Special Weather Discussion

Latest Weather Discussion by Kyle Elliott

* Brisk and Cold Again This Week; Watching Sunday-Monday Storm Threat *

11:00 a.m. Tuesday, January 14, 2025:

Following a long, 10-day stretch of unseasonably cold and rather blustery conditions, residents across the Lower Susquehanna Valley got a much-needed break from the chill over the last two days. The mercury reached the 40-degree mark for the first time in 10 days at Millersville on Sunday, and high temperatures topped out in the low-to-mid 40s area-wide Monday afternoon. Unfortunately, the brief warmup was cut short by last night's cold frontal passage, and another blast of frigid air will impact the Northeast and mid-Atlantic States during the middle of the week. In fact, a piece of the Tropospheric Polar Vortex (TPV) is currently located over northern New England. It will progress into the Canadian Maritimes tomorrow before finally lifting into the North Atlantic late this week. The mid-Atlantic States will be on the southern periphery of this TPV lobe, but we'll still endure another bout of brisk and frigid conditions over the next few days. A deep trough, or dip in the Jet Stream, associated with the TPV will swing through the Northeast over the next 48 hours (see below). As a result, it will be much colder today with highs only in the mid 20s north/west of I-81 to low 30s along the I-95 corridor. Factor in west-to-northwesterly winds of 10-20 mph with gusts up to 30 mph, and wind chills won't get out of the teens. Afternoon clouds will replace this morning's sunshine, and a moisture-starved disturbance will then swing through the Commonwealth later this afternoon and evening. It may bring a few stray flurries to northern MD and the Lower Susquehanna Valley between 4-9 PM, but most areas east of the Appalachians will remain dry (see below). This is just a disturbance and not an Arctic front, so there won't be any threat of "snow squalls" this evening.

Behind the disturbance, it will be equally as cold and even windier on Wednesday. Howling, northwesterly winds of 12-25 mph with gusts up to 35 mph will make it feel downright miserable outside. Due to the northwesterly flow over the still-unfrozen waters of Lake Erie, skies will generally be partly-to-mostly cloudy throughout the day. The pressure gradient, or difference in pressure, across the mid-Atlantic States will finally relax Wednesday night, so winds should subside rather quickly Wednesday evening. Clouds will also dissipate after sunset but then return Thursday morning. Another fast-moving disturbance will sweep through the mid-Atlantic States on Thursday and bring snow flurries or scattered, light snow showers to southern PA. Yet again, this system will be starved for moisture and associated solely with the Jet Stream's northern branch. Thus, I expect much of the day to be dry with little or no snowfall accumulation in most areas. However, the South Mountain Range and some spots north of the Turnpike and west of I-81 could receive a slick coating Thursday afternoon. If you live in or must travel in these areas, keep this in mind during the PM commute. Low temperatures and wind chills will bottom out in the teens and single digits, respectively, the next two nights, and high temperatures on Thursday will be virtually identical to today and tomorrow. Thus, aggregate temperatures will be around 6-10°F below normal, even by mid-January standards, through Thursday. Dress in layers and bundle up to stay warm this week! It won't be "dangerously cold" per se, but getting chilled for a prolonged period of time greatly increases the odds of getting sick. In addition, heating demands/bills will continue to skyrocket over the next 10 days. By month's end, they may be the highest many of you have seen in 7 years or more. Depressing..

Much like the last couple of days, the Jet Stream will briefly exhibit a slight northward bulge along the Eastern Seaboard following the departure of Thursday's disturbance. A warm front will move through the Commonwealth later Thursday night through Friday morning. Behind it, southwesterly winds will usher milder and more seasonable air into the region by Friday afternoon. As a result, high temperatures should approach or even reach 40°F again Friday afternoon under partly-to-mostly sunny skies, and lows will only drop back into the mid-to-upper 20s Friday night. However, a cold front will traverse the mid-Atlantic States from northwest-to-southeast spanning Saturday afternoon to Sunday morning, so the moderating trend will again be brief and "cut off at the knees." Scattered rain showers are expected to accompany Saturday's cold frontal passage, and some sleet pellets or wet snowflakes may mix in with the rain at times Saturday morning, especially north/west of I-76/Route 15. I do not, however, expect any snow/sleet accumulation or issues on roadways. It will certainly be a dreary start to the weekend, but precipitation will generally be light and intermittent, or of the "nuisance" variety. In fact, rainfall amounts probably won't exceed 0.10" in most parts of northern MD, southeastern PA and the Lower Susquehanna Valley. High temperatures on Saturday should be similar to Friday, so you'll still want to grab a coat.. and umbrella.. if you have any outdoor plans. Showers should taper off or push south/east of the I-95 corridor late Saturday afternoon or evening, but skies will remain mostly cloudy overnight with lows in the upper 20s to perhaps 30°F.

The forecast then becomes rife with uncertainty from Sunday into Monday. Many numerical computer models suggest that a wave of low pressure will develop near the tail end of the aforementioned cold front.. or in the southern Appalachians and Carolinas.. on Sunday. However, the existence, strength, track and evolution of this system are questionable, at best. It could easily fail to develop or do so "late in the game" and slip harmlessly out to sea Sunday night. A stronger cold front and faster intrusion of Arctic air in its wake would suppress the low pressure system and make this potential outcome reality. On the contrary, a weaker cold front and slower intrusion of Arctic air would allow the low pressure system to develop farther inland and intensify as it moves northeastward off the mid-Atlantic coastline. The North Atlantic Oscillation (NAO) will be transitioning from a weakly negative to strongly positive phase between January 19-22, making the forecast even more challenging. If the second outcome were to play out, then snow would likely develop Sunday afternoon or evening, continue for several hours, and taper off late Sunday night. Given the short duration of the event, it would almost certainly be of the "light" variety with regard to snowfall accumulations. However, this potential system is still 5-6 days away, so much can change over the next 72 hours. Regardless of the exact outcome, Martin Luther King Jr. Day will likely turn out partly sunny, blustery and much colder with highs in the 20s. Unfortunately, it will only be a harbinger of things to come for the rest of the week. 

After a few seasons of predominantly mild conditions, "Old Man Winter" is certainly taking his revenge this month. When combined with lingering, high-latitude blocking over northern Canada and Greenland (a -NAO) early next week, an extreme northward bulge in the Jet Stream extending from the West Coast of North America into Alaska will cause a deep trough to amplify over the central, southern and eastern United States, along with southeastern Canada. The main lobe of the TPV will be dislodged from northern Canada and forced to drop into southern parts of the nation or perhaps even the Upper Great Lakes region and northern New England during the middle of next week. In addition, the Madden-Julian Oscillation (MJO).. or an eastward-moving wave of convection between the Indian and central Pacific Oceans.. will continue to progress through the "cold phases" for the Central and Eastern States over the next week. The MJO can be active in 8 different phases, and each phase corresponds to a specific location of the tropical convection. Which phase the MJO is active in at any given time can alter the Jet Stream and, subsequently, large-scale weather patterns across North America on a week-to-week basis. Unfortunately, MJO activity in phases 1 and 2 are often correlated with cold air outbreaks across the eastern half of the U.S. in January, and this case will be no exception. There's often a lag effect of at least several days with MJO forcing, so the core of the Arctic air won't arrive until next week. The magnitude and duration of the cold are still somewhat uncertain, but next week will almost certainly be the most brutal of the entire 2024-2025 winter season. During the time of year with the lowest "normal" temperatures, they will likely average at least 10-15°F below that, in aggregate, next week (see below). On one or two days, temperature departures could even be 20°F or more below average.

In stark contrast to this week and last, next week's cold could indeed be of the "dangerous" variety. High temperatures on Tuesday and/or Wednesday may only be in the high single digits or teens, and overnight lows could bottom out at or below zero. Some daily minimum mean- and high temperature records might even be challenged or broken, and minimum wind chills will likely end up in the negative single digits or teens. The air mass will have a Siberian connection and be driven into the United States by "cross-polar flow." Quite frankly, this doesn't happen very often, and it's the only real means by which to drive temperatures so low along the Eastern Seaboard. Needless to say, there isn't much hope of any significant warmup or pattern change until at least January 25th. When all is said and done, this will be the longest stretch of bitterly cold air we've experienced in quite some time and the coldest winter month, relative to average, since February 2015. If you haven't already, it might be a good idea to invest in a backup generator as soon as possible. In the event of a power outage, the interior temperature of a home can drop quickly and to dangerously cold levels when outdoor temperatures are so low. I also encourage you to limit time outdoors next week and cover up ALL exposed skin to prevent frostbite.

As an FYI, I'll be on vacation and out of the office from tomorrow through Sunday to "recharge" before the Spring 2025 semester. Thus, I won't issue any "Storm Outlook" maps or special weather discussions over the next 5 days but will provide details on the severity of next week's cold air outbreak in Monday's videos and on Twitter(X). Warm-weather lovers like myself have nothing to be happy about or look forward to through the end of next week. Buckle.. err, bundle.. up! 🥶 -- Elliott