894
FXUS61 KCTP 201038
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
638 AM EDT SUN SEP 20 2026
WHAT HAS CHANGED
* TWEAKS TO RAINFALL AMOUNTS; INCREASED POPS ON MONDAY
KEY MESSAGES
1) PERIODS OF RAIN TODAY, PERHAPS A FEW THUNDERSTORMS IN THE
SOUTH.
2) RAINY POTENTIAL CONTINUES INTO MUCH OF THIS WEEK, ALTHOUGH
UNCERTAINTY REMAINS IN THE DETAILS. ON THE COOL SIDE AS WELL.
DISCUSSION
KEY MESSAGE 1: PERIODS OF RAIN TODAY, PERHAPS A FEW
THUNDERSTORMS IN THE SOUTH.
A WEAK AREA OF SFC LOW PRESSURE NEAR THE PA-OH BORDER WILL PUSH
EAST THROUGH THE DAY TODAY, RESULTING IN PERIODS OF RAINFALL. A
THUNDERSTORM OR TWO CAN NOT BE RULED OUT ACROSS THE SOUTH. RAIN
WILL BE STEADIEST AND HEAVIEST IN THE MORNING, AND TREND
LIGHTER AND MORE SCATTERED THROUGH THE DAY. ADDITIONAL RAINFALL
AMOUNTS GENERALLY 0.10 - 0.50" WITH LOCALIZED HIGHER AMTS
POSSIBLE IN REPEAT HEAVIER RAINFALL.
-------------------------------------------------------------
KEY MESSAGE 2: RAINY POTENTIAL CONTINUES INTO MUCH OF THIS
WEEK, ALTHOUGH UNCERTAINTY REMAINS IN THE DETAILS. ON THE COOL
SIDE AS WELL.
A LARGE HIGH OVER QUEBEC WILL PUSH SOUTHWARD ON MONDAY, GIVING
THE AREA A CHANCE FOR DRY CONDITIONS, ESPECIALLY ACROSS THE
NORTHERN TIER. HOWEVER, SEVERAL CAMS ARE NOW INDICATING A BATCH
OF LIGHT RAIN WILL MOVE INTO THE LAURELS FROM THE WEST. WINDS
WILL BE FROM THE E TO NE ON MONDAY, GIVING US OUR FIRST TASTE OF
COLD AIR DAMMING WITH HIGHS ONLY IN THE 60S TO NEAR 70.
HEADING INTO TUESDAY AND WEDNESDAY, THE WEDGE OF COLDER AND
MORE STABLE AIR WILL DEEPEN OVER THE AREA THANKS TO BUILDING
HIGH PRESSURE TO THE NORTH. AN UPPER TROUGH APPROACHING FROM THE
WEST WILL PUSH WARMER AIR UP AND OVER THIS COLD WEDGE, LIKELY
RESULTING IN RAIN. IN THIS COLD AIR DAMMING, HIGH TEMPS ARE
EXPECTED TO BE IN THE 50S TO NEAR 60. AT THIS TIME, THE HIGHEST
POPS ARE OVER THE WEST AND SOUTH, GIVEN AN INVERTED TROUGH.
THURSDAY AND FRIDAY MAY END UP DRY, AS A COASTAL STORM DEVELOPS
ALONG THE ATLANTIC COAST AND WRAPS DRY AIR AROUND THE WESTERN
SIDE. HOWEVER, MODEL GUIDANCE IS STILL SHOWING LARGE SPREAD IN
THE EVOLUTION OF A COASTAL SYSTEM REGARDING ITS FORWARD SPEED
AND LOCATION. SLOW MOVING REX BLOCK PATTERNS CAN BE PARTICULARLY
DIFFICULT TO FORECAST.
AVIATION /10Z SUNDAY THROUGH THURSDAY/
RAIN WILL CONTINUE OVERSPREADING CENTRAL PENNSYLVANIA THROUGH
THIS MORNING AS A LOW PRESSURE SYSTEM BEGINS TREKKING ACROSS THE
AREA. PERIODS OF +RA WITH IFR VISIBILITIES ARE POSSIBLE AS A
PLUME OF RICH MOISTURE (PWATS AROUND 2") ACCOMPANIES THIS
SYSTEM, WITH THE NORTHERN TIER (KBFD) BEING LESS LIKELY TO SEE
+RA BEING ON THE PERIPHERY OF GREATEST MOISTURE, THOUGH LOW
STRATUS WILL LIKELY BRING IFR-LIFR RESTRICTIONS TO KBFD
NONETHELESS.
A PERIOD OF BORDERLINE LLWS IS ALSO EXPECTED THROUGH THIS
MORNING, MAINLY SOUTH AND EAST OF KBFD, AS A LLJ DEVELOPS (925
MB WINDS TO AROUND 35 KTS FROM THE S/SSE).
TSRA CANNOT BE RULED OUT ACROSS OUR SOUTHERN TIER OF COUNTIES
(KJST/KAOO/KMDT/KLNS) THROUGH SUNDAY AFTERNOON AS MUCAPE
APPROACHES 1000 J/KG. HOWEVER, TALL/SKINNY CAPE PROFILE AND DEEP
WARM CLOUD LAYER (10-15 KFT BETWEEN MULCL AND FREEZING LEVEL)
WILL FAVOR RAINFALL EFFICIENCY OVER LIGHTNING PRODUCTION,
ULTIMATELY PRECLUDING TSRA MENTIONS IN THE TAFS.
AS THE SYSTEM PROGRESSES TOWARD THE COAST LATER THIS EVENING,
SURFACE WINDS WILL SHIFT NORTHERLY AND ADVECT DRY, CONTINENTAL
AIR ACROSS MUCH OF THE COMMONWEALTH. THIS WILL SCOUR OUT LOW
CLOUD CEILINGS AND RESULT IN A NORTH-TO-SOUTH VFR TREND SUNDAY
NIGHT. THE MAIN UNCERTAINTY WILL BE TIMING OF IMPROVEMENTS,
ESPECIALLY ACROSS SE PA (KMDT/KLNS) WHERE EASTERLY COMPONENT TO
THE WIND MAY SLOW IMPROVEMENTS DUE TO MARINE INFLUENCE, THOUGH
GUIDANCE NEVERTHELESS FAVORS VFR ACROSS ALL FORECAST TERMINALS
BY MONDAY MORNING.
OUTLOOK...
TUE-THU...RESTRICTIONS POSSIBLE FROM -SHRA/BR AND LOW CEILINGS,
MAINLY S.
CTP WATCHES/WARNINGS/ADVISORIES
NONE.
WHAT HAS CHANGED...COLBERT
KEY MESSAGES...COLBERT/MARTIN
DISCUSSION...COLBERT/MARTIN
AVIATION...TEARE
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