015
FXUS61 KCTP 012337
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
737 PM EDT TUE SEP 1 2026
WHAT HAS CHANGED
* 30% SEVERE WIND PROBABILITY ADDED TO NW PA FOR WEDNESDAY
KEY MESSAGES
1) LATE SUMMER SURGE OF HEAT AND HUMIDITY BRINGS MULTI-DAY
SEVERE THUNDERSTORM AND EXCESSIVE RAINFALL THREAT TO KICKOFF
SEPTEMBER
DISCUSSION
KEY MESSAGE 1:
MODERATE TO STRONG INSTABILITY (2-3000 J/KG MLCAPE) ANALYZED
OVER MOST OF CPA THIS AFTERNOON WITH VERY RICH TD'S IN THE
70-75F RANGE AND 30-40KT OF DEEP LAYER SHEAR INCREASING FROM SW
TO NE. SO IN OTHER WORDS, A CONVECTIVE ENVIRONMENT THAT IS
HIGHLY FAVORABLE TO SUPPORT ROBUST STORM ORGANIZATION. THAT
SAID, NEBULOUS LARGE SCALE FORCING CONTINUES TO FOSTER HIGH
UNCERTAINTY REGARDING OVERALL CONVECTIVE DEVELOPMENT AND
EVOLUTION THIS AFTERNOON/EVENING INTO TONIGHT. RECENT HIGH-
RESOLUTION GUIDANCE MAY BE CONVERGING ON ISOLATED TO WIDELY
SCATTERED THUNDERSTORMS DEVELOPING NEAR THE I80 CORRIDOR AND
ARCHING TO THE SOUTHEAST INTO THE LOWER SUSQ/DELAWARE VALLEY.
PERHAPS AFTER LATE NIGHT LULL, CAMS ARE SUGGESTING A CLUSTER OF
STORMS PROGRESSING SOUTHEAST FROM LAKE ERIE WEDNESDAY MORNING.
THIS COULD DELAY ONSET OF ADDITIONAL STORMS EXPECTED TO DEVELOP
LATER WEDNESDAY AFTERNOON INTO THE EVENING. THE ENVIRONMENT WILL
AGAIN BE SUPPORTIVE OF ORGANIZED STORM MODES INCLUDING
SUPERCELLS AND BOWING SEGMENTS WITH ELEVATED TORNADO POTENTIAL
WITHIN CORRIDOR OF LARGE SRH.
PREVIOUS DISCUSSION:
A SERIES OF MID LEVEL IMPULSES TRACKING EASTWARD ALONG THE
NORTHERN PERIPHERY OF AN EXPANSIVE 500MB RIDGE WILL INTERACT
WITH ANOMALOUS MOISTURE/INSTABILITY AND STRONG WNW FLOW ALOFT
TO PROMOTE A MULTI-DAY SEVERE STORM AND EXCESSIVE RAIN RISK
ACROSS PORTIONS OF CPA TODAY THROUGH THURSDAY.
A SURGE OF LATE SUMMER HEAT (MAX TEMPS 80-90F RANGE) WITH
DEWPOINTS IN UPPER 60S TO MID 70S WILL RESULT IN A VERY MOIST
BOUNDARY LAYER WITH IMPRESSIVE MLCAPE VALUES IN THE NEIGHBORHOOD
OF 1500-3000 J/KG GIVEN MID LEVEL LAPSE RATES AROUND 7 C/KM.
FORECAST SOUNDINGS ALSO SHOW ROBUST DEEP LAYER/EFFECTIVE SHEAR
VALUES AND APPRECIABLY CURVED LOW LEVEL HODOGRAPHS. AS SUCH, A
COUPLE OF SUPERCELLS WILL BE POSSIBLE.
FROM A LARGE SCALE LIFT PERSPECTIVE, RISING MOTION MAY BE AT
LEAST PARTIALLY SUPPRESSED BY THE RIGHT EXIT REGION OF AN UPPER
LEVEL JET MAX THROUGH MUCH OF TODAY UNTIL AT LEAST MID
AFTERNOON. CONVECTION INITIATION IS MORE LIKELY IN THE 4PM-9PM
TIME FRAME AS THE BOUNDARY LAYER RH INCREASES AND THE RIGHT
ENTRANCE REGION OF THE JET MAX APPROACHES.
INCREASING MUCAPE VALUES LATE TONIGHT THROUGH WED MORNING
SUGGEST STORMS/SEVERE RISK LIKELY WON'T BE TIED TO THE TYPICAL
DIURNAL CYCLE. ANY PREEXISTING MCS UPSTREAM COULD BE MAINTAINED
BY THE UNSTABLE ATMOSPHERE WITH US WEDNESDAY MORNING. HIRES
MODEL GUIDANCE ALSO SHOWS AN EASTERLY FLOW ACROSS OUR EASTERN
ZONES ASSOCIATED WITH A BACK DOOR COLD FRONT. ALONG THAT
BOUNDARY, MODELS DEPICT VERY LARGE HODOGRAPHS ASSOCIATED WITH A
STRONGLY VEERED WIND PROFILE, WITH 0-3 KM SRH ON THE ORDER OF
350 M2/S2 AND 0-3KM WIND SHEAR APPROACHING 40 KTS. IF SUPERCELLS
CAN RIDE SOUTHEASTWARD ON THE UNSTABLE SIDE OF THE BOUNDARY AND
INGEST THIS HIGHLY SHEARED INFLOW, A COUPLE STRONGER TORNADOES
CAN NOT BE RULED OUT WED AFTERNOON INTO WED EVENING.
THE SEVERE RISK WILL BE FOCUSED MORE ACROSS THE SOUTHERN TIER OF
CENTRAL PA BY THURSDAY, AND SOUTH OF THE PA-MD BORDER ON FRIDAY.
AN UPPER TROUGH PASSAGE SUGGESTS SOME LINGERING SHOWER ACTIVITY
INTO THE WEEKEND, OTHERWISE IT LOOKS MOSTLY DRY.
THE LATE SUMMER HEAT IS FORECAST TO PEAK TODAY AND WEDNESDAY
WITH VERY WARM NIGHTS +10-20F ABOVE THE HISTORICAL AVERAGE AND
MAX HEAT INDEX VALUES JUST SHORT OF HEAT ADVISORY CRITERIA
(100F). THE EXCEPTION WILL BE ACROSS THE EASTERN ZONES WED WHEN
THE BACK DOOR COLD FRONT COULD HOLD MAX TS DOWN A FEW TO SEVERAL
DEGREES. THE UPPER RIDGE IS FORECAST TO RETROGRADE BY THE END
OF THE WEEK WHICH ALLOWS FOR INCREASED TROUGHING AND A RETURN TO
MORE SEASONAL TEMPERATURES.
AVIATION /00Z WEDNESDAY THROUGH SUNDAY/
WIDESPREAD CONVECTION IS CONTINUING TO IMPACT AIRFIELDS ACROSS
CENTRAL PA. THESE THUNDERSTORMS HAVE A HISTORY OF PRODUCING
FREQUENT LIGHTNING, GUSTS OF 40KTS OR GREATER, AND HEAVY
DOWNPOURS. THESE STORMS WILL CONTINUE TO POSE A THREAT TO THE
AREA THROUGH 06Z TONIGHT. THE ENVIRONMENT IS STILL PROMOTIVE OF
STRONG UPDRAFTS AND HEAVY RAIN. EXPECT IFR COUNTDOWNS IF A
STORM MOVES DIRECTLY OVER AN AIRFIELD.
EVENING CONVECTION WILL WANE OVERNIGHT, GIVING WAY TO THE
POTENTIAL FOR OVERNIGHT FOG AND LOW STRATUS ACROSS THE REGION AS
WINDS DIMINISH AND MAINLY MID/HIGH LEVEL CLOUDS REMAIN. FARTHER
EAST (KMDT/KLNS), A BACKDOOR COLD FRONT MOVING IN OVERNIGHT
WILL RESULT IN WINDS TRENDING EASTERLY & CEILINGS LOWERING TO
MVFR-IFR. AREAS OF MORNING FOG AND LOW STRATUS WILL GRADUALLY
MIX OUT TO VFR THROUGH WEDNESDAY MORNING AND THE EARLY AFTERNOON
HOURS, WITH SLOWER IMPROVEMENTS EXPECTED AT KMDT/KLNS IN THE
VICINITY OF THE FRONT. OTHERWISE, PROB30 GROUPS FOR
-TSRA WERE ADDED TO MOST TERMINALS (EXCEPTION BEING KIPT AT THIS
TIME) GIVEN A SIGNAL ON CAMS FOR A POTENTIAL LINE OR CLUSTER OF
SHOWERS/STORMS WHICH MAY MOVE E/SEWARD ACROSS THE CWA, THOUGH
TIMING/CERTAINTY REMAINS LOW GIVEN ITS DEPENDENCY ON UPSTREAM
EVOLUTION.
OUTLOOK...
WED-FRI...SCATTERED SHRA/TSRA WITH BRIEF RESTRICTIONS POSSIBLE;
MORNING FOG POSSIBLE.
SAT...SHRA/TSRA TRENDING LESS LIKELY AS COLD FRONT MOVES
SOUTHWARD ACROSS THE COMMONWEALTH; MORNING FOG POSSIBLE.
SUN...VFR FAVORED; MORNING FOG POSSIBLE.
CTP WATCHES/WARNINGS/ADVISORIES
NONE.
WHAT HAS CHANGED...STEINBUGL
KEY MESSAGES...STEINBUGL
DISCUSSION...STEINBUGL/COLBERT
AVIATION...BOWEN/TEARE
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