Flash Flood Warning 137, NWS State College, PA

CENTRAL PENNSYLVANIA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
3 AM EDT WED AUG 21 1996

...ZONE SUGGESTIONS...
TODAY...
WUD CONSIDER RAISING POPS TO LIKELY OR 50 CHC POPS FOR RW/TRW TODAY
FOR NRN MTNS- C-SC MTNS TO MID/UPR SUS VLLY. LWR SUS VLLY CHC POPS
OK. TIMING WISE... THINK MOST ACVTY WILL OCCUR THIS MORNING NRN
MTNS. WITH REST OF FA SEEING ACTVY SPILL OVER INTO AFTRN.
TONIGHT... CLRG ALL ZONES... PATCHY FOG. CUD RETAIN MINIMAL CHC
POPS SC MTNS/LAURELS AND HV PC SKIES.
THU...
A TOSS-UP BTWN MO SUNNY/PC AFTER MORNING CLDS/FOG.

...DISCUSSION...
IR SATL IMAGERY SHOWG FLARE UP OF ACVTY ACRS NRN IND... NRN OH INTO
WRN PA AHEAD OF FRNTL BNDRY THAT SHOWS UP BEST IN THE LOW-LVL DWPTS
FIELDS (SFC ANYLS/850 MB UPR AIR). VWP FROM KCLE NOW SHWG A MORE
NWRLY FLO ABV NEARLY CALM B.L AS CLE IS NOW N OF MAIN CNVTIVE
ACTIVITY. PIT VWP SHOWS A W-SW LOW-LVL JET BTWN 4 AND 6 KFT FEEDING
HI DWPT AIR INTO CNVTN OVR WRN PA ATTM. ACVTY SHOWS THE TENDENCY
FOR BACK BUILDING AS MOST UNSTBL AIR/HIGHEST SFC DWPTS LIE TO THE
W OF PA. THUS... WITH WRLY FLO TRW/S KEEP FORMING TWD THE W AND
MORE UNSTBL AIR. KCCX 88D SHOWG SCTRD RW/TRW WORKG E INTO MORE STBL
AIR IN CNTRL/NC MTNS AND THUS DYING. SRN 1/2 OF PA IS ALMOST RAIN-
FREE. APPEARS ACVTY IS DVLPG IN THE CONVERGENCE ASSCTD W/ A
CORRIDOR OF STRGR LOW-LVL WINDS THAT PRECEDE THE FRNT/DRY LINE
FEATURE OVR SRN LAKES. LATEST RADAR TRENDS INDICATE QUITE A BIT OF
DVLPMENT JUST W OF CTP CWA AND WILL HV TO WATCH FOR POTENTIAL FOR
FLASH FLOODING AS BATCH OF ACVTY OVR NE OH WORKS SEWRD TWD THIS
SAME AREA. THINK C/SC MTNS MOST VULNERABLE.

MODELS INDICATE THAT THIS CORRIDOR A STRGR LOW-LVL WIND/HIER LOW-
LVL THETA-E AIR WORKS INTO PA TODAY AS DRIER AIR AND FRNTL BNDRY
CREEP INTO NRN PA BY THIS AFTRN. WUD HV LIKELY POPS FOR TRW NEARLY
ALL ZONES. WUD HV 40 POPS FOR LWR SUS VLLY AS WRLY FLO REGIME IN
THE LOW-LVL/S TYPICALLY DOESN/T FAVOR MUCH ACVTY IN LWR SUS VLLY
DUE TO OROGRAPHIC SUBSDC. THINK ACVTY WILL END IN NRN PA THIS
MORNING AS DRIER AIR WORKS S THIS AFTRN. THE 850 MB DWPT FIELDS
FROM ALL THREE MODELS SHOW SHARP DRYING ACRS NRN PA BTWB 18/00Z AND
ALL OF PA TONIGHT. AN UPR LVL RDG POPS UP OVR THE ERN U.S BY
TONIGHT IN RESPONSE TO AN UPR LVL TROF WHICH WORKS E TWD THE NRN
PLAINS. WITH AN AMPLIFYING RDG OVR ERN U.S TODAY/TONIGHT... THE FLO
TURNS NRNLY AT 850 MB WHICH ALLOWS THE DRY AIR TO SPILL S AND THE
FRNTL SYS TO WORKS THRU PA TONIGHT. THUS... WUD HV CLRG ALL ZONES
TONIGHT. CUD RETAIN CHC POPS AND PC SKIES SC MTNS/LAURELS AS DRIER
AIR WORKS INTO THE REGIONS LAST.

UPR LVL RDG DOMINATES THU AS MODELS INDICATE DRY AIR CONTINUES ABV
B.L THRU 850 AND 700 MB. MODEL SOUNDINGS FROM ETA SHOW LITTLE OR NO
CU AFTR MORNING CLDS/FOG. NGM KEEPS MORE LOW-LVL MOISTURE AND HAS
MUCH MORE CU DVLPMENT INFERRED BY LOW DWPT DEPRESSION AT TOP OF
INVERSION. WUD SPLIT DIFF FOR NOW AND HV PC. LITTLE IF ANY COOL AIR
SPILLS SWRD INTO PA. THUS... IT WILL REMAIN QUITE WARM THRU THU.

NICOSIA