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We were HOW cold? The numbers behind Boise’s record-setting winter

Weiser River ice jam forces flood water into homes and farmland

The Weiser River, jammed with ice, overflowed early Friday morning Feb. 10, 2017, flooding areas south of the river near Cove and Couper roads. Homes in the area were evacuated as well as several businesses. Flood water covered a portion of US 95
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The Weiser River, jammed with ice, overflowed early Friday morning Feb. 10, 2017, flooding areas south of the river near Cove and Couper roads. Homes in the area were evacuated as well as several businesses. Flood water covered a portion of US 95

Some Boiseans looked out their windows with dismay Tuesday morning: More snow? Really?

With spring just under three weeks away, it’s been a memorable — and historic — winter.

Typically, moisture from the Pacific combines with cold air from the Arctic to produce one blast of snow in Boise that lasts five to 10 days.

“This year, it lasted five weeks,” said Les Colin, lead forecaster at the Boise office of the National Weather Service. The snow load collapsed business roofs, onion sheds and carports. Conditions caused damaging ice dams to form on building rooftops, and February thaws led to severe flooding near the Oregon border and in the Magic Valley.

Here are some of the notable numbers that Colin helped us tease from mountains of data, going back to when recordkeeping began in the late 1800s:

▪  This winter was one of the coldest ever recorded. December was the sixth coldest on record; January ranked 11th.

“It’s rare to have it both cold and wet in the same month,” Colin said. “When it’s very cold, it tends to be dry. When it’s a mild month, it tends to be wet.”

The average monthly temperature for December was more than 7 degrees below normal. January averaged 10 degrees below normal.

▪  We ranked first in the record books for snowfall in December and January — the most ever for that two-month period. The total 35.5 inches handily surpassed the previous record of 30.5 inches in 1983-84.

There were 13 days in December and 14 days in January of measureable snow (one-hundredth of an inch or more). It was a very White Christmas, thanks to 7.7 inches that dumped on Dec. 23-24. Another 7.7 inches fell on Jan. 3-4.

▪  February was significantly less snowy with just 3.3 inches measured at the airport. But that was higher than normal — and the three-month period of January, December and February ranks fifth in the record books at 38.8 total inches.

The most ever measured during those three months was 43.3 inches in 1948-49.

Some years, of course, snow starts oddly early or ends very late. If we account for a broader season, 2016-2017 has been the 10th snowiest winter so far.

No. 1? The winter of 1917-17, when 50 inches fell.

Snow collapsed five greenhouses, and Tim Sommer, owner of Purple Sage Farms, slashed the plastic of three others to save them. Friends and other farmers started a GoFundMe to help him rebuild.

▪  Precipitation is a measure of the liquid equivalent of snow/hail/rain. The total for December, January and February is 6.17 inches — that ranks ninth for total precipitation.

The record is 7.40 inches in 1909-10.

▪  This winter we set a record for snow depth, with 15 inches measured on the ground at the airport on Jan. 5, the most since NWS began tracking that statistic in 1939. Colin noted that he found a reference in the Idaho Tri-Weekly Statesman that the U.S. Signal Corps measured 22 inches on the ground in 1884.

▪  It might seem counterintuitive but Boise didn’t set snowfall records for any individual month.

December: 14 inches. The record: 36.6 inches in 1884 (more recently, 26.2 inches in 1983).

January: 21.5 inches. The record: 27 inches in 1929.

February: 3.3 inches. The record: 25.2 in 1949.

Daniel Wittell, a senior operator with the Ada County Highway District, drives a snow plow along a few of Boise's major roadways and steeper streets Wednesday Jan. 4, 2017. Recent snowfall has kept the plows busy.

Katy Moeller: 208-377-6413, @KatyMoeller

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