144
FXUS61 KCTP 210929
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
529 AM EDT MON SEP 21 2026
WHAT HAS CHANGED
* TRENDING DRIER LATE WEEK
KEY MESSAGES
1) PERIODS OF RAIN TODAY THROUGH WEDNESDAY. GREATEST AREAL
COVERAGE TONIGHT.
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.
WHAT REMAINS OF AN MCV THAT DROPPED 3-5 INCHES OF RAIN IN OH/WV
WILL MOVE INTO THE LAUREL HIGHLANDS THIS MORNING AND SPREAD
NORTHWARD TOWARDS I-80 THROUGH THE DAY. GIVEN THE LACK OF
INSTABILITY IN CENTRAL PA, RAINFALL RATES WILL BE ON THE LIGHT
SIDE, GENERALLY UP TO 0.25 INCH/HR. WE EXPECT AN UPTICK IN AREAL
COVERAGE OF THE RAINFALL TONIGHT AS THE PRESSURE GRADIENT
BETWEEN A SUBTLE LOW PRESSURE SYSTEM MOVING INTO OHIO AND A
BUILDING HIGH TO OUR NORTH RESULTS IN INCREASING UPSLOPE SE
FLOW AT 850 MB. THIS WILL BE COUPLED WITH ISENTROPIC ASCENT AND
SOME FRONTOGENESIS IN THE 800-600 MB LAYER. EVEN DURING MAX
AREAL COVERAGE, RAIN MAY STRUGGLE TO GET TO THE PA-NY BORDER DUE
TO A SHARP CUTOFF IN MOISTURE (PW VALUES NEAR 1.50" ALONG I-80
VS 0.60" AT THE PA-NY BORDER AT MIDNIGHT TONIGHT). PERIODS OF
RAIN WILL CONTINUE THROUGH MUCH OF TUESDAY BEFORE THE DRY AIR TO
OUR NORTH SURGES SOUTHWESTWARD LATE TUESDAY NIGHT INTO
WEDNESDAY. HIGHS ON TUESDAY WILL BE IN THE 50S TO LOW 60S,
PERHAPS THE COOLEST AFTERNOON SINCE LATE MAY. LINGERING SHOWERS
ON WED WILL LIKELY BE CONFINED TO THE LAURELS. HIGHEST FORECAST
QPF IN THE MONDAY- WEDNESDAY TIME FRAME IS 1.00-1.50 INCH IN THE
LAUREL HIGHLANDS, WITH LOCALLY HIGHER AMOUNTS OF 2.00 INCHES
POSSIBLE IF SOME ELEVATED INSTABILITY MOVES INTO THE REGION.
-------------------------------------------------------------
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 /07Z MONDAY THROUGH FRIDAY/
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...COLBERT
KEY MESSAGES...LAMBERT/COLBERT
DISCUSSION...LAMBERT/DANGELO/COLBERT
AVIATION...TEARE
CLIMATE...MARTIN
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