663
FXUS61 KCTP 310054
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
854 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 /UNTIL 8 AM SATURDAY MORNING/
CURRENT SATELLITE IR IMAGERY DEPICTS THE CENTER OF LOW PRESSURE
OVER CENTRAL WV CONTINUING TO SPIN AS IT SLOWLY MOVES EASTWARD.
A LOCAL VORT MAX IS PRESENT OVER SW PA AND N WV WITH A WELL
DEFINED COMMA HEAD ON RADAR REFLECTIVITY. AS THESE FEATURES
PROPAGATE EASTWARD THEY WILL BRING ADDITIONAL RAINFALL AND
UNSETTLED CONDITIONS ACROSS CENTRAL PA TONIGHT. A ZONE OF
CONVERGENCE IS MOVING ACROSS NORTHERN VA AND CENTRAL MD,
BRINGING WITH IT SEMI-ORGANIZED CONVECTION AND LOCALIZED AREAS
OF ELEVATED EFFECTIVE BULK SHEAR. WITH THE TIGHT PRESSURE
GRADIENT ASSOCIATED WITH THE SURFACE LOW THERE REMAINS A
POSSIBILITY A SHORT FUSED WIND ADVISORY MAY NEED TO BE ISSUED
FOR THE OVERNIGHT HOURS WITH WIND GUSTS OF 40+ KTS POSSIBLE EAST
OF THE ALLEGHENY FRONT.
THERE REMAINS A POTENTIAL HIGH SHEAR/LOW CAPE SEVERE WEATHER
EVENT ACROSS SOUTHEASTERN PA OVER THE NEXT SEVERAL HOURS,
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. AS CONFIDENCE HAS INCREASED IN THE
PLACEMENT OF THIS CONVERGENCE ZONE MOVING ACROSS CENTRAL
MARYLAND A TORNADO WATCH HAS BEEN ISSUED FOR THE COUNTIES IN SE
PA WHICH SHOW INGREDIENTS MOST FAVORABLE FOR STRONG CONVECTION.
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 /8 AM SATURDAY MORNING 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 FRIDAY/
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 /01Z SATURDAY THROUGH WEDNESDAY/
MAIN CHANGE TO THE 00Z TAF PACKAGE WAS TO BACK OFF ON THE LOWER
CONDITIONS SOME. SHOWERS HAVE BEEN FALLING APART, AS THEY MOVED
TOWARD THE AREA LATE THIS AFTERNOON. OTHER CHANGE WAS TO MAKE
WINDS MORE FROM THE NE EARLY ON, INSTEAD OF NW AND INCREASE THE
SPEED SOME.
CONCERN EARLIER FOR AREAS SOUTH OF JST FOR GUSTY WINDS DUE TO
CONVECTION AND POSSIBLE GRAVITY WAVES, BUT THINGS HAVE BEEN
WEAKENING.
THUS THE MAIN ISSUE OVERNIGHT WILL BE BANDS OF SHOWERS LIFTING
NORTHWARD FROM MD AND VA. I DID PUT THUNDER IN AT LNS AND MDT.
FOR SATURDAY, WINDS WILL SHIFT TO THE NORTHWEST AND INCREASE
IN SPEED. THE SHOWERS SHOULD END BY LATE MORNING OR EARLY
AFTERNOON, AND CONDITIONS TREND VFR BY LATER IN THE AFT.
MORE INFORMATION BELOW.
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 UNTIL 5 AM EDT SATURDAY FOR PAZ064>066.
SYNOPSIS...COLBERT/BOWEN
NEAR TERM...COLBERT/BOWEN
SHORT TERM...COLBERT/BOWEN
LONG TERM...DANGELO/MARTIN
AVIATION...MARTIN/COLBERT
CLIMATE...STEINBUGL
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