textproduct: State College

WHAT HAS CHANGED

* Refined timing of storms across the N * Lowered temps a little on Wed and significantly on Thurs (mainly in the east)

KEY MESSAGES

1) Storms late today and tonight will cause localized heavy rain and likely cause strong, damaging winds and maybe large hail and an isolated tornado.

2) Slow moving front will move down from the north tonight and waggle north/south over the CWA for the next several days.

DISCUSSION

KEY MESSAGE 1: Storms late today and tonight will cause localized heavy rain and likely cause strong, damaging winds and maybe large hail and an isolated tornado.

Watch #79 has just been issued until 9 PM. While cloud cover and stabilization from earlier showers/storms is around at this time (18Z), some destabilization is expected before forcing arrives from the W. Line of light showers over CLE is likely along a weak trough and is attached to a particularly energetic storm over LE headed for BUF. We were OK with adding the northern tier of counties into the watch with an eye to that line having some hope of developing. In fact, a few CGs just showed up N of Ashtabula Co OH. So, it's on track, just more likely for NY than our CWA. We still feel the main event for Central PA will be a little later in the day (perhaps not until 5 or 6 PM onward). So, the watch running until 9 PM is a good start. If storms look like they will sneak to the south a bit more before that time, we could certainly expand the watch southward. We will probably need a second watch for later this evening as we expect the best forcing to arrive late in the day. Storm threats of all three flavors (wind, hail, and tornado) still look possible, but wind damage is the main worry. The shear along any differential heating boundaries or outflow boundaries (like the one the big LE cell may create) will be high, so the tornado threat is still non-zero. Deep layer shear of 50+KT and 100mb mixed-layer CAPE of 800-100J/kg in advance of that pre-frontal trough are cut off for the moment by CIN of some repute. Overall, the storm threats do look more likely after 5 PM, but we'll get the word out early today.

Heavy rain is also a potential trouble for the nrn tier. Earlier rain/storms that dipped south to near I-80 made light rainfall, but every little bit can add up when multiple storms are expected to affect the area this evening/tonight. Not strong enough reasons for a flood watch at this point, though, as the FFG is still in the .

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KEY MESSAGE 2: Slow moving front will move down from the north tonight and waggle north/south over the CWA for the next several days.

The front over ONT will drop southward into PA tonight, but not get too far into the CWA before sunrise. Plenty of clouds and scattered to numerous showers will still be around in the morning. These should get more numerous throughout the day, and there is a MRGL risk of severe wx (wind/hail) across the srn half of the CWA. The clouds and stable conditions in the AM will pose a challenge for storms to grow big. But, there will likely be some breaks in the clouds late in the AM and early aftn to get some destabilization going. Have nudged guidance temps down a bit for Wed -- and even more-so on Thursday, especially in the eastern half of the CWA. Deep easterly flow and cloud cover will make it a challenge to get temps out of the 40s over eastern PA, and above 55F in the eastern half of our CWA. JST and BFD will be laughing at us as they top out in the 60s and perhaps L70s - where the front pushes north as a warm front. They will have higher PoPs than the east as the front should help touch off sct/nmrs SHRA/TSRA.

The front lifts north/eastward through the rest of the CWA Thursday night or Friday morning. We will still carry PoPs thru the day Fri as many guidance models show the front returning as a cold front into the W. A train of sfc lows will carry moisture into the area through the weekend. A good push of colder air finally busts through late Sun or Sun night. It looks like it will be cold enough to make some snow mix in for the higher elevations of the NW in last could of hours. A stray SHSN is not out of the question Monday in the far NW, too. But, we'll leave PoPs unmentionable at this range.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

VFR conditions are expected through the afternoon for most of Central PA as an area of showers and embedded thunderstorms moves out of the region to the east. Expect additional showers and thunderstorms to develop over northwest PA later this afternoon, potentially bringing brief restrictions to BFD. These storms may be capable of producing strong wind gusts and very heavy rainfall.

Another round of showers and weakening thunderstorms will move in from the northwest after 00Z along a slow moving cold front. These will spread southeastward through the night, likely reaching MDT and LNS by sunrise. There is low confidence as to how far south and east any lightning associated with these storms will make it as they will be entering a more stable environment, but a few lightning strikes may be possible north and west of AOO and UNV. Ceilings lower from north to south as these move in, falling to IFR at BFD, JST, and IPT after 06Z. MVFR ceilings should develop at AOO and UNV, while MDT and LNS likely remain VFR.

Wind gusts decrease overnight, resulting in a period of LLWS at most TAF sites as a 40 to 55 knot low-level jet moves into Central PA.

Outlook...

Wed-Sat...Numerous SHRA with restrictions possible, especially on the cool side of a frontal boundary that oscillates across central PA during this timeframe.

Sun...Restrictions possible with showers and thunderstorms ahead of a strong cold front.

CTP WATCHES/WARNINGS/ADVISORIES

None.