Expanding cold increasing the chances for snow around Thanksgiving

AccuWeather

AccuWeather's Geoff Cornish breaks down the potential for snow in the days surrounding Thanksgiving.

Transcript

00:00The weekend is upon us, the weekend preceding Thanksgiving.

00:04The holidays are virtually here, whether you're ready for them or not.

00:07And with the forecast feed, we're going to be sniffing out snow.

00:10There will be some measurable snow in the north-central U.S.

00:15and into the Great Lakes region at times over the next seven days.

00:18The plows will be out, some of you will be shoveling,

00:20and it's time to get those snowblowers ready.

00:22Let's look at some headlines, then we're going to jump into the details here

00:26with some models, and we'll come back to our graphics

00:28to kind of summarize things.

00:30So we are saying there's a chance.

00:31This is inspired by Dumb and Dumber, but there's nothing dumb about our forecast.

00:36We're taking a look at a transition to much colder air

00:40across the Great Lakes, the upper Midwest especially,

00:44and into next weekend, the northeast as well,

00:47with potential for some significant snow near the Great Lakes.

00:49And even some of this may not be lake effect.

00:52We actually have a larger-scale storm system

00:54that could bring some meaningful snow as well.

00:57Denver, we're even looking at you.

00:59More extensive cold will follow into early December,

01:01and we're going to be watching the area from the northern plains to New England,

01:04and at times the front range.

01:06Denver will be watching.

01:08You have some snow potential in your forecast.

01:10Now, before we get into the models,

01:12just a quick look at Thanksgiving.

01:14We're going to be dealing with some colder air in the north-central U.S.

01:18There will be some lake effect snow.

01:20You can see the wind streamlines on here.

01:22I'm going to draw some arrows just to indicate the flow across the Great Lakes,

01:26and that is, again, what's going to deposit some snow

01:28in all the usual spots downwind of the Great Lakes.

01:32But as we jump into the models, we have a little bit of a disparity here,

01:36as always, between the GFS and the European model.

01:39These are two of the primary computer models that we look at

01:42that generally have the most success when we're looking at maybe 3 to 10 days into the future.

01:47And here we're looking 20,000 feet up into the atmosphere.

01:51These bright colors, I know it may be kind of a,

01:54it looks like just a kaleidoscope of nonsense,

01:56but this is vorticity, a measure of spin in the atmosphere.

02:00If you have those bright colors to your west,

02:02and if it's coming your way, the atmosphere is likely to produce lift.

02:06That leads to more cloud production, more precipitation production,

02:09and that's the stormy setup that we often look to.

02:12Now, with the GFS, this is kind of the more interesting of two scenarios.

02:17What I want you to notice is we're watching two separate disturbances.

02:21The primary trough in the northern branch of the jet stream,

02:24and then there's the southern branch of the jet stream that is contributing this disturbance.

02:29If these are close enough to one another, if the larger one can absorb the other,

02:34it's fed by some of the energy, it imports more moisture into the system,

02:38and we get into business in snowflake production.

02:41And you'll notice that the GFS model, they are close enough to one another.

02:46The disturbance over Nebraska gets generally ingested into the circulation for the most part.

02:53It's not perfectly together, but ultimately it gets ingested into that storm system,

02:58and it feeds, at least a contribution of that helps to feed the strength of the low-pressure system

03:04Tuesday night and Wednesday here in the central U.S.

03:06That's the GFS.

03:07With the European model, we actually see kind of more of a separation.

03:11Here we are Tuesday morning, and you can see this disturbance is all the way down in Indiana compared to the Dakotas.

03:18So Indiana and Dakotas compared to more of a Wisconsin, Iowa, and Dakotas.

03:25So again, there's more interaction in the GFS compared to the European,

03:29and that makes this midweek storm that will be causing travel trouble,

03:33Anna's been telling us about this here on the AccuWeather Network and on AccuWeather.com.

03:37You can see some of the videos.

03:38That leads to a difference.

03:39So in the real world, at the ground, where it all matters, that's where we live,

03:44again, the GFS, you get a slightly more energetic storm system with some pretty good snow

03:49into the Dakotas with this one Tuesday into Wednesday.

03:53Meanwhile, in the world of the European, remember, this was the weaker system

03:56because the two disturbances were more separated from one another.

04:00Here, you can see there's some snow out there, but it doesn't have much staying power,

04:04and it gets cold.

04:06It does get cold.

04:07In fact, if you look at the thickness lines here, the 540 thickness line,

04:12if the atmosphere is warm, it expands.

04:14If it's cold, it constricts.

04:15So we get lower thicknesses.

04:17The atmosphere is more compressed in a colder air mass.

04:19It's going to be colder regardless of how this plays out.

04:22But again, do we see decent snow last for a couple days in the Dakotas, Tuesday, Wednesday?

04:27Or is it really just a little bit of maybe a one- or two-inch event that quickly scoots away?

04:32And again, there's potential out there because of the interaction between the two.

04:37If the GFS is correct, it could be significant plowable snow,

04:41maybe half a foot in some parts of the upper Midwest.

04:44Now, that's the first storm system.

04:45Let's go back to the upper-level flow, and then we get into the weekend.

04:48And here we have the GFS model.

04:51It's one trough.

04:52It scoots east and pulls out.

04:54And then we have another big trough, really sets in, a big, deep one,

04:58across the southwest on Sunday afternoon.

05:01This is the Sunday following Thanksgiving.

05:03In the European, I'm going to take us from that time, a little bit different out there.

05:07Look at this.

05:08You can see this trough cuts in a little more aggressively, a little more eastward.

05:14And by Sunday evening in the European,

05:16we've got a pretty good negatively tilted trough sloped down and to the right.

05:20That's the type of storm system that produces a stronger impact.

05:25In the GFS, it's positively tilted.

05:28Therefore, it's a little bit weaker.

05:29We have impacts in California, but it would not have the same firepower.

05:34So weaker impacts for the central U.S. and the north central in the GFS.

05:39In the weekend storm, stronger set up here in the European.

05:43Remember, there's cold air in place ahead of this.

05:45So how does this play out at the surface?

05:47Let's go to the stronger solution here.

05:51Just again, just to get everybody on the same page, including myself,

05:54in the European stronger scenario for the weekend, GFS weaker scenario.

05:59So let's go to the European.

06:00Look at this.

06:01This is a pretty powerful storm system.

06:03Look at all these isobars, tightly packed, strong winds.

06:05This could lead to near blizzard conditions for some,

06:08and also some stronger storms in the southern plains.

06:11It'd be one of those late November storms that bring a variety of impacts.

06:15Pretty good snow there in Denver.

06:16Meanwhile, as this ramps up Sunday and Monday, that's a high-impact storm.

06:20Look at this Monday evening.

06:22Heavy snow for parts of the Dakotas and into Minnesota.

06:26And meanwhile, slightly weaker setup, but still an impactful storm,

06:30no matter how this plays out, scenario one or scenario two.

06:34It may be even more delayed with the one.

06:35But regardless, ending with just a summary forecast,

06:40next weekend, there is potential.

06:42We could even arguably include parts of the area around Denver in this,

06:47but especially in the upper Midwest, there's no potential.

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