NEAR TERM /UNTIL 7 AM THIS MORNING/
High pressure ridge over PA will result in fair weather overnight. Mostly clear skies and a calm wind should promote late night valley fog. The fog may become locally dense early Friday morning and result in slowdowns and increased travel times during the peak AM commute. See no reason to deviate significantly from NBM min temps, which range from near 50F in the coolest hollows of the Alleghenies, to around 60F in the Lower Susq Valley.

SHORT TERM /7 AM THIS MORNING THROUGH SUNDAY/
Fog to start Friday; otherwise ridging at the surface and aloft will result in a mostly sunny and warm Friday with max temps in the 75-85F range or +5-15F above daily climo. Dry air above a weak inversion in the model soundings supports undercutting NBM dewpoints by a couple of degrees during the afternoon.

Can't rule out patchy valley fog over parts of Eastern PA late Friday night. However, increasing clouds and a developing southeast breeze in advance of an approaching warm front should result in no fog for most of the area and a fairly warm night by late September standards.

Consensus/blended model data continues to signal increasing odds for rain showers (and perhaps a PM t-storm) on Saturday in response to a mid level shortwave diving southeast across the state. The emerging precip signal was strong enough to cause a notable change in the forecast for Saturday which had looked to be a dry one just a few days ago. A ribbon of relatively strong mid level flow over Southwest PA in the model guidance could support a few strong to severe afternoon tsra over that part of the state. There is some uncertainty if the surface warm front and greater instability pushes east of the Alleghenies, so the greatest severe threat currently appears to be over the Laurel Highlands.

The global guidance indicates the shortwave and weak surface low pass east of the region Sat night, then a cold air damming scenario begins to develop between a stalled warm front along the OH/PA border and high pressure over the Canadian Maritimes.
Forecast soundings indicate an upsloping southeast flow will result in persistent stratus and perhaps a bit of drizzle over the Central Mtns, with partly sunny skies possible over Eastern PA. The cloud cover and flow off of the Atlantic should result in markedly cooler afternoon temps Sunday than on Saturday, with highs likely stuck in the 60s over the Central Mtns.

LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/
A trend toward cooler and cloudier weather appears likely into the middle of next week associated with a cold air damming scenario ahead of a slow moving warm front in the Ohio Valley and high pressure over the Canadian Maritimes.

As for rainfall, a weak shortwave and associated plume of enhanced pwats overrunning the warm front could produce scattered showers Sunday night into early next week. Upsloping flow could also yield patchy drizzle over the Central Mtns early next week. The best chance for rainfall will come during the middle of the week as an upstream trough approaches the region.

AVIATION /06Z FRIDAY THROUGH TUESDAY/
No major changes for the 06Z package. As noted last night, less wind and less clouds overnight than last night, would expect some fog and low clouds.

Earlier discussion below.

A few scattered high clouds are lingering across the airspace this evening, but most sites will see mainly clear skies tonight into tomorrow morning. Current model soundings suggest that fog will form once again overnight across the northern half of Central Pennsylvania, with BFD, IPT, and UNV being most likely to see IFR or lower visibilities. The HRRR and GLAMP suggest that fog could be possible (~30% chance) at sites further to the south as well, but confidence is low. The fog will dissipate by 14Z and give way to VFR conditions for Friday. Most of Friday will feature calm winds and clear skies before clouds begin building into Friday night ahead of a frontal system expected to approach on Saturday.

Outlook...

Sat-Sun...Valley fog in the morning; scattered -SHRA/TSRA.

Mon-Wed...Scattered showers.

CLIMATE
The first day of Autumn 2024 (Fall Equinox) begins at 8:44 am EDT on September 22nd.

CTP WATCHES/WARNINGS/ADVISORIES
None.