Flash Flood Warning 75, NWS State College, PA

CENTRAL PENNSYLVANIA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
315 PM EDT SAT MAY 16 1998

...WORK ZONES SENT TO PIT/PHL AT 245 PM VIA ADM/S...

...DISCUSSION...
DECIDED TO GO WITH 40 CHC POPS FOR TSRA WRN ZONES AND SHRA/TSRA IN
ERN ZONES FOR TONIGHT. WENT WITH EVENING SHRA/TSRA WRN ZONES.
LATEST KPBZ AND KCCX 88D LOOPS SHOWS THE BEGINNINGS OF SCTRD CNVTN
FORMING FM NW PA SW TO SERN OH. ACVTY WAS LINING UP WITH THE SHARP
MOISTURE GRADIENT THAT EXISTS ACRS ERN OH IN ASSCTN WITH A LL FRNTL
BNDRY. DRIER AIR WILL CONT TO WORK E ACRS PA THIS EVE IN ASSCTN WITH
A SMALL LOBE OF UPR LVL PV AIR THAT STRETCHED S FM THE MAIN PV CORE
N OF THE UPR GREAT LAKES. THIS LOBE PASSES ACRS PA TONIGHT AND
FORCES THE FRNT THRU PA W/ STRG LL DRY ADVECTION ON W-NW WINDS. IN
ADVANCE OF THE WAVE/SFC FRNT... LL MOISTURE WAS ADVECTING INTO PA ON
SW WINDS WITH INCREASING LL CONV EVIDENT ON THE SFC ANLYSIS. THE AMS
WAS BECMG QUITE UNSTBL WITH AFTRN HEATING AS WELL. THUS WITH LL
MOISTURE INCREASING NR TIME OF MAX HEATING... CAPES ON MODIFIED AM
SOUNDINGS RUNNING BTWN 2000 AND 3000 J/KG. FOR MUCH OF THE AFTRN...
ACVTY REMAINED CAPPED OVER THE ERN OH VLLY DUE TO WARM MID-LVL
TEMPS. THE MOISTURE SURGE AHEAD OF THIS LL FRNT WILL BE
ENCOUNTERING COLDER MID-LVL TEMPS ALOFT OVR PA CLSR TO THE UPR RDG
AXIS. THUS... SCTRD STORMS SHUD CONT TO FIRE AS THIS MOISTURE WORKS
E OF THE CAP INTO CNTRL PA. TIMING DURING THE LATE AFTRN/EVE HOURS IN
WRN ZONES AND MID EVENING/OVERNIGHT IN THE ERN ZONES. WENT WITH CHC
SHRA OR TSRA IN ERN ZONES SINCE ACVTY COMES THRU LATER IN EVE AFTER
MAX DAYTIME TEMPS.

AS FOR THE POTENTIAL FOR SVR... WIND FIELDS ARE RATHER WEAK AND
MID-LVL TEMPS ARE WARM. HOWEVER WITH A HUGE SOURCE OF DRY AIR TO THE
W OF WHERE THE STORMS WILL DVLP... POTENTIAL EXISTS FOR A FEW STRGR
STORMS THAT GET WIND/HAIL ENHANCEMENT FM EVAP COOLING.

CD FRNT SWEEPS BY LATE TONIGHT AND ALLOWS FOR A SFC RDG TO BUILD
ACRS OH VLLY SUNDAY. PA FALLS UNDER A NW FLO OF QUITE DRY AIR.
POTENTIAL EXISTS FOR SOME CU FORMATION ONLY IN FAR ERN/SRN ZONES
SINCE IT WILL TAKE AWHILE FOR THE DRY NW FLO TO GET ESTABLISHED
SUNDAY AND LWR DWPTS. ANY AM CU THAT FORMS REST OF ZONES SHUD
QUICKLY MIX OUT. WENT WITH TEMPS A BIT LWR THAN MOS. LIKE AVN
NUMBERS BETTER.

SFC HIGH REMAINS W OF REGION SUNDAY NGT WITH MAINLY CLR SKIES. WENT FOR
SOME PC SKIES LATE NW PA GIVEN POTENTIAL FOR MID-UPR CLDS ADVECTING
DOWN INTO PA FM UPSTREAM MCS DVLPMENTS OVR THE GREAT LAKES.

MONDAY IS A QUESTION MARK TO ME. MOIST WRLY RETURN FLO ON THE N-SIDE
OF THE SFC HI SETS UP INTO THE GREAT LAKES/MID-ATLANTIC SUN NGT/MON
WITH THE AVN HINTING AT DECENT LL MOISTURE FEED INTO PA ON W WINDS.
AVN SHOWS LI/S DROP TO -3C BY LATE IN THE DAY OVR MUCH OF CNTRL/SRN
PA. GIVEN STRG UPR CONFLUENCE OVR NEW ENGLAND AND AN IMPLIED JET
STREAK CIRC... THERE CUD BE A LL BNDRY SOMEWHERE IN PA TO FOCUS
SHRA/TSRA. I THINK THIS WILL BE SOMETHING TO WATCH FOR LATER
SHIFTS... STILL TOO MUCH UNCERTAINITY AND COORD WITH PIT ABT LEAVING
PRECIP OUT MONDAY IN WRN ZONES.

NICOSIA