699
FXUS61 KCTP 211734
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
134 PM EDT MON SEP 21 2026
WHAT HAS CHANGED
* QPF SLIGHTLY LOWER FOR THE LAURELS, RISK OF FLOODING JUST TO
THE DRIER SIDE OF BORDERLINE.
KEY MESSAGES
1) PERIODS OF RAIN TODAY THROUGH WEDNESDAY. GREATEST AREAL
COVERAGE TONIGHT AND TUESDAY MORNING. WIDESPREAD FLOODING
UNLIKELY, ISOLATED MINOR FLOODING POSSIBLE.
2) TRENDING DRIER LATER IN THE WEEK AS A COASTAL STORM DEVELOPS
OFFSHORE.
DISCUSSION
KEY MESSAGE 1: PERIODS OF RAIN TODAY THROUGH WEDNESDAY.
GREATEST AREAL COVERAGE TONIGHT AND TUESDAY MORNING. WIDESPREAD
FLOODING UNLIKELY, ISOLATED MINOR FLOODING POSSIBLE.
CONVECTION CONTINUES TO SLIDE SOUTH OF THE CWA WITH MUCH
STABILITY OVERHEAD BOTH DUE TO THE CLOUDS I-80 SOUTHWARD, BUT
ALSO BECAUSE OF THE DRY AIR INFILTRATION FROM THE N. DEWPOINT
AT JST IS IN THE M40S AT 17Z. DEWPOINTS ARE CREEPING UP ACROSS
THE SOUTH-CENTRAL AND SOUTHEASTERN COUNTIES. BUT, JUST NEARING
60F NOW. THUS, IT WILL MAKE IT EASIER FOR RAIN TO GET TO THE
GROUND THERE. BUT, THEY ARE NOT THE MOST-RISKY LOCATIONS FOR
FLOODING. THE LAUREL HIGHLANDS, MAINLY OUR SW 4 COUNTIES, HAVE
THE LOWEST FFG/FFHS. BUT, MUCH OF THE STATISTICAL GUIDANCE KEEPS
RAIN INTENSITIES (QPF/1,3&6HR TIME FRAMES) ABOVE THOSE
THRESHOLDS FOR FLOODING TO OCCUR. THERE IS STILL A ~20% CHC FOR
RAINFALL INTENSITIES TO EXCEED FFG TONIGHT/TUES AM IN THE SW,
BUT WE'D NEED TO GET SOME INSTABILITY AND DEEP CONVECTION TO TAP
ALL THE 1.5" PWAT OVERHEAD. AFTER CONSULTATION WITH LWX, WE'RE
GOING TO CONTINUE TO HOLD OFF ON ANY FLOOD WATCHES. EXPECT SOME
MINOR (PONDING OF WATER ON ROADS/DITCHES, AND SMALL
CREEKS/STREAMS) FLOODING DUE TO THE EXTENDED DURATION OF THE
LIGHT TO MODERATE RAINFALL. DRY AIR CONTINUES TO BE SHOVED INTO
THE AREA FROM THE N THROUGH THE NEXT 48 HOURS. A TIGHT GRADIENT
OF PRECIP MAY OCCUR ALONG OR JUST NORTH OF I-80 THIS EVENING AS
A SLIGHT ENHANCEMENT TO THE RAIN IS EXPECTED WHILE A SHORT WAVE
TROUGH/MCV MOVES OVERHEAD W TO E ALONG I-80. THERE COULD BE A
LTG STRIKE/THUNDER RUMBLE HERE OR THERE, BUT IT WILL BE SPARSE.
WE'LL CONTINUE TO EVALUATE THE NEAR TERM GUIDANCE FOR HINTS OF
HEAVIER THAN CURRENTLY-EXPECTED PRECIP.
-------------------------------------------------------------
KEY MESSAGE 2: TRENDING DRIER LATER IN THE WEEK AS A COASTAL
STORM DEVELOPS OFFSHORE.
NORTHEAST FLOW WEDNESDAY INTO THURSDAY BETWEEN 1038 MB HIGH IN
QUEBEC AND A DEVELOPING COASTAL LOW WILL ADVECT IN DEWPOINTS IN
THE 40S AND PERHAPS EVEN THE 30S AT THE SFC WED-THU, WITH EVEN
DRIER AIR IN THE 500-850 MB LAYER. THIS SHOULD BRING AN END TO
THE RAINFALL FOR AT LEAST A COUPLE OF DAYS. THE NEXT FEATURE TO
MONITOR WILL BE THE COASTAL STORM, WHICH MAY MEANDER OFF THE NEW
ENGLAND AND MID ATLANTIC COAST INTO THE EARLY PART OF NEXT WEEK
WITH THIS BLOCKING HIGH TO ITS NORTH. SUCH BLOCKY PATTERNS
ARE NOTORIOUSLY DIFFICULT TO PREDICT WITH RESPECT TO SFC
FEATURES AND PRECIP POTENTIAL/PLACEMENT/TIMING. DEPENDING ON THE
SIZE OF THE COASTAL STORM AND HOW MUCH IT RETROGRADES, RAIN WILL
BE POSSIBLE IN AT LEAST EAST CENTRAL PA BETWEEN FRI AND EARLY
NEXT WEEK, BUT CONFIDENCE IS LOW. HIGHER CONFIDENCE IN WIND
GUSTS OF 15-25 MPH AND BELOW NORMAL TEMPS THROUGH THE END OF THE
WEEK.
AVIATION /18Z MONDAY THROUGH SATURDAY/
A SHIELD OF STRATIFORM RAIN IS APPROACHING FROM THE WEST AND
WILL SOON BEGIN IMPACTING THE WESTERN TERMINALS OF AOO, JST, AND
BFD BY 19Z. THE BRIEF IMPROVEMENT FROM THIS MORNING WILL NOT
LAST LONG, AS CEILINGS WILL GRADUALLY BEGIN TO DROP ONCE MORE AS
THE RAIN ARRIVES. MVFR CIGS WILL BEGIN TO OVERSPREAD THE REGION
ONCE MORE, AND IFR WILL BECOME PREVAILING AT MOST SITES BY 06Z
EXCEPT FOR MDT AND LNS WHICH WILL MOST LIKELY REMAIN LOW END
MVFR OVERNIGHT. THERE REMAINS A ~30% CHANCE FOR IFR AT THOSE
SITES, BUT CONFIDENCE IS OVERALL LOW. IMPROVEMENT INTO TUESDAY
LOOKS UNLIKELY WITH CONTINUED RAIN CHANCES AND THICK LOW CLOUDS
STICKING AROUND FOR MOST OF THE DAY.
OUTLOOK...
TUE-THU...RESTRICTIONS POSSIBLE FROM -SHRA/BR AND LOW CEILINGS,
MAINLY S.
FRI...VFR FAVORED AS A DEVELOPING COASTAL LOW LOOKS TO BRING SUBSIDENCE
OVERHEAD, THOUGH -RA AND LOWER CLOUD CEILINGS ASSOCIATED WITH THIS
SYSTEM MAY REACH OUR EASTERN TERMINALS.
CLIMATE
AS OF 5 PM, 1.05 INCHES OF RAIN FELL AT AOO (ALTOONA) PA TODAY.
THIS BROKE THE OLD RECORD OF 0.73 INCHES SET IN 1957.
CTP WATCHES/WARNINGS/ADVISORIES
NONE.
WHAT HAS CHANGED...DANGELO
KEY MESSAGES...DANGELO
DISCUSSION...DANGELO/COLBERT
AVIATION...BOWEN
CLIMATE...MARTIN
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