Colorado Weather Discussion #154: Dec. 10 - Dec. 12, 2021

Storm totals so far and a look at what's to come through Saturday morning.

Contents

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Updated Fri Dec 10, 2021 11:00am MST | Published Fri Dec 10, 2021

By Thomas Horner

7-Day Snow Planner (Through Dec. 17)

Northern Mountains

Park Range and N Front Range: Steamboat, Buffalo Pass, Rabbit Ears Pass, Bluebird, RMNP, IPW, Cameron Pass

6am New Snow

1-5"

Sat

0"

Sun

0"

Mon

0"

Tue

1-2"

Wed

2-6"

Thu

0-3"

Fri

6am Powder Potential

25%

Sat

0%

Sun

0%

Mon

0%

Tue

10%

Wed

30%

Thu

5%

Fri

I-70 Corridor

Front Range, Gore Range, etc.: Winter Park, Berthoud Pass, Jones Pass, Loveland, A-Basin, Keystone, Breck, Copper, Vail Pass, Vail, Beaver Creek

6am New Snow

1-4"

Sat

0"

Sun

0"

Mon

0"

Tue

1-2"

Wed

1-3"

Thu

0-1"

Fri

6am Powder Potential

20%

Sat

0%

Sun

0%

Mon

0%

Tue

10%

Wed

15%

Thu

0%

Fri

Central Mountains

Elk Mountains, Sawatch Range, Grand Mesa, West Elks: Aspen Resorts, Crested Butte, Powderhorn, Sunlight, Kebler Pass, Independence Pass, Cottonwood Pass, Monarch

6am New Snow

2-7"

Sat

0"

Sun

0"

Mon

0"

Tue

1-4"

Wed

2-5"

Thu

0-2"

Fri

6am Powder Potential

35%

Sat

0%

Sun

0%

Mon

0%

Tue

15%

Wed

20%

Thu

0%

Fri

Southern Mountains

San Juans: Telluride, Red Mountain Pass, Silverton, Coal Bank Pass, Purgatory, Wolf Creek

6am New Snow

1-4"

Sat

0"

Sun

0"

Mon

0-T

Tue

3-9"

Wed

1-5"

Thu

0-1"

Fri

6am Powder Potential

15%

Sat

0%

Sun

0%

Mon

0%

Tue

60%

Wed

25%

Thu

0%

Fri

Denver Metro

Denver and surrounding suburbs: Lakewood, Westminster, Aurora, Highlands Ranch

6am New Snow

0-1"

Sat

0"

Sun

0"

Mon

0"

Tue

0"

Wed

0"

Thu

0"

Fri

6am Snow Accum. Chance

60%

Sat

0%

Sun

0%

Mon

0%

Tue

0%

Wed

5%

Thu

0%

Fri

Retrospective

Snow! We’re excited to update you this morning – our storm has delivered, blowing out our forecast for many of the favored areas (and then some), with a few inches still in the forecast. Here are some notable reports this morning – many of these areas have continued to pick up snow since then!

vs. our forecast. Underpromise, overdeliver...
vs. our forecast. Underpromise, overdeliver...

We posted a little update around midnight – on Thursday evening, the storm moved into position (as expected) and started unleashing snowfall rates of 1”/hr or more. For a period of time, the Aspen Resorts and Crested Butte were regularly picking up 2” of snow per hour. Awesome!!

(via College of DuPage)
(via College of DuPage)

Cue the Crested Butte snowstake webcam…

Crested Butte snowstake
Crested Butte snowstake

It took a bit later into the night, but those snowfall rates crept northeast and soon Vail, Beaver Creek, and Steamboat got in on the action. The Steamboat snowstake this morning is a nice change of pace from their usual efforts.

Steamboat snowstake
Steamboat snowstake

Denver Snow

Denver International Airport also picked up 0.3” of snow which ends the second longest snowless streak on record (332 days) and sets the official latest date of first snowfall as December 10. Totals were higher in much of the metro area, with downtown picking up at least an inch of snow.

(via CoCoRaHS)
(via CoCoRaHS)

Jet-induced banding was the driver of this snowfall – we mentioned it was the most likely source for snowfall in the metro area, if any, and the global models ended up beating the high-resolution models pretty handily by being fairly consistent in their call for a lucky band to pop out over the metro area. Areas outside of the stronger band of snow got very little accumulations.

Kind of a weak way to end the snowless streak, but it’s a nice change of scenery around here. Check out the view of North Table Mountain from the Highpoint Weather HQ – we were just outside the main band of snowfall.

Current Conditions

The axis of the upper level trough is starting to move into Colorado, and the surface low ahead of it has strengthened on the lee side of the Rockies. Low-level northwest flow is now present over the Colorado high country, and this is confirmed by checking weather station observations in the mountains.

(via College of DuPage)
(via College of DuPage)

As stated previously, today provides a window for northwest flow to work with much colder air to bring some cold, fluffy snow to areas that missed out on the brunt of this storm – namely Summit County and the mountains of the Front Range. The atmosphere becomes very dry by this evening and snowfall should wrap up by tonight.

Short-Term Forecast

As the jet stream behind the trough axis moves over Colorado, we’ll see winds re-intensify ( gusts of 60mph+ were recorded yesterday). Strong downsloping winds will buffet the urban corridor starting this afternoon, and combined with the much colder air, make Friday PM a pretty miserable affair.

(via WeatherBell)
(via WeatherBell)

Overnight temperatures will be some of the coldest of the season.

Blended snowfall forecast suggests several more inches of snow across Colorado from 5am today to 5am Saturday.

It’s clear from the distribution that northwest flow will be the primary driver of snow, and areas that aren’t particularly favored by northwest flow (Crested Butte, Purgatory, Wolf Creek) may lose some ground to other ski areas in central and northern Colorado.

Forecast Verification Commentary

We were definitely conservative with this forecast, due to the large amount of uncertainty around mesoscale dynamics and the potential for a last minute, unfavorable change in the storm track. That proved to be unnecessary, and our forecast is getting blown out across the board with no low busts likely. Better than disappointment!

Overall, the best totals are generally in line with our highest forecasts (a little weirdness at the Aspen Resorts), but we’ve underdone the magnitude in southern and central western Colorado.

Note that SNODAS has absolutely sucked with snowfall analysis for this storm, so we’re not including any of the locations where we sometimes do estimates.

Unsurprisingly, the huge amount of uncertainty and epic shot of moisture means that verification rates and scores will be pretty low across the board. This was a tough storm and we painted with a broad brush.

Some commentary:

  • The National Weather Service’s grids were incredibly stingy with snow in central Colorado, but not too bad in southern Colorado (a little dry) and looking like they’ll mostly verify in northern Colorado.
  • Our app verified well, but that was expected with its outrageous spreads – it struggled with the large amount of uncertainty and put down annoyingly large ranges like ‘8-24”’ which isn’t particularly useful from a forecasting standpoint.
  • The Blend Probabilistic products were too dry, again.
  • OpenSnow vs. Highpoint Weather? It will be close! Our spreads were a little smaller, though that’s not exactly their fault due to the manner in which they convey 12hr forecasts.
  • The CAIC WRF looks to be doing okay, but with a large spread (quite a few forecast ranges of 15”, e.g. 10-25”).

Here are the standings so far. We continue to backfill other model data into this tool. Expect today to shake up the standings a bit!

―――――――

Last updated Monday December 13, 2021 6pm.

Forecast Start: Wednesday December 8, 2021 11am

Forecast End: Saturday December 11, 2021 5am

* = No reliable observations, verification uses SNODAS estimates which may be incorrect.
"Score" accounts for the spread/range of an accurate forecast. Lower spread = higher score. For instance, if 4" falls at a certain location, the forecast for 2-7" gets less points than the forecast for 3-5". Points are deducted for very inaccurate forecasts.

Thomas Horner Weather Forecaster @ Highpoint Weather

Issued Wed Dec. 8 3pm
✔️ Verified
66%
20/30
Score
18%
28/150
🎯 Spread
8.2
average
💥 High
10
33%
❌ Low
0
0%

Note: (Wed Dec. 8 6pm) Worked with consistent ranges. E.g. 3-8, 4-9, 5-10, 6-12, 7-14, 8-16, 9-18, 10-20, 12-24...

Central Colorado
5/35pts (14%) ✔️4/7 (57%) 💥3/7 (42%) ❌0/7 (0%)

Aspen Highlands: 10-20" Forecast Actual26" 💥️

-1pts
8" Dec 9 5am (Official)
16" Dec 10 5am (Official)
2" Dec 11 5am (Official)

Aspen Mountain: 9-18" Forecast Actual24" 💥️

-1pts
4" Dec 9 5am (Official)
15" Dec 10 5am (Official)
5" Dec 11 5am (Official)

Aspen Snowmass: 12-24" Forecast Actual23" ✔️

2pts
3" Dec 9 5am (Official)
14" Dec 10 5am (Official)
6" Dec 11 5am (Official)

Buttermilk: 9-18" Forecast Actual18" ✔️

2pts
1" Dec 9 5am (Official)
15" Dec 10 5am (Official)
2" Dec 11 5am (Official)

Cottonwood Pass*: 10-20" Forecast Actual15" ✔️

2pts
5" Dec 9 5am (SNOTEL)
8" Dec 10 5am (SNOTEL)
2" Dec 11 5am (SNOTEL)

Crested Butte: 12-24" Forecast Actual31" 💥️

-1pts
7" Dec 9 5am (Official)
22" Dec 10 5am (Official)
2" Dec 11 5am (Official)

Independence Pass*: 6-12" Forecast Actual N/A

Kebler Pass*: 15-30" Forecast Actual N/A

Monarch: 7-14" Forecast Actual11" ✔️

2pts
2" Dec 9 5am (Official)
7" Dec 10 5am (Official)
2" Dec 11 5am (Official)

Front Range
2/10pts (20%) ✔️2/2 (100%) 💥0/2 (0%) ❌0/2 (0%)

Cameron Pass: 8-16" Forecast Actual9" ✔️

2pts
0" Dec 9 5am (SNOTEL)
8" Dec 10 5am (SNOTEL)
1" Dec 11 5am (SNOTEL)

East Portal*: 3-8" Forecast Actual N/A

Eldora: 2-7" Forecast Actual2" ✔️

0" Dec 9 5am (Official)
2" Dec 10 5am (Official)
0" Dec 11 5am (Official)

Hidden Valley*: 5-10" Forecast Actual N/A

St. Mary's Glacier*: 3-8" Forecast Actual N/A

I-70 East
11/30pts (36%) ✔️6/6 (100%) 💥0/6 (0%) ❌0/6 (0%)

A-Basin: 4-9" Forecast Actual6" ✔️

2pts
2" Dec 9 5am (Official)
3" Dec 10 5am (Official)
1" Dec 11 5am (Official)

Berthoud Pass: 6-12" Forecast Actual7" ✔️

2pts
1" Dec 9 5am (SNOTEL)
5" Dec 10 5am (SNOTEL)
1" Dec 11 5am (SNOTEL)

Echo Mountain*: 0-4" Forecast Actual N/A

Jones Pass: 6-12" Forecast Actual9" ✔️

2pts
4" Dec 9 5am (SNOTEL)
4" Dec 10 5am (SNOTEL)
1" Dec 11 5am (SNOTEL)

Keystone: 3-8" Forecast Actual8" ✔️

1pts
1" Dec 9 5am (Official)
4" Dec 10 5am (Official)
3" Dec 11 5am (Official)

Loveland S.A.: 4-9" Forecast Actual5" ✔️

2pts
1" Dec 9 5am (Official)
3" Dec 10 5am (Official)
1" Dec 11 5am (Official)

Winter Park: 4-9" Forecast Actual7" ✔️

2pts
1" Dec 9 5am (Official)
5" Dec 10 5am (Official)
1" Dec 11 5am (Official)

I-70 West
4/25pts (16%) ✔️3/5 (60%) 💥2/5 (40%) ❌0/5 (0%)

Beaver Creek: 10-20" Forecast Actual15" ✔️

2pts
2" Dec 9 5am (Official)
10" Dec 10 5am (Official)
3" Dec 11 5am (Official)

Breckenridge S.A.: 4-9" Forecast Actual15" 💥️

-1pts
5" Dec 9 5am (Official)
5" Dec 10 5am (Official)
5" Dec 11 5am (Official)

Copper Mountain: 5-10" Forecast Actual16" 💥️

-1pts
6" Dec 9 5am (Official)
5" Dec 10 5am (Official)
5" Dec 11 5am (Official)

Powderhorn: 12-24" Forecast Actual23" ✔️

2pts
2" Dec 9 5am (Official)
20" Dec 10 5am (Official)
1" Dec 11 5am (Official)

Ski Cooper*: 6-12" Forecast Actual N/A

Sunlight*: 10-20" Forecast Actual N/A

Vail Pass*: 8-16" Forecast Actual N/A

Vail S.A.: 9-18" Forecast Actual16" ✔️

2pts
2" Dec 9 5am (Official)
11" Dec 10 5am (Official)
3" Dec 11 5am (Official)

Park Range / WY
6/20pts (30%) ✔️3/4 (75%) 💥1/4 (25%) ❌0/4 (0%)

Bluebird*: 8-16" Forecast Actual N/A

Buffalo Pass: 15-30" Forecast Actual28" ✔️

2pts
2" Dec 9 5am (SNOTEL)
11" Dec 10 5am (SNOTEL)
15" Dec 11 5am (SNOTEL)

Rabbit Ears Pass: 10-20" Forecast Actual15" ✔️

2pts
3" Dec 9 5am (SNOTEL)
7" Dec 10 5am (SNOTEL)
5" Dec 11 5am (Official)

Snowy Range: 8-16" Forecast Actual17" 💥️

17" Dec 11 5am (Official (3 Day Total))

Steamboat S.A.: 10-20" Forecast Actual18" ✔️

2pts
1" Dec 9 5am (Official)
10" Dec 10 5am (Official)
7" Dec 11 5am (Official)

Southern Colorado / NM
0/30pts (0%) ✔️2/6 (33%) 💥4/6 (66%) ❌0/6 (0%)

Cuchara*: 0-4" Forecast Actual1" ✔️

2pts
1" Dec 11 5am (Estimated 72hr)

Purgatory: 12-24" Forecast Actual29" 💥️

-1pts
2" Dec 9 5am (Official)
25" Dec 10 5am (Official)
2" Dec 11 5am (Official)

Red Mountain Pass: 12-24" Forecast Actual18" ✔️

2pts
2" Dec 9 5am (SNOTEL)
15" Dec 10 5am (SNOTEL)
1" Dec 11 5am (SNOTEL)

Silverton S.A.*: 10-20" Forecast Actual N/A

Taos S.A.: 4-9" Forecast Actual12" 💥️

1" Dec 9 5am (Official)
4" Dec 10 5am (Official)
7" Dec 11 5am (Official)

Telluride S.A.: 10-20" Forecast Actual26" 💥️

-1pts
2" Dec 9 5am (Official)
16" Dec 10 5am (Official)
8" Dec 11 5am (Official)

Wolf Creek: 12-24" Forecast Actual34" 💥️

-2pts
6" Dec 9 5am (Official)
25" Dec 10 5am (Official)
3" Dec 11 5am (Official)

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