Storms may bring lowland flooding

Although many of us certainly enjoyed the nice weather around Easter weekend nearly two weeks ago, much of the first half of April has brought some early-morning hard freezes, gusty winds, chilly afternoons and a couple of dustings of snow.

But, believe it or not, precipitation is currently below normal for 2007.

While I do see some shower activity and, possibly, even a thunderstorm with pea-size hail and gusty winds into at least early next week, I’m still looking for welcome warmer weather and increasing sunshine again before the end of the month as a ridge of high pressure moves in from the Pacific.

But enjoy the brief periods of beautiful spring weather, because they won’t last long.

By early May, a deep trough of low pressure will bring moderate to heavy rains at times to much of the Inland Northwest. The probabilities of some lowland flooding will increase as these spring storms intensify and combine with the additional snowmelt in the higher mountains.

Many of the ski resorts are still reporting snow depths of over 100 feet. During abnormally warm periods, as was the case last month, we’ll often see flood warnings issued for area rivers because of fast-melting snows.

Many of us have seen lowland flooding in the winter, but the Inland Northwest sees its greatest risk of high water in spring. Floods typically result from thunderstorm downpours plus rains falling on melting mountain snowpack.

This spring flooding generally occurs in the foothills of the Cascade Mountains, in the highlands of northeastern Washington and across portions of North Idaho and Western Montana. A disastrous flood hit Montana’s Flathead Valley in June 1964.

The chances for heavy rains and lowland flooding will greatly decrease by mid- to late June, much like last year. The rains should subside, and temperatures will soar back to above normal levels for the late spring/early summer period.

The region has seen its share of high waters. In November 1990, there was widespread major flooding on Western Washington rivers, especially in the northwest part of the state, and on several Eastern Washington rivers. The Interstate 90 Lake Washington floating bridge actually sank during that time.

Two deaths were recorded as damage was estimated at $250 million.

In February 1996, widespread flooding was seen in Washington, Oregon and Idaho, with rivers in Western and southeastern Washington rising far above flood stage. Major flooding occurred in North Idaho.

Three deaths were reported in Washington with overall damage in the region estimated at $800 million.

The worst flood seen in recent times, known as the “Greatest Spring Snowmelt Flooding,” happened in May and June of 1948, This event is listed as the second-biggest weather event in Washington’s history.

During that time, there was widespread flooding in North Idaho and Eastern Washington, especially along the Columbia River.

Below Priest Rapids, Wash., the Columbia River topped at 458.65 feet, an all-time record. Flood stage is 432 feet.

At Lake Pend Oreille near Hope, Idaho, a crest of 2071.2 feet was measured, with flood stage set at 2063.5 feet. The Methow River at Pateros, Wash., hit 12.30 feet with a flood stage of only 10 feet.

At the St. Joe River at Calder, Idaho, a record 18.10 feet was seen. That particular river’s flood stage is 13 feet.

From early May into mid-June or later, don’t be too surprised to see more flood warnings along area streams and rivers due to expected increased rain, thunderstorm activity and snowmelt, as there is still plenty of the white stuff left at the higher elevations. Stay tuned.