Area Forecast Discussion

WHAT HAS CHANGED

* No significant changes

KEY MESSAGES

1) Widespread damaging frost/freeze threat across all of central Pennsylvania tonight into Tuesday morning.

2) Dry conditions Tuesday may result in a marginal increase in the risk of wildfire spread.

3) Trending warmer through the week with only occasional chances for precipitation.

DISCUSSION

KEY MESSAGE 1: A second round of a widespread damaging frost/freeze will occur across all of Central Pennsylvania tonight into Tuesday morning.

A near certainty of a widespread freeze tonight into Tues morning as a result of a large area of sfc high pressure drifting overhead and producing optimal conditions for radiational cooling of the ground via clear skies, anomalously low PWAT air of just 0.2-0.3 of an inch, light wind, and 8H temps in the -5 to -10C range overhead.

Lows will range from the upper teens in the typical cold spots across the northwest mountains to near 30 in the Lower Susquehanna Valley.

The growing season has been activated for all but four zones (Tioga/Sullivan/Potter Counties and Northern Lycoming County) across central Pennsylvania as of 04/18/2026, see the latest Public Info Statement for those details. A Freeze Warning is in effect for all the zones with active growing season.

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KEY MESSAGE 2: Dry conditions through Tuesday may result in a marginal increase in the risk of wildfire spread.

Factoring in slightly warmer temperatures on Tuesday afternoon (highs in the 50s to low 60s) as well as drying fuels, there may be a slight uptick in wildfire risk compared to Monday. However, the wind will be comparatively lighter on Tuesday. All things considered, the threat for wildfire spread is still low to moderate. The recent greenup also helps the situation.

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KEY MESSAGE 3: Trending warmer through the week with only occasional chances for precipitation.

High pressure will be along the Delmarva Coast by Tuesday afternoon. West or southwesterly flow rotating around the north side of surface high pressure will usher in increasingly mild temperatures. Friday is progged to be the warmest day as temperatures rise to near 80F in the southwest corner of our forecast area and into the middle 60s F in the northeast.

A fairly moisture-starved weak cold front will drift across the region Tuesday night into Wednesday, bringing plenty of clouds and scattered rain showers. There is not much upper level support for thunderstorms at this point, but a few rumbles of thunder cannot be ruled out - mainly across the Laurel Highlands and southern tier. Rainfall will generally range from T-0.25"and Wednesday will certainly not be a washout.

Thursday looks rainfree as high pressure again takes over. The next considerable chance for rain returns Friday into Saturday, though there are notable timing differences between the faster GFS and slower EC members.

AVIATION /00Z TUESDAY THROUGH SATURDAY/

High pressure building in across the airspace will return widespread VFR conditions (mainly SKC, SCT100 northwest after 09Z Tuesday) and decrease winds later tonight into early Tuesday. Milder air aloft pushing in from the west will transport a thick layer of non-precipitating, mid-level clouds very late tonight (West) and by the morning/afternoon hours Tuesday across the far east. Showers will be very unlikely through the end of the TAF package (HREF probabilities at 0% through 00Z Wednesday), with scattered showers expected to west to east thereafter.

Outlook...

Tue night-Wed...Scattered rain showers/isolated t-storm possible.

Thu...VFR. Partly cloudy and rainfree.

Fri-Sat...Increasing odds for rain showers Friday into Sat. Periods of IFR CIGS and MVFR VSBYS...with the lowest conditions Friday night and Sat morning.

CLIMATE

A very warm March and April has resulted in a record number of 80 degree days so far this year at several climate sites.

Altoona recorded a high temperature of 80F on Saturday. It was the 7th 80+ degree day so far this year. Year to date, that shatters the previous record of 4 days with Max T >= 80F at the site, which occurred in 1976, 1977, and 1998.

March 22: 83F (daily record) April 04: 80F (daily record) April 13: 80F April 14: 81F April 15: 84F (daily record) April 16: 85F April 18: 80F

SITE YTD IN 2026 PREVIOUS RECORD Altoona 7 4 (1976, 1977, 1998) Harrisburg 8 6 (1945) State College 6 6 (2010)

Williamsport has recorded 5 day with MaxT >= 80F, which falls shy of the existing record of 7 such days through April 18, 2010.

CTP WATCHES / WARNINGS / ADVISORIES

Freeze Warning from midnight tonight to 11 AM EDT Tuesday for PAZ004-005-010>012-017-018. Freeze Warning from midnight tonight to 9 AM EDT Tuesday for PAZ019-024>028-033>036-045-046-049>053-056>059-063>066.