Recap: Storm #3 from Friday night - Saturday midday

I will start out by saying that this is going to be a long section.

A few mountains measured 4x the amount of snow that I thought would accumulate on Saturday and I spent many hours looking at the data to figure out what went wrong with the forecast and how we can apply these lessons to future forecasts.

If this type of weather detective work interests you, read on!

If not, no worries, skip to the section below to see the forecast for Sunday and beyond.

Let’s start by going back to see what happened.

On Friday night, most northern mountains received 2-7 inches of snow. This was in line with the forecast. All good.

On Saturday and Saturday evening, the forecast was for an additional 1-3 inches for the northern mountains. The reality was that 4-11 inches accumulated. That’s a big difference from the forecast!

This is a timelapse from the snow stake cam at Loveland from Saturday at 5 am to Sunday at 5 am. By the way, All-Access subscribers can view time-lapse video from all of the 1,000+ mountain cams we have on OpenSnow.

Below are the snow totals from the storm.

The first number is Friday night, the second number is Saturday and Saturday night, and the total is from Friday night through Saturday night.

Northern mountains with lots of snow on Saturday.
Breckenridge: 7” + 11” = 18”
Loveland: 3” + 11” = 14”
Cameron Pass: 3-4” + 10” = 13”-14”
Vail: 4” + 8” = 12”
Copper Mountain: 4” + 6”-10” = 10”-14”
Arapahoe Basin: 4” + 7” = 11”
Berthoud Pass: 3” + 5”-9” = 8”-12”
Rocky Mountain National Park: 3” + 7” = 10”
Steamboat: 1” + 6” = 7”

Other mountains that did NOT get lots of snow on Saturday.
Keystone: 3” + 4” = 7”
Aspen Highlands: 5” + 0” = 5”
Crested Butte: 3” + 1” = 4”
Eldora: 4” + 0” = 4”
Winter Park: 1” + 3” = 4”
Snowmass: 3” + 0” = 3”
Beaver Creek: 2” + 1” = 3”
Buttermilk: 2” + 0” = 2”
Sunlight: 2 + 0” = 2”
Telluride: 2” + 0” = 2”
Wolf Creek: 2” + 0” = 2”

Of course, I was thrilled that some mountains received more snow and not less snow, but I was also incredibly mad to have blown the forecast.

So what happened at some of the northern mountains to cause much more snow than forecast?

Did I misread the model precipitation forecasts?

Not that I can tell. I went back and looked at all of the models I have access to (ECMWF, GFS, GEM, NAM-WRF, CAIC-WRF, HRRR). The HRRR model showed the most precipitation at one particular area of about 0.4 inches = 6 inches of snow. Other models were between 0.1-0.3 inches of precipitation = 1.5 - 4.5 inches of snow. No models showed 10+ inches of snow, and the placement of the most intense precipitation wasn’t exactly correct, either.

Clue #1: Plenty of moisture

We had near or above a 3g/kg mixing ratio (a measure of the amount of water in the atmosphere), which is a pretty good threshold during the winter at 10,000 feet as this number roughly translates as a top 10% day during the winter in terms of the amount of moisture. Also, the depth of the moisture was good, up to 20,000-25,000 feet in elevation.

Clue #2: Northwest wind direction at adequate speed.

The northern mountains that saw the most snow on Saturday (the nine mountains listed at the top) all benefit from a northwest wind direction, which is what we had on Saturday at 15-30mph. Clearly, a wind from the northwest was key not just because of the mountains that saw lots of snow, but also because mountains that did NOT receive lots of snow do not benefit from a northwest wind. But there is likely more to this story than just favorable orographics (wind hitting a mountain, being forced to rise, and creating precipitation).

Clue #3: Instability!

We saw bursts of intense snow on Saturday and Saturday evening, and these bursts didn’t occur at the same time at each of the mountains. Also, I saw graupel (tiny balls of snow) on the snow stake cams. These factors point toward convection as being responsible for some of the snow (convection = warmer air rising, like a summer thunderstorm).

When I look at some of the detailed cross-section model maps as well as model Skew-T graphics (we’re getting REALLY nerdy here), I see plenty of CAPE (Convective Available Potential Energy). This means that the air is buoyant and able to rise on its own after being given a ‘nudge’. This instability existed up to 20,000-25,000 feet.

This is a big-time factor.

Clue #4: Jet Stream

This fast-moving river of air at around 30,000 feet helps to lift the air below it, if you’re in the correct spot under the jet stream (right entrance region or left exit region). The northern mountains were in the left exit region yesterday, which was a good spot.

Conclusion

The combination of adequate moisture way up into the atmosphere, a fast-enough wind from the northwest to create orographic lift, lots of instability, and the addition of the jet stream overhead all combined to create a perfect situation for “extra” snowfall.

While most models CORRECTLY predicted that each of these factors would exist, none of the models predicted that the combination of these factors would lead to so much snow.

I am writing this long explanation not just for you as a post-mortem of the forecast, but also as a reference for me so that I can know what to look for in the models and will have a better chance of making the correct prediction next time.

Thanks for going deep on this one!

Storm #4: Sunday midday to Monday midday

On Sunday morning, most mountains are seeing dry weather with low clouds over the northern and some central mountains.

The dry weather will not last long.

In the radar animation below, from Sunday morning, the snow and rain you see over the Pacific Northwest (upper-left) is heading in our direction.

Timing:

Expect snow to re-start for the northern and central mountains around midday Sunday and continue through around sunrise on Monday.

Amount:

I am going to stick with 5-10 inches for the northern and central mountains with 3-6 inches in the northern part of the southern mountains (Telluride and Silverton). The track of this storm will be further south than the previous storm which is why the central mountains will get more snow from this system.

Factors:

During the brunt of the storm, from Sunday afternoon through Monday early morning, we will have adequate moisture, a wind from the west and west-northwest, OK instability, and stronger energy (vorticity) compared to the Friday night / Saturday storm. If we have these factors for 12-18 hours, a forecast of 5-10 inches is reasonable, and we could wind up with over 10 inches in a few spots.

The big difference between this storm and the surprise from Saturday’s storm is that the middle and upper atmosphere will quickly dry out and stabilize on Monday morning. This means that it’s highly likely that we will NOT see a 4x snowfall surprise on Monday during the day on the backside of the storm.

Series of storms

What we just saw over the last few days and coming up is what we want to see during the heart of winter. Storm-after-storm, every 1-2 days. This keeps the snow surface fresh, soft, and fun. Let’s hope we get more of these storm trains during the winter!

Where can you ride?

I’m repeating myself in this section, so if you’ve read it before, please skip!

As of right now, only Loveland and Arapahoe Basin are open for full-time operations with very limited terrain (2 runs) and Wolf Creek is open on weekends only with a good amount of terrain (90% this weekend). These are the inbounds spots to get turns.

If you head into the backcountry, remember that avalanche risk can exist anytime there is snow on the ground so do not brush this off as early season and lose focus. Also, in the northern mountains, with 12+ inches falling in the past two days and another 10+ inches possible, along with strong winds, it’s time to put away the “this is just the early season” idea. Check CAIC (Colorado Avalanche Information Center) as they are the best resource for avalanche information and forecasts.

Monday to Wednesday, November 5-7

Intense snow should end by Monday morning and then the northern mountains will see clouds and light snow showers through midweek. Other mountains will stay dry and sunnier.

Thursday, November 8

A storm will likely bring light snow to areas near and east of the divide and out east to the eastern plains. This does NOT look like a significant storm for most mountains.

Sunday, November 11

We could see another storm similar to the one on November 8th, focusing mostly near and east of the divide.

Thanks for reading, enjoy the storm on Sunday afternoon and Sunday night, and look for my next update on Monday, November 5.

JOEL GRATZ

My upcoming presentations about the winter forecast and tips for chasing pow!

* Thursday, November 8 in Evergreen at Boone Mountain Sports / Evergreen Brewery. Free to attend. Beer and food available for purchase, and the talk starts at 7 pm. Details here.

* Friday, November 9 in Breckenridge at the Breckenridge Backstage Theater. Party, my talk, and a movie. Time from 500-830pm. Details here.

* November 28 in Vail.

* December 5 in Denver. 

OpenSummit

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Geography Key

Northern Mountains
Steamboat, Granby, Beaver Creek, Vail, Ski Cooper, Copper, Breckenridge, Keystone, Loveland, Abasin, Winter Park, Berthoud Pass, Eldora, Rocky Mountain National Park, Cameron Pass

Along the Divide
Loveland, Arapahoe Basin, Winter Park, Berthoud Pass

East of the Divide
Eldora, Echo, Rocky Mountain National Park, Cameron Pass

Central Mountains
Aspen, Sunlight, Monarch, Crested Butte, Irwin, Powderhorn

Southern Mountains
Telluride, Silverton – north side of the southern mountains | Purgatory, Wolf Creek – south side of the southern mountains