Major Early-Season Winter Storm Becoming More Likely But Uncertainty Remains

In my last article, I primarily discussed the big picture and detailed the regions that could be at risk for wintry precipitation this weekend. We’re now getting to the point that we can begin discussing precipitation-type; however, we won’t be releasing accumulation maps until later in the week. Let’s get right into things.

The surface low will develop and trek across southern Texas Friday into early Saturday. This feature will strengthen as it moves across the lower Gulf coast states over the weekend and then off or along the East Coast late weekend/Monday.

The models have recently begun to project another shortwave feature swinging across the Great Plains and then phasing (combining) with the southern stream system moving eastward from California. This could result in a stronger surface low, especially as it approaches the East Coast, and given these trends, I fully anticipate that most of the southern right quadrant of the U.S. will receive heavy precipitation this weekend. The Weather Prediction Center graphic below shows this quite well in their days 4-5 forecast that covers Friday night through Sunday night. Of course, some of these areas will be getting snow and/or ice (or a combo), so for example, an inch or two of rain equates to quite a lot of snow if an all-snow event occurs for a given location. For the regions that manage to be on the snowy/icy side of this system, I expect a significant, early-season winter storm event.

weather prediction center forecast

Let’s start from the Four Corners region and the Southern Plains and then work our way eastward. I’ll reference the latest operational European model, and then tell you what I agree and disagree with.

The swath of snowfall accumulations shown to occur from New Mexico to the Texas panhandle and over northern and central Oklahoma and Arkansas look well-placed. Most of Texas (outside of the panhandle), Louisiana, and most of Mississippi (expect possibly the northern part of the state) should only experience a cold rain.

Southern Plains winter storm forecast

Tennessee, the northern third of Alabama/Georgia, and the Carolinas poses the greatest forecast challenge. Strong high pressure will be located to the north, as discussed in my last article, but the low pressure system will deepen as it crosses the Gulf coast states. Additionally, cold air damming will establish itself along the east side of the Appalachians, which will allow cold air at and near the surface to spill into western and central North Carolina, northern South Carolina (including the Upstate), and northeast Georgia. Places such as Atlanta, GA and Chattanooga, TN will likely be placed relatively close to the cold rain/frozen precipitation line.

Given the latest trends in surface low strength, warm air will likely get advected over the colder air at the surface; thus, a transition from snow to ice (sleet/freezing rain) will probably eventually occur across some locations. Since I anticipate the presence of this warm nose aloft, I currently am not ruling out the possibility of an ice storm somewhere across northeastern Georgia, South Carolina, and across central parts of North Carolina. Colder air will be deeper across western North Carolina and into Virginia; thus a significant snowstorm will be more probable across those locations. The latest European model depicts this well. It has the heavier snowfall totals across northern Upstate SC, western and central NC, and southern Virginia. The European model is a bit more bullish on snowfall totals south of I-85 across northeast Georgia and the Carolinas than I would be at this point, but that’s because I believe ice could cut back on total snowfall amounts in those areas. The Atlanta area needs to cautiously monitor the latest forecasts, even though I believe the main event will be to your north and northeast. BUT, it only takes a ‘little’ snow and ice to cause a big mess. That currently is my biggest uncertainty with this forecast.

Southeast winter storm forecast

The European model is a bit more generous with snowfall accumulations into southeastern Tennessee than the GFS model (and the Firsthand Weather forecast, for that matter) has been. I have higher confidence that snowfall accumulations will occur in northern Tennessee and southern Kentucky, due to the availability of colder air. However, I continue to monitor southern Tennessee closely. That’s still a very tough call.

I expect only rain along the southern half to two-thirds of all Gulf coast states from Mississippi eastward. In fact, there could be thunderstorms within the warm sector of this system.

To summarize, the big story will be the swath of snow that falls from parts of the Southern Plains/Southwest eastward into parts of Tennessee and Kentucky. The biggest story will likely be the significant winter storm that unfolds across parts of the Carolinas, northeast Georgia and Virginia. Determining the exact cut-off between frozen precipitation and cold rain remains extremely challenging. For those located along and near the southern edge of potential accumulations, please be aware that significant modifications to the current forecast may need to be made over the next couple of days.

Please continue to follow Firsthand Weather on Facebook, and please follow us on Instagram if you haven’t already. We will have an accumulations forecast later this week.

What’s All Of This Talk About A Southern Winter Storm Next Weekend?

Is it really that time of year again already? For most of us, we skipped fall and went straight into winter last month. Although wintry precipitation has already impacted parts of the United States, the first legitimate chance for a winter event farther to the south will come in about 6 or 7 days. The goal is never to address local-scale specifics in the long-range, but we can begin discussing the pattern that could support a winter storm. This allows us to establish an initial framework by looking at the big picture first, and then we can build upon that foundation with specific details in the coming days.

Will the mid and upper-level atmosphere support an early-season winter storm across portions of the South?

The first step, especially at this point, is to look at what’s currently going on well-above the surface and attempt to determine how that pattern will evolve over time. From this, it’s possible to infer what could occur at the surface without it being necessary to look at modeled surface output at this point. A closed mid-to-upper level low pressure system was located over the central U.S. yesterday (Saturday) and has now moved northeastward over the Great Lakes. A cold front, associated with a surface low that developed in response, will push all the way through Florida by mid-week. Broad troughing will remain established over the eastern U.S., keeping an anomalously cold air mass in place.

Now, here’s the main reason I made a post on November 29th about the possibility of a winter storm. A split-flow regime is expected to become established over the far western U.S. Let me explain what that means. With this setup, the jet stream splits into northern and southern components. The northern component (the polar jet) will extend well into western Canada and Alaska, while the southern component (the southern jet) will eventually dip into Baja California. Now, check out the map I posted under this paragraph. You can see the broad trough over the eastern U.S., ridging over western Canada and Alaska, and a shortwave extending into southern California and Baja California. I drew arrows to indicate mid and upper-level flow. Do you see how the flow begins to merge back together over the central U.S.? When this occurs, this is called confluence. As this confluence occurs, this will result in sinking motion over the Great Plains and will support the development/maintenance of strong high pressure over that area. Winds flow clockwise around a high pressure system in the Northern Hemisphere, and cold, Canadian air, will wrap around on the east side of this high. There’s your cold air source.

GFS 500 mb map

This will allow another cold front to push southward, and a surface low will develop in response to favorable dynamics just to the east of the shortwave over California. As this shortwave treks eastward late week into early weekend, so will the surface low, which will probably ride somewhere along the frontal boundary. This will result in rainfall across drought-stricken southern California and the Southwest and a swath of wintry precipitation that will extend somewhere from the Southwest/Southern Plains to the East Coast.

If you were to ask me how far to the south I believe frozen precipitation will occur, in short, I’ll tell you I don’t know. But, I’ll give you some insight on this. With conditions favoring high pressure over the central U.S., I’m comfortable saying that it wouldn’t be too difficult to get frozen precipitation (snow and/or ice) as far south as parts of Oklahoma, Arkansas, and Texas. Farther eastward into Tennessee and northern Mississippi/Alabama/Georgia, it becomes a bit more of a tough call. I’m especially paying close attention to northern South Carolina, most of North Carolina, and parts of Virginia, due to the potential for cold air damming to establish itself east of the Appalachians as surface high pressure moves eastward. That’s why in our ‘best chance for wintry precipitation’ map (shown below), we currently depict higher probabilities across those locations. Of course, it should go without saying that we will have to modify this map between now and next weekend, and keep in mind that wintry precipitation is not exclusively snow. We can iron out all of those details later.

southern snow/ice forecast

Conclusion:

Again, we’re simply trying to determine how this pattern will evolve. Any unforeseen changes in that would completely throw off my current expectations for next weekend. Have fun looking at all of the snowfall projection maps, but it’s important to understand the major limitations of accumulation projections this early in the game. And no, I’m not expecting nearly 3 feet of snow in parts of South Carolina like what the European model is showing.

european model snow forecast

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A special thank you to Kimberly Gnat for sharing a picture with us of the snowstorm near Chicago late last month, which we used as the featured photo.