651
FXUS61 KCTP 210935
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
535 AM EDT THU MAY 21 2026
WHAT HAS CHANGED
* SLIGHT DECREASE IN RAINFALL TOTAL FORECAST FOR FRI-SAT.
KEY MESSAGES
1) PERIODS OF LIGHT RAIN OVER SOUTH CENTRAL PA TODAY NORTH OF
DEPARTING COLD FRONT.
2) MAJOR COOLDOWN INTO SATURDAY WITH WIDESPREAD SOAKING
RAINFALL NEAR 1 INCH LATE FRIDAY AND SATURDAY.
DISCUSSION
KEY MESSAGE 1: PERIODS OF LIGHT RAIN OVER SOUTH CENTRAL PA
TODAY NORTH OF DEPARTING COLD FRONT.
WITH A COLD FRONT SLOWLY MOVING SOUTHWARD AWAY FROM OUR REGION
TODAY, THE RIGHT ENTRANCE REGION OF AN UPPER JET MAX TO OUR
NORTH WILL MOVE OVERHEAD, EXTENDING THE CHANCE FOR RAIN ESP
ACROSS THE SOUTHEAST (NEAREST THE SFC FRONT). REMOVED THUNDER
FROM THE GRIDS AS MODELS ARE NOT SUGGESTING ANY CAPE ABOVE THE
-10C LEVEL, BUT RAIN MAY BE BRIEFLY MODERATE AT TIMES. THIS
ROUND OF RAIN WILL END FROM NW TO SE ACROSS THE REGION - OVER
THE CENTRAL MTNS DURING THE LATE MORNING TO EARLY AFTERNOON, AND
ACROSS THE LOWER SUSQ VALLEY DURING LATE AFTERNOON TO EARLY
EVENING.
ACROSS THE NORTHERN TIER, THERE COULD BE ENOUGH DRY AIR MOVING
IN BY THIS EVENING THAT RADIATIVE COOLING WOULD BE QUITE
EFFECTIVE TONIGHT, BRINGING LOW TEMPS INTO THE UPPER 30S.
ELSEWHERE, LOWS TONIGHT WILL RANGE FROM THE 40S TO NEAR 50.
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KEY MESSAGE 2: MAJOR COOLDOWN INTO SATURDAY WITH WIDESPREAD
SOAKING RAINFALL NEAR 1 INCH LATE FRIDAY AND SATURDAY.
AS HIGH PRESSURE MOVES FROM THE GREAT LAKES TO NEW ENGLAND,
WE WILL SEE A LULL IN THE PRECIP FOR MUCH OF TONIGHT AND INTO
THE FIRST PART OF FRIDAY. RAIN WILL BEGIN TO RETURN FROM SOUTH
TO NORTH DURING THE DAYTIME AND EVENING ON FRIDAY. MODEL DATA
SHOWS THE HIGH PRESSURE SYSTEM CHANNELING SOUTHWARD DOWN THE
EAST SIDE OF THE APPALACHIANS, SETTING UP A COLD AIR DAMMING
(CAD) EVENT HEADING INTO MEMORIAL DAY WEEKEND. COMBINED WITH
STEADY RAINFALL ON SATURDAY, HIGHS WILL LIKELY BE NEAR DAILY
RECORD LOWS AT SEVERAL LOCATIONS (MINI-MAX), AND ONLY A FEW
DEGREES WARMER THAN THE SAT MORNING LOWS. WIND GUSTS AROUND 30
MPH IN THE LAURELS AND NW MOUNTAINS (SE FLOW) WILL MAKE IT FEEL
ESPECIALLY RAW. GUIDANCE MAY BE TOO OPTIMISTIC IN REBOUNDING
TEMPS SUNDAY INTO MONDAY, BUT OPTED TO KEEP BASELINE NBM FOR
NOW. THAT SAID, THE TREND WILL BE TO WARM WITH STEADIER RAIN
GIVING WAY TO MORE SHOWERY CONDITIONS FOR SUNDAY INTO MONDAY.
NBM QPF HAS DROPPED A BIT TO NEAR 1 INCH FOR FRI-SAT. WPC HAS
REMOVED THE MRGL ERO FROM OUR AREA. THE COOL/STABLE AIR WILL
CAP RATES FROM BECOMING EXCESSIVE. THE FORECAST RAINFALL IS
MUCH NEEDED OVER THE FAR SOUTH CENTRAL/SOUTHEASTERN COUNTIES WHO
REMAIN UNDER D1-D2 MODERATE TO SEVERE DROUGHT CONDITIONS.
AVIATION /08Z THURSDAY THROUGH MONDAY/
ANAFRONTAL RAIN ALONG COLD FRONT DRIFTING SOUTH ACROSS THE MID-
ATLANTIC WILL FAVOR FLIGHT RESTRICTIONS OVER THE SOUTH-CENTRAL
MOUNTAINS (KJST/KAOO) AND LOWER SUSQUEHANNA VALLEY (KMDT/KLNS)
DURING THE TAF PERIOD, WITH VFR FAVORED ACROSS THE NORTH-CENTRAL
MOUNTAINS (KUNV/KIPT) AND NORTHERN TIER (KBFD) WHERE DRIER AIR
HAS MIXED INTO THE LOWER LEVELS FARTHER BEHIND THE COLD FRONT.
PERIODS OF STEADIER RAIN ARE POSSIBLE ACROSS THE LOWER
SUSQUEHANNA VALLEY THURSDAY MORNING GIVEN ELEVATED INSTABILITY
IN PLACE (HREF MEAN MUCAPE OF 0-100 J/KG), PROVIDING SOME
ENHANCEMENT TO RAINFALL RATES WITH PRIMARY IMPACT BEING
VISIBILITIES TO ~6 SM. LIGHTNING THREAT IS LOW WITH MEAGER
MUCAPE VALUES FAVORING POCKETS OF STEADIER RAIN VS. ENHANCEMENT
TO THUNDERSTORMS, THOUGH ISOLATED LIGHTNING (10-20% CHANCE) IS
POSSIBLE (PRIMARILY SOUTH OF MASON- DIXON LINE WHERE MUCAPE
VALUES OF MARGINALLY HIGHER).
WINDS WILL TREND EASTERLY DURING THE DAY ON THURSDAY AS SLOW-
MOVING HIGH PRESSURE BUILDS INTO NEW ENGLAND, BRINGING COLD AIR
DAMMING SIGNATURE WITH COLD FRONT DRIFTING SOUTH ON THE LEEWARD
SIDE OF THE ALLEGHENIES. A LULL IN RAIN ACTIVITY IS EXPECTED
THURSDAY AFTERNOON THROUGH FRIDAY MORNING WITH THE COLD FRONT
SHIFTING SOUTH OF THE REGION, FOLLOWED BY INCREASING RAIN
CHANCES SOUTH-TO-NORTH OVER THE COURSE OF THE DAY ON FRIDAY AS
LOW PRESSURE MOVES ACROSS THE OHIO VALLEY & SLOWLY BRINGS MID-
ATLANTIC FRONTAL BOUNDARY NORTHWARD AS A WARM FRONT.
OUTLOOK...
FRI...RESTRICTIONS LIKELY WITH RAIN MOVING IN FROM SOUTH TO
NORTH, LASTING INTO FRI NIGHT.
SAT-SUN-MON...RESTRICTIONS LIKELY WITH RAIN.
CTP WATCHES/WARNINGS/ADVISORIES
NONE.
WHAT HAS CHANGED...COLBERT
KEY MESSAGES...LAMBERT/COLBERT
DISCUSSION...LAMBERT/COLBERT
AVIATION...TEARE
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