Colorado Weather Forecast #189: May. 18, 2022 - May. 22, 2022

After a dramatic swing in the trend of model guidance, an impactful winter storm for the Front Range and northern Colorado seems highly likely.

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Updated Wed May 18, 2022 5:00pm MST | Published Wed May 18, 2022

By Thomas Horner

Summary

  • Higher-end impacts from a winter storm (Thursday night to Saturday) have become much more likely in northern Colorado.
  • Snow should accumulate across much of northern and northeastern Colorado from Friday morning to Saturday morning:
    • 10-20” in the Front Range mountains, potentially a bit higher near the Divide
    • 3-10” to the west of the Divide (i.e. Summit County west of the tunnels)
    • Lesser amounts from the Sawatch Range and southwest, almost nothing in the San Juans
    • 10-20” in the foothills, with 1-3ft. possible in favored areas and elevations
    • 3-10” in the Denver metro area and along the urban corridor, though much of this may melt. This is in addition to widespread rain chances on Friday, changing over to snow at least by the evening. Damage to vegetation is likely.
  • Temperatures below freezing along the I-25 corridor on both Friday night and Saturday night
  • Quite chilly all weekend
  • Unsettled into Tuesday with a weaker system moving in quickly behind the first system

Forecast Discussion: Storm Thursday night to Saturday

Let’s talk about an impactful winter storm for northern Colorado, which will cause colder temperatures and widespread precipitation from Thursday night to Saturday.

In our previous forecast we discussed the downwards precipitation trend of various models and ensembles over the prior few days, and how we were basically giving up on a more serious storm though we were careful to mention that the possibility couldn’t entirely be ruled out.

As it turns out, we couldn’t have picked a worse time to write a forecast based off the available data. Immediately after posting the previous forecast, we watched models and ensembles surge in lock step towards a very impactful winter storm (for northern Colorado, at least), with historic snow totals being thrown around on some of the latest model runs today. Yeesh!

These graphs show the trend of forecasted snow totals, and how we wrote the previous forecast near the bottom of the trend curve:

The general reason for the increase in snow totals is a less progressive storm (larger, more prolonged impacts), which is important as the best precipitation is now expected to come overnight on Friday which will help snow to actually accumulate at lower elevations.

General Snow Totals

We are now furiously backpedalling as models are in pretty good agreement that the Front Range will, in fact, see quite a decent storm. The numbers coming out of the previously-stingy Blend are starting to look impressive and are indicative of the overall consensus for decent snow across the Front Range:

In the mountains, the spreads are starting to look quite good if you haven’t yet put your skis into storage:

…and elsewhere, it seems very likely that most of the Front Range will experience some heavy snow. This product is a little more conservative – any numbers of 30% or higher should be taken into high consideration:

With the latest set of data, we’ll issue the following snowfall forecast:

Subject to change, of course. Let’s get into the details!

Timings and Distributions

We’re waiting on a large trough to drop into our region on Friday:

(via WeatherBell)
(via WeatherBell)

Thursday will be warm and windy ahead of this system. The Front Range will see highs in the high 80s or low 90s before the arrival of a cold front that evening. Denver could go from 90 degrees on Thursday to 25 degrees on Saturday night, with highs all weekend not exceeding the 30s.

(via WeatherBell)
(via WeatherBell)

Friday is when things really ramp up. Widespread precip will slowly spread southwards from the Wyoming border after midnight, reaching Denver around noon. Most of this precipitation will stretch from the Flat Tops to the eastern Colorado border, and from Wyoming down to just south of the Palmer Divide.

In the mountains, this will fall as snow, but the foothills below 8-9,000ft. will likely see rain initially before things start to changeover in the afternoon as colder and colder air works its way into the state. By noon, the rain-snow level will be about 6,000-,7000ft., until it drops to 5,000ft. later in the evening. Highs down on the plains will likely not exceed the 40s, depending on the timing of the frontal passage from north to south.

Lots of uncertainty here, and this doesn’t factor in the idea that heavier precip will cause a quicker changeover. Some models have Friday’s precipitation mostly as snow by noon, even in the urban corridor.

As a surface low sets up, we’ll see an upslope start to form, and this will really deepen for the Front Range by around 8pm. There’s some disagreement about the location of surface low pressure (this mostly impacts whether Colorado Springs gets skunked or not) but right now guidance is leaning towards a north-northeasterly upslope. This would favor the foothills of northern Colorado (from west of Boulder to west of Fort Collins) as opposed to a bit further south (i.e. Central City to Bailey) – generally speaking.

It’s likely the best mountain snow totals will be along / just east of the James Peak Wilderness, Indian Peaks, RMNP, and Medicine Bow mountains. Whether or not the upslope will be deep enough or oriented properly to really work its way up the upper regions of I-70 (Berthoud Pass, A-Basin) is more in question, but this does look to be more robust than many previous upslope storms than we’ve seen this season. There are more dynamics at play than just the upslope, anyways, and we could see some nice totals before the sun even sets on Friday if banding sets up in the right areas.

Probabilistic guidance backs up this line of thinking:

In summary: we’re looking at totals of 1-3ft. for parts of the foothills, with the mountains likely not doing quite as well as some models are expecting, though widespread double digit totals along the Divide seem likely at this point. Further west of the tunnels, totals start to drop into a general 4-10” range with less significant accumulations to the west of Vail Pass.

Though the Park Range (Steamboat) doesn’t do too well with this sort of setup, the opening phase of the storm on Friday looks to have some favorable dynamics for heavy banding – which could get them off to an early lead even if they don’t get much from Friday night’s heavy snow.

Friday night will feature temperatures at or just below freeing in parts of the plains, especially in the urban corridor. Combined with the heavy snow, there could be major impacts to vegetation (gardens, broken tree limbs) and some power outages.

It’s worth noting that east of the foothills, snow will be melting rapidly as it falls. The first several inches of snow likely wont result in any meaningful accumulations on most surfaces. It will take some time before snow starts adding up, so 6” of snow may only result in a 2” measurement the next morning! Tricky.

Snow should start tapering off by noon on Saturday, though southern Colorado will still be experiencing some lingering impacts. The lower elevations of the Front Range likely wont get out of the 30s on Saturday… or Sunday. In fact, the Front Range (including the metro area) will likely see another round of below freezing temperatures on Saturday night (lows in the mid to upper 20s for Denver are possible).

Unsettled / System 2: Sunday to Tuesday

Sunday is likely another chilly day ahead of a shortwave quickly following the previous system. This has a chance of bringing more precipitation and a reinforcement of colder air, with impacts possible into Tuesday morning. This could be good for a few more inches of snow in the mountains, and scattered rain/snow concerns elsewhere in the Front Range. More on that later…

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