Colorado Weather Discussion #142: Nov. 9, 2021

Updates and further discussion about snow potential from Tuesday night to Friday.

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Updated Tue Nov 9, 2021 3:30pm MST | Published Tue Nov 9, 2021

By Thomas Horner

This is an update for our current valid forecast, please consult that article for any other details about the future weather forecast.

A day has passed since we wrote our forecast and discussed our concern about potential snow totals for the rest of the week and model uncertainty.

Model guidance has converged fairly nicely over the past 24 hours, both between different weather models and between different runs of the same model. There is still some tangible uncertainty, but on a larger scale the potential impacts of this storm are looking a little more clear.

Unfortunately, it just isn’t looking like that strong of an event for much of Colorado’s ski areas – we think most will come in shy of double digits despite a few days of snow. While double digit snow potential still exists in parts of northern Colorado (looking at you, Buffalo Pass), we’re struggling to find much evidence that many areas, such as those in Summit County, will get close to that.

First Wave of Snow: Tuesday night to Wednesday morning

Lifting energy enters Colorado today ahead of a trough. The trough axis crosses over the state in the early hours of Wednesday.

(via WeatherBell)
(via WeatherBell)

Lift remains in place into later Wednesday morning as Colorado sits in the left exit region of the jet, with a strong jet max upstream of us.

This period of decent large-scale lift from Tuesday night to Wednesday morning coincides with the remnants of an atmospheric river which provides a significant source of moisture over our region. This provides a 12 hour period of fairly widespread snowfall, from approximately 8pm Tuesday to 8am Wednesday.

The western mountains are most favored by flow aloft during this initial wave of snow. On Tuesday, flow is west-southwesterly to westerly, turning westerly by around midnight, and then becoming west-northwesterly to northwesterly through the end of the week.

There isn’t enough of a southwesterly component to deliver prolonged snowfall to areas like Wolf Creek that usually only benefit from SW flow. Impacts from this initial wave will also be limited in the eastern mountains (the Front Range, Summit County, Mosquito Range, Sangres) due to the westerly flow.

That said, most areas will at least see a period of heavy snowfall, and the western ranges should get several hours of moderate snow by Wednesday morning, with totals ranging from 2-9”. We think the eastern mountains would pick up around 1-4”.

Light Snow: Wednesday through Thursday AM

By late Wednesday morning, the jet max behinds to move towards northeastern Colorado. This puts the mountains in the right exit region of the jet, which results in subsidence over the area.

(via WeatherBell)
(via WeatherBell)

Though orographic flow continues during this time, it will not be very productive especially considering the lack of moisture.

That said, the northern Colorado mountains should pick up another few inches during this time, especially the Park Range (Buffalo Pass, Steamboat, Rabbit Ears Pass). Areas near and west of Vail Pass could sneak a few inches out as well.

Second Wave of Snow: Thursday to Friday

Another push of moisture should hit Colorado later Thursday morning. This moisture is relatively shallow and short-lived but it coincides with an embedded disturbance aloft and some jet streaking which will provide additional dynamics to help turn moisture into snow.

(via WeatherBell)
(via WeatherBell)

This is in response to the development of a strong closed low over Minnesota which is the result of the initial wave on Tuesday undergoing lee cyclogenesis on the east side of the Rockies.

This period of time provides the largest amount of uncertainty for our forecast. There are a few ways this could be a boom or a bust:

  • 💥 Boom: The center of low pressure tracks further north and keeps a dry air intrusion from entering the mountains.
  • 💥 Boom: Jet streaking creates bands of strong snow that sit over small regions for a few hours. This will likely happen somewhere, but it’s unknown where.
  • 💥 Boom: A stronger embedded disturbance enters flow aloft over Colorado as the closed low retrogrades a bit later on Thursday.
  • ❌ Bust: A change in the track of the closed low brings a dry air intrusion into Colorado quicker or more directly.
  • ❌ Bust: Dynamics end up too far east of the mountains, and downwards vertical velocity limits the production of snowfall by orographics.
  • ❌ Bust: Temperatures and dynamics result in lower snow-liquid ratios than may be otherwise expected.

This uncertainty is the difference between 2” of additional snow or 8” by Friday at noon.

Maps

The Blend has held fairly steady with its snowfall product, so lets look at its expectations.

In northern Colorado, we see up to two feet of snow in parts of the Park Range, and a foot of snow (or a bit more) on the high peaks of the northern Front Range (particularly RMNP, IPW, and the James Peak Wilderness), Gore Range, and Flat Tops. Totals drop off very quickly east of the Divide due to downsloping winds.

Despite a few days of light to moderate snow with northwest flow, models haven’t been too excited to bring particularly exciting totals to many parts of Summit County. We think these numbers are a bit underdone, and the potential for major overperformance is not something that can be ignored.

For instance, the latest HRRR model run has a consistent band of jet-driven snow park over Breck on Thursday, which provides a cool 8” of snow. Other models have Breck picking up only a couple inches.

In central Colorado, the West Elks and northern Sawatch Range soak up a lot of snow especially in the initial wave of westerly flow. The ski resorts to the east of these high peaks don’t typically do as well from this sort of flow. Instead, they’ll be relying on northwest flow after Wednesday AM to make the difference between a mediocre or exciting event.

The San Juans are not favored by this storm, missing the best moisture and lifting dynamics. Despite that, the western San Juans will still get a good piece of the initial wave of snow, and the northern San Juans could sneak several inches of snow out of NW flow through Friday.

Probabilities

Probabilistic guidance is surprisingly stingy, which is why our forecast (at the end of this discussion) is not as optimistic as some sources. Are these numbers too low, or are the ensembles seeing something that the deterministic models aren’t? You can decide if these expectations are valid or not.

Even the SREF’s snowfall products look mediocre, despite often being overly optimistic for these sorts of events.

Berthoud Pass:

(via University of Utah)
(via University of Utah)

Cameron Pass:

(via University of Utah)
(via University of Utah)

Buffalo Pass:

(via University of Utah)
(via University of Utah)

Vail:

(via University of Utah)
(via University of Utah)

Our Snow Forecast

We’ve discussed the data and uncertainty at length, so hopefully our snow expectations are not too surprising. These ranges have been selected so that we should see minimal busts, with the potential for some upside surprises, especially by Friday morning after the jet dynamics and better orographics play out on Thursday. But it’s a real possibility that this storm could be a lot more wind than snow for many areas.

This forecast is through 5am on Friday – snow will continue to fall in some areas through the day, but this should capture the bulk of the snowfall along with being able to cross-reference ski resort reports.

Park Range

  • Buffalo Pass: 10-16”. (Up from yesterday. Serious bust high potential)
  • Steamboat: 6-12”. (Up from yesterday)
  • Rabbit Ears Pass: 6-12”. (Up from yesterday)
  • Bluebird: 5-10”. (Up from yesterday)

Front Range

  • Cameron Pass: 5-10”. (No change from yesterday)
  • Hidden Valley: 2-6”. (No change from yesterday)
  • Highest peaks of the Medicine Bow Mountains, RMNP, and IPW: 6-12”. (Up from yesterday)
  • Eldora: 2-6”. (Up from yesterday)
  • Winter Park: 4-9”. (No change from yesterday)
  • East Portal and St. Mary’s Glacier: 5-10”. (Up from yesterday)
  • Berthoud Pass: 4-9”. (No change from yesterday)
  • Jones Pass: 5-10”. (Up from yesterday)
  • Loveland: 4-9”. (Up from yesterday)
  • A-Basin: 2-7”. (No change from yesterday)
  • Keystone: 2-7”. (No change from yesterday)
  • Denver: 0-T. (No change from yesterday)
  • Ft. Collins: 0-T. (No change from yesterday)
  • Boulder: 0-T. (No change from yesterday)
  • Castle Rock: 0-T. (No change from yesterday)
  • Colorado Springs: 0-T. (No change from yesterday)

Gore, Tenmile, and north Sawatch

  • Breck: 2-7”. (No change from yesterday)
  • Copper: 3-8”. (No change from yesterday)
  • Vail Pass: 4-9”. (Up from yesterday)
  • Vail: 4-9”. (Up from yesterday)
  • Beaver Creek: 4-9”. (Up from yesterday)
  • Ski Cooper: 2-7”. (No change from yesterday)

Elk Range

  • Aspen Mountain: 3-8”. (Up from yesterday)
  • Aspen Highlands: 3-8”. (Up from yesterday)
  • Buttermilk: 2-7”. (Up from yesterday)
  • Aspen Snowmass: 4-9”. (Up from yesterday)
  • Crested Butte: 2-6”. (Up from yesterday)
  • Kebler Pass: 4-9”. (Up from yesterday)
  • Indy Pass: 3-7”. (No change from yesterday)

Sawatch

  • Cottonwood Pass: 1-5”. (No change from yesterday)
  • Monarch: 2-6”. (Up from yesterday)

San Juans

  • Telluride SA: 1-5”. (Up from yesterday)
  • Red Mountain Pass: 2-6”. (Up from yesterday)
  • Silverton: 1-5”. (Up from yesterday)
  • Purgatory: 0-3”. (Up from yesterday)
  • Wolf Creek: 0-3”. (Up from yesterday)

Other

  • Powderhorn: 2-6”. (Up from yesterday)
  • Sunlight: 1-5”. (Up from yesterday)
  • Cuchara: 0-1”. (No change from yesterday)
  • Taos: 0-1”. (No change from yesterday)
  • Snowy Range: 4-9”. (Up from yesterday)

We’ll keep you updated as the storm unfolds.

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