Historical flooding across North Idaho and the Inland Empire

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We’re now at a time of year when flooding is a concern across the Inland Northwest. On Friday, Feb. 10, ice jams along the St. Joe River at Calder quickly caused the river to rise 17 feet above normal to 17.04 feet. The flood stage is at 13 feet. The following day, the ice jam broke apart allowing the river to flow and reduce the flood threat.

An ice blockage on a river, known as an ice jam or ice dam, is formed by blocks of ice. They are often more destructive than open-water flooding and can lead to much deeper and faster flooding.

With the recent rains, milder temperatures and snowmelt, many of us have seen some street and residential basement flooding. One subscriber told me of “relentless runoff” in his carport. It’s quite possible we’ll see more localized flooding as we expect more above normal moisture through the rest of February and into March.

Most of the time, the Inland Empire sees its greatest risk of high waters during the spring season. The big floods typically result from torrential thunderstorm downpours plus warm rains falling on melting snowpacks in the higher elevations. Much of the flooding generally occurs in the foothills of the Cascade Mountains, in the highlands of northeastern Washington as well as across portions of North Idaho and western Montana. The ski resorts in our area are currently reporting base depths of 70 to just over 100 inches of snow.

Historically, North Idaho and the rest of the Inland Empire has seen its share of high waters. In November of 1990, there was widespread major flooding on western Washington rivers, especially the ones in the northwest and several eastern Washington rivers. The Interstate 90 Lake Washington floating bridge actually sank during that time. Two death were recorded as damage was estimated at $250 million.

In February, 1996, widespread flooding was seen in Washington, Oregon and Idaho. The rivers across the region went far above flood stage due to a “rain-on-snow” event combined with ice jams in area rivers. Temperatures were near zero degrees at the end of January which led to ice along many rivers along with deep snows. The most severe flooding occurred on the Coeur d’Alene River basin, the St. Joe River basin and the Palouse, Orofino and Lapwai creeks. The overall damage in the region was estimated at a staggering $800 million.

At Cataldo, the flood stage along the Coeur d’Alene River is 43 feet. In February of 1996, the river went to 51.62 feet. The highest level ever recorded at Cataldo was in January, 1974 when the river rose to 58.23 feet.

Perhaps the worst flood ever seen in recent times across our region happened in May and June of 1948, known as the “Greatest Spring Snowmelt Flooding.” During that time, there was widespread flooding in North Idaho and eastern Washington, especially along the Columbia River. Below Priest Rapids, Washington, the Columbia River topped at 458.65 feet, an all-time record. Flood stage is 432 feet. At Lake Pend Oreille near Hope, a crest of 2071.2 feet was measured with a flood stage of 2063.5 feet. Methow River at Pateros, Wash., hit 12.30 feet with a flood stage of only 10 feet. At the St. Joe River at Calder, a record 18.10 feet was seen.

IN TERMS of our local weather, Cliff and I see more wet weather through the rest of the winter season. In-between these storm systems, there will some days with dry and mild weather.

February will indeed be another wet month across North Idaho. Our normal precipitation for this month is 2.14 inches. Believe it or not, we received our entire normal February precipitation in several days. Cliff measured 2.19 inches from last Wednesday into Friday morning. As of late Sunday, Coeur d’Alene’s moisture total was around 6.20 inches. The record for this month was 6.49 inches set back in 1940, so there’s a very good chance that we’ll have another record-breaking month for moisture. Remember, October was a record-breaker with a whopping 8.88 inches.

As we get toward the end of February, we may also see more snow across the Inland Empire. Right now, we’re close to 90 inches for the 2016-17 season. Cliff and I think that our final snowfall total will end up around the mid 90s, but there’s a chance we could once again top the 100-inch mark for the fourth time in less than 10 years.

It was announced earlier this month that the cooler sea-surface temperature event, “La Nina,” is gone and has been replaced by the in-between La Nina and warmer El Nino event. In fact, it’s possible we may see a new El Nino later this year. More on that next week.

Contact Randy Mann at randy@longrangeweather.com

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