Atmospheric River, Potential Flooding, and Gusty Winds to Begin June

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A strong atmospheric river, potential flooding, and even gusty winds are ahead as we begin June. This is an odd combination of weather conditions for June, and there will be some impacts across the region, so let's take a look at the forecast!

We'll start with the precipitable water forecast (amount of water vapor in the atmosphere), from the European model, for Sunday evening.

Notice the large area of high moisture content aimed at the Pacific Northwest. That's the atmospheric river that will impact the region from Sunday to Monday. An additional, faster-moving atmospheric river will move through from late Monday through Tuesday, before rain ends by Wednesday.

Next, let's look at how much rain is expected through late Tuesday night. We'll start with the European model forecast.

This forecast shows 1.2-1.75" of rain for the lowlands, with a rain-shadowed area from the Northern Kitsap Peninsula to Victoria BC getting 0.6-0.9". The coast will get 2-2.5", with the Cascade foothills and areas from Skagit County northward getting 1.5-2". The Cascades and Olympics will receive 2-4", with Eastern Washington getting 0.1-0.2" in the basin to 0.5-1" along the Cascades and along the Idaho border.

Let's compare this to a higher-resolution forecast, the NWS NBM model, also showing total rain through Tuesday night.

This forecast shows 1.3-1.7" for the lowlands, with a rain shadow from Seattle to Victoria (0.4-0.9"). The coast gets 2-3" in this forecast, with a substantial 3-7" in the mountains. In Eastern WA, significant rain (0.5-1") is limited to counties bordering Idaho, except in the Blue Mountains, where up to 2" is possible.

With significant amounts of rain (especially for June) expected, many rivers will rise, and some will reach bankfull. Below is the NWS forecast for river flooding.

Yellow squares mean a river reaches bankfull. This is possible on the Snoqualmie, Snohomish, Skykomish, White, Nisqually, Naches, Stehekin, and Skokomish Rivers, with most cresting on Monday.

There is one additional aspect to this incoming storm, and that is region-wide gusty winds. Winds will likely be strongest across the state on Monday, potentially remaining gusty for some areas through Tuesday. 

Below is the high-resolution NAM forecast for peak winds through Tuesday.

This forecast is definitely on the higher end of possibilities, showing gusts across the lowlands of 35-45 mph, with the Seattle metro area having gusts on Monday morning up to 40-45 mph, which would be very significant for June. This forecast also shows gusts of 40-45 mph across Eastern WA and 45-50 mph along the WA & OR coasts.

For a forecast showing somewhat lesser winds (at least for Western WA), check out the European model forecast below.

This forecast shows gusts of 35-40 mph from Tacoma northward, 35-40 mph along the coast, and potentially 40-45 mph for Island, San Juan, and Whatcom Counties. Notably, this forecast also has stronger winds for Eastern WA, with gusts of 40-50 mph, including 45-50 mph in Spokane.

This blog sure feels like it belongs somewhere in our storm season, but this is all happening in June! Be sure to treat this like a typical storm, with potential impacts being standing water, ponding, low visibility, and downed tree limbs. Stay safe!