...LA CORTE/LAMBERT
HYDROLOGY...

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE STATE COLLEGE PA
1001 PM EST TUE NOV 30 2010

PAZ004>006-010>012-017>019-024>028-033>037-041-042-045-046-049>053-
056>059-063>066-020315-
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-
1001 PM EST TUE NOV 30 2010

...FLOOD WATCH IN EFFECT THROUGH WEDNESDAY EVENING...

THIS HAZARDOUS WEATHER OUTLOOK IS FOR CENTRAL PENNSYLVANIA.

.DAY ONE...TONIGHT.

PLEASE LISTEN TO NOAA WEATHER RADIO OR GO TO
WEATHER.GOV/STATECOLLEGE ON THE INTERNET FOR MORE
INFORMATION ABOUT THE FOLLOWING HAZARDS.

   FLOOD WATCH.

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

PLEASE LISTEN TO NOAA WEATHER RADIO OR GO TO
WEATHER.GOV/STATECOLLEGE ON THE INTERNET FOR MORE
INFORMATION ABOUT THE FOLLOWING HAZARDS.

   FLOOD WATCH.

.SPOTTER INFORMATION STATEMENT...

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

RXR

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE STATE COLLEGE PA
453 AM EST WED DEC 01 2010

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0445 AM     FLOOD            2 WSW BRADFORD          41.94N 78.67W
12/01/2010                   MCKEAN             PA   LAW ENFORCEMENT

            HAD TO EVACUATE DORMS AT UNIVERSITY OF PITTSBURGH AT
            BRADFORD DUE TO FLOODING. MULTIPLE ROAD CLOSURES ACROSS
            THE SOUTHEASTERN PART OF THE COUNTY.

&&

CERU