188
FXUS61 KCTP 301930
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
330 PM EDT FRI MAY 30 2025
SYNOPSIS
* WET AND STORMY END TO ONE OF THE WETTEST MAY'S ON RECORD
* POTENTIAL FOR FLOODING AND STRONG WIND GUSTS IN THE LOWER
SUSQUEHANNA VALLEY LATE THIS EVENING THROUGH LATE TONIGHT. A
BRIEF TORNADO CAN NOT BE RULED OUT.
* STRETCH OF DRY WEATHER PROBABLE SUNDAY THROUGH TUESDAY WITH
TEMPERATURES WARMING UP TO SUMMERTIME LEVELS BY MIDWEEK.
NEAR TERM /THROUGH TONIGHT/
AFTERNOON UPDATE: IN ADDITION TO THE ONGOING FLOOD WATCH, THE
SEVERE WEATHER OUTLOOK HAS BEEN UPGRADED TO SLGT FOR SOUTHERN
FRANKLIN, ADAMS, YORK, AND LANCASTER COUNTIES. IN ADDITION TO
HEAVY RAIN AND GUSTY WINDS, A BRIEF TORNADO CAN NOT BE RULED
OUT. THE MOST ACTIVE PERIOD OF WEATHER WILL BE FROM 7 PM TO 1
AM.
LATEST SATELLITE AND RADAR TRENDS SHOW A POTENT AND COMPACT MID-
UPPER VORT MAX MOVING THROUGH THE OHIO VALLEY. MUCH OF THE RAIN
IMPACTING PA AS OF 245 PM FRI IS STRATIFORM IN NATURE, BUT
CONVECTIVE LINES HAVE DEVELOPED ACROSS WEST VIRGINIA OVER THE
PAST FEW HOURS. VIRTUALLY ALL NEAR TERM GUIDANCE HAS THIS
CONVECTION EXPANDING IN COVERAGE AND INCREASING IN INTENSITY AS
IT MOVES NORTHEAST INTO THIS EVENING. A SHARP GRADIENT IN
DEWPOINTS EXISTS ACROSS THE SOUTHERN TIER OF PA AT THE MOMENT,
BUT MORE UNSTABLE AIR WILL LIKELY ADVECT IN AHEAD OF THE
CONVECTION AS IT APPROACHES. THIS WILL SET THE STAGE FOR A
POTENTIAL HIGH SHEAR/LOW CAPE SEVERE WEATHER EVENT ACROSS
SOUTHEASTERN PA, POTENTIALLY AS FAR NORTH/WEST AS FRANKLIN,
ADAMS, YORK, AND LANCASTER COUNTIES. THE HRRR DEPICTS 30-40 KTS
OF EFFECTIVE BULK SHEAR AT 00Z THIS EVENING, ALONG WITH POCKETS
OF 125-150 M2/S2 OF SFC-1KM SRH AND NEARLY 1000 J/KG OF MLCAPE.
ALSO NOTEWORTHY IS THE AMOUNT OF SFC VORTICITY AND CONVERGENCE
AS THE SFC LOW SLIDES ACROSS THE DELMARVA. ALTHOUGH THE EXACT
PLACEMENT OF THE CONVERGENCE AXIS AND NORTHWARD EXTENT OF THE
UNSTABLE AIRMASS IS UNCERTAIN, AN ENVIRONMENT SUPPORTIVE OF AT
LEAST BRIEF TORNADOES WILL LIKELY BE WITHIN 1 COUNTY OR SO FROM
OUR SOUTHERN TIER ZONES, SO WE ARE WATCHING THIS THREAT CLOSELY.
THE LINEAR AXIS UPON WHICH CONVECTION DEVELOPS THIS EVENING MAY
BE SLOW TO MOVE THROUGH THE LOWER SUSQ VALLEY, PERPETUATING THE
HEAVY RAIN AND INCREASING THE LIKELIHOOD FOR LOCAL AMOUNTS OF
1.50-2.50" IN THE FLOOD WATCH AREA. NOT ONLY WILL THE STRONGLY
FORCED SFC LOW (CYCLOGENESIS) DRIVE CONVECTION WITH MODERATE TO
HEAVY PRECIPITATION, BUT IT WILL ALSO ACT TO TIGHTEN THE
PRESSURE GRADIENT ACROSS THE LOWER SUSQ VALLEY, PARTICULARLY AS
THE SFC LOW PULLS AWAY. NW WIND GUSTS OF 30-40 MPH ARE NOT OUT
OF THE QUESTION IN THE SECOND HALF OF THE NIGHT. THE COMMA
HEAD/DEFORMATION RAINFALL APPEARS TO ADD ANOTHER 0.25 TO 0.75"
BETWEEN 06-12Z AS THE HEAVY QPF AXIS SHIFTS TO THE NORTHEAST
ALONG THE PA/NY BORDER.
SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/
AN APPROACHING COLD FRONT COINCIDING WITH REINFORCING SHORTWAVE
ENERGY AND COOLING TEMPS ALOFT WILL FAVOR FREQUENT SHOWER/ISOT
ACTIVITY ON SATURDAY -- AND COULD EVEN BE ENOUGH TO SUPPORT A
MARGINAL WIND THREAT ACROSS SOUTHEAST PA. THE LAST DAY OF MAY
WILL BE QUITE BREEZY AND NOTICEABLY COOLER WITH MAXT DEPARTURES
10 TO 15 DEGREES BELOW THE HISTORICAL AVERAGE.
TYPICAL STRATOCU FIELD IS LIKELY TO COVER AREAS DOWNWIND OF
LAKE ERIE SATURDAY NIGHT INTO SUNDAY MORNING WITHIN THE BRISK NW
FLOW REGIME. APPARENT TEMPS EARLY SUNDAY MORNING ARE FORECAST
IN THE 35-45F RANGE - WHAT A CHILLY START TO JUNE! ONE MORE COLD
NIGHT SUNDAY NIGHT BEFORE THE WARM UP BEGINS NEXT WEEK. THERE
IS A LOW, BUT NON ZERO CHANCE FOR AT LEAST SOME PATCHY FROST
OVER THE WESTERN ALLEGHENIES SUNDAY NIGHT INTO MONDAY MORNING AS
HIGH PRESSURE BUILDS INTO THE REGION.
LONG TERM /MONDAY THROUGH THURSDAY/
HIGH PRESSURE SFC AND ALOFT BUILDS ACROSS THE SOUTHEAST PART OF
THE COUNTRY EARLY NEXT WEEK. EXPECT THIS TO BRING THE
TEMPERATURES MORE IN LINE WITH NORMAL FOR EARLY JUNE.
LOOKS LIKE MOST OF THE TIME MONDAY INTO WEDNESDAY WILL BE DRY
NEXT WEEK AS GUIDANCE AGREES ON A BUBBLE OF HIGH PRESSURE
FENDING OFF MOISTURE. THE MAXES SHOULD GET INTO THE 80S FOR
T-W-R. SOME URBAN LOCATIONS COULD TOUCH 90F WED AFTN. THE NEXT
COLD FRONT MAY BRING SOME SHOWERS AND PERHAPS A THUNDERSTORM OR
TWO TO THE AREA NEXT THURSDAY. THE UPPER FLOW THEN STAYS OUT OF
THE SW WITH A RIDGE OFF THE COAST. THAT WILL ALLOW A MORE OR
LESS CONTINUOUS FLOW OF MOISTURE INTO THE AREA FOR THE WEEKEND.
(READ: SHOWERS/TSTORMS)
AVIATION /19Z FRIDAY THROUGH WEDNESDAY/
LIGHT RAIN HAS BEGUN ACROSS SOME OF THE WESTERN AIRFIELDS AS OF
19Z FRI, ALTHOUGH CIGS/VSBY REMAIN LARGELY VFR. JST WILL LIKELY
BE FIRST TO SEE MVFR CONDITIONS, PRIOR TO SUNSET.
DETERIORATING CONDITIONS WILL SPREAD EASTWARD THIS EVENING,
WITH SOME OF THE HEAVIEST RAINFALL AND CHANCE FOR THUNDERSTORMS
IMPACTING MDT AND LNS BETWEEN 23Z AND 05Z. SOME STORMS MAY BE
SEVERE. NW WINDS WILL PICK UP AS A SFC LOW INTENSIFIES, WITH
GUSTS 20-30 KTS, STRONGEST IN THE SOUTHEAST. THE NW UPSLOPE FLOW
WILL PUSH TYPICAL IFR STRATUS INTO BFD/JST AFTER 06Z AND
LASTING INTO AT LEAST LATE SAT MORNING. MOST OF THE HEAVY RAIN
WILL MOVES OUT OF THE AREA BY 06Z, BUT ANOTHER ROUND OF
SCATTERED SHRA/TSRA WILL DEVELOP BENEATH THE COLD UPPER LEVEL
LOW SAT AFTERNOON.
OUTLOOK...
SUNDAY...MAINLY VFR WITH GUSTY NORTHWEST WINDS.
MONDAY-WEDNESDAY...MAINLY VFR.
CLIMATE
MAY 2025 PRECIPITATION RANKINGS
SITE MAY 1-29, 2025 | WETTEST MAY ON RECORD
-----------------------------------------------------------
HARRISBURG 7.97" 2ND WETTEST | 9.71" IN 1989
WILLIAMSPORT 6.66" 6TH WETTEST | 9.91" IN 1919
ALTOONA 6.84" 3RD WETTEST | 7.31" IN 1960
STATE COLLEGE 6.47" 9TH WETTEST | 9.45" IN 1894
ADDITIONAL RAINFALL FORECAST AT HARRISBURG AND ALTOONA THROUGH
TONIGHT PUTS THE RECORDS FOR WETTEST MAY VERY MUCH IN JEOPARDY.
A SEASONABLY STRONG/DEEP AREA OF LOW PRESSURE (~990MB) IS
FORECAST TO MOVE ACROSS SOUTHEASTERN PENNSYLVANIA OVERNIGHT. THE
RECORD LOW PRESSURE FOR MAY AT HARRISBURG IS 983.4MB.
CTP WATCHES/WARNINGS/ADVISORIES
FLOOD WATCH FROM 7 PM EDT THIS EVENING THROUGH LATE TONIGHT
FOR PAZ064>066.
SYNOPSIS...STEINBUGL/COLBERT
NEAR TERM...STEINBUGL/COLBERT
SHORT TERM...STEINBUGL/COLBERT
LONG TERM...DANGELO/MARTIN
AVIATION...BANGHOFF/BOWEN/COLBERT
CLIMATE...STEINBUGL
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