Heavy Rain in Pennsylvania, September 24 to 25, 2001

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
1012 AM EDT MON SEP 24 2001

FOG AND LOW CLDS A BIT SLOW TO LIFT...SO HOLDING UPDATE TIL 11 AM OR
SO. OTRW...CURRENT FCST LOOKS RNSBL...JUST SOME MINOR TWEAKS ON CLDS
AND AFTN TEMPS.

NO CHGS ON MARINE.

.PHI...SML CRAFT ADVY CST AND LWR DE BAY.

KRAUS

DEZ001>004-MDZ008-012-015-019-020-NJZ001-007>010-012>026-PAZ054-055-
060>062-067>071-242100-

SEVERE WEATHER OUTLOOK
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
1121 AM EDT MON SEP 24 2001

...SLIGHT RISK OF SEVERE THUNDERSTORMS LATER THIS AFTERNOON AND
EVENING OVER MUCH OF EASTERN PENNSYLVANIA - NORTHERN DELAWARE AND
MOST OF THE MARYLAND EASTERN SHORE...
...LOCALLY HEAVY DOWNPOURS POSSIBLE THROUGHOUT THE REGION TONIGHT...

A VERY STRONG AND IMPRESSIVE STORM SYSTEM FOR LATE SEPTEMBER IS
FORECAST TO MOVE EAST TOWARD THE REGION THIS AFTERNOON. THE AREA HAS
BEEN STUCK IN A RELATIVELY HUMID AIR MASS FOR LATE SEPTEMBER THE
PAST SEVERAL DAYS. AS A STRONG COLD FRONT MOVES INTO PENNSYLVANIA
LATER THIS AFTERNOON...SHOWERS AND THUNDERSTORMS ARE FORECAST TO
DEVELOP. AT THE SAME TIME VERY STRONG WINDS...ASSOCIATED WITH A LOW
LEVEL JET STREAM...WILL BE MOVING INTO PENNSYLVANIA AND MARYLAND.
THUNDERSTORMS IN CENTRAL AND WESTERN PENNSYLVANIA WILL CONTINUE TO
DEVELOP AND MOVE EAST. IF THEY COINCIDE WITH THE MAXIMUM HEATING OF
THE DAY...THEY MIGHT BE POWERFUL ENOUGH TO TAP INTO THE STRONG WINDS
ALOFT. BASED ON THE CURRENT TIMING...THE GREATEST LIKELIHOOD OF THIS
OCCURRING WILL BE WEST OF THE REGION. BUT IF THE STORMS MOVE FAST
ENOUGH AND ARRIVE BY AROUND SUNSET...SEVERE THUNDERSTORMS MIGHT
MAKE IT AS FAR EAST AS THE MARYLAND EASTERN SHORE...NORTHERN
DELAWARE AND EASTERN PENNSYLVANIA. GIVEN THE STRONG WINDS AND THE
EXPECTED CHANGE OF WIND DIRECTION WITH HEIGHT...KNOWN AS SHEAR...AN
ISOLATED TORNADO COULD NOT BE RULED OUT. THAT IS WHY THE STORM
PREDICTION CENTER IN NORMAN OKLAHOMA HAS PLACED THESE LOCATIONS IN
THE SLIGHT RISK FOR SEVERE THUNDERSTORMS THIS AFTERNOON AND EVENING.

IN ADDITION TO THE SEVERE WEATHER THREAT...THE COLD FRONT WILL WRING
OUT THE MOISTURE OVER THE REGION. THUNDERSTORMS WITH HEAVY RAIN ARE
POSSIBLE TONIGHT. STORM TOTALS SHOULD AVERAGE AROUND ONE INCH...BUT
COULD REACH AS MUCH AS TWO TO THREE INCHES IN LOCALIZED AREAS. THE
GREATEST THREAT OF THIS OCCURRING IS IN NORTHERN PENNSYLVANIA.
PONDING OF WATER WILL OCCUR IN LOW LYING AND POOR DRAINAGE AREAS.
BE WARY WHILE DRIVING TONIGHT BECAUSE IT WILL BECOME DIFFICULT TO
JUDGE THE DEPTH OF WATER ON ROADWAYS. UNLESS STORM TOTALS EXCEED
THESE AMOUNTS...FLOODING OF MAJOR STREAMS AND RIVERS IS NOT
EXPECTED.

THE LOW CLOUDS THAT SPREAD ACROSS THE REGION THIS MORNING ARE
CURRENTLY LIMITING HEATING CAUSED BY THE SUN. THESE CLOUDS ARE
EXPECTED TO BREAK THIS AFTERNOON BUT MAY STILL LIMIT THE AMOUNT OF
SUN AND THUS SAP SOME OF THE STRENGTH OF THE THUNDERSTORMS. A DRIER
AND MUCH COOLER AIR MASS IS EXPECTED TO MOVE INTO THE AREA DURING
THE SECOND HALF OF TUESDAY. STAY TUNED TO NOAA WEATHER RADIO AND
OTHER LOCAL MEDIA FOR FURTHER DETAILS OR UPDATES.

FOR ADDITIONAL WEATHER INFORMATION, CHECK OUR WEB SITE AT
WWW.NWS.NOAA.GOV/ER/PHI IN SMALL LETTERS.

RPW