Here's What We Do (And Don't) Know About This Weekend's Snowstorm

A winter storm will move across the Midwest and Mid-Atlantic this weekend, bringing a blanket of snow to the center of the country and a mix of rain, snow, and ice to the Mid-Atlantic. A significant chunk of Missouri stands to see more than half a foot of snow from this storm. Exact totals—and even what kind of precipitation will fall—is still uncertain farther to the east.

What We Know

A low-pressure system will develop in the southern Plains on Friday.

This storm system will likely track farther north than the one we saw a month ago that produced epic snowfall totals in North Carolina and Virginia. My little town north of Greensboro, N.C., saw an entire season's worth of snow in one day back on December 9. What does that mean in practical terms? A track farther to the north will also force the warm air farther to the north. This storm also isn't as juicy or intense as the storm we saw last month, either. That will help to cut down on snowfall amounts in many places.

The best chance for snow exists in the Midwest.

If you're looking for a good snowstorm, your best bet is probably to stake out in central or eastern Missouri on Friday and Saturday. The latest forecast from the Weather Prediction Center, which I've mapped out above, calls for a widespread area of 6"+ across a huge chunk of Missouri and central Illinois. The bullseye for the heaviest snow will very likely shift around and change over the next couple of days as forecasters get a better idea of what the storm will do, but if you're looking for snow, it's probably a safe bet to meet it in St. Louis. (Booo. Sorry.)

Aside from specific amounts, the storm's life in the Midwest is a fairly straightforward event. From here on, I'll mostly talk about the effects of the storm once it crosses the Appalachian Mountains.

Something's gonna happen back east.

That's the best non-answer I can give for what is likely to unfold overnight Saturday and into Sunday. The storm will run into too much cold air for everyone in Virginia and North Carolina to wind up seeing plain old rain. Some folks will have a decent, shovelable thumping of snow. Others may see a prolonged period of freezing rain or sleet. Many communities—likely to the south of I-85—will just deal with a cold, annoying rain.

Cold air damming will determine the rain/ice/snow line.

This point is in a similar vein to the big storm back on December 9. That storm was able to produce prolific snowfall totals across N.C. and Virginia in part due to the resilient wedge of cold air that dammed up against the eastern slopes of the Appalachian Mountains. This allowed precipitation to almost entirely fall as snow, plopping a foot or more of snow across dozens of counties.

The cold air damming ahead of this storm likely won't be as intense or resilient as what we saw the last time around. There's going to be a layer of warm air forcing its way above the cold air during the storm, causing at least some of the snow to turn into freezing rain or sleet before it reaches the surface. It looks like the best chances for an ice storm exist in the Piedmont Triad, the border region between Winston-Salem, Greensboro, and Burlington in North Carolina and Danville and Martinsville up in Virginia.

What We Don't Know

What kind of precipitation will fall.

Snow is more likely closer to the Appalachian Mountains in the Mid-Atlantic and along a relatively narrow path between the mountains and the Atlantic Ocean. Delightfully vague, right? That's because it depends on how much precipitation is able to coincide with the best profile of cold air through the atmosphere.

Since Saturday night and Sunday are too far out right now for me to post any WPC/NWS forecasts, here's a look at (forgive me, Weather Twitter, for I am about to sin) what the last ten runs of the GFS weather model have shown in terms of precipitation types. Each image shows what the model thinks will happen at 7:00 AM EST on Sunday. The first image starts with the Monday afternoon run of the GFS model and shows 7:00 AM Sunday according to each successive run of the model through Wednesday evening. This shows us the trends from run to run.

Source: Tropical Tidbits

Don't take it literally—it's just a weather model and there's a bunch of caveats to what it's showing above. But you can see how the rain/mix/snow line shimmies with each update of the model. That's due to changes in the track of the storm and temperature profile through the atmosphere near that transition point. Folks close to that transition zone will likely see multiple precipitation types during this storm, complicating predictions of how much will fall and making conditions exceptionally dangerous for travel by car or foot.

How much will fall.

We can't quantify snow/ice that may or may not exist. Not yet, anyway. The best chance for an all-snow storm will lie well to the north of the low-pressure system's track. The folks who manage to stay all snow will see the greatest snowfall totals, since freezing rain and sleet pack significantly pack down accumulated snow.

Right now, it looks like the higher elevations of the Appalachians and central Virginia stand the best chance of seeing all (or mostly) snow from this storm, which would give them a shot at the best snowfall totals. Farther south, enough ice is possible that it could damage to trees and power lines. Again, it'll depend on how much precipitation falls as freezing rain and how long it lasts.

We'll know a lot more about this storm on Thursday evening and Friday.

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