Potential for Severe Thunderstorms in Western Oregon

 FastCast—Wednesday, Apr. 20 to Sunday, Apr. 24:

An interesting cold front will approach the Pacific Northwest on Wednesday. This front will bring rain, breezy conditions, and a chance of thunderstorms to the region. The biggest weather headline is a “marginal” risk of severe thunderstorms in Western Oregon and extreme SW Washington. This marginal risk area (designated by the NWS Storm Prediction Center) includes a threat of winds 60+ mph, brief severe hail, and a slight chance of a weak tornado. For the rest of the region, expect a chance of non-severe thunderstorms, especially on Wednesday afternoon and evening. More showers can be expected on Thursday, with 0.2-0.5” possible by Thursday evening in the lowlands. Expect highs in the low to mid 50s and lows in the upper 30s to low 40s through Thursday. Friday and Saturday bring a brief ridge and warmer weather, with highs in the upper 50s to low 60s and partly sunny conditions! Light showers return late on Sunday, but highs will still be in the upper 50s to low 60s, with partly sunny conditions.

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Continue reading the full blog below!

An interesting weather day is ahead for the Pacific Northwest on Wednesday. Due to a cold front moving in with unstable air in place…there is a “marginal” chance of severe thunderstorms in Western Oregon. The NWS Storm Prediction Center (SPC) graphic below shows the risk area (dark green).

This risk area includes the entire Oregon Coast, Coast Range, and most of the Willamette Valley, including Salem, Eugene, and areas around Portland. Extreme SW Washington is also included in the risk area.

What does a “marginal” risk mean? Take a look at the SPC graphic below that explains severe thunderstorm risk categories.

Despite being the lowest category of severe thunderstorms, a marginal risk is still notable for the Pacific Northwest.

The HRRR forecast below for Wednesday afternoon shows CAPE (Convective Available Potential Energy), another way of saying the amount of instability in the atmosphere.

Notice the gray shading over parts of the Pacific Northwest. This indicates CAPE values of approximately 250-700, notable for our region (but laughable for other parts of the country). 

Note that there is a chance of thunderstorms for Western Washington as well, particularly in the afternoon as the front moves through. However, storms in Western Washington are not expected to reach severe status (except a slight chance in extreme SW Washington, including parts of Wahkiakum and Pacific Counties, and the southern half of the Long Beach Peninsula).

Back in Western Oregon, there is also a slight chance of weak tornadoes. The SPC indicates a 2% chance of a tornado for Western Oregon.

This is a slight chance, and any tornado or waterspout will be short-lived and on the weak side. There is also a slight chance (5%) of damaging thunderstorm winds (58+ mph gusts) and severe hail (1” or greater diameter) in the marginal risk area. However, these are will also be short-lived if they occur. 

The best chance for thunderstorms around the Pacific Northwest will be in the afternoon to evening on Wednesday. Stay tuned to our local meteorologists on Twitter, the SPC, and Michael Snyder’s Pacific Northwest Weather Watch YouTube channel for updates!