761
FXUS61 KCTP 211724
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
124 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 BECASUE OF THE DRY AIR INFILRATION 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/
N/NE'ERLY SURFACE WINDS WILL GUIDE DRIER/CONTINENTAL AIR
SOUTHWARD ACROSS MUCH OF THE COMMONWEALTH THROUGH MONDAY
MORNING, WITH DEWPOINTS TRENDING DOWN INTO THE 50S AREAWIDE.
ALTHOUGH CONDITIONS WILL TREND DRIER NEAR THE SURFACE, LINGERING
MOISTURE ALOFT WILL BLANKET MUCH OF THE AREA IN MID/HIGH CLOUDS
(VFR), WITH SUB-VFR CEILINGS FAVORED THROUGHOUT THE DAY ALONG
THE ALLEGHENY RIDGE TERRAIN (MAINLY MVFR FOR KJST/KAOO, AND
PERHAPS IFR AT KJST). MOREOVER, PERIODIC MVFR IS POSSIBLE
THROUGH MONDAY MORNING AT KMDT/KLNS DOWNWIND OF THE ATLANTIC
OCEAN.
ANOTHER ROUND OF RAIN WILL GRADUALLY OVERSPREAD THE SOUTHERN
2/3RDS OF THE COMMONWEALTH THROUGHOUT THE DAY ON MONDAY AS A LOW
PRESSURE DRIFTS ACROSS THE MID-ATLANTIC, WITH A STOUT 1030-1040
MB HIGH PRESSURE OVER SOUTHERN CANADA LOOKING TO KEEP THE
NORTHERN TIER (KBFD) MAINLY DRY. SURFACE WINDS WILL TREND
E/NE'ERLY AT THE SURFACE MONDAY NIGHT AND BRING MARINE AIR BACK
INTO MUCH OF OUR AREA, WITH MID-LEVEL (850 MB) SE'ERLY FLOW ALSO
HELPING TO SLOWLY BRING MOISTURE BACK NORTH. THIS LOOKS TO
FAVOR A TREND TOWARDS MVFR-IFR ACROSS ALL TERMINALS MONDAY NIGHT
AS MOISTURE REBOUNDS.
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...TEARE
CLIMATE...MARTIN
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