Snow Quality--the Issue of Water Content and Temperature

Early on I realized I needed to qualify some of the snowfall quantity data by reviewing snow quality, since this has a major effect on snow coverage and skiability of big dumps as well as subsequent surface conditions. The Westwide Network data sheets showed water precipitation as well as snow from 1979 to 1995. I selected 8 western areas plus more extensive independent data from Mammoth and Mt. Washington, the highest mountain in the Northeast, and calculated air temperatures for 50-90 months of data, shown here:

Area

 

December

 

January

 

February

 

March

 

 

 

High

Low

High

Low

High

Low

High

Low

Alpine Meadows

 

35.4

22.9

36.6

22.5

37.7

23.2

39.5

24.2

Mammoth

 

33.8

18.4

33.8

17.9

32.6

19.5

34.6

21.5

Mt. Hood Meadows

 

33.1

21.4

34.2

22.2

35.2

23.2

39.2

24.4

Stevens Pass

 

28.2

19.3

29.2

20.5

32.0

22.4

38.5

26.7

Bridger Bowl

 

27.2

12.5

27.9

13.6

29.9

14.5

35.2

19.2

Jackson Hole

 

18.1

9.7

17.2

8.7

19.0

10.6

23.2

13.8

Snowbird

 

29.4

14.4

30.2

14.1

33.8

15.2

38.0

19.8

Aspen

 

26.0

10.3

25.5

8.9

27.6

10.5

31.4

14.5

Vail

 

22.5

7.0

21.3

5.9

23.8

7.8

28.4

12.0

Taos

 

24.3

10.7

24.3

9.5

27.4

12.1

32.2

14.8

Mt. Washington

 

17.1

1.1

13.4

-3.4

13.7

-3.7

19.6

4.9

Originally I determined for the same Westwide sample areas how many of those months had 15-20 percent water (heavy, wet snow) and over 20 percent water (a strong indicator of rain). In 2013 I reviewed all water content info from the 1979-1995 Westwide areas with sufficient data. I have also included more extensive independent data from Gothic in Colorado and from Mammoth. The results are grouped among the 3 snowpack classifications defined by avalanche researchers.

Continental Total Wet Snow Months
Water Content  Water to Months: with Rain:
  Total Snow 15-20% Water  Over 20% Water
A-Basin, CO 7.4% 0.0% 0.0%
Berthoud Pass, CO 7.2% 0.0% 0.0%
Breckenridge, CO 7.6% 0.0% 0.0%
Copper Mt., CO 6.7% 0.0% 0.0%
Vail, Co 6.9% 0.0% 0.0%
Winter Park, Co 7.0% 0.0% 0.0%
Aspen Mt., CO 7.6% 0.0% 0.0%
Aspen Highlands, CO 8.0% 0.0% 0.0%
Gothic, CO 6.3% 0.0% 0.0%
Crested Butte, CO 7.7% 0.0% 0.0%
Monarch, CO 7.2% 0.0% 0.0%
Telluride, CO 7.0% 2.0% 0.0%
Purgatory, CO 7.4% 0.0% 0.0%
Taos, NM 6.3% 0.0% 0.0%

Intermountain Total Wet Snow Months
Water Content  Water to Months: with Rain:
  Total Snow 15-20% Water  Over 20% Water
Bridger Bowl, MT 8.0% 0.0% 0.0%
Jackson Hole, WY 9.1% 0.0% 0.0%
Sun Valley, ID 8.2% 0.0% 0.0%
Snowbird, UT 8.5% 3.1% 0.0%
Solitude, UT 8.6% 0.0% 0.0%
Wolf Creek, CO 9.3% 1.4% 0.0%

Most of the results in the above tables shouldn't surprise anybody. Rain or snow over 15 percent water are basically nonexistent at any of the Rocky Mountain sites. Nearly all the Colorado sites are all continental with water content from 6-8% while the Rockies areas farther west are all intermountain with water content from 8-9+%. The exception is Wolf Creek, which has a well known microclimate funneling southern storm tracks, greatly boosting snowfall and moderately increasing snow density into the intermountain bracket. The avalanche research article above classified Wolf Creek as intermountain in 14 out of 17 seasons.

Coastal Total SWE Wet Snow Months
Water Content  Water to Melted Months: with Rain:
  Total Snow Snow 15-20% Water  Over 20% Water
Alyeska, AK 9.8% 9.1% 5.3% 7.4%
Stevens Pass, WA 12.3% 10.0% 19.5% 15.6%
Crystal 6,000, WA 11.1% 9.7% 10.6% 8.5%
Rainier Paradise, WA 12.4% 11.6% 20.0% 13.3%
Mt. Hood Meadows, OR 15.6% 11.1% 14.5% 34.5%
Alpine Meadows, CA 13.1% 11.9% 14.4% 13.3%
Squaw 6,200, CA 15.4% 10.9% 13.0% 26.1%
Mammoth, CA 12.9% 12.8% 19.1% 0.8%
Mt. Washington, NH 17.6% N/A 37.5% 35.0%

For the coastal sites in the Westwide Network I have included an extra column showing the water content of snow only. The difference between this and the first column total water to total snow is an indication of how much winter precipitation is in the form of rain. Most of these sites show significant winter rain. The one that does not is Mammoth, which has only recorded 14 winter days of rain over 31 seasons due to its measuring site being at 9,000 feet. Only over New Year's 1997 was there sustained rain at Mammoth's 11,000 foot summit. Note that despite Mammoth's near immunity to rain the density of its snow is very bit as high as other coastal sites in WA, OR and CA. The avalanche research article classified Mammoth as coastal in 12 out of 18 seasons.

Alyeska's climate deviates from most coastal areas in a different way. The under 10% density of its snow is more like the intermountain areas. However, rain incidence is still significant at its very low altitude. The avalanche research article classified Alyeska as coastal in 14 out of 19 seasons. I was disappointed that the Westwide data sheets included snowfall but not water content for the "interior Northwest" areas of Schwietzer, ID and Whitefish, MT. My guess is that these areas would average intermountain snow density but still show some rain incidence, similar to Alyeska.
Mt. Washington, NH receives more rain than any of the western sites despite much lower average temperatures.


The following table dramatically illustrates the incidence of rain between East and West. The Mt. Mansfield (Stowe, Vermont) figures are based upon daily records from 1982 to 2010 at 3,950 feet, near the top of the ski area. Southern California figures are based upon snow reports from 1978 to 2010 at an average elevation of 7,500 feet. In the East precipitation is as high in fall and spring as in the winter and is much more likely to be rain. In the West fall and spring are drier than winter but at most ski areas the precipitation will still be snow.--T.C.

Month (Stowe)

Nov.

Dec.

Jan.

Feb.

Mar.

Apr.

Total

Avg. Days Rain

3.78

1.88

1.44

1.03

2.26

4.74

15.13

Avg. Rainfall

2.32

1.26

0.89

0.50

1.04

2.02

8.03

 

 

 

 

 

 

 

 

Month (So. Cal)

Nov.

Dec.

Jan.

Feb.

Mar.

Apr.

Total

Avg. Days Rain

0.35

0.89

1.14

0.97

0.35

0.08

3.78


The tables above still do not shed light upon snow density in New England vs. western ski areas. To do this I have further analyzed daily snow records at Alta, Mammoth and the Mansfield stake. The graph below shows the distribution of snowfall only by water content of the snow.

This graph confirms the subjective opinion of most powder skiers. The slight majority of Alta's snow is in the 5-7% range of water content. The plurality of Mammoth's snow is in the 10-14% range. The snow on Mt. Mansfield in Vermont has a wider distribution range of water content than either, but the peak of that distribution is only about 2% denser than Alta's snow and much lighter than Mammoth's. The final graph shows the distribution of all winter precipitation by water content.

At the low and mid-density levels the patterns are similar to the first graph. However 14% of Mt. Mansfield's winter precipitation is rain, and another 7% mixed at 40+% water/snow ratio vs. only 1% of Mammoth's and essentially none of Alta's winter precipitation being of the mixed or liquid kind.