Severe Thunderstorm Warning 137, NWS State College, PA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
200 PM EDT TUE JUL 17 2001

15Z MESO-ANALYSIS SHOWS THE FRONT HAS FORMED A TIGHTER GRADIENT FROM
NEAR ERIE SOUTHEAST TO WILLIAMSPORT. THIS IS IN RESPONSE TO THE
MORNING SHOWERS AT THE NEW YORK/PENNSYLVANIA BORDER. TOWERING CU
AROUND THE STATE SUGGESTS THE INSTABILITY ACROSS THE REGION THIS
AFTERNOON AS FORECAST BY THE MODELS. RADAR SHOWS SOME CONVECTION
THIS AFTERNOON...BEST CELLS IN SOUTHWEST PA AT THIS TIME. THIS EVENING AND
TONIGHT THERE IS STILL A CHANCE...ESPECIALLY AS A VORTICITY AXIS
APPROACHES. SHORT RANGE ENSEMBLE FORECAST GUIDANCE SUGGEST BEST POPS
IN NORTHEASTERN MOST COUNTIES TONIGHT WITH MAINLY SCATTERED RAINFALL
OVER CENTRAL AND SOUTHERN SECTIONS.  A SECOND PRECIP MAX IS FORECAST
TO PASS ALONG AND SOUTH OF THE PA BORDER INTO OH AND WV.  IF THIS
TRACKS FARTHER NORTH...IT COULD CLIP SOMERSET/CAMBRIA COUNTIES.

MCC NEAR CHICAGO SHOULD CLIP EXTREME SOUTHWEST PENNSYLVANIA TONIGHT.
THIS AREA COULD MISS OUR CWA BUT POPS WILL REFLECT POSSIBILITY OF
THIS SYSTEM AFFECTING SOUTHWEST PA.

SURFACE ANTICYLCONE RIDGES DOWN ALONG COAST CREATING MORE
COLD-SEASON-LIKE DAMMING SITUATION. THE SURFACE FRONT SAGS
SOUTHWARD...AS THE 850MB FLOW BECOMES MORE EASTERLY. LOW-LEVEL COOL
AIR DAMMING BEGINS LATE TOMORROW INTO TOMORROW NIGHT. THIS WILL
BRING A LOT OF ATLANTIC MOISTURE (ATLANTIC TEMPS ARE LOW SO HUMIDITY
ANOMALIES IN EASTERN PA ARE NEGATIVE) INTO THE AREA WITH A GOOD
TEMPERATURE GRADIENT BETWEEN OUR WESTERN ZONES AND EASTERN ZONES.
THREAT OF RAINFALL WILL DROP TOWARD MARYLAND BORDER DURING THE DAY
WEDNESDAY.

AS THIS OCCURS...THE UPPER LEVEL RIDGE AMPLIFIES IN THE MIDWEST.
CONDITIONS LOOK FAVORABLE FOR A MCC TO DROP SOUTHEAST INTO THE
SOUTHWESTERN PORTIONS OF PENNSYLVANIA WEDNESDAY NIGHT (SEE SPC DAY 2
OUTLOOK). THE EASTERLY FLOW WILL CONTINUE TO PUMP MOISTURE INTO THE
EASTERN ZONES. THE EASTERLY FLOW GETS OVER -3 STANDARD DEVIATIONS
ABOVE NORMAL LATE WEDNESDAY OVER EASTERN PA AND EAST TOWARDS THE
COAST. BEST CHANCE OF RAIN WILL BE SOUTHWESTERN ZONES WEDNESDAY
NIGHT. SREF SHOWS UP TO 90 PERCENT OF MEMBERS WITH 0.1 TO 0.25
INCHES OF QPF IN SOUTHWEST.

A SHORT WAVE DROPS DOWN ON THURSDAY WITH A -4.5 STANDARD DEVIATION
EASTERLY 850MB FLOW INTO OUR EASTERN PA AND NJ CONTINUING A COOL AND
WET PATTERN. HOWEVER THE SHORT RANGE ENSEMBLE FORECAST SHOWS A TREND
TO DRCRESE PRECIPITATION DURING THE AFTERNOON HOURS...AS THE FRONT
SLIDES EVEN FURTHER SOUTH AND COOLER AIR MOVES IN.

IN THE EXTENDED...
SURFACE HIGH PRESSURE BUILDS DOWN THE EASTERN APPALACHIANS DURING
FRIDAY PROVIDING BEAUTIFUL CONDITIONS. THIS TREND WILL CONTINUE
UNDER HIGH PRESSURE THROUGH AT LEAST SUNDAY. THE MRF ENSEMBLES SHOW
A SURFACE TROUGH APPROACHING FROM THE WEST WILL BRINGING A CHANCE OF
PRECIPITATION ON MONDAY IN THE WEST. THE ENSEMBLES ALSO SHOW A
CHANCE OF (SHOWERY PRECIPITATION FOR THE ENTIRE CWA FOR TUESDAY.

ENSEMBLES SUGGEST FRIDAY AND SATURDAY WILL SEE HIGH TEMPS A FEW
DEGREES BELOW NORMAL THEN RETURNING TOWARD NORMAL BY SUNDAY.

.CTP...NONE.

ROGOWSKI/GRUMM