textproduct: State College

WHAT HAS CHANGED

* Tweaked timing on convection this evening

KEY MESSAGES

1) Severe threat over the northwest part of the CWA this evening. Much lower threat Thurs.

2) Dry, windy conditions Thurs may lead to a increased risk of rapid wildfire spread.

3) Summer-like heat and humidity into Thursday.

4) Cold front brings precipitation and relief from summer heat late this weekend.

DISCUSSION

KEY MESSAGE 1: Severe threat over the northwest part of the CWA this evening. Much lower threat Thurs.

Morning convection helped to raise dewpoints slightly, but they have started to lower with deeper mixing in between shots of forcing. Gusty SWrly wind is topped by Wrly flow in mid levels. The forecast soundings/profiles do support CAPE rising to 1000-1500 J/kg this afternoon and evening over the NW. Forcing from a short wave trough will arrive late in the day, and help flare some deep convection. Shear is close to 45KTs at BFD around 6 PM. Most num guid develops storms over nrn OH and slides it into Warren Co around 5 PM. Mid level flow of 60+ KTs, too. Fast moving storms with multi-cellular or even super- cellular mode are expected. Coverage is expected to increase through 8 or 9 PM before struggling to hold together and push too far S of I-80. An isolated storm or two could pop S of there, but we'll have lots of CINH to erase for that to happen.

The storms should start to wane as we lose heating and the trough passes to the east late this evening/early tonight. The threat for severe wx should be done by 10 or 11 PM. A weak boundary will likely lay out W-E right thru the middle of the CWA as they die off. The wet areas will probably develop some fog overnight.

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KEY MESSAGE 2: Dry, windy conditions Thurs may lead to a increased risk of rapid wildfire spread.

South of the boundary mentioned above will be dry as the drought conditions beget more drought for the southern third of the CWA. Dewpoints will drop into the lower 50s or even upper 40s over the southern half of the CWA, especially in the Laurels and south-central mountains. At the same time, the heat of Wed will be replicated. The resulting RHs will get into the 20s over the s-c mtns. Gradient winds will be 10-15 MPH with some higher gusts during the afternoon there, too. While the fine fuels are not dry enough to warrant a fire weather watch/red flag warning, the wind and low RH may warrant a mention more than here in the discussion.

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KEY MESSAGE 3: Summer-like heat and humidity into Thursday.

The main, wavy front will be laying out to our north for the next day and a half. Deep mixing here in the warm sector has already pushed temps well above normal, with 3 PM temps already near records in many spots and even higher than normal high temperatures in July. Expect this to repeat Thursday (tomorrow). The possibility of clouds and some morning fog across the nrn tier could hold them just a deg or two below what we see right now. The earlier boundary

Additional showers/storms are expected Thurs in just about the same timing and location as this evening. The mid-level winds will not be as strong, though. So, the threat for severe weather is not as great nor as widespread as this evening - staying confined to the far NW. SPC MRGL is appropriate.

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KEY MESSAGE 4: Cold front brings precipitation and relief from summer heat late this weekend.

Low pressure rolls to the east along the main front to our N Thursday night. Fri looks mainly dry and 5-10F cooler, but Saturday holds the next chc for SHRA/TSRA. The bigger change will come later in the weekend as a significant cold front ushers in much, much colder air. In fact, Monday night could hold a freeze or frost for most of the CWA. New fcst takes everyone down AOB 32F. Monday will be 10-12F colder than Sunday as the big high pressure area floats in from central Canada.

Day 6-7 look warmer again as we get into a SW flow due to the high sliding rather quickly east.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

Current satellite as of 18Z/2PM EDT outlines partly cloudy skies across W PA ahead of showers and thunderstorms in western Ohio approaching the forecast area. These showers and thunderstorms will continue to track eastward this afternoon/evening with increasing chances of showers and thunderstorms across the northwestern half of the airspace (BFD/IPT/UNV) between 22Z Wednesday through 06Z Thursday. Recent HREF/NBM/RAP model guidance continues to highlight BFD as the airfield under the gun for TSRA mentions, mainly between 22Z Wednesday and 02Z Thursday, which could bring lower visibility and ceilings in this timeframe. At this time, model guidance tends to keep everything above MVFR thresholds; however, cannot rule out brief drops towards MVFR/IFR thresholds in heavier thunderstorms this evening. Strong-to-severe thunderstorms will be most likely at BFD in the aforementioned timeframe, which could bring gusts above 40kts so radar trends will need to be monitored closer to the time for this threat. Further south, model guidance has trended back on precipitation mentions which lines up fairly well with recent GLAMP model guidance, thus have nixed mentions of SHRA/TSRA south of a IDI-UNV-HZL line in the 18Z TAF package.

Between 06Z-12Z, TSRA threat decreases due to lack of instability; however, could continue to have some lingering SHRA at BFD which could bring MVFR ceilings/visibilities with relatively low (~20-30%) confidence. Have outlined this potential with a scattered low-level deck; however, there is a lower bound solution where this low-level deck trends slightly lower in future TAF packages. After 12Z, widespread VFR conditions are progged by the bulk of model guidance so have penciled these in with moderate-to-high (~60-80%) confidence through 18Z Thursday. Main aviation concern between 12Z-18Z Thursday will be the presence of breezy (20-25kt) northwesterly winds across all of central PA's airfields.

Outlook...

Fri...Restrictions possible early, then improving to VFR in the afternoon.

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

Mon...Lingering SHSN possible early across N PA with restrictions possible; otherwise, dry conditions with VFR prevailing.

CLIMATE

Record high daily maxes and mins are possible this week as summerlike warmth visits the region. Here's a look at the records as they stand right now, with a * indicating that the forecast is equal to or greater than the record.

Record High Daily Max / Daily Min...

For Harrisburg: April 15: 87* (1941) / 61* (2023) April 16: 89 (2002) / 63* (1941) April 17: 91 (2002) / 60* (2002)

For Williamsport: April 15: 86 (1994) / 57* (2023) April 16: 90 (2002) / 55* (2023) April 17: 91 (2002) / 58* (1896)

CTP WATCHES/WARNINGS/ADVISORIES

None.