Closer look at this Atmospheric River: Snow levels, magnitude, impact on UT, CO, WY

The first moderate to strong atmospheric river (AR) of the season is on track for Central and Northern California. Let’s drill down on the details.

Forecast Integrated Vapor Transport (IVT) at 38N/123W, Central CA, GEFS/GFS interpretation

The main surge hits California Sunday-Monday (10/24-25). It’s preceded by 1-2 smaller waves with high snow levels.

TAHOE ZONER/S LINE
THR/FRI>10,000′
SAT8,000′
SUN6,000′
MON6,000′
Tomer forecast snow levels for Lake Tahoe Zone, 10/21/2021.

Overall, total precipitation through Monday could run +500% of normal for parts of Central and Northern California with flash flooding possible. Localized 8-11″ liquid totals possible in the deep purple color. Snowfall at higher elevations would be significant.

Forecast total liquid precipitation for through 10/25/2021. GFS interpretation.

Impacts to UT, WY, CO

Looking down the road, moisture from this Pineapple Express should hit the mountains of UT, WY, and CO. The key timeframes to watch:

SNOW TIMEFRAME10/23-2410/25-28
TETONSMINORMAJOR
WASATCHMINORMAJOR
CO ROCKIESMINORMIX
TOMER FORECAST SNOW TIMELINE 10/21/2021

Atmospheric river setting up for California

The first moderate to strong atmospheric river (AR) of this Fall/Winter is on the horizon for California between Sunday-Monday.

Forecast Integrated Vapor Transport (IVT) through next week in Central CA.

You’ll also notice two weaker atmospheric river waves prior to Sunday-Monday. Forecast liquid precipitation totals are impressive through Tuesday.

Liquid forecast totals (inches) through 10/26/2021. GFS interpretation.

This moisture is what California needs after a bone-dry Summer, but the downside is that it almost always comes too fast and results in flash flooding.

How much snow? Snow levels will be a problem as usual with AR’s. The surge on Sunday-Monday might be the best chance for heavy high elevation Sierra snow from Mammoth to Tahoe to Shasta. It could be measured in feet.

What kind of pattern supports this “Pineapple Express”? Upper level winds reach back towards Hawaii (and elsewhere) and transport rich plumes of moisture into California. That moisture gets slammed into the Sierra Mountain Range and squeezed-out.

IVT Forecast for CA valid 10/25-26/2021.

La Nina has officially arrived, again

La Nina is here for the 2nd straight Fall/Winter. Sea surface temps (SST’s) in the equatorial south Pacific have cooled to -0.5C (the official minimal threshold).

Sea Surface Temperature Anomalies, NOAA.

The bulk of data suggests that La Nina continues through the entire upcoming Winter (87% chance according to NOAA). If you haven’t yet, please check out my Winter forecast. In that video I explain why it’s important to identify the phase each season, and what it means for the storm track in mountainous environments.

History of La Nina phase (Blue) and El Nino phase (Red), NOAA.

Lingering Questions

A lingering question in my mind is California. Where will the average storm track position itself? Will it be north or south of Tahoe? I believe Tahoe ends up with a normal winter with 1-3 strong atmospheric river setups this Winter.

Another question: How cold will this La Nina phase go? Will SST’s cool below the bulk of data? If so then we could be looking at what meteorologist Cory Gates and Ryan Boudreau are forecasting. I highlighted their 2nd opinion in an earlier post.

Monday morning thoughts

The golden days of October roll on.

Monday morning sunrise across Denver, CO, 10/18/2021

Snow is ending at Tahoe and Mammoth, CA, but wind continues to blow.

Windy Monday morning at Palisades Tahoe.

This fast moving, windy cold front hits Utah next then Colorado. Gusts on the higher peaks will increase to 30-60mph.

Satellite: Water Vapor 10/18/2021 6am

Utah’s Wasatch Front should do well with this particular flow. Less accumulation in Colorado.

LocationForecast
Alta12″
Solitude11″
Park City10″
Steamboat3″
Cameron Pass3″
Loveland2″
Crested Butte2″
Jackson Hole1″
Forecast snow totals next 48 hours.

This front departs by Wednesday followed by high pressure for the interior Rockies. The West Coast will remain active in the storm track.

Mountain weather update 10/17

One storm system remains on the horizon this week across the West. It’s fast-moving and is minor compared to the storm cycle last week.

It will spread strong wind (30-70mph) from the Sierra into Utah and Colorado.

Wind gust forecast for Longs Peak summit, 10/17/2021.

Beyond this, it’s going to be a waiting game unless you’re in the higher elevations of PNW. Whistler/Blackcomb, BC higher elevations will find itself with snow chances almost every day for the next 8-9 days.

Chances for snow next 8-9 days, 10/17/2021.

Mountain weather update 10/16: On the horizon

There is one storm system on the horizon for the West early next week. Overall, it’s not major and the pattern doesn’t look as active as last week.

Forecast pressure pattern anomalies at about 18,000′ valid 10/18-19/2021. GFS interpretation.

Whistler/Blackcomb, BC will do the best with the jet stream positioned favorably. You’ll also notice some snowfall in my forecast below for Tahoe ski areas and Mammoth, CA (2-6″).

Snowfall forecast chart, Meteorologist Chris Tomer, 10/16/2021.

Wolf Creek ski area is officially open in Colorado – the first ski area to open. They are no longer the dark horse in this yearly race. This is the 2nd year in a row opening first. Wolf Creek is a magical place meteorologically speaking. More on that in a later post.

Opening day sunrise at Wolf Creek, 10/16/2021.

Arapahoe Basin opens tomorrow, Sunday 10/17/2021. I talked with a friend who works at Loveland Ski Area and they think it might take another 1-2 weeks for their opening.

What happened at the 2021 DC Peaks 50mile race?

I work for race directors and climbing/skiing teams as a meteorologist in mountain settings, so i’m very familiar with how this process works. The objective is risk management. My approach is to put a spotlight on any potential bad weather, alert the race director, and then runners get an email blast with a forewarning so they can pack extra gear. There is responsibility with both parties. Runners also need to monitor the forecast weather on their own.

iRunFar’s Alex Potter put together an informative article with more race details and even video/photos from race participants in the snow.

If you only looked at standard point-and-click NOAA forecasts you likely missed the snow risk for 10/9/2021. More in-depth meteorological analysis supported at least six inches of snow in the Wasatch. That’s a clear signal that extra gear was necessary.

Check out the DC Peaks website for more info.

12″ New Snow Alta, Snowbird

The first of two storm systems delivered a foot (or more) of new snow to Little Cottonwood Canyon, Utah. The 2nd storm system arrives late Wednesday and runs through Thursday.

Snowbird snow stake 10/12/2021 6am.
Alta, UT 10/12/2021.

In Colorado, this same storm system arrives today. I’m forecasting 2-6 inches at the ski areas with storm #1. Similar additional amounts with storm #2. Strong wind is likely on all the 13ers/14ers with gusts 40-90mph Tuesday afternoon through Wednesday.

Also of note, 6-8 inches of new snow fell at Mammoth Mountain, CA over the last 36 hours. This is great to see after a bone-dry Summer.

Mammoth Mountain 10/12/2021.

In Wyoming, I’m forecasting 2-6″ with storm #2 between Wednesday night through Thursday afternoon.

Cody Bowl, Jackson Hole, WY 10/12/2021.

2nd Opinion: Winter forecast from Boudreau & Gates

I want to share another perspective on this winter’s forecast – this one is Colorado specific. AspenWeather.net‘s forecaster Ryan Boudreau and meteorologist Cory Gates issued their official winter forecast last week. I’ve known Ryan for a few years and I know Cory to be an exceptional meteorologist. Their combined passion for skiing is contagious.

Winter Forecast

There is overlap with my winter forecast, but there are also slight differences including the potential for a stronger/colder La Nina.

  • La Nina driven winter (Gates says it could go stronger than mainline forecasts indicate).
  • Optimistic about snowfall Central and Northern Mountains.
  • Gates notes that 10 of Aspen’s snowiest winters on modern record occurred with La Nina.
ForecastNormal
Aspen320″295″
Snowmass360″325″
Highlands350″325″
Gates & Boudreau Winter Forecast 2021-2022.
Cory Gates (Left) and Ryan Boudreau (Right)

Visit their website to learn more about Cory Gates and Ryan Boudreau.

A-Basin starts making snow; More in the forecast this week CO, UT, WY, MT

Stellar crystal sight this morning with A-Basin making snow. The ingredients all came together with a few inches of new natural snow and colder temps in the teens and 20s.

Natural new snow + blowing artificial snow. A-Basin is off and running. 10/10/2021.

I’m forecasting a good week ahead for the intermountain West including Colorado, Wyoming, Utah, Idaho, and Montana. A stronger, colder front will drive through Tuesday-Thursday followed by a kicker on the backside through UT, WY, and CO with an early season brief, weak NW Flow. What to expect:

  • Winter Storm Watches for higher elevations
  • Several inches of accumulation
  • Temps drop 20 degrees on the highest peaks
  • 14er temps near zero by Friday-Saturday
  • Wind gusts hit 50-90mph Tuesday-Wednesday higher up
My forecast for Colorado’s highest peaks. 10/10/2021.
  • Jackson Hole, WY (10k+): 6-12 inches
  • Alta, UT: 4-10″
  • Big Sky, MT: 4-10″

Here’s my forecast video so can graphically see how this week plays out:

Forecast video 10/10/2021.