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.
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.
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.
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.