Mountain snow depth and snow water equivalent

It has been an agonizing transition from winter to spring this year. Cool, wet weather dominated during April and May. It was beginning to look like summer might never happen. But now we are into June, with warmer, sunnier days becoming more common.

In this week’s column, I will do a quick review of our spring’s weather and summarize what is happening with the snowpack, which has yet to melt in the mountains.

Wet April and May

Data from the Jackson Climate Station in April and May confirmed what we already knew, that both months were much wetter than normal. April this year had more than double the norm, with 2.48 inches of precipitation. The April average is 1.14 inches.

April had twice as much snow as normal, with almost 8 inches recorded for the month, which has an in-town historic average snowfall of 4 inches.

May’s long-term average monthly precipitation in town is 1.8 inches, making it the wettest month of the year, on average. May 2019 had just over 2.5 inches of precipitation.

Lower temps this spring

Temperatures, as you might also suspect, were lower than normal, especially daily high temperatures.

April has an average high temperature of 52 degrees. This April the average high temperature in town was only 49 degrees.

May usually has an average high temperature in the low 60s for the whole month. This May the monthly average barely cracked the upper 50s. We also usually have more days that crack the 70-degree mark in May. This May we had only two days with highs of 70.

Mountain snow to river runoff

Snow at lower elevations in essentially gone. Hope we don’t see more days like we had just a couple weeks ago, waking up May 20 to new snow on the valley floor.

The snow in the mountains, with those lower-than-normal temperatures in April and May, never really had a chance to melt.

As of the end of the May, around the 9,500-foot elevation in the Tetons there was still over 7 feet of snow on the ground.

Snotel sites around the region, which measure the water content of the snowpack, were all reporting above-average “SWE” for this time of year. Snow-water equivalent is the measure of the water content of the snowpack.

The Philips Bench Snotel site, at an elevation of 8,200 feet, showed a snow depth of 39 inches at the end of May, with just over 17 inches of water content. That’s 141 percent of average for this time of year at that location.

Grand Targhee’s Snotel instrument at 9,200 feet showed 88 inches of snow depth with 45 inches of water. That’s not too far ahead of the average for Targhee at this time of year, at 112 percent of normal.

Higher temps for peak runoff

Temperatures here in early June have been on the rise already, from what they were the last week or so of May. A stretch of several days in a row with temperatures rising well above freezing at higher elevations, both day and night, would be necessary to reach peak runoff.

From my experience, I’ve noticed that when temperatures start reaching 50 degrees at around 9,000 feet, then snowmelt will accelerate, especially if overnight lows stay well above freezing.

A delay of two or three days from the onset of a significant warmup usually occurs before runoff reaches its peak.

From a potential flooding perspective, temperatures rising slowly, with a night or two dipping back below freezing, would be preferrable to a quick warmup. That would allow those 7 feet of snow to shrink at a slower pace.

In the meantime we have to take the weather as it comes. I think it is safe to say the winter weather is behind us.

I’ll stick my neck out a bit and say that summer weather surely lies ahead.

Jim Woodmencey is the chief meteorologist at MountainWeather.com and has provided weather forecasting for the Jackson Hole and Teton range for over 25 years. Contact him via columnists@jhnewsandguide.com.

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