textproduct: State College

WHAT HAS CHANGED

* Severe threat has increased for Friday afternoon and early evening

KEY MESSAGES

1) Potent storm system moves across PA tonight and Fri with a severe threat Fri aftn/eve.

2) Windy with first flakes on the higher terrain of the north Fri night/Sat morning

3) Cold weather may end the growing season for many places this weekend, with Sun morning the coldest.

DISCUSSION

KEY MESSAGE 1: Potent storm system moves across PA tonight and Fri with a severe threat Fri aftn/eve.

A surface low moving through the Midwest will cross the Great Lakes tonight and Fri. A warm front will bring widespread rain/showers overnight, with some elevated thunder possible (20 pct chc). A break with some sunshine during the morning and early afternoon will destabilize the atmos over much of the CWA Fri. The break may not be an hour over our NW few counties, but the SE will have 6-9hrs to recover from the overnight rain. This could allow storms to form - mainly right along the front as it passes through. But, some could pop before it arrives in any location. The bulk shear will get between 40-60KT and CAPE between 500-1000 J/kg over the SE third to half of the CWA, highest in the Lower Susq. SPC mentions a 2% tornado risk over the Susq valley as some positive EHI shows up and LCLs may stay below 3kft there. It is still 2026, after all. The frontal timing is roughly 15Z in Warren Co, and 00Z in Lancaster Co. Added enhanced TS wording to the grids and mentions of severe and poss tornadoes to the HWO.

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KEY MESSAGE 2: Windy with first flakes possible on the higher terrain of the north Fri night/Sat morning

Post-frontal gradient is pretty tight with 10mb of drop across the state overnight and Sat morning. 50+KT winds behind the front look like they will stay AOA 6-7kft. This should be tough to mix down, esp without the wind dir in the llvls being more vertically-homogenous than currently expected. While we have continued to mention some 35-40MPH gusts, the risk for advy level (40+KT) gusts looks quite a bit lower than it has looked recently.

The CAA will drop 8H temps 15-20C in less than a day. The initial surge of cold will make a very short-fetch flow of sig lower air vs lake water temps which is 64F at ERI and 61F off Oswego, NY. Expect lake effect clouds later Fri night and very early Sat AM. However, many models are not generating much meas precip then. GFS sounding at BFD puts the inversion height at only 5kft starting at 06Z and it stays there all night/morning, with the NAM even more-shallow with the cold air coming across the lower lakes. Temps are favorable for SN up north. So, we still expect any lingering SHRA to turn to SHSN overnight. But, the fetch turns quickly northerly and then the air becomes drier in the sunrise to mid-morning time frame. A dusting is possible, but unlikely in the northern mtns.

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KEY MESSAGE 3: Cold weather may end the growing season for many places Sun morning.

Big sfc high moves in for the weekend, supplying dry but cold weather for Sat and Sun. Sat will hold the coldest daytime temps with temps getting just above 40F in the NE and 52F in the SE. Those maxes will be 22-28F lower than Friday's maxes.

Sat AM could be sub-freezing for the nrn tier. But, the clouds expected may keep temps milder than the current NBM mean. MAV/MET numbers are slightly milder. So far, only McKean Co has been taken off the list of zones to need any further frost/freeze products. But, we could add a county or two in the N to that list Sat AM.

Sunday morning will be the most-likely time for sub-freezing temps across much of the CWA. However, it will be Sunday morning's temps which could end the growing season for a significant portion of the CWA. A widespread frost is almost a certainty as winds decrease and go mainly calm Sun AM. We'll be considering appropriate frost/freeze products, but it is still too early to be that confident on details. Pretty cold again Mon AM, but not quite as cold - and some of the area may not need any more frost/freeze products by then. High clouds from a possible coastal low could reach up this far north, and may affect the temps Mon AM.

AVIATION /07Z THURSDAY THROUGH MONDAY/

Winds have shifted northerly in the wake of yesterday's weak frontal passage, allowing for drier air to filter in across the Commonwealth. A subsidence inversion at around 1500 ft is contributing to periods of MVFR ceilings across the Allegheny Plateau and Laurels (KBFD/KJST/KAOO) as low-level moisture remains trapped beneath the inversion. While the central mountain terminals (KUNV/KIPT) are favored to remain VFR through Thursday evening, intermittent MVFR ceilings will be possible (20-30% chance) into the morning hours on the periphery of greater low-level moisture to the north and west. Farther southeast (KMDT/KLNS), restrictions are less likely through Thursday evening due to lower relative humidity values at the inversion height (RH to around 80% vs. 90-100% farther northwest).

As the weak front slides southward across the Mid-Atlantic, southerly return flow will build out ahead of a more potent low pressure system approaching the southern Great Lakes, allowing for the boundary to lift northward as a warm front this afternoon and evening. Winds of 5 to 10 kts will veer throughout today, shifting from N-NW in the morning to S-SE in the afternoon. Scattered showers and lowering ceilings will accompany the warm front later today, with IFR ceilings likely (50-70% chance) to overspread central Pennsylvania from west to east between 00-06Z Friday as warm air advection drives moisture back in across the region.

Moreover, nocturnal LLWS is likely (50-70% chance) over the western airfields (KBFD/KJST) Thursday night as an LLJ ahead of the system brings southwesterly winds at 925 mb to 35-40 kts. LLWS is less likely with points eastward, farther from the low pressure center moving over the southern Great Lakes.

Outlook...

Fri...Higher chances of SHRA with isolated TSRA. Restrictions increasingly likely. Gusty S-SW winds likely ahead of front, with gusty NW winds behind front.

Sat...Lingering SHRA across N/W PA with some -SHSN mixing in early Saturday morning. Restrictions likely at airfields that mix over to SHSN. Precipitation tapers off by sunrise, VFR prevails with gusty winds.

Sun-Mon...AM fog possible; otherwise, VFR conditions prevail.

CTP WATCHES/WARNINGS/ADVISORIES

None.