textproduct: State College

WHAT HAS CHANGED

* Took out mention of TSRA with gusty wind for much of the region this evening * Revised dewpoints downward and temps upward a bit over the S for this aftn and evening. * Freezing/sub-freezing temps look even more likely Monday and Tuesday mornings.

KEY MESSAGES

1) MRGL severe threat diminishing quickly across the NW early this evening.

2) Dry, windy conditions through early this evening make a risk of rapid wildfire spread. Risk decreases Friday.

3) Heat and humidity decrease Friday and Saturday, but remain above normal due to the arrival of some cooler air and NW winds.

4) Cold front brings precipitation and a break from summer heat late this weekend. Freezing temps likely or even certain for Monday night.

DISCUSSION

KEY MESSAGE 1: MRGL severe threat diminishing quickly across the NW early this evening.

6 PM Update... Earlier, locally robust convection with several warned storms across NW PA have diminished quite rapidly over the past hour as they encounter a much more stable airmass closer to (and east of) the RT 219 corridor along with notable surface llvl divergence and the complete absence of sfc-925 mb based CAPE (a rarity other than at times of CAD with clouds and a LLVL easterly flow).

Without significant deep layer theta-E advection and a ramp up in instability tonight, took out the mention of higher POPs for TSRA and gusty winds and may remove the mention of TSRA from most areas shortly.

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KEY MESSAGE 2: Dry, windy conditions through early this evening make a risk of rapid wildfire spread. Risk decreases Friday.

Dewpoints have dropped slightly lower than expected - thus far - and may drop more, esp over the S. Temps also running a little higher than forecast (1-2F). The result is that much of the srn tier is AOB 30pct RH and some locations may eventually dip into the teens. The wind is on track. The fine fuels and wind speeds are not critical enough to warrant a fire weather watch/red flag warning. Conditions improve tomorrow (Fri) as wind decreases and temps cool and dewpoints lower a little. Thus, the RH should be higher on the whole for the srn tier.

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KEY MESSAGE 3: Heat and humidity decrease but remain above normals due to the arrival of some cooler air and NW winds.

The trough coming through tonight and a weak cold front on Friday will knock temps down 5-10 degrees between today and tomorrow, but they will still be well above normal. We go up a few degrees on Saturday as southerly flow increases ahead of an approaching cold front.

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KEY MESSAGE 4: Cold front brings precipitation and a break from summer heat late this weekend. Freezing temps likely or even certain for Monday night.

The next round of showers and storms will come along and ahead of a cold front Sat - Sat night. SPC has introduced a SLGT severe weather outlook for eastern OH and western PA Sat, with the MRGL risk area clipping our western zones. The showers will probably linger in the Se half of the area Sunday morning despite the front clearing our zones by 12Z. The significant cold front ushers in much, much colder air beginning Sat night. In fact, there could even be some snow showers on Sunday. While it will be getting near freezing in the NW half of the CWA Sunday night/Mon AM. Sunday night may be too windy for frost to form, but some places will get down to freezing anyway, which could necessitate a freeze warning being issued at some point. Most certain time frame for sub-freezing temps is Monday night/Tues AM. Latest forecast (as of Thurs aftn) drops temps just a deg more than last cycle for everyone = down below 32F, and as cold as 20 in the northern tier.

Temps rebound Tue afternoon and remain mild into the middle of next week. But, colder air could sneak back in from the N/NE in the second half of the week.

AVIATION /21Z THURSDAY THROUGH TUESDAY/

Showers and some isolated thunderstorms across eastern Ohio will continue moving northeastward late this afternoon and into the evening hours. The main uncertainty with respect to the 18Z TAF package comes with respect to the southern edge of convection, where SHRA/TSRA will remain possible across many of central PA's airfields through 06Z Friday. Recent NBM/HREF model guidance indicates high chances (~70-80%) in precipitation at BFD/JST with slightly different timing horizons. Have tried to narrow TSRA mentions at BFD to a targeted two-hour window where a combination of radar trends and hi-res model guidance suggests TSRA mentions will be highest. Further S/E, lower chances in TSRA at the airfields with much less TSRA coverage compared to yesterday's event. SHRA mentions have been retained at all airfields outside of MDT/LNS where much more low-level dry air in place will allow for SHRA to fall apart this evening. Inside SHRA/TSRA, VFR is expected to prevail for the majority of the evening; however, locally heavier rainfall could bring brief restrictions towards MVFR/IFR thresholds but confidence remains too low at this juncture.

Any area that receives heavier rainfall this evening (highest at BFD, lower JST/IPT/UNV) will have some potential for low- level moisture to linger and low-level ceilings to be reinforced through ~15Z Friday. Given current radar trends and HREF model guidance, have decided to tank BFD/JST in this timeframe with IFR thresholds. Some potential exists for LIFR conditions; however, have kept these mentions out of the 18Z TAF package due to lower confidence. MVFR thresholds possible (~40-50%) at AOO/UNV/IPT; however, have tried to use current radar trends along with hi-res guidance in order to highlight this potential closer to sunrise. Improvement at first between 12Z-15Z will be on the slower end, with high confidence in VFR thresholds being reached across all airfields by 15Z Friday and into the end of the 18Z TAF package.

Outlook...

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.

Tue...Dry with VFR conditions prevailing early, rain showers move south-to-north across the area during the afternoon and evening hours.

CLIMATE

MDT and IPT both had high temps of 87F on Wed Apr 15, which ties the record at MDT (set in 1941) and breaks the record of 86 at IPT (set in 1994). IPT also broke the Apr 15 record for warmest daily low temp, where 58F broke the record of 57F set in 2023.

Record high daily mins are possible again today and tomorrow. 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 16: 89 (2002) / 63* (1941) April 17: 91 (2002) / 60* (2002)

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

CTP WATCHES/WARNINGS/ADVISORIES

None.