Weathercatch: What caused our region’s widespread flooding this week in 2017?

Five years ago this week, an ark might have come in handy for some residents of Eastern Washington.

Numerous rivers, streams and lakes overtopped their banks, prompting flood warnings from Ferry County to the Palouse. Ducks paddled in overflow ponds in parks and water seeped over roadways and into homes.

The Spokane River, which usually sits at 22 feet and rose to nearly 28 feet, crested over footbridges at Riverfront Park and crept into nearby driveways. In North Idaho, water levels in Lake Coeur d’Alene and the St. Joe River in St. Maries spilled across parking lots and closed segments of roads. Flood waters even inundated parts of the sunnier and more arid city of Yakima – the “Palm Springs of Washington.” On March 16, fast-rising waters forced the evacuation of 19 residents of a private gated community and a business park.

Four days later, Gov. Jay Inslee declared a state of emergency for flooding in 20 counties, including Spokane, Whitman, Walla Walla and Yakima.

The deluge of water wasn’t caused by a sprawling super storm. Rather, it resulted from a combination of abnormal weather conditions that occurred during the weeks that preceded it.

The 2016-17 winter was abnormally cold. From December through February, temperatures ran colder than normal for 62 out of 90 days, according to the Office of the Washington State Climatologist. In Spokane, temperatures hit zero or below for 10 days, compared with the average number of four days.

Then came January, which ran 9 degrees below normal and fairly deep snow covered the ground through most of it. On Jan. 11, the snow depth stood at 11 inches at Spokane International Airport.

In February, the action really picked up. Nearly 20 inches of snow fell in the Spokane area – 13 inches more than normal for that month. At the same time, several days with mild temperatures triggered rainfall in addition to snow. On Feb. 15, the city received nearly three-quarters of an inch of rain. As the month drew to a close, it became the second-wettest February in 136 years of recorded history. In high elevations, it left a “much above average snowpack,” according to the National Oceanic and Atmospheric Administration’s National Climate Report.

In March, temperatures ran slightly above normal and precipitation continued to fall across the Inland Northwest. The 4.11 inches of rain that fell in Spokane that month was well above the average 1.83 inches. On March 13, it rained 0.56 of an inch. On March 14, the high temperature reached 60 degrees. That week, literally, was the tipping point.

Waterways, swollen with above-average rainfall and a massive surge of melting snow, began vaulting their crests. Runoff was further amplified by still-frozen ground that kept water from soaking into the soil.

This occurred five years ago in mid-March. Could we experience a similar, widespread flooding event this spring? It’s highly unlikely. We didn’t just emerge from an abnormally cold, snowy winter and we haven’t experienced prolonged heavy rain. Although a series of rainstorms or an intense downpour could lead to springtime flooding, its effects would probably be localized.

There are chances of periodic rainfall this weekend and into next week, but it’s not expected to be heavy or long-term.

Nic Loyd is a meteorologist in Washington state. Linda Weiford is a writer in Moscow, Idaho, who’s also a weather geek. Contact: ldweiford@gmail.com.