Rare June atmospheric river targets Seattle, Portland this weekend.

Title: Unusual June Weather: Two Atmospheric River Storms Approach Pacific Northwest

The Pacific Northwest is set to experience an unexpected weather pattern as two atmospheric river-type storms are forecasted to hit the region this weekend. These storms, remnants of a former tropical storm in the western Pacific Ocean, could result in record-breaking rainfall and near-flood conditions.

Atmospheric rivers are long, narrow regions in the atmosphere—typically 250-350 miles wide and over 1,000 miles long—that can carry large amounts of moisture, acting as conduits for precipitation. While beneficial, they can also cause significant flooding and damage, especially in coastal areas.

The first storm is expected to bring heavy rain starting from Sunday afternoon, with drenching rains likely Sunday night into Monday morning. A brief lull will follow later on Monday, but a second atmospheric river storm is set to hit the region Tuesday into Wednesday. Both storms have tapped into subtropical moisture and the latter storm may even harvest some moisture from the remnants of a typhoon that was in the western Pacific earlier in the week.

Computer projections indicate that these atmospheric river storms could reach a level 4 out of 5 on the Center for Western Weather and Water Extremes scale, making it only the fifth time a level 4 storm has reached the region in June since 1959.

In the Seattle and Puget Sound region, about 1-2 inches of rain is likely, which is significant considering that the area only averages 1.45 inches for the entire month of June. Urban areas could see flooding, and some rivers, such as the Snoqualmie River, may even reach minor flood stage.

A similar forecast is in store for northwestern Oregon, with the Portland and western Oregon lowlands expected to see 1-3 inches of rain and 2-5 inches or more across the mountains.

These storms may also bring other impacts, such as issues with agriculture and crops, delays or complications in regional road construction projects, and increased dangers to outdoor recreation due to heavy rains and gusty winds.

However, the winter-like weather pattern could shift into a hot and dry one by the end of next week in the Northwest, according to some long-range forecasts.