Special Weather Discussion

Latest Weather Discussion by Kyle Elliott

* Another year without a white christmas *

1:15 p.m. Friday, December 19, 2025, Update:

As expected, a general 0.50-1.25" of rain fell across northern MD and the Lower Susquehanna Valley since Thursday evening. However, areas near Philadelphia received slightly more rain (1.25-1.75") and certainly "cashed in" on the event (see below). Due to the moderate drought conditions in place across most of the region, the rain was highly beneficial and much needed. Prior to this morning's cold frontal passage, temperatures and dewpoints soared into the upper 50s and even low 60s in some spots for several hours (see below). The incredibly warm and humid air mass completely routed the lingering snowpack and pretty much "sealed the deal" on yet another year without a White Christmas.

At the time of this writing, a secondary cold front is traversing the region from west-to-east. A narrow band of showers along the front will clear southeastern PA within the next 60-90 minutes, and westerly winds will increase to 20-30 mph with gusts up to 50 mph behind it (see below). As such, a Wind Advisory remains in effect through 1 AM Saturday. The highest and locally damaging wind gusts will occur before 10 PM, and motorists should expect downed tree limbs, blowing objects, and debris on roadways and keep a tight grip on the steering wheel, especially on north-south oriented highways, during the PM commute. In addition, the howling winds will usher much colder and drier air into the Commonwealth and cause isolated power outages. Tie down loose/unsecured objects now to prevent them from being blown away this evening. Temperatures will plummet some 20°F in just 3-4 hours and drop into the 30s by sunset with wind chills in the teens and 20s (see below). Talk about a wild temperature rollercoaster ride in just a 36-hour time span.. phew! It's the epitome of "pneumonia weather," so don't forget the winter coat and gloves later this afternoon and evening.

Fortunately, a high pressure system will settle into the Carolinas and southern mid-Atlantic States from tonight into tomorrow and cause winds to subside. The weekend itself is actually shaping up to be a dry, seasonable and completely uneventful in terms of precipitation, and that's great news for holiday travelers! The area of high pressure will promote partly sunny and colder conditions on Saturday.. at least compared to this morning.. with highs around 40°F. After a partly cloudy and relatively mild Saturday night with lows around 30°F, another cold front will sweep through the Commonwealth on Sunday. However, the front will be devoid of both moisture and energy, so not one drop of rain or flake of snow will accompany its passage across the Lower Susquehanna Valley. Unfortunately, we'll deal with another bout of blustery conditions Sunday afternoon and evening, but at least high temperatures should reach the mid 40s during the late-morning and early-afternoon hours under mostly sunny skies before falling back into the 30s by sundown. West-northwesterly winds will likely be sustained at 15-30 mph with gusts up to 40 mph Sunday afternoon and evening.. not as strong as this evening but still an unpleasant inconvenience (see below). 

Another high pressure system will then settle into the mid-Atlantic States from Sunday night into Monday and cause winds to diminish again. The high will also be of Canadian origin, so Christmas week will kick off on a mostly sunny but chilly note with highs in the mid- to perhaps upper 30s Monday afternoon. Thereafter, a clipper-type system will zip from the northern Great Lakes region into southeastern Canada and northern New England from Monday night into Tuesday. To its south, a warm front will lift northeastward through the Ohio Valley and central Appalachians and be the focal point for a few rain, snow and/or sleet showers late Monday night into Tuesday morning. Most of the activity should remain north of the Lower Susquehanna Valley and closer to the center of the storm system, but it will only take a coating of snow or sleet to make the Tuesday morning commute slick and slippery. At this point, odds of that happening are highest north of the Turnpike, but I cannot yet rule it out farther south. I will have an update on this potential threat in Monday's short-term video. Behind the warm front, skies will stay mostly cloudy Tuesday afternoon, but temperatures should climb into the upper 30s to low 40s. Thus, any snow or slush on roadways will melt quickly during the afternoon hours. An area of high pressure is then expected to settle into the region on Christmas Eve, and it won't truly be of Canadian origin. Therefore, Tuesday night should turn out mostly cloudy and quite mild with lows in the 30s, and we will likely be graced with partly sunny and pleasantly mild conditions on Christmas Eve with highs in the mid-to-upper 40s.

Another clipper-type system and its associated warm front may then lift northeastward into the mid-Atlantic States on Christmas Day, but the air mass will be too mild for anything but rain showers. Thus, the odds of a White Christmas now appear "nil" again in 2025. Call it bad timing, bad luck, or whatever you want, but we just can't seem to break the streak of snowless Christmases across northern MD and southeastern PA. If the warm front manages to lift north/east of the region on Friday, then an air mass more typical of spring would infiltrate the mid-Atlantic States and perhaps cause record highs to be challenged or broken. Given the uncertainty in the forecast at this distance, I'll stop there for now and provide an update on Tuesday. Either way you slice it, winter is now on a prolonged hiatus after a frigid and active start. It may be awhile until we have another legitimate "winter storm" threat.. -- Elliott 

2:00 p.m. Wednesday, December 17, 2025:

In terms of temperatures, the first half of December has been nothing short of BRUTAL across the mid-Atlantic States. There has yet to be a single day with an above-average high temperature at Millersville University, and the highest temperature of the month (to date) has been 43°F. Average highs across northern MD and southeastern PA are in the mid-to-upper 40s during the first week of the month, so sustained cold of this magnitude is extremely uncommon in early December. In fact, the aggregate temperature departure between December 1-16 was about 6.5°F below average at the 'Ville. Despite the miserably cold weather, no record lows or record low maximum (i.e. "coldest high") temperatures have been set. Fortunately, the large-scale pattern across the Northern Hemisphere is in the process of "reshuffling" and undergoing a large change. As a result, a much milder and more seasonable pattern will grace the Eastern States during the last two weeks of the month. I dove into the weeds behind this pattern change in last week's discussion and have kept it up below this one so as not to rehash the same points. Despite the overall moderation, it won't come without "growing pains" in the form of some high wind events and brief blasts of colder air.

Anyhow, southwesterly winds of 8-16 mph on the backside of a high pressure system over the western Atlantic have ushered the first surge of milder air into the region this afternoon. The deep trough, or dip in the Jet Stream, over the Northeast has finally lifted back into northern Canada and will be temporarily replaced by a Jet Stream ridge over the next 24-36 hours. At the time of this writing, temperatures have reached the low 40s across most of Lebanon and Lancaster Counties but have soared into the low-to-mid 50s west of the South Mountain Range. It's not "warm" by any means, but at least some of the snowpack is melting! After a partly cloudy and seasonably cold Wednesday night with lows between 20-25°F, clouds will increase on Thursday in advance of an approaching storm system. However, there should be enough morning sunshine to boost high temperatures back into the mid-to-upper 40s. The actual center of low pressure will track from the northern Great Lakes region into southeastern Canada spanning Thursday-Friday. As a result, the entire Northeast will be in the system's warm sector, so precipitation will fall in the form of plain rain.

A deep fetch of moisture originating from the Gulf and western Atlantic will be drawn northward into the mid-Atlantic States by broad, southerly flow across the Eastern States. In turn, a soaking and much-needed rain event will unfold from Thursday evening through Friday morning. The rain will overspread northern MD, southeastern PA and the Lower Susquehanna Valley from southwest-to-northeast between ~5-10 PM Thursday, fall heavily at times overnight, and then taper off from west-to-east between ~5-9 AM Friday morning. The cold front trailing southward from our late-week storm system will be a potent and well-defined one. Due to strong, southerly winds of 12-25 mph with gusts up to 35 mph Thursday night, temperatures and dewpoints should briefly climb into the 50s for a few hours. Thus, there could be just enough instability for a few rumbles of thunder within a gusty line of heavy showers along and immediately ahead of the front between ~3-9 AM Friday (see below). Most areas will receive 0.75-1.25" of rain with locally higher amounts up to 1.50". Due to the abnormally dry and moderate drought conditions in place, the rain will be largely beneficial. However, the combination of some heavier downpours and snowmelt will cause flooding of low-lying, urban- and poor-drainage areas during the Friday morning commute, as well as standing water on roadways (see below). Expect delays and areas of slow travel, and drive within the speed limit on the wet roads and in areas of reduced visibility. 

Behind the front, winds will turn westerly and usher a much colder and drier air mass into the mid-Atlantic States. A tight pressure gradient, or difference in pressure, between the storm system and an area of high pressure over the Tennessee River Valley will lead to strong, westerly wind gusts up to 50 mph across the region between 12-7 PM Friday. Winds will be sustained at 20-30 mph during that time, and temperatures will plunge from the low-to-mid 50s in the pre-dawn hours to the 30s by the PM commute (see below). Motorists should be alert for downed tree limbs, blowing objects, and debris on roadways late this week. Keep a tight grip on the steering wheel, especially on north-south oriented highways, as well, and expect isolated power outages. After a mild start to the day, wind chills could be as low as the high teens to low 20s by sunset. Talk about a wild ride.. phew!

Fortunately, winds will gradually subside Friday night as the aforementioned high pressure system shifts into the Carolinas and southern mid-Atlantic States. The high will then move quickly into the western Atlantic by Saturday afternoon, so winds should turn back around to the south by the afternoon hours. However, temperatures will be starting out in the low-to-mid 20s early Saturday morning, and the southerly flow won't be very strong until late in the day. Thus, high temperatures will only reach "normal" levels (upper 30s to perhaps 40°F) on Saturday. Another cold front will then sweep through the Commonwealth later Saturday night into Sunday morning, but this system will be starved for moisture and MUCH weaker than the late-week front. Therefore, I don't anticipate one drop of rain or flake of snow across the Lower Susquehanna Valley this weekend, and that's good news in terms of outdoor activities. Unfortunately, we'll deal with another bout of blustery conditions on Sunday, but at least high temperatures should reach the mid-to-upper 40s during the early-afternoon hours before falling later in the day. West-northwesterly winds will likely be sustained at 15-30 mph with gusts up to 40 mph Sunday afternoon and evening.. not as strong as Friday but still enough to be an inconvenience. Another high pressure system will then settle into the Commonwealth from Sunday night into Monday and cause winds to subside. The high will also be of Canadian origin, so Christmas week should start out on a partly-to-mostly sunny but unseasonably cold note with highs in the low-to-mid 30s Monday afternoon. Thereafter, uncertainty in the forecast increases dramatically, but odds favor another clipper system zipping through southeastern Canada and New England from Tuesday into Christmas Eve. If so, then Tuesday could turn out mostly cloudy and chilly with a chance of rain showers prior to a drier, brighter, and milder (40/50s?) Christmas Eve. I'll refine the details on Friday and provide another update early next week, so check back then! -- Elliott 

12:30 p.m. Wednesday, December 10, 2025:

The first 10 days of December have been persistently and unseasonably cold across the Central and Eastern States, but there has been very little snow to show for it across the Lower Susquehanna Valley. Other than the December 2nd system, the storm tracks of subsequent systems simply haven't aligned correctly for winter-weather events across our region. Instead, snow-lovers in Virginia and the southern mid-Atlantic States have "cashed in" on the pattern with predominantly dry conditions farther north between I-70 and I-76. Why are we stuck in a "cold but dry" pattern? It's actually quite simple. The northern and southern branches of the Jet Stream have not linked up or joined forces. Additionally, the southern branch has and will continue to be very weak. Strong, northwesterly flow from Canada associated with the much stronger northern branch has directed multiple shots of Arctic air into the Northeast, but these air masses have also been incredibly dry. As a result, we've dealt with frequent, clipper-type systems diving southeastward out of Alberta, Canada, and into the Midwest and Great Lakes region (see below). From there, they have either tracked into New England or continued on their southeastward journey into the Carolinas and southern mid-Atlantic States. Essentially, northern MD and southeastern PA have been caught in the middle and, therefore, received very little snow in the past week. Clipper-type systems are a staple of La Niña winters, and that's not ideal for snowhounds. They move very quickly, are often starved for moisture, and rarely produce more than "minor" or "light" snowfalls. In addition, accumulating snow typically only falls in a narrow swath along and just north/east of their track, so they have to take the "perfect path" to produce accumulating snow in a given region. Over the next 7 days, this large-scale pattern should change very little, and the only meaningful chance for measurable snow will come on Saturday night.

Last Thursday, I expected no more than a few rain/snow showers to impact northern MD and southeastern PA this week. Despite plenty of hype from the "usual suspects" on Twitter(X) and other social media platforms, that forecast is certainly coming to fruition due to the factors outlined above. One such clipper system is currently zipping from the Great Lakes region into southern New England. It will bring rain showers to the Lower Susquehanna Valley this afternoon, but more significant precipitation will remain north of Interstate 80 due to the system's track. Southerly winds of 12-25 mph have ushered more seasonable air back into the region and already boosted temperatures well above 32°F as of midday, so only a few wet snowflakes or sleet pellets are expected to mix in with the rain at times across Perry, Lebanon and Dauphin Counties (see below). Showers should push south/east of the I-95 corridor by 7 PM, and most areas will only pick up 0.10-0.20" or less of rain from the event. Due to the abnormally dry and moderate drought conditions in place, any precipitation will be largely beneficial (see below). Just make sure to reduce speed on any wet roadways this afternoon.

A cold front trailing southward from the clipper system will sweep through the Commonwealth tonight. In its wake, west-northwesterly winds of 15-30 mph with gusts up to 40 mph will usher another colder and drier air mass into the mid-Atlantic States on Thursday. Under partly-to-mostly cloudy skies, temperatures will only rebound a few degrees throughout the day with highs in the upper 20s to mid 30s from northwest-to-southeast across the region. That's about 10°F below average for mid-December, and it will feel even worse outside with wind chills in the mid teens to low 20s. You may even see a few snow flurries in the air at times, as well. Fortunately, a bubble of high pressure will then settle into southern New England from Thursday night into Friday and cause winds to gradually subside. However, it will remain unseasonably cold on Friday with highs in the low-to-mid 30s and wind chills in the mid-to-upper 20s under mostly cloudy skies. Needless to say, you'll need to dress in layers and bundle up before heading out the door late this week! The cold won't be of the "dangerous" variety, but it will still feel downright miserable outside. 

In terms of snow, I'm monitoring two additional clipper systems for a potential "light" event or two through the weekend. The first of these systems will likely track too far south (Tennessee River Valley to the Carolina coastline) to bring any measurable snow to the Lower Susquehanna Valley later Friday into Friday night. Instead, Friday night should just turn out mostly cloudy and seasonably cold with lows in the mid-to-upper 20s. I won't rule out some flurries or very intermittent, light snow south of the Turnpike, but I'm not expecting any accumulation north of the Mason-Dixon Line and perhaps even I-70 (see below). Behind the first system, the weekend will then kick off on a mostly cloudy but somewhat more seasonable note with highs around 40°F Saturday afternoon. However, the next system will then track through the mid-Atlantic States Saturday night and bring the chance for snow back into the forecast.

Of the two systems, the second one has a much greater likelihood of producing accumulating snow across northern MD and southeastern PA. The weak low pressure system will originate in a similar location to Friday's system, but it will then veer east-northeastward from the Lower Ohio Valley/central Appalachians into the Delmarva Region Saturday night. A clipper track through northern VA or MD/DE is "ideal" for a light snowfall event between I-70/76 and I-81/95, and this case should be no exception. However, the system will be starved for moisture and moving very quickly, so there will only be about a 4-6-hour window for snow Saturday night. Thus, I expect no more than a general coating to 2" of snow across the region with the highest totals near I-95. The clipper is still ~3.5 days away, so there can be some changes over the next 24-36 hours. Either way, it should be a low-impact event and not commence until the overnight hours. Better yet, any snow will have already exited southeastern PA prior to Sunday morning church services. Paved surfaces may still be slick and slippery, however, so use extra caution on the roadways Sunday morning. 

Behind the clipper, northwesterly winds of 15-30 mph with gusts up to 40 mph will usher one more reinforcing shot of Arctic air into the mid-Atlantic States from Sunday into early next week. The weather looks downright awful Sunday afternoon with temperatures in the mid-to-upper 20s and wind chills in the single digits and teens. Partial cloud cover and a persistent breeze should keep temperatures in the mid teens to perhaps 20°F Sunday night, but minimum wind chills could certainly bottom out near 0°F early Monday morning. A Canadian high pressure system should then shift from the Midwest into the central Appalachians and Southeast early next week. As the system gets closer to our region, winds will certainly slacken Sunday night into Monday. However, next week will still kick off on a brisk and frigid note under partly-to-mostly cloudy skies. High temperatures will only reach the mid-to-upper 20s again Monday afternoon, and a westerly breeze of 12-25 mph will keep wind chills in the single digits and teens throughout the day. From Sunday night through Monday morning, the cold may actually fall into the "dangerous" category, so it will be imperative to limit time outside and cover up exposed skin to limit the risk of frostbite or hypothermia. 

Fortunately, the large-scale weather pattern should finally ease and "reshuffle" by the middle-to-latter part of next week, and aggregate temperatures will likely be much closer to or slightly above average in the week leading up to Christmas. The Madden-Julian Oscillation (MJO), or eastward-moving wave of tropical convection between the Indian and central Pacific Oceans, was active in "Phase 8" between December 2-8. Phase 8 is a notorious "cold phase" for the eastern U.S. during the winter months, so our frigid start to December comes as no surprise. However, the wave of convection died out over the past 24-48 hours, and the MJO is now in the "null phase." It is projected to remain very weak or simply stay in the null phase over the next few weeks. When in the null phase, the MJO typically has very little influence on the large-scale pattern across the mid-latitudes, and other factors take precedence. One such factor is the Stratospheric Polar Vortex (SPV). After being remarkably weak through the middle of the month, it is projected to rapidly strengthen between December 16-23 and then become abnormally strong in January. A strong SPV lessens the likelihood of Arctic outbreaks across the mid-latitudes. In addition, the Pacific Jet Stream is expected to undergo a major retraction between December 17-22. As a result, a massive ridge, or northward bulge in the Jet Stream, is already developing over the Bering Sea, and this feature will only amplify and become more pronounced over the next 2 weeks. The Bering Sea ridge often precedes an eastern U.S. warmup and flareup of the "Southeast Ridge" by 6-10 days, and this case should be no exception (see below). Thus, I expect a big moderation in temperatures during the middle of next week.

At the surface, the high pressure system mentioned above will shift into the mid-Atlantic States on Tuesday and western Atlantic by Wednesday, ultimately establishing itself as said "Southeast Ridge." On its backside, south-to-southwesterly flow should return on Tuesday and persist through at least Thursday. A gradual warming trend will ensue, and I expect high temperatures to be back in the 30s Tuesday afternoon under partly sunny skies. They should then reach the 40s next Wednesday-Friday and may even sneak into the low 50s on on or two of those days. A cold front may follow later Friday into Saturday and temporarily "beat down" the Southeast ridge for a day or two, but milder conditions should make a quick comeback by the start of Christmas week. If so, then odds of a White Christmas would dwindle significantly, and the weather could end up being quite mild and benign over the holidays. Time will tell! I'll be out of town and away from Twitter(X) and e-mail later tomorrow afternoon through Sunday, so check back early next week for an update! -- Elliott