Atmospheric River takes aim at Pacific Northwest


Last Atmospheric River in summer was 2007

Atmospheric River aiming at the Pacific Northwest July 2019 (KOIN)

PORTLAND, Ore. (KOIN) — Is this summer or winter? I think our atmosphere has forgotten.

The Pacific Northwest is expecting an unseasonably wet weather pattern over the next several days as a moderately strong atmospheric river takes aim at the West Coast.

Typically a winter time event, atmospheric rivers act as warm and wet conveyor belts, transporting water across the globe. In the winter months, they can bring heavy rain to the low lands and hefty snow pack to the high mountains.

The looming atmospheric river currently offshore will bring soaking rains to the coast of Oregon and Washington, and a wet evening commute to the PDX metro area and Willamette Valley Tuesday night.

Forecast models have projected roughly 0.25 to 0.4 inches of rainfall at PDX through Thursday with this event. Rain showers may develop through early Tuesday afternoon. However, folks should prepare for a wet commute home Tuesday evening as widespread rain moves in around 5 p.m.

Rain showers will linger into Wednesday before tapering off Thursday night.

Even though this atmospheric river event is unusual during summertime, it has happened before. The National Weather Service in Portland believes the last Atmospheric River in July was back in 2007.

But what about this summer in general? Where’s the heat? Where’s the sun? Many folks have been questioning our not-so-summer-like summer thus far in Portland.

Let’s debunk this idea by looking at observed temperatures at PDX. The month of June recorded daytime highs about 2 degrees above normal. That’s a bit hard to believe with many days in the low 70s. Our warmer-than-normal summers the past 5 years have been the culprit for the expected 90 degree heat waves.

The graphic below shows the noticeably warmer-than-normal July months we’ve seen over previous years. Just last year, PDX broke multiple 90+ degree heat records and is now the second warmest July on record, based on the average mean monthly temperature. July 2015 comes in third.

What was also unusual about our summer thus far was the EF-0 tornado that touched down in north Portland on July 1. Tornadoes are rare in the summer months. There have only been 5 tornadoes ever recorded in July in the NW Oregon/ SW Washington region since the early 1900’s.

On July 1, thunderstorms also dropped a whopping 0.54 inches of rain at PDX which broke the rainfall record that day.

This rainfall is a welcome event to our drought ridden region. The Willamette Valley and north coast is back in the Moderate Drought category.

The incoming rain will also work to benefit our wildfire season by delaying the start once again. There are currently no major fires burning in Oregon. Let’s try to keep it that way.

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