Colorado Weather Forecast #157: Dec. 22 - Jan. 1, 2021

Active pattern starts Dec. 23, with several feet of snow for the Colorado mountains through the rest of the month.

This forecast is no longer valid. Please return to our list of forecast articles to find more recent posts.

Updated Fri Dec 24, 2021 2:15pm MST | Published Tue Dec 21, 2021

By Thomas Horner

Updated Dec. 24 @ 2:15pm.

7-Day Snow Planner (Through Dec. 31)

Northern Mountains

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

6am New Snow

2-11"

Mon

2-12"

Tue

1-5"

Wed

T-5"

Thu

T-6"

Fri

1-8"

Sat

T-3"

Sun

6am Powder Potential

45%

Mon

35%

Tue

12%

Wed

14%

Thu

12%

Fri

32%

Sat

10%

Sun

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

1-9"

Mon

2-8"

Tue

1-4"

Wed

T-4"

Thu

T-3"

Fri

1-6"

Sat

T-3"

Sun

6am Powder Potential

31%

Mon

25%

Tue

13%

Wed

13%

Thu

11%

Fri

23%

Sat

10%

Sun

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

1-11"

Mon

2-12"

Tue

1-8"

Wed

1-6"

Thu

T-5"

Fri

1-10"

Sat

T-4"

Sun

6am Powder Potential

58%

Mon

60%

Tue

22%

Wed

16%

Thu

15%

Fri

40%

Sat

14%

Sun

Southern Mountains

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

6am New Snow

2-15"

Mon

4-17"

Tue

2-14"

Wed

1-9"

Thu

1-9"

Fri

3-15"

Sat

T-6"

Sun

6am Powder Potential

47%

Mon

67%

Tue

45%

Wed

28%

Thu

23%

Fri

54%

Sat

20%

Sun

Denver Metro

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

6am New Snow

0-T

Mon

0-T

Tue

0-T

Wed

0"

Thu

0-T

Fri

T-1"

Sat

T-1"

Sun

6am Snow Accum. Chance

11%

Mon

42%

Tue

38%

Wed

7%

Thu

11%

Fri

57%

Sat

64%

Sun

Summary

Active pattern starts of on Dec. 23 with a powerful atmospheric river event likely bringing a foot or more of snow to several mountain ranges. Snow continues on and off into the start of January, with many feet of snow expected in most of Colorado’s mountain ranges, particularly those that benefit from southwest flow. Very little snow will be had east of the Divide.

Conditions will be predominantly gusty in the high country.

Forecast Discussion: Active Pattern Overall

We are close to the start of our prolonged, consistently active pattern. We discussed this in decent detail in our last forecast, so we’ll spare you the details about stratospheric coupling and all that.

Snow lovers: for the mountains, things still look good. To go with that, for the Front Range urban corridor, things still look bad. Analogs for this setup continue to show scenarios of above average precipitation in the mountains. Ensembles now lean well on the side of accumulating snow as we look towards the start of January. The blocking pattern has a pronounced signal even at range.

There’s still an obvious dipole on the two week Euro ensemble forecast. You love to see it:

(via WeatherBell)
(via WeatherBell)

So, we’re still confident that the mountains will see snow almost every day into at least the start of January. Again, there may be days where there’s only some light snowfall, and maybe not a ton of epic fresh pow days (our initial event Dec. 23-25 still looks the strongest), but we can’t imagine skiing conditions won’t be pretty great by the start of 2022.

Overall Totals & Distribution

Here’s a map Thomas put together (he’s guest forecasting on Seth’s Weather Report right now, so sorry if there’s some overlap, because he’s also writing this article. Also, if you found this page from over there – hi.).

This map was updated on Dec. 22 as confidence grows and the forecast continues to trend upwards.

Is it a long range forecast? Yup. Does it have aggressive totals? Oh yeah. Is it in the ballpark though? We think so. If anything, this might lean on the conservative side in spots, what with a few models casually throwing down 6-10ft. of snow in places. You know how pessimistic our forecasts are so we think the above map is saying a lot.

It’s really not that crazy though. The normally super-stingy Euro ensemble has 100% chance of >2ft. of snow in most of western Colorado’s mountains for that same time period.

(via WeatherBell)
(via WeatherBell)

This is not a relaxing situation for us to be in, with a very complex pattern ahead and our own *HYPE* building up to dangerous levels. We’ve been pretty content with mildly underforecasting discrete 4-8” storms, so you can bet we’ll be fretting about whether we’ll actually get squarely into the ranges we so carelessly threw out several days before a 10 day long event…

…and don’t forget about the libations that will be coming down the pipe later in the holiday week. Hopefully we can just sit back and let it snow (or let it be slightly chilly and dry, here in Golden).

But yeah. The evidently pessimistic NBM has some uh, appreciable totals through the end of 2021:

Colorado is of course not the only place benefiting from this pattern. The active storm track will bring eye popping totals throughout the western United States.

Overall Powder and Snow Chances - Probabilistic

Numerical forecasts are for squares though, honestly. Probabilistic forecasting would be the future if humans weren’t so innately poor at understanding probabilities. Still, if that’s your cup of tea, we have you covered.

Southwest Flow: Winners and Losers

The devil is in the details, but overall, our first map we posted in this article shows who stands to gain the most from this setup.

Model guidance is consolidating around a solution where we predominantly have southwesterly flow, with only a few opportunities for westerly flow. Any stronger waves which could at least briefly introduce northwesterly flow look to be unlikely. So in general, we’re looking for the highest totals in areas that benefit from southwesterly flow.

This includes most of Colorado’s western ranges, with the best chances in the San Juans (especially from Red Mountain Pass and south, and over to Wolf Creek), followed by the West Elks (Crested Butte, Kebler Pass), and the high Elks (Capitol Peak to Castle Peak). Powderhorn/Grand Mesa and the Flat Tops usually do pretty well, though elevation can be an issue.

The west side of the Park Range (Steamboat, Buffalo Pass) is a little more hit and miss but sometimes can come away with the highest totals – it really depends on the exact setup as they are quite a ways north of the San Juans. The Aspen resorts also tend do well, though they benefit more from northwest flow.

Is this what they're calling a 'flow state?' (via WeatherBell)
Is this what they're calling a 'flow state?' (via WeatherBell)

Further to the north and east, flow becomes less and less productive after it dumps snow out on the higher peaks of the San Juans and Elks. The Sangres don’t typically do well, despite what the NAM 3km model always seems to think.

Monarch and parts of the Sawatch can do okay. Vail / Beaver Creek is definitely spotty but can do well under the right circumstances (especially with a more westerly component).

East of the Park Range (Rabbit Ears Pass, Bluebird), totals can drop off pretty quick if flow is more southerly. Once you get towards the Divide (Medicine Bow Range, Cameron Pass), totals tend to get pretty dismal, despite models frequently overforecasting this region. However, the slightly higher terrain in this area than ranges to the southwest can unexpectedly cash in on moist flow, even if it’s not an ideal direction.

Breck and Copper are also a bit closer to the action, with totals typically dropping off sharply towards the east side of Grand County and Summit County (Keystone, A-Basin, Loveland, Winter Park).

East of the Divide (Hidden Valley/RMNP, Brainard Lake, Eldora, Echo), totals tend to be only a couple of inches at best from events that bring a couple feet of snow to the western ranges. Very little snow usually makes it down to the foothills or Front Range urban corridor, with the exception of some mesoscale dynamics like jet-induced banding (which is what brought Denver’s first official snowfall this season earlier in the month under southwest flow – a whole 0.3”).

Now that you know all that, we don’t even need to write our forecast. We believe in you!

Winds

If you noticed in the above animation that the jet stream is position over Colorado almost constantly, it shouldn’t come as a surprise that winds will be an issue during this pattern. Gusts of 30-80mph in the high country could be the norm rather than the exception.

(via WeatherBell)
(via WeatherBell)

Probably not enough for widespread lift closures mostly, but it will definitely feel like a storm is active, and it will wreak some havoc on the fresh snow.

First Wave: Dec. 23-25 (Now With an Official Forecast)

The initial wave of this prolonged active pattern looks to be the strongest, as an atmospheric river gets positioned over the Four Corners region.

(via WeatherBell)
(via WeatherBell)

This initially passes over the Sierra Nevada range in California, with the Euro forecasting something like 4-7 feet of snow up there.

The onset of heaviest snow begins around 5pm on the 23rd, and snow continues hard well into the 24th. Snow should taper off by Christmas morning, before it kicks back up again later that day in response to the next shortwave.

Here’s out forecast through December 25th 5am, with some other model data as well…once we populate it.

Last updated Thursday December 25, 2021 5pm.

Forecast Start: Tuesday December 23, 2021 5am

Forecast End: Thursday December 25, 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 Tue Dec. 23 8:30pm
✔️ Verified
68%
22/32
Score
21%
34/160
🎯 Spread
9.5
average
💥 High
10
31%
❌ Low
0
0%

Central Colorado
0/30pts (0%) ✔️3/6 (50%) 💥3/6 (50%) 0/6 (0%)

Aspen Highlands: 10-20" Forecast Actual28" 💥️

-2pts
12" Dec 24 5am (Official)
16" Dec 25 5am (Official)

Aspen Mountain: 9-18" Forecast Actual22" 💥️

-1pts
8" Dec 24 5am (Official)
14" Dec 25 5am (Official)

Aspen Snowmass: 12-24" Forecast Actual21" ✔️

2pts
7" Dec 24 5am (Official)
14" Dec 25 5am (Official)

Buttermilk: 9-18" Forecast Actual17" ✔️

2pts
7" Dec 24 5am (Official)
10" Dec 25 5am (Official)

Cottonwood Pass*: 9-18" Forecast Actual N/A

Crested Butte S.A.: 13-26" Forecast Actual41" 💥️

-3pts
20" Dec 24 5am (Official)
21" Dec 25 5am (Official)

Independence Pass*: 12-24" Forecast Actual N/A

Kebler Pass*: 16-32" Forecast Actual N/A

Monarch: 9-18" Forecast Actual16" ✔️

2pts
10" Dec 24 5am (Official)
6" Dec 25 5am (Official)

Front Range
2/10pts (20%) ✔️1/2 (50%) 💥1/2 (50%) 0/2 (0%)

Cameron Pass: 8-16" Forecast Actual18" 💥️

14" Dec 24 11am (SNOTEL)
4" Dec 25 5am (SNOTEL)

East Portal*: 4-9" Forecast Actual N/A

Eldora: 3-7" Forecast Actual7" ✔️

2pts
4" Dec 24 5am (Official)
3" Dec 25 5am (Official)

Hidden Valley*: 6-12" Forecast Actual N/A

St. Mary's Glacier*: 4-9" Forecast Actual N/A

I-70 East
4/35pts (11%) ✔️3/7 (42%) 💥4/7 (57%) 0/7 (0%)

A-Basin: 6-12" Forecast Actual13" 💥️

6" Dec 24 5am (Official)
7" Dec 25 5am (Official)

Berthoud Pass: 7-15" Forecast Actual11" ✔️

2pts
6" Dec 24 11am (SNOTEL)
5" Dec 25 5am (SNOTEL)

Echo Mountain: 2-6" Forecast Actual2" ✔️

1pts
0" Dec 24 5am (Official)
2" Dec 25 5am (Official)

Jones Pass: 8-16" Forecast Actual12" ✔️

2pts
8" Dec 24 11am (SNOTEL)
4" Dec 25 5am (SNOTEL)

Keystone: 6-12" Forecast Actual14" 💥️

6" Dec 24 5am (Official)
8" Dec 25 5am (Official)

Loveland S.A.: 7-15" Forecast Actual19" 💥️

-1pts
8" Dec 24 5am (Official)
11" Dec 25 5am (Official)

Winter Park: 6-12" Forecast Actual15" 💥️

7" Dec 24 5am (Official)
8" Dec 25 5am (Official)

I-70 West
9/35pts (25%) ✔️5/7 (71%) 💥2/7 (28%) 0/7 (0%)

Beaver Creek: 10-20" Forecast Actual15" ✔️

2pts
6" Dec 24 5am (Official)
9" Dec 25 5am (Official)

Breckenridge S.A.: 8-16" Forecast Actual19" 💥️

7" Dec 24 5am (Official)
12" Dec 25 5am (Official)

Copper Mountain: 8-16" Forecast Actual22" 💥️

-1pts
9" Dec 24 5am (Official)
13" Dec 25 5am (Official)

Powderhorn: 8-16" Forecast Actual16" ✔️

2pts
7" Dec 24 5am (Official)
9" Dec 25 5am (Official)

Ski Cooper: 8-16" Forecast Actual16" ✔️

2pts
9" Dec 24 5am (Official)
7" Dec 25 5am (Official)

Sunlight: 8-16" Forecast Actual14" ✔️

2pts
9" Dec 24 5am (Official)
5" Dec 25 5am (Official)

Vail Pass*: 9-18" Forecast Actual N/A

Vail S.A.: 9-18" Forecast Actual15" ✔️

2pts
6" Dec 24 5am (Official)
9" Dec 25 5am (Official)

Park Range / WY
8/20pts (40%) ✔️4/4 (100%) 💥0/4 (0%) 0/4 (0%)

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

Buffalo Pass: 16-32" Forecast Actual20" ✔️

2pts
14" Dec 24 11am (SNOTEL)
6" Dec 25 5am (SNOTEL)

Rabbit Ears Pass: 11-22" Forecast Actual14" ✔️

2pts
7" Dec 24 11am (SNOTEL)
7" Dec 25 5am (SNOTEL)

Snowy Range: 8-16" Forecast Actual12" ✔️

2pts
6" Dec 24 5am (Official)
6" Dec 25 5am (Official)

Steamboat S.A.: 12-24" Forecast Actual14" ✔️

2pts
6" Dec 24 5am (Official)
8" Dec 25 5am (Official)

Southern Colorado / NM
11/30pts (36%) ✔️6/6 (100%) 💥0/6 (0%) 0/6 (0%)

Cuchara*: 3-8" Forecast Actual3" ✔️

1pts
3" Dec 25 5am (SNOTEL)

Purgatory: 15-30" Forecast Actual19" ✔️

2pts
8" Dec 24 5am (Official)
11" Dec 25 5am (Official)

Red Mountain Pass: 15-30" Forecast Actual19" ✔️

2pts
16" Dec 24 11am (SNOTEL)
3" Dec 25 5am (SNOTEL)

Silverton S.A.*: 14-28" Forecast Actual N/A

Taos S.V.: 9-18" Forecast Actual13" ✔️

2pts
3" Dec 24 5am (Official)
10" Dec 25 5am (Official)

Telluride S.A.: 8-16" Forecast Actual12" ✔️

2pts
5" Dec 24 5am (Official)
7" Dec 25 5am (Official)

Wolf Creek: 24-48" Forecast Actual33" ✔️

2pts
14" Dec 24 5am (Official)
19" Dec 25 5am (Official)

Here’s a middle of the road forecast, perhaps even a conservative one, from the Blend:

Temperatures aloft will be an issue. The snow level will start out above 7-8,000ft. and SLRs could struggle to hit even 10:1 for the first day of this event or so.

Conversely, a difficulty in the opposite direction could be jet-induced banding (this will be an issue throughout this pattern) – this could produce some surprisingly nice totals in areas that aren’t expected to get much from southwest flow (like Summit County).

These bands could jump the Divide and bring a little bit of snow to the I-25 corridor as well.

These mesoscale dynamics look like more of a sure thing, and also appear to be more consistent, so we’ve upped our forecast for the more eastern mountains a bit.

We’ll update our forecast one last time tomorrow.

(via WeatherBell)
(via WeatherBell)

Next Wave: Dec. 26

Another shortwave looks to move across the region on the 26th. This is a bit more progressive so a quicker event wrapping up late the 26th or early the 27th.

Overall, here’s a glimpse at snow potential from Dec. 26 to Dec. 29.

Uncertainty: Dec. 27 to Jan. 1

After the 26th there is far too much disagreement and uncertainty to pinpoint the exact timings and impacts of stronger waves. The 28th to the 30th looks to have some decent chances, and there is a bit of a signal appearing for the 30th to 31st. These signals have been fairly transient, so we wont investigate them too much.

Here’s another map.

--

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