What is the Probability of a Powder Day?

Many people and resorts define 6+ inches new snow as "a powder day," so I analyzed snowfall data for a few areas where I have daily info:

1) 7 years of the Jay Peak "snow tracker," both upper and lower
2) 10 years from Squaw Valley's similar web pages, also both upper and lower
3) 23 years from Steamboat mid-mountain

The objective was to find if there was a consistent relationship between monthly snowfall (where I have lots of data from over 100 areas) and number of 6+ inch snowfall days (I also tested 12+ inch days) per month. If this works for the West Coast, Rockies and East Coast examples, then it could be applied to my entire data set.

The known high volatility in the Sierra was most likely to cause a problem I thought. But I was pleasantly surprised to find that Squaw and Jay Peak produced almost identical best fit lines for 6+ inch powder days. These days were somewhat more likely at Steamboat for average or better levels of snowfall, but the numbers for 6+ inches are so close overall that modelling that blended dark blue line in the graph below to other areas should be very reasonable.

The relationship between monthly snowfall and percent of powder days in that month appears to be reasonably linear.

The 12+ inch data conformed to my expectation, quite a bit more likely at Squaw than the other places. The other impression that was reinforced was the greater likelihood of small consistent snows in Colorado. Steamboat's lowest month in the entire data set was 16.5 inches. 16% of Jay's months and 18% of Squaw's were lower than that.

A couple of examples of expected powder days to illustrate:

A month with 105 inches snowfall expects:
7.4 days of 6+ including 2.6 days of 12+ at Jay
7.3 days of 6+ including 3.9 days of 12+ at Squaw
8.0 days of 6+ including 2.0 days of 12+ at Steamboat
7.5 days of 6+ including 2.8 days of 12+ blending all 3 areas as shown in the graph below.

A month with 51 inches snowfall expects:
3.5 days of 6+ including 0.7 days of 12+ at Jay
3.5 days of 6+ including 1.3 days of 12+ at Squaw
3.5 days of 6+ including 0.6 days of 12+ at Steamboat
3.5 days of 6+ including 0.9 days of 12+ blending all 3 areas as shown in the graph below.

I used the relationship of 6+ days to estimate the percentage of days between December 1 and March 31 with 6+ inches of new snow for all 106 of the areas shown on my regional pages. Here's a sample from well known areas:

Area

6+ Inch Days

Whistler, BC 6,000 ft.

18.0%

Fernie, BC 5,400 ft.

15.7%

Lake Louise, AB 6,700 ft.

6.1%

Mt. Bachelor, OR 6,300 ft.

16.2%

Squaw Valley, CA 8,000 ft.

20.7%

Mammoth, CA 8.900 ft.

16.0%

Alta, UT 8,650 ft.

22.0%

Park City, UT 9,200 ft.

12.6%

Sun Valley, ID 8,800 ft.

8.5%

Jackson Hole, WY 8,250 ft.

16.5%

Aspen, CO 11,190 ft.

10.0%

Vail, CO 11,250 ft.

16.2%

Breckenridge, CO 11,100 ft.

12.0%

Taos, NM 11,200 ft.

10.1%

Killington, VT 4,142 ft.

11.1%

Jay Peak, VT 3,000 ft.

16.1%

Le Massif, QC 2,600 ft.

10.1%


How Likely am I to Get Some Good Powder on My One Week Vacation?

I also used the daily data to assemble weekly data, to answer that perennial question. I scaled up the Steamboat and Jay daily data to fit Alta's (the consensus powder icon of North America) December-March monthly average of 93 inches. I did not use Squaw in this exercise because its volatility is much higher than the other 3 areas.

So what is the expectation of a 7-day advance-booked trip to Alta between Dec. 1 and Mar. 31?

Alta Weeks

Powder Days

23% of weeks will have

no days of 6+ inches

28% of weeks will have

one day of 6-11 inches

23% of weeks will have

2 days of 6+ inches. For 15% of that 23% one of those days will be 12+

The top 26% of weeks will have

at least 3 days of 6+

The top 12% of weeks will have

at least 2 days of 12+

The top 10% of weeks will have

at least 4 days of 6+

The top 5% of weeks will have

at least 5 days of 6+ including 3 days of 12+

Most people know that Alta is a best case scenario.

The Jay and Steamboat data can be used to represent above average snowfall areas in the 350 inches per year range, such as Mt. Bachelor, Vail, Jackson Hole and Fernie. Here are the powder probabilities of a 7-day trip to a 350-inches-per-season (64 inches per winter month) North American resort:

Weeks at a 350-Inch Rockies Area

Powder Days

41% of weeks will have

no days of 6+ inches

31% of weeks will have

one day of 6-11 inches

16% of weeks will have

2 days of 6+ inches. For 4% of that 16% one of those days will be 12+

The top 12% of weeks will have

at least 3 days of 6+

The top 4% of weeks will have

at least 2 days of 12+

Many Sierra Nevada resorts are in the 350 inch range also, but with higher volatility. Here are the powder probabilities of a 7-day trip to Mammoth, based upon 22 years of daily data:

Mammoth Weeks

Powder Days

49% of weeks will have

no days of 6+ inches

22% of weeks will have

one day of 6-11 inches. For 2% of that 22% one of those days will be 12+

15% of weeks will have

2 days of 6+ inches including one day of 12+

The top 13% of weeks will have

at least 3 days of 6+

The top 12% of weeks will have

at least 2 days of 12+

The top 4% of weeks will have

at least 4 days of 6+ and 3 or more with 12+

Notice that the odds of 12+ inches are much higher in the Sierra Nevada than in Rockies areas with similar annual snowfall but that the probability of essentially no powder in a week is nearly 50%

Here's a list of popular North America destinations with winter monthly snowfall averages between 42 and 50 inches and similar variability of snowfall as the Steamboat/Jay model: A-Basin, Breckenridge, Copper Mt., Aspen/Snowmass, Crested Butte, Purgatory, Telluride, Taos, Killington, Sugarbush, the Park City group, Big Sky, Big White, Kicking Horse, Sunshine Village. This is the most common snowfall range for major destination resorts in North America. Anyone listed on my website with an annual average less than about 240 inches is probably under 42 inches per winter month.

Therefore a winter month (Dec.-Mar.) average is typically something like 46 inches, which I put into the Steamboat/Jay model. Here are the powder probabilities for a 7-day trip to these popular destinations:

Weeks at a 270-Inch Rockies Area

Powder Days

60% of weeks will have

no days of 6+ inches

26% of weeks will have

one day of 6-11 inches

9% of weeks will have

2 days of 6+ inches

Only the top 5% of weeks will have

a day with 12+ inches or more than 2 with 6+

What is going on here is that there are a lot of days at these places with some new snow but less than 6 inches. So if the area is remote with good stashes and low skier density you can get some good powder after a few days of small accumulations.

I should also mention that 240 inches is typical annual snowfall in the Alps or high Andes resorts. Volatility is higher, so there would be more 12+ days than in the Steamboat/Jay model. You also might get a month with practically nothing, like I saw in France and Chile in seasons that were considered above average overall. It is fortunate there is a lot of lift accessible off-piste in these places where powder can preserve for a week or more.

For most skiers who think they are unlucky for powder on advance-booked destination trips, the reality is they are probably not.


Can You Improve Your Powder Opportunities?

The most expensive option is snowcat or helicopter skiing. I became frustrated with slow progress in learning to ski powder in resorts and started incorporating a few cat or heli days into my trips starting in 1997. I've since had 60 days of snowcat and 25 of heliskiing. I would describe 5% of those days as bad snow and a few more than that as decent skiing but not powder. But based on my experience a mid-season snowcat or heli day will produce nearly all powder skiing about 85% of the time. Weather/conditions may dictate choice of terrain and perhaps shorter runs, but at least you will be skiing powder. And the powder will be easier for the inexperienced as it's untracked vs. the often more competitive situation in resorts.

Japan (particularly the northern island of Hokkaido) is the one lift served destination where the powder odds can be in your favor. Not only is the snowfall more than Alta's with similar light density, but it is more concentrated midwinter rather than spread fairly evenly over 4-5 months as in most of the Rockies. Niseko's average January snowfall of 177 inches compares to Alta's 95 inches. As a consequence here are the powder probabilities for a week in Niseko in January or the first half of February:

Niseko Weeks

Powder Days

6% of weeks will have

no days of 6+ inches

16% of weeks will have

one day of 6-11 inches

22% of weeks will have

2 days of 6+ inches

22% of weeks will have

3 days of 6+ inches. For 4% of that 22% one of those days will be 12+

The top 34% of weeks will have

at least 4 days of 6+

The top 19% of weeks will have

at least 5 days of 6+

The top 13% of weeks will have

at least 2 days of 12+

The top 5% of weeks will have

at least 6 days of 6+ including 3 days of 12+

For most skiers flexibility is the key to powder skiing. Your local drive up area may have less than 10% of days with 6+ inches, but if you make last minute calls and ski most of those days you may be skiing more powder in the long run than many destination skiers' trips scheduled far in advance. From many metro areas there are 10-15% powder probability areas within a day's drive. If powder is your priority be willing to spend your some of your ski vacation days one or two at a time when it snows within drive distance rather than a week or more scheduled far ahead.

Some people are willing to storm chase from a greater distance. Weather forecasts for big storms are generally reliable only 3-5 days in advance. A short notice plane ticket to someplace like Salt Lake City may seem expensive, but it could be less than a single day in the snowcat or helicopter and you may get several powder days out of a trip like that.

All content herein copyright 1996-2013 Bestsnow.net
All Rights Reserved.
No copies or reproductions may be made in whole or in part without express permission by Tony Crocker.
Prices for commercial users will be determined based upon intended use and distribution.