As we cautioned you on Tuesday, the potential for a weekend snow event existed but was generally hanging on by a thread for the D.C. region. As it turns out, that system will take a track well to the south of our region. While we cannot fully rule out the possibilities of some light snow or flurries coming up into portions of northern Virginia during the morning hours of Sunday, the threat for an impactful event has largely faded from the forecast.
What has not changed with the forecast is the big time cold that is heading our way for the weekend. After sunset on Thursday evening, temperatures will be in a nearly constant fall all the way through Saturday morning. Most will wake up Saturday in a completely different season with temperatures dipping down into the lower twenties with teens likely for those northwest of the I-95 corridor, as you can see in the image above. The cold will stick around all weekend long, with most of the region seeing temperatures fail to rise above the 40 degrees mark both Saturday and Sunday. The cold this weekend extending into next week is one of the main reasons the National Park Service pushed back the bloom dates for the cherry blossoms until March 19th - 22nd.
Now, on to the snow chances! Let us first start with what you may see around the region Friday morning because we do not want it to catch anyone by surprise. An Arctic boundary will cross the region early Friday morning, ushering in the colder air mass that will affect the region this weekend. A clipper system across the region will spread a mix of rain and snow across the region beginning in the pre-down hours of Friday. Here in Washington, it is likely to begin as a period of rain sometime after 4 a.m., before changing over to a brief period of snow sometime during the morning commute. North and west of town, this change will happen a bit sooner while south and east of town it is more likely to remain mostly rain showers.
As for snowfall amounts we are really not expecting too much. With abundant sunshine this afternoon and temperatures expected to stretch into the lower 70s, ground temperatures will be well above levels needed to support snow accumulations. If it comes down heavily enough it may briefly coast the grass, cars, decks, etc. (with the best chances of this north and west of town) but even that should melt pretty quickly within a couple hours of the snow stopping. We do not anticipate any roadway issues with this event, with the lone exception being the high elevation roads of the mountain west where the best chance for some delays would be, if there are any at all. The second half of the day may feature some snow flurries, but the bigger story will be the strong winds and the falling temperatures.
As the title of this article hinted at, the weekend snow risks have largely faded. There are several reasons for this, including the cold being locked in a little too strongly this weekend, the air mass being a little too dry, the storm being too disorganized and passing a little too far to the south. Now, we cannot totally rule out a little bit of snow falling across portions of northern Virginia early Sunday morning, but the more measurable snow looks to fall across portions of southern Virginia and North Carolina. The storm system passing this far to our south through will only enhance the cold air mass in place over our region this weekend, allowing the cold to extend into next week as well.
When this weekend's storm system fell apart, social media quickly shifted gears to early next week. So what's up? Various weather models are one again hinting at a potential coastal storm system sometime between Monday night and Wednesday morning along the East Coast of the United States. One thing this particular storm has going for it at this stage is pretty good weather model agreement between both the American and European model and their respective ensembles. This is something that the weekend system never really managed to have at any time, there were always hints that it may not happen. From an atmospheric perspective, the setup shown above is what you want to see if you want to see snow somewhere along the East Coast. Strong areas of high pressure (the red zones) are wrapped around north of the storm (the blue zone) in a feature known in the weather world as a "banana high". This feature locks in colder air down south, while at the same time forcing the storm to hug the coastline pretty closely. Dynamics wise, without getting too technical, know that the upper level features are stronger and much more favorable for a storm then they were modeled to be at any point in time for the potential weekend event.
The good news for snow lovers at least is that there is another event worth watching, one that could perhaps be our last chance of the season for some worthwhile snow in the Mid-Atlantic. The bad news is, as with most winter storm system, there are plenty of things that could go wrong. Remember, many weather models back on Monday were hinting at a big storm here in D.C. this weekend which no longer is expected to happen. The moral of the story is these weather models can change, especially when a storm is out beyond the 3-4 day forecast period. So, once again, we ask that you be careful with any forecast numbers being thrown around on social media over the next few days. We will have to wait until we get into the weekend before models will handle the situation well enough to start putting forecast snow amounts out there.
As for the system itself, a big concern I have is the type of storm system this is. It is what is known as a transferring low, where an area of low pressure will move across the United States, fades as it transfer its energy to a developing area of low pressure of the coastline, which then heads northward as it travels. The reasons these storms occur is due to the mountains to the Appalachian Mountain Range and its vicinity to the Atlantic Ocean. Some of the biggest blizzards in D.C. history are transferring lows, such as the blizzard of January 2016. However, the key with these storms is where the inland low tracks and where the coastal low pops up. The big snow makers here in D.C. tend to dip well down into the southern United States, gathering Gulf moisture, and then transferring their energy off the Southeast coastline before turning north. Currently, models are hinting that the interior may come across southern portions of the Midwest, before transferring the energy off the Mid-Atlantic coastline. Typically, this is a setup that is much better at bringing the higher snow totals to the Northeast/New England as opposed to the Mid-Atlantic.
Another potential concern is the fact this potential storm is forecasted to come after Arctic blocks present this weekend over Canada and Greenland, which are upper atmospheric features that help push cold air southward, are not present early next week. With these factors not in place, the amount of cold air needed for a good March snow event may not be present this far south.
Much like the Sunday system, all we can guarantee at this time is that this is an evolving situation and the forecast can and will change as we go through the next several days. It is worth watching and staying informed on, and we will continue to bring you updates on this system as we get new model data into the weather center. Much like the weekend though (and what seems to have been a theme this winter), there is the chance we could end up with very little or nothing at all here in Washington. Snow lovers, given this winter so far, I think it is best to keep expectations lower for this event, and then be pleasantly surprised if all the pieces come together. We will likely have a good idea of what this system will do by Saturday night or Sunday morning.
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