textproduct: State College

WHAT HAS CHANGED

* Added discussion of weak severe threat today

KEY MESSAGES

1) Weak cold front today, then a stronger system moves across PA on Thursday night and Friday

2) Windy and wet end to the week with first flakes in the higher terrain

3) Cold weather may end the growing season for many places Sat and Sun mornings.

DISCUSSION

KEY MESSAGE 1: Weak cold front today, then a stronger system moves across PA on Thursday night and Friday

The front moving over central PA today has stalled out. Isolated showers are present along the PA turnpike and the southern half of the state, but heavy cloud cover and morning convection is keeping instability limited for additional storm development. The environment is not ideal for any additional storms that do manage to initiate this afternoon. Bulk shear is progged >40kt at JST, but tops are only expected to be 20-25kft. Pretty rare that we get any severe gusts with CAPE only in the 200-500J/kg range and no favorable thermodynamic environment to allow winds to accelerate completely down to the sfc.

QPF for today is low with just 0.50" as the top end in the Laurels. Any TSRA should be moving along steadily. So, we should have no risk for flooding rains today.

The next storm system will be driven by a sharp upper trough with a strong sfc high behind it. PWAT does increase to 1.8" in the S. The showers and any storms will be moving very quickly Thursday night and Friday. 1hr FFG is currently 0.8" and higher - but could decrease very slightly due to any rain today. Storm total QPF in the 0.1-0.2" range in the SC-SE and near 0.75" in the NW (where FFG is higher) should not lead to flooding.

-----------------------------------------------------------

KEY MESSAGE 2: Windy end to the week with first flakes in the higher terrain

Wind gusts 30-45 mph are forecast on the backside of the cold front and will deliver much colder air downwind of the Great Lakes this weekend. Latest NBM probs hold only 10pct chc for advy gusts - and only on the very highest elevations. JST BUFKIT profile from GFS does nudge 60KT winds down to 5kft AGL. So, it will be windy, and worth monitoring for an advy at some point - but only for the highest elevations - probably not for 90pct of the CWA.

The shot of colder air will allow for rain to mix or changeover to snow showers Friday night into Saturday morning across the higher terrain along the Allegheny Mtns. Any minor accum (<0.5") would have to occur overnight and be limited to non paved surfaces.

------------------------------------------------------------

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. Sat AM could be sub-freezing for the nrn tier. So far, only McKean Co has been taken off the list of zones to need any further frost/freeze products. But, we could add to that list Sat AM - and especially on Sun AM. Sunday morning lows expected to be in the upper 20s to mid 30s may kill the growing season for a significant portion of the CWA. We'll be considering appropriate frost/freeze products, but it is still too early to be that confident on details. Pretty cold again Monday AM, but not quite as cold - and some of the area may not need any more frost/freeze products by then.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

A weak frontal boundary sliding southward across the Commonwealth will continue to bring spotty showers over southern and central Pennsylvania this afternoon, with shower activity tapering off from north to south during the evening as the front moves through. A few additional thunderstorms cannot be ruled out across southern PA (KJST/KAOO/KMDT/KLNS) as MUCAPE values remain around 250-500 J/kg, though with the best forcing trending southward into the Mid-Atlantic and Ohio Valley regions, confidence is too low for mentions of thunder in the TAFs at this time.

Intermittent MVFR ceilings are possible (40-50% chance) across the central mountains (KAOO/KUNV) as the front moves through this evening, with predominantly MVFR ceilings more likely (60-80%) over much of the Northern Tier (KBFD) and on the windward side of the Alleghenies (KJST) throughout the 18Z TAF period. Flight restrictions are less likely across the Lower Susquehanna Valley (KMDT/KLNS) and to KIPT as drier low-level air noses in from the Northeast, though for KIPT in particular, ridgetop stratocumulus may develop beneath a subsidence inversion at around 1500 ft and result in intermittent MVFR ceilings overnight.

Areawide winds of around 5 to 10 kts will veer throughout the 18Z TAF period, starting off northwesterly behind the front this afternoon/evening and becoming southeasterly by Thursday afternoon.

Outlook...

Thu PM...-RA with restrictions possible later in the day as Wed's frontal boundary moves northward as a warm front.

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.