The DC area’s first chance for plowable snowfall this winter is expected this coming Monday, and it could be the biggest for some in several years
January 4th, 2025 – By Washingtonian Weather Geeks (follow them on X/Twitter, Instagram or Facebook). First posted on their substack here.
Some folks, especially northwest of DC, saw their first accumulating snow yesterday as some strong squalls pivoted through the area, but this was just an appetizer for what is looming on Monday.
The Setup
A strong shortwave, which is essentially an area of energy in the atmosphere, has just moved ashore on the West Coast of the US near Oregon. This wave will track across the country from west to east over the next few days. Once over the Great Plains, this wave will wrap up and amplify into a Bonafide low pressure system, drawing moisture up from the Gulf of Mexico and flinging it into a very cold airmass in place over the middle part of the country. This will kickstart a major winter storm over areas like Kansas, Missouri, Illinois, Indiana, and Kentucky.
Now, normally, a low pressure system amplifying that far northwest would lead to a cutting storm track that brings pure rain to the DMV. However, that will not happen here because of a piece of energy sitting over the Great Lakes that is working to suppress the storm south. Instead, the low pressure center will track straight east across the lower Midwest, southern Appalachians, and southern Mid Atlantic. This will put us on the cold northern side of the system, and will ample cold air in place before the storm arrives, significant wintry precipitation is likely across the entire area beginning Sunday night and lasting into Tuesday morning.
However, despite how close in range we are to this system, there is still a large amount of model discrepancy on how far north this tracks. The degree to which the shortwave amplifies over the Midwest, as well as the strength of the suppressive energy to our north, will determine who exactly sees the heaviest snow, who has to worry about sleet and/or freezing rain mixing in, and who has to worry about being too far north. As of right now, however, the highest totals look to be concentrated in and around the DC area – possibly a bit north, possibly a bit south.
The Storm – Phase One
Precipitation will likely begin to move into the area around or just after midnight Sunday night. It should start as snow for the entire area considering the extremely cold airmass in place upon arrival. However, a process known as warm air advection will begin to cause the sleet line to creep north towards DC as the night progresses. At this point, the low pressure system is still to our west, so all of our winter weather is being caused by an enormous amount of gulf moisture ramming into our cold air. However, with strong southerly winds in place, the sleet line will likely make it quite far north, possibly more than modeled. DC proper may mix for a period of time, and if this happens, it would push the highest totals further north into Maryland.
However, for whatever length of time you see snow on this front end, it is likely to be very heavy and accumulate quite rapidly. This storm has a very impressive moisture pull straight from the Gulf of Mexico to our region, so snow rates will be quite impressive as long as this atmospheric river is aimed at us. Wherever the heaviest banding sets up in this front part of the storm will likely experience the highest totals overall, as this “front-end thump” will make up the majority of the precipitation totals.
The Storm – Phase Two
The second part of the storm will commence when the low pressure system begins to approach our longitude and slide off to our south. At this point, we will lose the strong southerly flow forcing our heavy precipitation and snow/sleet rates will lighten up quite a bit. There may even be somewhat of a dry slot, which is typical with systems approaching from the west, as the low transfers to the coast and we lose most of our forcing. This will likely begin to happen around noon on Monday, or possibly a bit later. For many, it may seem like the storm is coming to a close when this dry slot moves in, but that is not the case.
The Storm – Phase Three
The final part of the storm will likely start Monday evening as the low pressure moves offshore and an inverted trough feature begins to set up over the region. These interesting and oftentimes difficult to forecast events happen on the backside of low pressure systems where converging lower-level winds force atmospheric ascent, and, in turn, precipitation. While likely not as intense as the front side of the storm, this may catch some people by surprise. These features can produce very heavy localized bands of precipitation, and with the screaming southerly winds no longer a factor, areas that may have seen sleet or even rain beforehand will have a shot to see snow with this.
Impacts
The entire region will likely see significant interruptions to daily life from this winter storm. With such a cold airmass in place ahead of the storm, snow will have no issue sticking to roads immediately upon precipitation onset. Impacts will be no less severe in areas that mix, as, while sleet cuts down on final totals, it is much denser and more difficult to remove from roads. Areas of southwest and also possibly central Virginia will also likely see dangerous freezing rain from this setup, as surface temps remain colder than the temps aloft.
One positive to this storm is that, since the snow is not being forced by a strong low pressure system and instead occurs in a more overrunning fashion, there will be little to no wind as the heaviest of the snow falls. This should prevent drifting and also make damage to trees in areas that see heavy wet snow and/or ice less likely.
Now, as for snow totals, which is what many people are most interested in, there is still a large amount of uncertainty. Some models, such as the European, Canadian, and UKMET, show the heaviest axis of snowfall south of DC, while others, such as the GFS, NAM, and HRRR, show it near of even north of DC. While important to take note of, the furthest south solutions are mostly likely incorrect, as warm air advection usually overperforms in the short range and drags low pressure systems north. However, a range of outcomes is still on the table.
For now, a widespread 4-10” of snow is likely across much of the region, with locally even higher amounts possible depending on banding. Our second call is attached below, along with the National Blend of Models and the official NWS forecast.
We hope everyone stays safe and warm during this winter, and make sure to follow us on Twitter/X for more frequent upda
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