Severe Thunderstorm Warning 200, NWS State College, PA

CENTRAL PENNSYLVANIA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
900 PM EDT SUN SEP 6 1998

...WORK ZONES TO BE SENT TO PHL/PIT AT 930 PM...

...DISCUSSION...
SATL IMAGERY REVEALS A WELL DEFINED SHRT WAVE RIPPLING ACRS THE ERN
LAKES AND SRN CANADA. THIS WAVE WAS ENHANCING THE LL WRLY FLO AHEAD
OF A SFC FRNTL BNDRY THAT WAS DRAPED ACRS SRN ONT AND LWR MI. THERE
WAS A WELL-DEFINED POOLING OF LOW-LVL MOISTURE AHEAD OF THIS BNDRY
WITH A RIBBON OF 70 TO 75+ DWPTS STREAMING INTO THE ERN LAKES AND
UPR OH VLLY. AS THIS WAVE PUSHES E... IT WAS TRIGGERING A FEW
STRG(SVR?)TSRA OVR THE ERN LAKES. KCLE 88D SHOWG A NASTY CELL OVR
SRN ONT WITH A VIL OF 74 KG/M2 SATL INDICATES THAT THIS
PRE-FRONTAL ZONE OF HIGH LL DWPTS WAS A HOTBED OF ACVTY THIS EVENING
WHICH WILL SLOWLY SETTLED S. THIS INITIAL WAVE WILL SHARPEN UP AN
UPR LVL JET STREAK OVR SERN CANADA OVERNGT. THIS WILL INCREASE A
THERMALLY DIRECT CIRC AND SUPPORT NRLY LL AGEO FLO WHICH WILL PRESS
THE SFC BNDRY SOUTHWARD. SIGNFNCT FGEN FRCG IN A REGION OF UNSTBL
AIR WILL ALLOW ACVTY OVR THE LWR LAKES TO WORK S INTO WRN/NRN PA B4
12Z. W/ WRLY LL FLO PREVALENT FEEL SOME ACVTY MAY  MAKE IT S OF
I-80 IN WRN PA B4 DAWN AND WILL KEEP SOME LO CHC POPS IN OVRNGT FOR
SW ZONES.

WITH UPR LVL JET STREAK MAINTAINED TO THE NE OF PA THRU MON AM...
THIS FRNT WILL BEHAVE MORE LIKE AN ANAFRNT INITIALLY SO I EXPECT A MASS
OF PRECIP NR AND ESP BEHIND THE FRNT. SOME TSRA WILL BE FOUND NR THE
SFC FRNT WITH MORE STRATIFORMISH RAINS BEHIND IT. W/ A WRLY FLO
REGIME MONDAY AM... EXPECT ACVTY TO TAKE LONGER TO REACH SUS VLLY OF ERN
PA. THINK THERE WILL BE A PERIOD OF SS AND DESTABILIZATION FOR THE
SUS VLLY AS A RESULT. MORE IMPORTANTLY... AFTER THE INITIAL WAVE RIDES OFF
TO THE NE TONIGHT A MUCH MORE SIGNIFICANT WAVE WILL LITERALLY DROP S
OUT OF CANADA AND AMPLIFY SIGNIFICANTLY... AND BEGIN THE PROCESS OF
CARVING OUT AN UNSEASONABLY COLD TROF IN THE ERN U.S. WITH A
SHARPENING UPR LVL TROF AXIS JUST TO OUR W MONDAY... INTENSE UPR LVL
DVRG WILL FOCUS STRGR ASCENT CLSE TO AND BEHIND FRNT... CHARGING  UP
THE UVV/S. THUS... PRECIP MASS OVR ERN LAKES SHUD GROW UPON REACHG
NRN/WRN PA MON AM. BY THE TIME IT REACHES THE SUS VLLY MONDAY
AFTRN... IT SHUD BE FAIRLY EXTENSIVE. SINCE I EXPECT SOME SS IN THE
LWR/MID SUS VLLY FOR A PERIOD ON MONDAY... THINK SOME SIGNFT TSRA
ACVTY WILL FIRE UP DURG AFTRN AS THE WHOLE MASS OF PRECIP DVLPS INTO
THIS AREA...MAKING IT OVR THE TYPICAL OROGRAPHIC BARRIER OF THE MTNS
OF WRN PA.

WINDS WILL BE ROARING MONDAY AFTRN (50-60 KTS AT 500 MB/30-40 KTS AT
700 MB... WITH DECENT MID-LVL DRYING TO BOOT. THINK A FEW STORMS CUD
BECOME SVR AND THINK SLIGHT RISK LOOKS GOOD FOR MUCH OF CNTRL/SRN PA
MONDAY. HVY RAIN ALSO CUD BECOME A PROBLEM... ESP IF AVN VERIFIES.
UNLIKE THE OTHER MODELS... THE AVN FOCUSES SO MUCH ASCENT OVR ERN
PA/NJ THAT IT DVLPS A SFC LO IN THIS AREA WHICH IN EFFECT KEEPS
THE PRECIP ON THE COLD SIDE OF THE FRNT LONGER IN ERN/SRN PA. THIS
SCENARIO CUD LEAVE TO SIG RAINS ERN/SRN PA. OTHER MODELS DON/T DVLP
SFC LO UNTIL IT IS MUCH FARTHER N AND FOR NOW AM LEANING TWD THE
OTHERS (ETA/MESO-ETA/NGM) SOLTNS. HYDROLOGICALLY... FLOWS ON AREA
STREAMS VERY LOW SO DON/T THINK THERE IS ANY THREAT FOR SMALLER
STREAM FLOODING.

AFTER THIS INITIAL SHOT OF PRECIP WITH FRNT PASSES BY MON NGT... THERE
LIKELY WILL BE ANTHR SHOT OF SHWRS IN ASSCTN WITH THE ARRIVAL OF THE
MID-LVL COLD FRNT/UPR LVL PV CORE MON EVE. THIS FEATURE WAS
REFLECTED WELL BY A SECONDARY SFC FRNT OVR THE UPR LAKES. THE
MESO-ETA TAKES THIS FEATURES DOWN INTO NRN PA MONDAY EVE AND THINK
PTNL IS THERE FOR ANTHR ROUND OF SHRA AS VERY COLD AIR ALOFT POURS
INTO PA.

BY TUESDAY... THERE WILL BE NO INVERSION OVR PA WHICH WILL BE
ENTRENCHED DEEP IN THIS CHILLY AIR MASS. MODELS PROGGED STRG
UNI-DIRECTIONAL NW FLO WITH STRG SPEED SHEAR. 850 MB TEMPS DROP TO
+2C TO +5C AND WITH LAKE TEMPS RUNNING ABV 20C... LAKE-EFFECT RAIN
SHOWERS PSBL FOR MTNS OF NRN AND WRN PA TUESDAY. THE STRG SPEED
SHEAR LIKELY WILL FORCE THE CNVTN INTO ROLL CIRCULATIONS AND
MULTIPLE BANDS. THIS TYPICALLY FAVORS SHWRS FAR AWAY FROM THE LAKES
AND THINK ACVTY CUD REACH ALL THE WAY INTO THE SUS VLLY. POPS FOR
TUESDAY ALL ZONES LOOKS GOOD... WITH HIGHER POPS TO THE NW.

.CTP...NONE.

NICOSIA

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