textproduct: State College

WHAT HAS CHANGED

* Included more timing/threat assessment for thunderstorm potential this afternoon/evening. * Added mentions of flash flooding this evening and into Sunday morning across portions of northern Pennsylvania. * Brief mention of fire weather concerns through the middle of the work week.

KEY MESSAGES

1) Cold front brings showers and thunderstorms to central Pennsylvania Saturday afternoon into Sunday morning. Some storms could be severe across western Pennsylvania late this afternoon and into the evening, flash flooding possible across northern Pennsylvania.

2) Frost/freeze potential across northern/western Pennsylvania Sunday night into Monday morning. Widespread damaging frost/freeze threat extends across all of central Pennsylvania Monday night into Tuesday morning.

3) Marginal fire weather concerns this afternoon ahead of the cold front. Drier conditions early this week into the middle of the week will fuel multiple days of marginal fire weather risk.

DISCUSSION

KEY MESSAGE 1: Cold front brings showers and thunderstorms to central Pennsylvania Saturday afternoon into Sunday morning. Some storms could be severe across western Pennsylvania late this afternoon and into the evening, flash flooding possible across northern Pennsylvania.

A line of showers with isolated thunderstorms along a cold front is currently stationed across eastern Michigan extending southwestward towards the St. Louis metro area. Current radar trends outline gradually weakening of embedded thunderstorms with potentially a slight decrease in overall coverage of showers as of 8Z/4A EDT due to much more stable air in place across the region. More recent hi-res model guidance suggests that the main leading line will become more broken in nature by sunrise and continue to fizzle out as it approaches western OH/KY. Ahead of this front, daytime heating will allow for some destabilization, with recent guidance guidance indicating a narrow corridor of SBCAPE between 500-1000 J/kg. At this time, probably looking towards closer to 500-700 J/kg with highest model solutions outlining slightly less in the way of cloud cover; however, also want to outline favorable shear in place for the severe threat this afternoon/evening. The western half of Pennsylvania looks to be at most risk for some damaging wind threat this afternoon/evening with favorable shear and slightly better chances at getting some higher-end instability values mentioned earlier. In this area, cannot rule out an isolated spin-up tornado; however LCLs remain unfavorable for this risk. Further east, shear will remain favorable; however, stable air is more likely to be in place, especially closer to sunset in this locations. All this jives fairly well with SPC's Slight Risk (level 2/5) for severe weather across western Pennsylvania with a Marginal Risk (level 1/2) extending slightly east of this area. The best timing based on a consensus of hi-res model guidance looks to be in the 3PM to 7PM timeframe; however, cannot rule out storms an hour or two on either side of that timeframe today.

Flash flood risk is non-zero later this evening and into the Sunday morning hours. Ample PWATs in place between 1.00-1.50" are well-above average climatologically, pushing closer to the 90-95th percentile in some locations. Looking at forecast HREF PWATs at ILN at 12Z would be pushing closer to ~1.25", where sounding climatology would outline this above the 90th percentile for a 12Z sounding at ILN. That, on top of multiple rounds of showers could lead to isolated instances of flash flooding across the fairly wet soils on northern Pennsylvania this evening. FFGs in this area are super low, even at six-hour time horizons with most of the northern tier looking at less than an inch in six hours for some flooding concerns. Localized downpours in thunderstorms in this region would make this fairly easy to be accomplished across the northern tier, thus there is no surprise that the Weather Prediction Center has outlined a Marginal Risk (level 1/4) of Excessive Rainfall across much of the northern tier of our counties.

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KEY MESSAGE 2: Frost/freeze potential across northern/western Pennsylvania Sunday night into Monday morning. Widespread damaging frost/freeze threat extends across all of central Pennsylvania Monday night into Tuesday morning.

Cold temperatures in the wake of the cold front are virtually certain to bring widespread frost/freeze concerns for all of central Pennsylvania for the second half of the weekend and into the beginning stages of the work week. Cold front will be halfway through the area on Sunday night, which will allow for much cooler temperatures across the northwestern half of the Commonwealth Sunday night into Monday morning. Newest forecast has freeze concerns for much of northern and western halves of the area by Monday morning. An area of high pressure setting up over the Great Lakes will allow for some reinforcing cold air to settle into the region late Monday evening into Tuesday morning. Widespread sub-freezing temperatures are very likely north of the Turnpike and likely could extend southward to the PA-MD border, and we'll likely need a Freeze Watch in the next cycle or two in order to message this threat. Those with agricultural interests will need to monitor this threat, especially given the mild conditions much of the area has experienced over the past couple of days. 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 PNSCTP for those details.

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KEY MESSAGE 3: Marginal fire weather concerns this afternoon ahead of the cold front. Drier conditions early this week into the middle of the week will fuel multiple days of marginal fire weather risk.

Sneaky fire weather day across the southwestern zones of central Pennsylvania (Somerset, Bedford, Fulton) with marginal minimum relative humidities and gusty winds ahead of a cold frontal passage. Current relative humidity forecast in this region remains above critical thresholds, with lowest point values across much of Bedford County reaching into the 30-35% range this afternoon. This runs fairly close with the RH minimum ensemble member for relative humidity values today, so hard time seeing them break much lower into the ~25-30% range. Gusty winds will tick one of the boxes for the potential for elevated risk for wildfire spread this afternoon; however, given the marginal nature of RHs, will need to talk to our forestry partners to gather the fuel moisture situation in these regions.

Looking into the beginning of next week, relative humidities dip down closer to the ~30% critical threshold with Monday outlining the best potential for some post-frontal gusty winds. We'll likely need to see where wetting rain falls over the next 24 hours and reassess fuel moistures into the beginning of next week; however, Monday will be a day to watch going forward due to gusty winds and marginal RHs. Tuesday will also be a notable day to watch in the fire weather realm with current forecast outlining RHs dipping below 30% in spots; however, less wind to contend with so that's where further evaluation of fuels will become increasingly important after rainfall exits the area.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/

A marine layer moving in from the east this morning will bring some MVFR or IFR cigs to MDT, LNS, and perhaps IPT lasting until 15-17z before scattering out. Farther west of the marine layer, clouds will be scattered with high bases. Showers and thunderstorms will start to impact western airfields by 21-23Z. Lightning activity will wane as storms continue moving east after 00Z Sun. However periods of showers will continue into Sat night. MVFR ceilings are favored areawide Saturday night with some IFR possible as well. Winds will shift and become NW later Sat night with gusts to 20-30 kts. Snow may mix with rain in the northern tier, but no significant visibility reductions are expected. Conditions will improve after sunrise Sunday with VFR eventually prevailing.

Outlook...

Sun...Restrictions in -SHRA possible mainly N/W, transition to SHSN across higher elevations overnight Sunday night into Monday morning.

Mon...Lingering -SHSN possible early N/W; otherwise, dry conditions with VFR prevailing.

Tue...Dry with VFR conditions prevailing early, rain showers possible during the afternoon and evening hours.

Wed...NW flow with potential restrictions and a chc of -SHRA N/W

CTP WATCHES/WARNINGS/ADVISORIES

None.