Severe Thunderstorm Warning 180, NWS State College, PA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
216 PM EDT WED SEP 22 2010

.SYNOPSIS...
A COLD FRONT WILL PUSH INTO PENNSYLVANIA AND BECOME STATIONARY
OVER SOUTHERN PENNSYLVANIA TONIGHT. IT WILL THEN RETREAT NORTHWARD
AS A WARM FRONT ON THURSDAY. UNSEASONABLY WARM TO EVEN HOT WEATHER
WILL CONTINUE UNTIL ANOTHER COLD FRONT MOVES THROUGH THE REGION
LATER FRIDAY OR EARLY SATURDAY.

&&

.NEAR TERM /UNTIL 11 PM THIS EVENING/...
SWOMCD ISSUED FOR THE REGION AS CAPE RISING AND CINS DECREASING WITH
ABNORMALLY HIGH TEMPS FOR SEPT OCCURRING. S/WV NOTED BY SPC OVER
NWRN PA MAY BE THE FIRST TRIGGER FOR CONVECTION TO BECOME BETTER
ORGANIZED FOR THIS EVENING. STORM CELLS ARE GENERALLY MOVING
40-50KTS WITH GOOD MID LEVEL FLOW. LAPSE RATES STEEPENING SLIGHTLY
AT MID LVLS. LLVL HELICITY NOT IMPRESSIVE AND MAINLY UNIDIR SHEAR
ALOFT. SO...MOST STORMS WILL BE ORGANIZED AS BOW SEGMENTS OR
MULTI-CELL CLUSTERS.

CU FIELD DEVELOPING OVER SC MTS THE FIRST SIGN OF LLVL INSTABILITY
AND EXPECT STORMS TO GROW FROM THERE AS WELL...ESP SINCE A WEAK VORT
MAX IS MOVING THRU EARLY THIS EVENING. THIS COULD GROW INTO A
PRE-FRONTAL LINE AS THE VORT MAX PUSHES INTO THE SERN PIEDMONT.

EXPECT TSTMS ASSOCD WITH THE MAIN MID-LVL CIRCULATION TO CROSS THE
NRN MTS AND ALSO THE CENT MTS LATE THIS AFTN AND EVENING...DYING OUT
AS THE SUN SETS ON THIS SUMMER SEASON.

&&

.SHORT TERM /11 PM THIS EVENING THROUGH THURSDAY NIGHT/...
COLD FRONT CURR N OF THE AREA SHOULD PRESS SWRD AND STALL OUT
SOMEWHERE OVER OUR SRN TIER TONIGHT...ENDING THE SHRA/TSRA BY
MIDNIGHT. WHILE IT MAY CLEAR OUT INITIALLY IN THE NRN MTS...EXPECT
LOW STRATUS AND/OR FOG TO DEVELOP LATER TONIGHT IN RESPONSE TO
RADIATIONAL COOLING AND LITTLE MOVEMENT TO THE DEWPOINTS.

THE FRONT SHOULD RETURN NWRD AS A WARM FRONT ON THUR...BUT MSTR
LACKING AND FORCING WEAK...SO WILL KEEP POPS IN THE 20-30 PCT
RANGE FOR THE DAYLIGHT HRS. THEN...FORCING GOES WELL TO THE N BY
EARLY EVENING...SO NIL POPS PLANNED FOR THUR NIGHT.

TEMPS TONIGHT WILL DIP INTO THE M50S IN THE N WITH FULL COOLING TO
SLIGHTLY DECREASING DEWPOINTS. ELSEWHERE...U50S TO M60S WILL BE
GOOD AS...AGAIN...DEWPOINTS DIP VERY LITTLE. TEMPS THURSDAY WILL
RETURN TO THE VERY WARM RANGE WITH 8H TEMPS CLIMBING BACK INTO THE
UPPER TEENS BY LATE IN THE DAY. THUR NIGHT SHOULD BE MAINLY CLEAR
AND WARM FOR EARLT AUTUMN.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
MEDIUM RANGE MODELS NOW COMING INTO MUCH BETTER AGREEMENT ON
TRANSITION FROM EARLY PERIOD ZONAL ACROSS NORTHERN CONUS AND
SOUTHERN CANADA TO MID LATITUDE BLOCKING ACROSS THE CONUS BY EARLY
NEXT WEEK. IN PARTICULAR...THE TIMING AND EVOLUTION OF A DEEP
CUTOFF LOW THIS WEEKEND FROM A NOW OFFSHORE PACIFIC SYSTEM IS MUCH
MORE CONSISTENT BETWEEN THE ECMWF AND GFS...WHICH HAD BEEN SEVERAL
HUNDRED MILES APART IN THEIR SOLUTIONS BY MON AND TUE. THE CURRENT
SIMULATIONS SUGGEST THE STRONG PACIFIC SHORTWAVE WILL CREST THE
PACNW WILL CROSS THE CANADIAN ROCKIES AND THEN DIG SOUTHWARD
ACROSS ALBERTA AND SASKATCHEWAN BY FRIDAY NIGHT AND SATURDAY
BEFORE CUTTING OFF OVER THE UPPER MIDWEST ON SATURDAY.

AT THE SAME TIME...DEEP SUBTROPICAL MOISTURE WILL GATHER IN THE
NORTHERN GULF AND BE ADVECTED NORTHWARD LATE THIS WEEKEND AND
EARLY NEXT WEEK OVER THE SOUTHEASTERN STATES INTO THE OHIO VALLEY.
THE POTENTIAL EXISTS FOR LOCALLY HEAVY RAINFALL OVER THE CENTRAL
APPALACHIANS AND PORTIONS OF THE OHIO VALLEY IN THIS SCENARIO...
WITH AT LEAST SOME RAINFALL EXPECTED TO REACH CENTRAL PENNSYLVANIA
BY TUESDAY AND OR WEDNESDAY AS SURGING DEEP LAYER MOISTURE AND AN
INVERTED SURFACE TROF TAKE SHAPE ACROSS THE REGION.

FRIDAY COULD TURN OUT TO BE THE WARMEST DAY WE'LL SEE UNTIL NEXT
SPRING AS A TONGUE OF +16-18C AIR AT 850 MB SPREADS NE ACROSS THE
CWA. MAX TEMPS FRIDAY SHOULD BE A COUPLE DEG F WARMER THAN WEDNESDAY
AND THURSDAY'S ACROSS THE NRN AND WRN MTNS...BUT SIMILAR TO
WEDNESDAY'S ACROSS THE REST OF THE FCST AREA. MAXS FRIDAY WILL BE
77-82F OVER THE NRN AND WRN MTNS...AND IN THE MID TO UPPER 80S
ACROSS THE CENTRAL AND SOUTHERN VALLEYS.

BETTER DEEP LAYER SHEAR /NEAR AN APPROACHING COLD FRONT AND THE
RIGHT ENTRANCE REGION OF 100 KT 300 MB JET/ WILL BRING THE THREAT OF
SCTD STRONG TO POSSIBLY SVR TSRA FRIDAY AFTERNOON AND EVENING.

AFTER SOME CLOUDS AND SCATTERED MORNING SHOWERS SATURDAY...MOST OF
THE DAY WILL BE DRY AND MUCH COOLER UNDER STRONG LLVL NEG THETA-E
ADVECTION FROM THE NORTH. TEMPS SATURDAY WILL ONLY REACH THE LOWER
60S FOR A HIGH ACROSS THE NW MTNS...WITH UPPER 60S TO LOWER 70S
THROUGHOUT THE CENTRAL THIRD OF THE STATE. HIGHS ACROSS THE FAR SE
SHOULD STILL MAKE IT TO THE UPPER 70S THANKS TO LAGGING STRONG COLD
ADVECTION AND ABUNDANT LATE MORNING/AFTERNOON SUNSHINE.

FOR THE LAST SEVERAL DAYS THE WEEKEND LOOKED TO BE DRY AND
SEASONABLY COOL. TODAY...A GREAT DEAL OF UNCERTAINTY EXITS AT THE
END OF THE PD WITH LONG TERM GUIDANCE INDICATING A POTENTIAL
SIGNIFICANT PATTERN CHANGE. THE GFS AND ECMWF AMONG OTHERS
FORECAST NRN STREAM ENERGY TO EMERGE FROM THE ROCKIES AND DIVE
SOUTH THROUGH THE TN VALLEY...ULTIMATELY LEADING TO A CLOSED OFF
UPPER LOW SOMEWHERE OVER THE SOUTHEASTERN U.S.  WHILE SEASONABLY
COOL WOULD STILL BE THE CALL GIVEN THIS SITU...CHANCES FOR PCPN
COULD BE QUITE A BIT HIGHER FOR SUNDAY INTO TUESDAY SHOULD THIS
PATTERN PAN OUT.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
A COLD FRONT IS MAKING ITS WAY ACROSS NORTHERN PENNSYLVANIA AND
SOUTHERN NEW YORK THIS AFTERNOON. THIS FRONT WILL MOVE A LINE OF
THUNDERSTORMS AND SHOWERS THROUGH CENTRAL PA THIS AFTERNOON AND
EVENING. A WARM FRONT SHOULD MOVE THROUGH TOMORROW. WITH ANOTHER COLD
FRONT EXPECTED TO MOVE THROUGH THE AREA LATE FRIDAY OR EARLY
SATURDAY.

EXPECT TEMPORARILY IFR CONDITIONS IN AND AROUND THE SCATTERED
SHOWERS AND THUNDERSTORMS THIS AFTERNOON. THE LINE OF STORMS WILL
MOVE THROUGH CENTRAL PA FROM 19Z-00Z. LOW CLOUDS/FOG IS PROGGED
FOR THE NRN MTS POST FROPA TONIGHT. CONFIDENCE IN IFR OR LOWER
VIS/CIGS AT BFD IS MEDIUM/MODERATE BASED ON CATG PROBABILISTIC
GUIDANCE AND MOS. THE DATA ALSO SUGGESTS IFR CONDS AT JST AND IPT.

EXPECT PREDOMINATELY VFR FLYING THURS AS A WEAK RIDGE OF HIGH PRES
WILL BRIEFLY SLIDE INTO THE AREA TONIGHT...ENDING ANY LINGERING
SHOWER OR TSTM ACTIVITY BY MIDNIGHT. THE WARM FRONT LIFTING BACK N
COULD MAKE SOME LIGHT SHRA - MAINLY IN THE NW ON THURS.

OUTLOOK...
FRI...VFR. MVFR SHRA/ISOLD TSRA POSSIBLE LATE.
SAT...MAINLY VFR W/MVFR PSBL NRN TIER. GUSTY NW WNDS.
SUN...VFR.

&&

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

&&

SYNOPSIS...DANGELO
NEAR TERM...DANGELO
SHORT TERM...DANGELO
LONG TERM...DEVOIR/GARTNER
AVIATION...CERU/STEINBUGL

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