Marine Weather and Tide Forecast for Shippensburg, PA

NEAR TERM /THROUGH TODAY/
A deep cold airmass will continue to mix down to the surface and intrude into Central PA this morning, with the morning lows on track to dip into the low 20s across the NW highlands. This will be a stark difference to the Lower Susquehanna Valley with their lows only expected to reach the low 40s as the milder air retreats southeast. The surface low from Sunday continues to work its way up through New England. Upslope and lake effect snow has begun to fall on the backside of this low where surface temps have already dropped below freezing. No significant snowfall is expected during the early morning hours today; however 1-2 inches of snow could fall across Warren and McKean counties by this late afternoon.

The cloud-layer flow moving across the lakes on Monday will be light and directionally-sheared at first, then settle into a more-stacked NW direction. Lake induced CAPE (51F lake water at ERI) could reach into the 1000J range with clouds tops in the 5-10kft range. However, the cross-fetch is short at that angle and would likely keep all but NWrn Warren Co from getting much accum, esp as temps get close to freezing (and the sun makes the ground/sfc slightly warmer). Anywhere further south or east of Warren Co will struggle to see too much in the way of snow during the day as the extent of the moisture transport from Lake Erie will struggle to extend beyond NW PA during the day.

SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/
As the sun lowers, the flow will back to west a little and get a significant addition of Lake Huron moisture. This two-lake fetch and a llJet of 40-45KT will be pointed right into Warren/McKean Cos for much of Mon night (and into Tues). The SLRs thru the period will lower to about 17:1 in the nrn mtns.
So, it's not out of the question for the healthy band/bands to drop >6" in Warren Co as the moisture rolls uphill. Not so sure about McKean and Potter Cos, as they are farther from the lakes and the moisture might not last that long/far into the CWA The amount of snow reaching that far south will all depend on the strength of the Huron connection.

At the same time, the upslope flow into the highest hills of Somerset Co (and all of PA, really) moistens up again as the flow backs there, too, and brings the best moisture back N from WV/MD. The residence time of the (combined) best moisture and uplift over the Laurels looks short, though. Thus, additional snowfall Mon night and early Tues is very much in question.
Also, the lower 2/3rds (elevation-wise) of the county will likely get (way) less than 3" for the whole stretch. So, we've decided not to issue an advisory for Somerset Co at this point in time. Confidence has increased for the northwest, and a lake effect snow warning has been issued for Warren Co. Additionally, confidence is highest in Elk and McKean Cos also seeing 3+" of snowfall overnight tonight, thus an advisory has been issued for those counties. Monday night into Tuesday morning will also feature the coldest temperatures of the week, and gusty winds will place windchills into the single digits for most of our northern and western zones.

LONG TERM /WEDNESDAY THROUGH SUNDAY/
Upper-level troughing will remain in place through the end of the week, keeping the chance for rain and snow showers in the forecast each day through Friday, especially over northwest PA.
A tight pressure gradient will allow for winds gusts in the 30 to 35 mph range Wednesday, with some guidance suggesting the potential for gusts over the Laurel Highlands to approach 40 to 45 mph.

The December- like cold airmass is forecast to retreat later in the week, with temperatures returning closer to seasonal averages. High pressure attempts to briefly build in from the west which should keep us mainly dry into the beginning of the weekend, but uncertainty increases by Sunday regarding the timing of an approaching frontal system.

AVIATION /07Z MONDAY THROUGH FRIDAY/
A chilly northwesterly flow will maintain IFR cigs across the northern and western highlands (BFD/JST) through daybreak, with occasional -SHSN. Southeast of the Allegheny Front, predominantly MVFR cigs are expected for the central mtns (AOO/UNV/IPT) overnight. Light rain across the Lower Susq Valley (MDT/LNS) will taper off overnight, with cigs dipping to borderline MVFR/VFR by daybreak.

A continued northwesterly flow of chilly air will maintain low clouds across the northern and western highlands today, along with occasional -SHSN. Cigs should improve to low-end MVFR for JST and BFD this afternoon. The central mtns should see cigs improve to low-end VFR this aftn, with borderline MVFR/VFR cigs over the Lower Susq Valley improving to VFR. Northwesterly winds will occasionally gust 20+ kts areawide today.

Expect more of the same into Tuesday, with wind gusts increasing to ~30 kts.

Outlook...

Wed-Thu...-SHSN and occasional restrictions continue across NW PA; becoming VFR elsewhere. Breezy W/NW winds continue areawide.

Fri...Continued improvement, with winds diminishing and lingering -SHSN across NW PA tapering off.

CTP WATCHES/WARNINGS/ADVISORIES
Lake Effect Snow Warning from 10 AM this morning to 1 PM EST Tuesday for PAZ004.
Winter Weather Advisory from 10 AM this morning to 1 PM EST Tuesday for PAZ005-010.