Marine Weather and Tide Forecast for Mercersburg, PA

KEY MESSAGES
1) Seasonably cool today into the upcoming week with the bulk of showers from the next, fast-moving upper level disturbance confined to the Northern Mountains of PA late tonight and Monday morning

DISCUSSION
KEY MESSAGE 1: Seasonably cool today into the upcoming week with the bulk of showers from the next, fast-moving upper level disturbance confined to the Northern Mountains of PA late tonight and Monday morning

A weak ridge of high pressure at the surface and aloft will move over Pennsylvania today, leading to a gradual backing of the wind from the west to the southwest by the midday hours.

Non-precipitating, shallow stratocu clouds blanketing much of the region early today will clear out for about a 7 to 9 hour period this afternoon and evening before another fast moving upper level disturbance and weak cold front moves southeast from the Great Lakes. This next weather feature will spread clouds across the region later tonight into Monday morning with occasional showers focused primarily across the Northern Mountains of Pennsylvania. Rainfall amounts of 1 to 2 tenths of an inch are likely across the Northwest Mountains of PA tonight and Monday Morning with much lighter amounts further to the Southeast.

A few brief showers could sneak into areas of the state south of Interstate 80 late tonight and early Monday.

Otherwise, it will be breezy and cooler through early in the upcoming week. Wind gusts today will range through the 20s (mph)
but northwest winds on Monday could gust as high as 35 and 40 mph.

There is a growing model signal for a more substantial long wave trough to carve out over the eastern U.S. by the end of the week. While still very preliminary given the extended forecast length and associated uncertainly/low confidence, it appears the coldest air of the Fall season will attempt to expand southward late next week with the upper trough and could be a factor with a potential coastal storm supplying a swath of precipitation including accumulating snow particularly in the higher elevations.

AVIATION /09Z SUNDAY THROUGH THURSDAY/
Typical westerly postfrontal upslope flow pattern stays locked in through Sunday morning with IFR to LIFR conds at KBFD/KJST and MVFR conds at KUNV/KAOO/KIPT. Periods of drizzle are likely in the central and western mountains through daybreak. Frequent wind gusts 20-25kt from 260-300 degrees are expected through Sunday. Improvements to VFR are expected by late Sunday morning as low-level moisture clears out, giving way to sunshine with some high clouds for the afternoon.

Another upper-level low will swing across the Northeastern US Sunday night through Monday and bring a return of lower clouds and -SHRA across our area. Flight restrictions will be most likely at KBFD (MVFR to IFR) and KJST (mainly MVFR), with intermittent MVFR possible across the Ridge and Valley region (KAOO/KUNV/KIPT) and VFR favored across the Lower Susquehanna Valley (KMDT/KLNS). Over NW PA (KBFD), cold air aloft may even support graupel in a few showers during this timeframe.
Additionally, wind shear may approach LLWS thresholds across south-central PA (primarily KJST/KAOO/KUNV) Sunday night as westerly winds in the lowest 1000-1500 ft approach 35-40 kts.

Outlook...

Tue-Wed...Mainly VFR with SW to W winds gusting up to around 15-25 kts during the daytime.

Thu...Leaning sub-VFR with rain and snow possible into late next week.

CLIMATE
The sun set at 5PM Saturday 11/7 in State College, marked the beginning of a 2 month stretch during which sunsets will occur before 5PM.

It has been one of the warmest starts to November on record in central PA. Here are the average temperature rankings from Nov.
1-5th:

SITE AVG Temp Rank Harrisburg 57.9F #13th warmest Williamsport 55.8F #7th warmest Altoona 57.9F #6th warmest Bradford 54.6F #5th warmest State College 57.1F #4th warmest Johnstown 59.1F #2nd warmest *since 2000

CTP WATCHES/WARNINGS/ADVISORIES
None.