Significant Winter Storm To Likely Impact Parts of the Southeast Late Week

snowfall map

Synopsis

A potent shortwave will dive southeastward across the Rockies and enter the Southern Plains on Wednesday. The feature will develop into a closed low on Thursday over the Mid-South, triggering the development of a surface cyclone along the Gulf coast the same day. By early Friday, the system will reach the Georgia/South Carolina coast and trek up along the Southeast coast on Friday.

This system has a chance to bring a round of accumulating snowfall on Wednesday to far eastern Oklahoma and Kansas, northwestern Arkansas, southern/western Missouri and areas northward on Wednesday. A snowstorm will impact parts of the Southeast late Thursday into Friday, potentially including far northern Alabama and Georgia, eastern Tennessee, far southeastern Kentucky, far southern Virginia, Upstate South Carolina, and western/central North Carolina.

Forecast Discussion

As the low strengthens late Thursday into early Friday, a warm nose will attempt to works its way into southeastern Tennessee, northern Georgia, northern South Carolina, and western North Carolina. However, the passage of the strong mid-level closed will offset the magnitude of warming that otherwise would have occurred in the low levels. Strong frontogenesis across northern Georgia, upstate South Carolina, and central North Carolina could provide the necessary forcing to bring the freezing/melting level close to the surface in those areas. Evaporational cooling will also initially lower temperatures at and just above the surface. Despite lackluster cold in place across lower elevation regions in Georgia, the Carolinas, and even Southeast Tennessee, the dynamics of this storm system may actually ‘make up’ for it. Plus, the system will pass during a timeframe when temperatures are normally colder anyway (at night and early morning!).

We have quite an interesting scenario taking shape for the end of the week. The surface low on Thursday into Friday will take the classic track that favors significant winter weather across the Southeast. However, the pre-existing air mass across the region will only be marginally cold. Although colder air will get wrapped around the backside of the storm system, even it will be marginal. As a result, most regions across the Mid-South and western half of the Southeast region will likely just get a nasty, cold rain on Thursday.

Snow accumulation forecast for late-week winter storm

Snow Accumulation Forecast (Attempt #1)

  • I included a 5–10+ inch accumulation zone in the mountains of Georgia, South Carolina, North Carolina, and Tennessee, where soil temperatures are already relatively cool and low-level temperatures should be sufficient for snow (or a rain to snow transition).
  • I expect noteworthy accumulations to fall across the Cumberland Plateau, far northern Alabama, northern Upstate South Carolina, and western central North Carolina. A transition of rain to snow will likely occur as the mid-level and surface low wraps around colder air.
  • Far southeastern Kentucky and lower Virginia could get accumulating snow; however, if the surface low jogs slightly south, most precipitation will remain south of the area.
  • I outlined a region in pink, where this storm system could potentially bring unexpected accumulating snowfall. I currently have included the northern metro of Atlanta in this zone. Again, strong forcing will need to offset the very marginal air mass in place. Otherwise, expect a cold rain.
  • I expect only a cold rain across the rest of the Southeast and Mid-South.

Please stayed tuned for subsequent forecasts on this potential winter storm. Don’t forget to download our Southern Snow app. Our app provides you with snow forecasts from both Firsthand Weather AND your local National Weather Service office. Check it out!

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Southeast White Christmas? Part 1

southern snowstorm

We made a post the other day asking our followers when they had experienced their last White Christmas. Quite a few said never. A few others said back in 2010. Since many of our readers live in the Southeast, those responses weren’t all that surprising. Climatologically, having snow on the ground at some point on Christmas Day in the Southeast is exceptionally rare. Though, not impossible. . .

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In the coming days, we’re going to discuss those years that the Southeast had a White Christmas. They may be few and far between, but there’s value in revisiting the conditions and overall pattern that brought those rare snowy Christmases.

In this article, we will take a peek at how the pattern will likely evolve from now through Christmas Day. The overall pattern will remain quite progressive. Meaning, most regions of the U.S. will not remain under the influence of troughing or ridging for more than a few days at a time, if that. Unfortunately, such a setup favors lots of swings in temperatures.

For the first time in a while, temperatures MAY actually feel like Christmas on Christmas Day in the Southeast (give or take a day). Most model guidance agrees that a longwave trough will develop across the eastern half of the U.S., as ridging amplifies across western Canada and eastern Alaska. This pattern configuration favors anomalous warmth along the West Coast and into the Southwest. An anomalously cold air mass will sweep across most locations along and east of the Rockies. Even Florida could get in on this chilly air mass!

Projected departure from average temperatures Christmas Day morning

Most reading this post are already wondering, will there be any precipitation to go along with that brief shot of cold air in the Southeast? Maybe. The models indicate that a shortwave could become detached from the main flow and close off into a mid-level low as it approaches southern California and Baja California sometime next week. It would eventually get swept eastward by the southern stream. But features like these can meander for a while or even retrograde westward before getting reabsorbed back into the main flow. If the cold air intrusion is a strong as modeled, there could be about a two-day window, probably a day or two after Christmas, that any passing southern stream system could produce wintry weather for parts of the Southeast.  

Taking a look at projected 500mb geopotential height anomalies from the latest European model, it already has the longwave trough lifting northeastward by the 26th. At the same time, the closed low quickly moves eastward across Texas/northern Mexico. Residual cold air may hang around for a day or two tops, thanks to a departing surface high. This closed low, or any southern stream feature for that matter, would need to encroach upon the Mid-South and Southeast just as the long-wave trough begins lifting out.

Longwave trough lifts out the day after Christmas

If I were a betting man, I wouldn’t put anything down on a White Christmas happening across the Southeast at this time. Yes, there could be a very brief window for some action right after Christmas Day, but that window appears to be short. I’d certainly recommend not getting too hung up on model guidance in the coming days. Large inconsistencies may exist in how models handle any closed low that develops. But hey, a small chance is always something to watch!

Make sure you download our new mobile app that’s dedicated to providing you with detailed snow forecasts. Firsthand Weather recently launched a new mobile app called Southern Snow for iOS devices, which gives you a snow forecast for anywhere in the U.S! If snow starts showing up in the forecast, Southern Snow will let you know.

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Be sure to join us on the Firsthand Weather this Saturday at 2pm ET to get our official White Christmas forecast for the entire U.S.

Find out if you’ll have a White Christmas 2020 this Saturday on Firsthand Weather

The featured image used in this post is courtesy of Jennifer Kyzer, who captured a great shot of an early season snowstorm in SC in 2014. 

Updated Snowfall Forecast

We continue to monitor the chance for snow across much of the South and Southeast from Monday night into Tuesday. Most of this region will see the opportunity for snow accumulations that could impact travel. The worst travel conditions appear to be on Tuesday from northern Louisiana eastward into northern Georgia.

The first areas to experience snow will be far eastern Oklahoma, northeast Texas, Arkansas, western Tennessee and northern Louisiana by late Monday night. The rain & snow will move east and southward by early Tuesday morning into central Tennessee and parts of Mississippi (see Fig. 1) before moving further east into parts of Alabama and Georgia later on Tuesday (see Fig. 2). Parts of upstate South Carolina and North Carolina should get in on the rain & snow later in the day on Tuesday (see Fig. 3).

Fig. 1: Future radar late Monday night (please note: this should be used as an estimate–exact placement of precipitation may change)
Fig. 2: Future radar early Tuesday morning (please note: this should be used as an estimate–exact placement of precipitation may change)
Fig. 3: Future radar Tuesday afternoon (please note: this should be used as an estimate–exact placement of precipitation may change)

Accumulations do look likely from late Monday though Tuesday. The event being a few days out makes it extremely difficult to forecast snow accumulations, however. There are two negative factors for accumulations. I) Monday (the day before the snow) will be warm across this region, which will lead to warmer ground temperatures, and II) the window for snow is only about a 4-6 hour period. Even with these two mitigating factors, this event will be the best chance so far this season for accumulating snow across the South and Southeast.

The snow rates should exceed melting and the best chance for accumulations will across northern & central Mississippi, Tennessee, northern & central Alabama, northern Louisiana and northern Georgia. Guidance is evening indicating some instability, which could lead to convective banding of snow (this is where the heaviest snow totals are possible). It is too difficult to pinpoint where those bands may setup. That is almost a nowcasting scenario. Secondly, areas that see snow pre-dawn on Tuesday will have the best chance to see accumulations and nasty road conditions. Even though it is difficult to forecast snow accumulations this far out, I wanted to provide you with a second preliminary snow accumulations map (see Fig. 4). Please note, this will likely change over the next 48-72 hours as we get closer to the event. It is possible the polygons may need to me reduced or expanded, and snow totals may need to be increased or decreased.

Fig. 4: Preliminary snow accumulation map

The South and Southeast are not the only regions that have snow in the forecast. Coastal areas of North Carolina and Virginia may see snow beginning Monday due to a coastal low that will quickly deepen off the coast. This could allow a band of snow to setup from Virginia Beach down into eastern North Carolina. If this happens, it is possible heavy accumulations may occur, which is why this small area is included in the 2-5″ zone. It should be noted, most numerical guidance indicates the low will be too far off shore to aid in precipitation chances for this area, but we believe the low may closer to the coast, thus, have reflected this in the snow accumulation forecast. Regardless, snow chances increase for this area by Tuesday night into Wednesday. Those snow chances also increase for the rest of the Mid-Atlantic and the Northeast by Wednesday. Parts of the Northeast, Great Lakes and Ohio Valley will see multiple snow opportunities from Sunday through Wednesday so accumulations are likely (see Fig. 5). More than one foot of snow is possible for parts of the Great Lakes region where lake effect snow band establish themselves.

Fig. 4: Preliminary snow accumulation map

Please keep checking back for updates as this is a fluid forecast and changes may be needed!

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

Be sure to follow us on Facebook for numerous updates on this event throughout this week. Also, please give us a follow on Instagram. We’re really trying to grow that account. As always, continue to check back with us daily for new updates.

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.

Early-Season Winter Event Looking More Likely For Parts Of The Southeast

It’s only December 6th and we’re already talking about the potential for a winter event across parts of the Southern Plains and the Southeast. Since we’ve already covered the forecast for the Southern Plains, I’m going to focus primarily on the Southeast. A system earlier in the week moved across the Northern Plains and has now trekked northeastward into Canada. A cold front associated with that system pushed across the eastern U.S. earlier in the week and has now made its way to the Gulf coast and along the East coast. Behind the front, a broad trough has become established over the eastern two-thirds of the nation. With this kind of setup, mid to upper-level wind flow across the southeastern U.S. is generally from the southwest; thus, the initial cold front has already slowing down and will eventually stall out near the Gulf coast and East Coast. The shortwave feature that will be responsible for bringing snow to Texas is going to interact with the broad trough and a second shortwave feature. This interaction is going to sharpen the trough, which will eventually extend into the Southeast. Given that the frontal boundary will be stalled out near the coast as all of this is unfolding, this is going to induce the development of a surface low pressure system that will ride along that boundary along the Gulf coast and up the East coast.

For those in the Southeast, most who have lived in that region for any extended period of time know that most winter storms that unfold across that region involve a low pressure system developing near the coast along the Gulf of Mexico, which then crosses over and moves off or along the East coast. Since cold air is often limited, forecasting these events can be challenging throughout the extent of the event. Since it’s still early December, that even adds additional challenges.

First and foremost, it should be noted that most of the model guidance suggests at least some wintry weather (snow!!) across the Southeast (more on specific locations in a bit). However, snowfall accumulation projections range from no accumulations to several inches of snow for parts of the Gulf coast northeastward to the East coast. For events such as these, I either like to see that a pre-existing colder air mass has become established over the region before the event, or that there is going to be sufficiently cold air provided by a certain atmospheric feature in time for the event (for example, high pressure over the Northeast). The first cold front that has now pushed through the region has brought in much colder conditions, but given the broadness of the trough and the time of the year, there really needs to be an additional source of colder air spilling into the region. Throughout the day on Thursday, the colder air to the north-northwest of the area will continue pushing southeastward, but despite that, we’re still going to be dealing with the classic borderline winter storm/event in the South.

The NAM model has generally been the most aggressive with snowfall accumulations across the Southeast, which extend those accumulations down the Gulf coast. The hefty snowfall accumulations occur for most locations later on Friday into Friday night, even though it has precipitation (mostly rain) spreading across many locations in the Southeast tomorrow. If you’re looking to get noteworthy accumulating snow, it’s best this event occur later on Friday like what the NAM is showing for many locations, and given that it would be getting dark or already dark, this would greatly increase the odds that temperatures would be sufficiently cold throughout the atmosphere to support snow or a transition from rain to wet snow. This would also allow more time for colder air to seep southeastward. The GFS is less aggressive, primarily because it has the heaviest precipitation moving out more quickly. The European model, which is generally more reliable, falls somewhere in between with accumulations. Remarkably, all of the guidance is at least showing some accumulating snowfall for some locations in the Southeast. However, it should be noted that these maps depict a 10:1 snow to liquid ratio, but given the warmer ground temperatures and the fact that rain will mix in (at least initially), these totals could be overestimated for some locations on all three models. However, higher snowfall rates across some locations could offset some of these hindrances for snowfall accumulations.

NAM model snowfall map

Figure 1: NAM model snowfall accumulation forecast for the next 72 hours. Source: Tropical Tidbits

GFS model snowfall map

Figure 2: GFS model snowfall accumulation forecast for the next 72 hours. Source: Tropical Tidbits

European model snowfall map

Figure 3: European model snowfall accumulation forecast for the next 90 hours. Source: Ryan Maue

Remarkably, residents living in southeast Louisiana, southern Mississippi and possibly extending into western parts of Alabama have the greatest chance of this event unfolding for them. Since this region will be some of the first locations to feel the effects of the colder air mass digging southeastward, precipitation developing and moving across the region will have the greatest chance of making the transition to snow either late Thursday or early Friday. Predicting snowfall accumulations from eastern parts of Alabama into Georgia and South Carolina gets quite challenging. The later this event unfolds for those locations on Friday, the better for accumulating snowfall. The more aggressive snowfall totals that span across parts of North Carolina into southeastern Virginia are warranted. That’s another region that I feel has a pretty decent chance of this event unfolding.

Due to the uncertainty that exists, this will require me to post a follow-up update tomorrow. However, residents in the general swath of accumulations that are being depicted by the model guidance should prepare for this event. I expect the majority of accumulations to occur over grassy surfaces; however, issues on the roadways could occur for localized regions where the snowfall rates are higher. That will be something that we’ll have to determine tomorrow. Nonetheless, it is still very early in the meteorological winter, and it’s remarkable that we even have an event such as this to forecast! Firsthand Weather will keep everyone updated as much as possible before and during this event and will be posting numerous updates on our Facebook page.

Major, Possibly Historic, Winter Storm On The Way

snowstorm analog

There are is definitely a lot to discuss with the upcoming Friday/Saturday winter storm that could end up being significant and potentially historic. While it has become certain that there will be a big winter storm, the uncertainty lies in determining the overall storm track and placement of heaviest snowfall accumulations. Given that it’s only Tuesday night, a lot can change on specifics, so it’s important to keep that in mind, especially when reading any forecasts that are based entirely on forecast models. I know I bring this up a lot, but I always want my audience to be aware of the limitations of such an approach. I’ll be discussing the various solutions that are being shown on the latest model guidance, but in addition, I’ll be pointing out specifics that the models may not be handling well with this system. Due to the complex nature of this upcoming system, I may be required to do a follow-up article that includes some changes, if needed.

Discussion (Friday through Weekend System):

A vigorous shortwave (disturbance) will be moving into the Pacific Northwest, and as it moves southeastward, it will dig into the Southern Plains. A surface low will move/develop over the Plains in response to this disturbance and move eastward across the Southeast, as this disturbance treks eastward. This will eventually trigger the development of a long-wave trough in the eastern U.S., and colder air should begin getting wrapped around the low pressure system. This energy will eventually transfer to the coast, and a coastal low should move up the coast.

There is higher than average confidence on how this system will evolve, but the specifics on the exact track are going to be difficult to nail down. The GFS model and most of its ensembles, along with the Canadian model, have the original surface low moving up through Tennessee before its energy gets transferred to the coast. The European model is now showing a more southerly track across the Gulf Coast states, which would allow for some accumulating snow to fall farther to the south and would shift the core of heaviest snowfall farther south, also. On almost all guidance that I have seen, a pretty stout warm nose is initially present well north into eastern Tennessee and even southern regions of Kentucky. This is likely due to the placement of the original surface low and the orientation of the long-wave trough.

To complicate this forecast even further, a cold air damming scenario could set up east of the Appalachians, allowing temperatures to stay below freezing at the surface in places, despite the warm air advection that will likely try to pump northward, overrunning this cold. This sets up a tricky forecast from Northeast Georgia, parts of Upstate South Carolina/extending east and central-east North Carolina (excluding the coast) Even with the system taking a more northerly track, the colder air at the surface may not get out quickly enough before a nasty ice situation unfolds across the mentioned areas.

The latest Canadian represents this possible ice situation well on Friday:

Canadian ice

Snowfall will likely start falling across northern and central Arkansas Thursday night going into Friday and expand into parts of southern Missouri and into the western third of Tennessee. Snow will eventually spread eastward into Kentucky and parts of the lower Ohio Valley through Friday and eventually expand into the Mid-Atlantic states including West Virginia, Virginia, North Carolina, Washington, D.C., and into the Mid-Atlantic states later on Friday going into Saturday. Southern Pennsylvania, including Philadelphia could be hit hard, along with parts of New England, especially along the coast. This is going to be a slow-moving system, and backend snow could fall as far south as the northern third of Mississippi, Alabama, Georgia, much of Tennessee, and into northern parts of South Carolina. Depending on track, there will likely be a region of very heavy snowfall amounts falling, including many of the regions that I just mentioned. This system has the potential to rival or beat some of the historical winter storms of the past and is looking similar to the January 1996 blizzard.

Just To Reiterate A Few Points:

• The European model has been depicting a more southern track. I’m skeptical of this solution currently, although I’m not ruling it out entirely. If there is a southern trend in the track, snowfall accumulations would likely fall farther south and the heaviest snowfall accumulations would shift south. This would also exclude the most northern regions mentioned in this article from getting heavier accumulations.
• A warm nose extending as far north as eastern Tennessee could cause many of these regions to get rain before possibly seeing a transition to some snow (possibly heavy) on the backend of this system. Accumulations would be possible but not as heavy as in surrounding regions.
• Due to cold air damming, an icy situation could setup initially across northeastern parts of Georgia, Upstate SC and possibly extending eastward across the state and into central-eastern portions of North Carolina (excluding the coast). A transition to snow could eventually occur in these regions, with higher accumulations occurring the farther north one goes.
• The core of heaviest snow accumulations could fall somewhere from northern Arkansas/southern Missouri into northwest and north-central Tennessee, across Kentucky, and particularly into the Mid-Atlantic states extending into parts of North Carolina. Many regions in this zone could be measuring snow in feet before all is said and done.

I will continue to monitor this situation closely. I posted a map that shows a 72-hour snowfall output map based on 15 previous winter storms that look similar to this one, courtesy of CIPS Analog Guidance:

snowstorm analog

Just keep in mind that I’m expecting snow to fall west of this region as mentioned in my article, but I did want to show you this map.

Anyway, I will definitely have to make edits to this forecast, since it’s a difficult and tricky forecast. Someone is going to get hit very hard with this winter storm, and at this point, it’s a matter of determining where. More updates to come. . .