Prolonged December Dry Spell Decreases Early Season Snowpack Totals

After a cold and snowy fall, forecasts of a ‘La Nina’ winter have stalled

By Tristan Scott
Sunset over the Swan Range. Beacon File Photo

Entering the “2021 Water Year” on Oct. 1, winter-sports enthusiasts were ecstatic about the possible “La Nina” forecast, which was expected to raise stoke levels while bolstering one of Montana’s most precious resources — the snowpack.

In October, the predicted outcome materialized in well-below normal temperatures statewide and above-average precipitation for most areas of Montana, including the Flathead and Kootenai river basins. Only the eastern border and southwest corner of the state missed the passing storms.

“Ending the month, snowpack was off to a strong start in most mountain locations,” according to Lucas Zukiewicz, water supply specialist for the U.S. Department of Agriculture’s Natural Resources Conservation Service (NRCS).

But weather patterns changed in November. The northern half of the state was favored for precipitation while the southern half of the state experienced below-normal monthly totals. November air temperatures registered at near to slightly above average for many locations in the western half of Montana, but well above average in the southeast corner of the state.

“Unfortunately, as we have seen in previous La Nina years in Montana, a forecasted La Nina winter isn’t a guarantee of cold and wet conditions during every month of the snow season, it’s only an increased probability of that occurring over a given period of time,” Zukiewicz said.

The last week of November marked the beginning of a prolonged dry period for almost all mountain locations, with many mountain Snowpack Telemetry (SNOTEL) sites receiving little snowfall between Nov. 20 and Dec. 12. This prolonged dry period caused snowpack percentages to decline across the state, especially at low- to mid-elevation mountain locations.

“The weather over the final two weeks of December was more active, and storms before the new year began helped to build the mountain snowpack and stop the decline in percentages,” Zukiewicz said.

As of Jan. 8, snowpack varied widely across Montana. Snowpack in some river basins along the Rocky Mountain Front is above normal for this date while snowpack is near to slightly below normal in other western Montana river basins, including prominent drainages in the Columbia River Basin.

For example, as of Jan. 11 the Flathead Basin’s snowpack was at 99% of normal, according to NRCS data, while the Kootenai was at 96%. The Rocky Mountain Front east of Marias Pass and Glacier National Park stands out as the only region in western Montana registering above normal snowpack, with 105% of average.

The contrast between Northwest Montana, where a weather station at Flattop Mountain in Glacier National Park registered 77 inches of settled snow depth this week, for 119% of normal, and Southwest Montana is stark.

“Southwest Montana, which didn’t receive the early boost in snowpack totals during October, is the only region in the state with snowpack that is well below normal for this date,” stated Zukiewicz. Snowpack in the Gallatin, Madison and Jefferson River basins ranges from 66 to 87 percent of normal.

Typically, only about 35 to 45 percent of the seasonal peak snowpack has accumulated at mountain locations across the state by Jan. 1, leaving plenty of time for snow totals to recover before runoff begins this spring and summer.

“You don’t have to look far back in time to find a winter where early season snowpack totals weren’t looking good in certain parts of the state,” said Zukiewicz. “Just last winter, snowpack totals in many river basins in western Montana along the Idaho border were below normal, only to have the weather patterns change and improve conditions before we got to runoff.”

According to forecasts published Jan. 6 by the National Oceanic and Atmospheric Administration’s (NOAA) Climate Prediction Center, the next two weeks are predicted to bring higher probabilities of above normal precipitation to many parts on Montana and the warmer than normal temperatures are likely to persist.

“At this point we’ll take what precipitation we can get, especially in southwestern Montana,” said Zukiewicz.

Check out additional NRCS data and view the water supply outlook reports here.

Stay Connected with the Daily Roundup.

Sign up for our newsletter and get the best of the Beacon delivered every day to your inbox.