710
FXUS61 KCTP 210527
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
127 AM EDT THU MAY 21 2026
WHAT HAS CHANGED
* BOOSTED RAINFALL AMOUNTS TO MAXES OVER 0.50 INCH ACROSS THE SE
1/4 OR SO OF THE CWA VERY LATE TONIGHT THROUGH THU AFTERNOON.
* REITERATING BEARISH TREND FOR MAX TEMPS FRIDAY AND SATURDAY.
KEY MESSAGES
1) PERIODS OF LIGHT RAIN/SHOWERS OVER CENTRAL AND SOUTHERN PA
TONIGHT/THURSDAY JUST TO THE NORTH OF A SLOW MOVING COLD FRONT.
2) MAJOR COOLDOWN TO CLOSE OUT THE WEEK AND START MEMORIAL DAY
WEEKEND WITH WIDESPREAD SOAKING RAINFALL OVER 1 INCH FRIDAY AND
SATURDAY.
DISCUSSION
KEY MESSAGE 1: PERIODS OF LIGHT RAIN/SHOWERS OVER CENTRAL AND
SOUTHERN PA TONIGHT JUST TO THE NORTH OF A SLOW MOVING COLD
FRONT.
SURFACE COLD FRONT WAS PUSH SOUTH ACROSS DE AND CENTRAL VA THIS
EVENING AND WILL STALL OUT FOR A PERIOD LATE TONIGHT THROUGH
THURSDAY AS ONE OR TWO WAVES OF LOW PRESSURE MOVE NE ALONG IT.
THE MOST NOTABLE WAVE IS SEEN QUITE WELL VIA THE
BACKING/STRENGTHENING OF THE FLOW AND ISENTROPIC ASCENT WITHIN
THE 300-305K THETA CHANNEL (ABOUT 5-9 KFT AGL) ACROSS VA AND FAR
SOUTHERN PA LATE TONIGHT THROUGH THE LATE MORNING HOURS ACROSS
THE CENTRAL APPALACHIANS.
THIS WILL HELP TO EXPAND A SHIELD OF STEADY LIGHT (TO BRIEFLY
MODERATE) RAIN ACROSS THE CWA WITH EVENTUAL CONSOLIDATION OF THE
RAIN OVER THE SE THIRD OF THE STATE THURSDAY MORNING.
SREF (AND GEFS PROB OF GRTN 0.50"/12 HOURS) SHOWS THE STEADIEST
AND HEAVIEST RAIN OVER SCENT PA ACROSS THE REGION - BOUNDED BY
1-99 (WEST), RT 322 (NORTH) AND RT 15 (EAST).
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 THE MID TO
LATE AFTERNOON.
TEMPS WILL COOL OFF SIGNIFICANTLY WITH EARLY MORNING LOWS
RANGING FROM THE LOW TO MID 40S ACROSS THE NORTHERN MOUNTAINS TO
BETWEEN 50-55F THROUGHOUT THE CENTRAL AND SOUTHERN VALLEYS.
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KEY MESSAGE 2:
MAJOR COOLDOWN TO CLOSE OUT THE WEEK AND START MEMORIAL DAY
WEEKEND WITH WIDESPREAD SOAKING RAINFALL OVER 1 INCH FRIDAY AND
SATURDAY.
RELIEF FROM THE EARLY SEASON HEAT WAVE ARRIVES IN EARNEST ON
THURSDAY WITH MAX TEMPS 20-30 DEGREES LOWER VS. WEDNESDAY ACROSS
THE LSV. STRONG HIGH PRESSURE SLIDES FROM THE LOWER GREAT LAKES
TO OFF THE NEW ENGLAND COAST TO CLOSE OUT THE WEEK. MODEL DATA
SHOWS THE HIGH CHANNELING SOUTHWARD DOWN THE EAST-SIDE OF THE
APPALACHIANS, SETTING UP A COLD AIR DAMMING (CAD) EVENT HEADING
INTO MEMORIAL DAY WEEKEND.
INCREASING CAD SIGNAL STRENGTH ENHANCED BY MODERATELY STRONG
EAST/SOUTHEAST LOW LEVEL FLOW AND SOAKING RAINFALL HAS PROMPTED
A CONSIDERABLE BEARISH/LOWER ADJUSTMENT TO MAX TEMPS FRIDAY AND
SATURDAY. IN FACT, HIGHS ON SATURDAY ARE NEAR DAILY RECORD LOWS
AT SEVERAL LOCATIONS (MINI/MAX). 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 MODERATE
WARMER WITH STEADIER RAIN GIVING WAY TO MORE SHOWERY CONDITIONS
FOR THE UNOFFICIAL START OF SUMMER.
NBM/WPC QPF CONTINUES TO SHOW WIDESPREAD 48HR RAINFALL TOTALS
IN THE 1-2 INCH RANGE FRIDAY-SATURDAY. THE COOL/STABLE AIR WILL
CAP RATES WITH LONGER DURATION HELPING TO MITIGATE FLOODING
RISK IN MOST AREAS. THE FORECAST RAINFALL IS MUCH NEEDED OVER
THE FAR SOUTH CENTRAL/SOUTHEASTERN COUNTIES WHO REMAIN UNDER
D1-D2 MODERATE TO SEVERE DROUGHT CONDITIONS.
AVIATION /06Z 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...LAMBERT
KEY MESSAGES...LAMBERT
DISCUSSION...LAMBERT/STEINBUGL/BOWEN
AVIATION...TEARE
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