Highpoint Weather Blog

Forecast Discussion

It's been cold this week and it's about to get colder as an arctic airmass pushes into Colorado tomorrow (Thursday) morning.

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An incredibly strong ridge over the eastern Pacific (and north into the Gulf of Alaska / the Alaskan interior) has the jet stream running north to south from the Arctic Circle down to the central Rockies, which is transporting frigid air into the continental United States.

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Many low temperature records are expected to fall from Thursday to Saturday, and parts of every state in the continental United States (except Florida) will see freezing temperatures.

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This airmass is quite dry, but we will see a ribbon of modest atmospheric moisture ahead of it, which will help drive snow in northern Colorado from Thursday morning to Friday afternoon.

Snow will initially impact the northern mountains (generally the Park Range, northern Front Range, Flat Tops, and Gore Range) on Thursday morning with the jet driving some bands of snow over the northern Colorado plains as well. Generally, less snow further west in Colorado, and significantly less snow in southern and central Colorado.

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Early Thursday morning, there will also be some strong winds over the northern Divide (40-70mph) so if you're heading up I-70 before 7am on Thursday, be wary of that.

The leading edge of the cold front is expected to cross the northern Colorado border by 5am, reaching Denver around 7am (give or take an hour for these estimates). On the plains, winds behind the front will be northeasterly and thus get upslope snow going for the I-25 corridor and foothills, at least from Castle Rock and north.

This upslope looks to slacken by the afternoon, before re-strengthening by Thursday evening and possibly into the early Friday AM hours. Thus, for much of the northern I-25 corridor (including Denver), the best chances of snow are Thursday morning and Thursday evening/night.

Looking at a meteogram for Denver, we can see the best upslope comes during both morning and evening rush hour.

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Models remain somewhat undecided on just how deep this upslope will be, and the amount of available moisture, but neither of these factors look particularly potent, so we're forecasting a rather low-end snow storm.

That said, a major wildcard is the snow-liquid ratio, which could be well over 20:1, falling onto surfaces that are plenty cold -- limited melting. Even a little more moisture than expected would translate into several more inches of snow than expected.

So... there is a bit of a boom potential here along the I-25 corridor considering those factors, but we took the conservative road with our forecast -- which was hard not to do with multiple models calling for only 1" of snow in Denver. However, we wouldn't be shocked if parts of the western metro got 8". Our gut says that isn't going to happen, but that may just be the Thai food.

Colder and drier air continues to advect into Colorado into Friday, which will cause snowfall in the northern mountains to decrease and likely wrap up by Friday afternoon. Most of Friday's snow should be pretty light -- the moisture ahead of the front on Thursday should account for a majority of the final snow totals.

Here's what we're thinking for snow totals overall. Note that we didn't include some areas which were expected to receive insignificant snowfall.

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If snow totals end up looking more like the latest HRRR model suggests, then we could bust low in a bunch of spots. However, this model has been struggling a bit this season and generally underforecasting, so we're not reading into it too much.

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Thursday night will be frigid, and with the coldest air not arriving until Friday, Friday night will be even colder. Thursday's overnight lows, according to the HRRR model, are considerable:

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Single digits are likely along the I-25 corridor, with negatives in the mountains. On Friday night, maybe a few degrees colder, with some mountain valleys going deep into the negatives.

Saturday will be cold. In the mountains, temperatures will creep up into the teens by the afternoon, with 20-30mph wind gusts along the Divide.

Sunday will be warmer (20s in the mountains) but still blustery.

The warming trend continues into Wednesday morning before our next storm, which may arrive around that evening or a bit later, with the heaviest snow likely on the 24th. Here's a middle-of-the-road product from the Blend for Wednesday to Saturday:

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Models are converging on a storm at least happening around that time period, but with vastly different snow totals (GFS: almost nothing, Euro: Double digit totals possible). We'll keep an eye on it.