Special Weather Discussion

Latest Weather Discussion by Kyle Elliott

* unseasonably cold through the weekend, but big changes next week *

11:45 a.m. Friday, January 2, 2026, Update:

Due in large part to a frigid first half of the month, aggregate temperatures at Millersville University in December 2025 ended up "slightly below average." Liquid equivalent precipitation (LEP) was "below average" at the 'Ville due to persistent, northwesterly flow from Canada and relatively weak storm systems, but total snowfall was "near normal." In fact, the 3.7" of snow was the most in the month of December since 2020 (see below). It's been a rough stretch for snowhounds, especially early on in each of the past 4 winter seasons. 2025 concluded as the 15th-warmest year on record (since 1914) at Millersville with an aggregate temperature departure of +1.75°F. Despite long stretches of bone-dry conditions, the 'Ville received 38.83" of LEP last year.. just 2.72" below average.

As expected, 2026 kicked off on a blustery, unseasonably cold and "wild" note in terms of winter weather. A dangerous snow squall accompanied an Arctic cold frontal passage between 2:30-6:30 AM Thursday morning and reduced visibility to near-zero in many areas for about 15-20 minutes. Wind gusts reached 40-50 mph within the squall, and thundersnow was even reported in Harrisburg. In fact, Millersville Meteorology Alumnus Gabe Keller captured the phenomenon on video in the wee hours of the morning (see below). Most areas received 0.2-0.8" of snow from the squall in a matter of minutes, and brief, whiteout conditions were common across southeastern PA and the Lower Susquehanna Valley. Millersville Meteorology student Peter Corman measured 0.4" of snow at the 'Ville, and I picked up 0.6-0.7" of accumulation at my house in York (see below). Behind the Arctic front, northwesterly winds of 12-25 mph with gusts up to 35 mph buffeted the region throughout the day. Despite mostly sunny skies, temperatures hovered in the mid-to-upper 20s, and wind chills were stuck in the teens all afternoon. Needless to say, New Year's Day 2026 was certainly a memorable one for cold- and snow-lovers.

Fortunately, a Canadian high pressure system has settled into the southern mid-Atlantic States this morning and caused winds to subside. A westerly breeze of 10-20 mph will return this afternoon, but high temperatures should be around 5°F higher than Thursday and generally in the low-to-mid 30s. That's still 5-10°F below average by early-January standards, but it certainly won't feel as harsh outside compared to yesterday. Clouds should give way to partial sunshine this afternoon, but they'll return overnight following a mainly clear Friday evening. Temperatures should bottom out in the high teens to low 20s early Saturday morning. As discussed on Wednesday, the day-to-day weather from Saturday-Monday will remain unseasonably cold and change very little. A weak, clipper-type system will zip through the eastern Great Lakes region and southern New England Saturday night, but no more than a few flurries should fly across the Lower Susquehanna Valley (see below). Residents south of Route 30 or the Turnpike may not see any snowflakes whatsoever, and only in some parts of Perry, northern Dauphin and Lebanon Counties might a light dusting occur between 1-5 AM Sunday morning. After a mostly cloudy and cold Saturday with highs around 30°F, Sunday should turn out partly-to-mostly sunny and breezy behind the system with highs in the low-to-mid 30s and wind chills in the 20s.

Looking ahead into early next week, Monday's clipper disturbance now looks like a "flop" in terms of accumulating snow across south-central PA. Similar to Saturday night, it is expected to zip from the Great Lakes region into New England from Monday into Monday night. Its track will likely end up even farther north than Saturday night's disturbance and be too far away for any snow south of Interstate 80 (see below). Instead, Monday will just turn out mostly cloudy, dry and cold again with highs around freezing (32°F). In summary, continue to dress in layers and bundle up before heading outside through early next week!

Thereafter, the "gradual warming trend" is still very much on track from Tuesday-Friday. Reasons for this pattern change and big moderation in temperatures were outlined on Wednesday (see previous discussion below) and have not changed. As for the nitty-gritty details, a warm front will lift through the Commonwealth from southwest-to-northeast spanning Monday afternoon into Tuesday morning. In addition, the aforementioned high pressure system will shift into the western Atlantic, and southerly winds on its backside will usher noticeably milder air into the region Tuesday afternoon. Despite a continuation of mostly cloudy skies, high temperatures should easily reach the low-to-mid 40s and end up "slightly-above average" for the first time since December 29th. Yet another weak disturbance may zip through the eastern Great Lakes region and northern mid-Atlantic States on Tuesday night and bring an isolated shower or two to the Lower Susquehanna Valley, but no wintry precipitation is expected with overnight lows in the relatively mild 30s. Behind the disturbance, broad, west-to-southwesterly flow should persist through the end of the week and direct even warmer air into the Eastern States. In fact, high temperatures from Wednesday-Friday could be 10-15°F above average and end up in the 50s on one or two afternoons. The amount of sunshine each day will be a key factor in determining just how high temperatures get, so check back next Tuesday for an update! There is indeed some light at the end of the frozen tunnel.. -- Elliott

4:30 p.m. Wednesday, December 31, 2025:

As anticipated, 2025 is wrapping up on an unseasonably cold note across the mid-Atlantic States. In the wake of Monday morning's cold frontal passage, howling, westerly winds of 20-30 mph with gusts as high as 55-60 mph buffeted northern MD, southeastern PA and the Lower Susquehanna Valley through early Tuesday afternoon and caused numerous power outages, along with tree- and powerline damage. After a morning high in the 50s, temperatures plummeted into the 30s late Monday afternoon and bottomed out in the mid-to-upper 20s early Tuesday morning. The storm system responsible for the locally damaging winds has lifted farther north into eastern Canada and is now centered over Hudson Bay. As a result, winds slackened significantly over the past 24 hours but still gusted up to 25 mph at times today. Temperatures only reached the low 30s across most of the region this afternoon, and wind chills have been stuck in the low-to-mid 20s. It may be the end of December, but highs in the low 30s are still 5-10°F below average this time of year. Due to overcast skies across the region, temperatures won't fall much this evening, and they should still be around 30°F at midnight for the White Rose Drop in York, Red Rose Drop in Lancaster and Strawberry Drop in Harrisburg. Factor in a light, 6-12 mph breeze, and it will feel about 5-10°F colder outside (see below). Needless to say, you'll want to dress in layers and bundle up in a winter coat and gloves if you have outdoor plans this New Year's Eve. Other than a few stray flurries, you won't have to contend with any snow, sleet or freezing rain during New Year's Eve festivities and celebrations. However, that will change later tonight.

An Arctic cold front will sweep through the Commonwealth from northwest-to-southeast between 2-7 AM Thursday and be accompanied by a band of intense snow showers or squalls. Within these squalls, visibility could fall to "near zero" for ~15-20 minutes, leading to whiteout conditions in spots. Many areas will receive a coating to 0.5" of snow, and untreated roadways will turn slick and slippery early Thursday morning (see below). If you must travel, do so with extreme caution and drive within the speed limit. If a snow squall warning is issued, delay travel or safely exit the highway ASAP. Fortunately, the squalls are not coming during an AM or PM commute. Instead, they're coming in the wee hours of the morning on a federal holiday. If there's a silver lining to be found, that's it..

Behind the Arctic front, northwesterly winds of 12-25 mph with gusts up to 35 mph will usher an even colder air mass into the mid-Atlantic States to ring in 2026. Despite partial sunshine, high temperatures will only reach the mid-to-upper 20s in most locations, and wind chills should hover in the teens throughout the entire day. Quite frankly, this New Year's Day will be remembered for its blustery and downright frigid conditions. The cold will not be of the "dangerous" variety, but you'll certainly want to keep the winter coat and gloves handy through the first weekend of 2026. Speaking of the weekend, a Canadian high pressure system will shift from the Upper Midwest into the Ohio Valley and western PA spanning Thursday night to Friday and cause winds to subside. Low temperatures will bottom out in the high teens to perhaps 20°F Thursday night, but that's only about 5°F below average for early January. Thereafter, the magnitude of the cold will ease from Friday-Sunday. The core of the Arctic air mass is essentially a lobe of the Troposphere Polar Vortex (TPV) rotating through the northeastern United States. Fortunately, this TPV lobe won't have much "staying power." Instead, it will make a "quick pass" through the Northeast and lift back over Hudson Bay by the end of the weekend. Thereafter, the entire large-scale pattern will "reshuffle" early next week, and the TPV will ultimately retrograde into northwestern Canada and Alaska.

As a consequence of this pattern reversal, the deep trough, or dip in the Jet Stream, over the Eastern States will be replaced by zonal flow and a subtle, Jet Stream ridge. The persistent ridge over western North America will finally collapse and be replaced by much colder and stormier conditions. From late this week through the middle of next week, a slew of storm systems will crash into California and the Pacific Northwest, and the strong, west-to-southwesterly flow ahead of them will flood the eastern two-thirds of the nation with significantly milder air. A subsequent, gradual warming trend will take shape from Monday-Wednesday, and afternoon highs in the 30s should be replaced by 40s and perhaps even low 50s from Tuesday through at least the end of next week. Before then, the day-to-day weather will change very little from Friday-Monday. Partly-to-mostly cloudy skies will accompany highs in the low-to-mid 30s and overnight lows in the low-to-mid 20s. Winds will be relatively light throughout the period with the exception of a 12-25 mph breeze on Sunday, and the odds of any precipitation from Friday-Sunday are low (<10%). A weak clipper system zipping from the Great Lakes region into southern New England may graze the Lower Susquehanna Valley with intermittent snow showers or a period of light snow on Monday, but I expect no more than a coating to 1" of snow at the absolute most. Monday could just as easily end up dry. I'll stop there for now, but check back Friday for an update on the clipper and next Tuesday for a more extensive discussion. Until then, stay safe this evening, and I wish you a happy and healthy start to 2026! -- Elliott