Severe Thunderstorm Warning 125, NWS Philadelphia/Mount Holly

CENTRAL PENNSYLVANIA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
1220 PM EDT MON JUL 20 1998

...ZONES WL BE AVBL TO PIT/PHL VIA ADMCTP AROUND 3 PM...

...DISCUSSION...

MCS ACTIVITY SLIDING EAST OUT OF MIDWEST IS HINDERING HEATING SO
FAR. STRONGEST STORM AT THIS TIME IS TRUCKING THRU NRN TIER. IT HAS
TAKEN ON SUPERCELLULAR CHARACTERISTICS WITH 35KT GATE TO GATE SHEAR
PROMPTING TORNADO WARNINGS.

BIG SCALE WARM FRONT LOOKS LIKE IT IS OVER NERN PA WHICH IS
PROVIDING SHEAR ATMOSPHERE FAVORABLE FOR RAPID SPINUPS. DEWPOINTS IN
THE UPPER 60S AND 70S POURING INTO THE REGION WILL KEEP AREA PRIMED
FOR CONVECTION NEXT COUPLE OF DAYS. YESTERDAY IT LOOKED LIKE WARM
MID LEVELS WUD BE ABLE TO PROVIDE EFFECTIVE CAP TO CONVECTION..BUT
LOW LEVEL DYNAMICS ARE OVERCOMING TENDENCY FOR CAPPING. ALSO HGTS
ALOFT ARE NOT PROGGED AS HIGH AS PREVIOUS RUNS WHICH IS KEEPING MID
LEVEL TEMPS JUST A TAD COOLER.

AFTER THIS LOAD OF CONVECTION SHOOTS THRU THE REGION WE LOOK TO BE
UNDER THE GUN AGAIN LATER TONITE AS ETA/MESO ETA COOKS UP 40+ KT LOW
LEVEL WESTERLY JET AND PUSHES IT INTO THE AREA. WITH FRONT SAGGING
INTO REGION OF STRONG LOW LEVEL WINDS...HAVE TO BELIEVE MORE STORMS
WILL FIRE AND CONTINUE TO SLIDE INTO THE REGION FROM THE MIDWEST.

PROBLEM TURNS TO POTENTIAL HEAVY RAIN EVENT. SUPER MOISTURE SHUD
KEEP FUNELLING INTO THIS DEVELOPING CONVECTION COURTESY OF STRONG
LOW LEVEL WESTERLY JET. RIBBON OF HIGH THETA-E AIR SURGES INTO THE
REGION AND KEEPS ATMOSPHERE PRIMED FOR HEAVY CONVECTION. ALREADY
CONVECTION IS FORMING OVER MIDWEST ON THE NOSE OF WHAT ETA PROGS AS
NEXT LLJ IN THE SERIES. STILL TOO EARLY TO ISSUE FLASH FLOOD
WATCHES...BUT WILL ENHANCE WORDING TO MENTION LOCALLY HEAVY RAIN.

CONVECTIVE DEBRIS HAS SO FAR KEPT HEAT INDICES FROM GOING THRU THE
ROOF. DEWPOINTS ARE HIGH AND ATMOS SHUD REBOUND A BIT LATER TODAY
AFTER CONVECTION WINDS DOWN. BUT IT APPEARS AS IF REAL HIGH HEAT
IND`ICES WILL BE HELD OFF FOR A TIME.

LA CORTE

PAZ004>006-010>012-017-018-024>028-033>037-041-042-045>046-049>053
-212300-

SEVERE WEATHER OUTLOOK...HEAVY RAIN POTENTIAL
NATIONAL WEATHER SERVICE STATE COLLEGE PA
300 PM EDT TUE JUL 21 1998

...HEAVY RAIN IS POSSIBLE TONIGHT OVER PORTIONS OF WESTERN AND
NORTHERN PENNSYLVANIA...

HUMID AND VERY UNSTABLE AIR WILL CONTINUE TO FEED INTO THE REGION
FOR THE NEXT 24 TO 36 HOURS. THIS WILL PROVIDE FUEL FOR POTENTIALLY
HEAVY SHOWERS AND THUNDERSTORMS.

SHOWERS AND THUNDERSTORMS ARE ONCE AGAIN EXPECTED TO DEVELOP OVER
THE LOWER GREAT LAKES AND MIDWEST THIS EVENING...AND THEN MOVE
EASTWARD INTO WESTERN AND NORTHWESTERN PENNSYLVANIA LATER THIS
EVENING AND TONIGHT.

DUE TO RECENT DRY WEATHER...IT WOULD TAKE MORE THAN 2 INCHES OF RAIN
IN ONE HOUR...OR MORE THAN 3 INCHES OF RAIN IN 3 HOURS TO CAUSE
STREAMS AND CREEKS TO FLOOD.

WHILE SOME OF THESE SHOWERS AND THUNDERSTORMS WILL HAVE THE
POTENTIAL TO CAUSE TORRENTIAL DOWNPOURS...WIDESPREAD FLOODING OF
STREAMS AND CREEKS IS NOT EXPECTED AT THIS TIME. HOWEVER...POOR DRAINAGE
AND LOW LYING AREAS MAY SEE PROBLEMS DEVELOP SHOULD VERY HEAVY RAINS
OCCUR.

THE WARM HUMID AIRMASS WILL BE WITH US THROUGH WEDNESDAY...WHICH
WILL KEEP THE THREAT OF SHOWERS AND THUNDERSTORMS IN THE FORECAST.
AT THIS TIME IT APPEARS AS IF THE AREA NORTH AND WEST OF A LINE FROM
ABOUT ALTOONA TO WELLSBORO WILL BE MOST AT RISK FOR THE THREAT OF
HEAVY RAIN. THE BEST CHANCE FOR THIS WILL BE FROM LATER THIS EVENING
INTO WEDNESDAY MORNING.

STAY TUNED TO NOAA WEATHER RADIO...OR YOUR FAVORITE LOCAL RADIO OR
TELEVISION STATION FOR THE LATEST FORECASTS...STATEMENTS AND
POSSIBLE WARNINGS.

LA CORTE/BOOKBINDER