Global Warming and Snow in the PNW

The average global temperature is rising. In 2015, the contiguous United States (CONUS) average temperature was 2.4°F above the 20th century average. In 2016 it was 2.8°F above the the avg. In 2017 it was 2.6°F above the average. What does this mean for snowfall in the Pacific Northwest? We can look at historical weather data and do math.

Weather Station Map

The northwest avalanche center has 48 weather stations operating in Washington and the northern part of Oregon. Each of these stations has a temperature sensor and 21 have a precipitation can. Most of the stations without a precipitation can are close to one with it. It's a simple matching exercise to add precipitation to the 27 stations that need it. Here's a table with each temperature sensor and how close the nearest precipitation can is:

Weather StationElevationDistance to Precip measurment
Alpental Base31000.00km
Alpental Mid-Mountain43500.00km
Alpental Summit54700.78km
Berne Snow Camp27000.00km
Blewett Pass410013.66km
Camp Muir101105.51km
Chinook Pass Base55000.00km
Chinook Pass Summit62400.82km
Crystal Base45700.00km
Crystal Green Valley62301.83km
Crystal Summit68302.03km
Dirty Face Summit59807.37km
Hurricane Ridge52500.00km
Lake Wenatchee19300.00km
Mission Ridge Mid-Mountain51600.00km
Mission Ridge Summit67301.75km
Mt Baker - Heather Meadows42100.00km
Mt Baker - Pan Dome50201.11km
Mt Hood Meadows Base53800.00km
Mt Hood Meadows Blue65401.31km
Mt Hood Meadows Cascade Express73002.21km
Mt St Helens - Coldwater32600.00km
Mt Washington434019.89km
Paradise Wind53800.00km
Ski Bowl Base36600.00km
Ski Bowl Summit50101.67km
Snoqualmie Pass30100.00km
Snoqualmie Pass - Dodge Ridge37601.14km
Snoqualmie Pass - East Shed37708.52km
Stevens Pass - Brooks48000.00km
Stevens Pass - Brooks Wind48500.08km
Stevens Pass - Grace Lakes48000.81km
Stevens Pass - Schmidt Haus39500.00km
Stevens Pass - Skyline52500.40km
Stevens Pass - Tye Mill51801.70km
Sunrise Base641010.65km
Sunrise Upper688011.39km
Timberline Lodge58800.00km
Timberline Magic Mile69901.71km
Tumwater Mountain418020.60km
Washington Pass Base54500.00km
Washington Pass Upper66800.93km
White Pass Base44701.87km
White Pass Pigtail Peak59700.36km
White Pass Upper58000.00km

These stations produce data every hour, and there are three seasons worth of data readily available. That creates 941,370 weather station-hours to work from. We can estimate the snowfall at each station by doing some simple math on the temperature and precipitation. If it's 25°F out, and there is .1 inch of precipitation (water) measured, there will be about 1 inch of snow. If it's 35°F out, it's raining. Using this logic I created a simple linear scheme to calculate the snow density off of temperature. In this manner we can build hourly snowfall for each weather station. I then subtracted the annual climate temperature anomaly from each temperature sensor and redid the math. Difference between the two snow calculations is the change the temperature anomaly would make. Here's an example from Crystal during February 2017. Blue is the actual snowfall. Orange is what is estimated to fall had it been 2.6°F cooler. Small difference in snow density during colder temperatures, big difference when we are near the rain/snow threshold.

Crystal Snow vs Climate Snow

What's it all add up to? The below is the snow loss in inches due to global warming by weather station.

Snow loss in inches

Here is the same chart but expressed as a percent loss compared to the 20th century average temperature:

Snow loss in percent

Let's step it forward. Here are projections from 8 different climate models.

Snow loss in percent

By 2050, we are looking at just over an additional 1°C of warming, or 2.2°F. Here's the decrease in snowfall as a % of what would have been expected given 20th century climatological norms:

Snow loss in percent

This puts many of the ski areas in the Northwest out of business. For reference the Paris Climate Accord is attempting to limit our warming to an additional 1C. This is the best case scenario. In a high emissions scenario, the generally accepted warming in the 21st century would be 2.6 to 4.8 °C (4.7 to 8.6 °F). Here's the percent of snow loss at the high end of the scale (8.6 °F):

Snow loss in percent

There's a lot of assumptions with the above, accurately modeling the future state of the climate,especially in a regional manner is an insanely complex challenge. I took a very simple approach, but I think most of the sources of error cancel each other out, as most are on either end of the transition from rain to snow. One area I don't have good data is at Stevens and Snoqualmie Pass. East flow creates difficulties in predicting snow vs rain due to freezing rain being a possibility. I could flag freezing rain by mathing out the snowfall being measured vs the temperature and precipitation, however you would not be able to effectively model a freezing rain prediction for the warming scenario using the same methods. For the time being I just left it as is, this will inflate snowfall totals for those areas. There are also a number of sensor errors and of the sort in this data, I'm doing some basic cleaning but not getting into the weeds. I would be interested in working with anyone that has ideas on calculating snowfall density using only temperature and precipitation at the surface, plus possibly RH.