497
FXUS61 KCTP 201713
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
113 PM EDT WED MAY 20 2026
WHAT HAS CHANGED
* RISK FOR SEVERE STORMS OVER THE SOUTHERN HALF OF PENNSYLVANIA
HAS INCREASED WITH A SEVERE THUNDERSTORM WATCH IN EFFECT
UNTIL 00Z.
* REITERATING BEARISH TREND FOR MAX TEMPS FRIDAY AND SATURDAY
KEY MESSAGES
1) SCATTERED STORMS WITH ISOLATED SEVERE WIND GUSTS AND HAIL
WILL BE POSSIBLE OVER THE SOUTHERN TIER OF CPA THIS
AFTERNOON/EVENING
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:
SCATTERED STORMS WITH ISOLATED SEVERE WIND GUSTS AND HAIL WILL
BE POSSIBLE OVER THE SOUTHERN TIER OF CPA THIS AFTERNOON/EVENING
THE SURFACE COLD FRONT CURRENTLY OVER THE NORTHERN TIER OF
PENNSYLVANIA WILL ADVANCE SOUTH AND EAST ACROSS CPA TODAY
BEFORE STALLING OUT TO THE SOUTH OF THE MD LINE TONIGHT INTO
THURSDAY. CONVECTIVE INITIATION IS ALREADY BEING OBSERVED OVER
SOUTHERN PA ALONG THE MD/PA BOARDER AHEAD OF THE FRONT. MOIST
AND UNSTABLE AIR AHEAD OF THE COLD FRONT COMBINED WITH
INCREASING LOW LEVEL CONVERGENCE WILL LEAD TO ADDITIONAL
THUNDERSTORM DEVELOPMENT AS WE MOVE THROUGH THE AFTERNOON
ACROSS THE SOUTHEAST 1/2 TO 1/3 OF THE FORECAST AREA. THE
ATMOSPHERE IS CONTINUING TO DESTABLIZE WITH CAPE BETWEEN 1500
AND 2000 J/KG OVER THE LOWER SUSQUEHANNA VALLEY AND SEVEN
MOUNTAINS. STEEP LOW LEVEL LAPS RATES ALONG WITH SUFFICIENT
0-6KM SHEAR AND PREVIOUSLY MENTIONED INSTABILITY SHOULD SUPPORT
A FEW STRONGER STORMS WITH POTENTIAL FOR SEVERE WIND GUSTS AND
ISOLATED HAIL. SPC HAS UPGRADED PORTIONS OF OUR CWA TO A D1
SLIGHT RISK OVER THE SOUTH, AND A SEVERE THUNDERSTORM WATCH
IS NOW IN EFFECT UNTIL 00Z TONIGHT. HREF/REFS ALSO INDICATE
POTENTIAL FOR LOCALLY HEAVY RAINFALL >1" NEAR THE MD LINE AS
SHOWERS AND STORMS LIKELY PERSIST THROUGH THE EVENING INTO THE
OVERNIGHT PERIOD ACROSS THE SOUTHERN TIER OF CPA.
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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 /18Z WEDNESDAY THROUGH MONDAY/
THE MCS ACROSS WESTERN PA THIS EVENING HAS LARGELY DECAYED,
WITH THE MAIN FLIGHT IMPACTS BEING BRIEF WESTERLY WIND GUSTS
AROUND 20-25 KTS & SPOTTY SHOWERS FOR THE CENTRAL MOUNTAINS
(PRIMARILY KAOO/KUNV) THROUGH 07-08Z WEDNESDAY. CEILINGS ARE
EXPECTED TO LOWER NW-SE AS A COLD FRONT APPROACHES, WITH HIGHEST
CONFIDENCE IN RESTRICTIONS AT KBFD/KJST. DOWNSLOPING W/NW WINDS
ARE EXPECTED TO LIMIT THE EXTENT OF CEILING RESTRICTIONS TO
MVFR ELSEWHERE, WITH IMPROVEMENTS TO VFR AFTER THE FRONT PASSES
DURING THE EVENING.
THERE IS HIGH (~70-80%) CONFIDENCE ON SHRA/TSRA REFORMING
DURING THE LATE MORNING TO EARLY AFTERNOON HOURS (MAINLY AFTER
16Z) WITH INCREASING COVERAGE INTO THE EVENING HOURS. CURRENT
SHRA MENTIONS HAVE BEEN INCLUDED AT ALL TERMINALS BASED ON
RECENT FORECAST/HREF/GLAMP MODEL GUIDANCE WITH MOST UNCERTAINTY
WITH RESPECT TO TIMING. IN TERMS OF TSRA COVERAGE, THE HIGHEST
POTENTIAL AT THIS TIME IS OUTLINED ACROSS SE PA (MDT/LNS) WHERE
HREF HIGHLIGHTS SBCAPE UPWARDS OF AROUND 1000 J/KG, THOUGH
SBCAPE AROUND 500-1000 J/KG MAY SUPPORT TSRA ACROSS
KJST/KAOO/KUNV/KIPT AS WELL, WITH PROB30S ADDED TO ADDRESS THIS
POSSIBILITY. LOCALLY GUSTY WINDS ARE POSSIBLE AS WELL GIVEN LOW-
LEVEL LAPSE RATES AROUND 8-9 C/KM IN THE AFTERNOON, THOUGH
CONFIDENCE IS LOW REGARDING THE EXTENT AND STRENGTH OF WIND
GUSTS.
WINDS SHIFT NORTHERLY BEHIND THE FRONTAL PASSAGE THIS EVENING,
WITH ANAFRONTAL RAIN DEVELOPING ACROSS SOUTH/EAST PA DURING THE
EVENING/OVERNIGHT HOURS.
OUTLOOK...
THU...LINGERING SHOWERS ACROSS S PA, RESTRICTIONS POSSIBLE.
FRI...RESTRICTIONS LIKELY WITH RAIN MOVING IN FROM SOUTH TO
NORTH, LASTING INTO FRI NIGHT.
SAT-SUN...RESTRICTIONS LIKELY WITH RAIN.
CTP WATCHES/WARNINGS/ADVISORIES
NONE.
WHAT HAS CHANGED...STEINBUGL/BOWEN
KEY MESSAGES...STEINBUGL/BOWEN
DISCUSSION...STEINBUGL/BOWEN
AVIATION...BEATY/TEARE
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