Sunday, May 1, 2022

Active Start to May Expected

FastCast—Monday, May 2 to Saturday, May 7:
A wet start to May is ahead for Western Washington. Sunday was a nice day, with highs in the low to mid 60s. Rain returns late Sunday night, continuing through midday Monday. Expect 0.2 to 0.5 inches of rain around the region. Drier and cloudy weather is expected on Tuesday and Wednesday. Highs will be in the mid to upper 50s on Monday and Tuesday, and in the mid to upper 60s on Wednesday. Rain returns again very late Wednesday night or early Thursday morning, continuing at times through Saturday evening. This will be a much wetter period (especially Friday), with a total of 1 to 1.75 inches of rain in the lowlands, 1.5 to 4 inches on the coast and in the mountains, and 0.5 to 0.8 inches in Eastern Washington. Breezy weather is also possible on Saturday. Highs from Thursday to Saturday will be in the mid to upper 50s, with lows in the entire period (Monday to Saturday) in the 40s.

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Continue reading the full blog below!

All four months of 2022 have had above normal rainfall in Western Washington, and it appears that May will follow that trend. May’s average rainfall at Sea-Tac Airport is around 1.9 inches, and even more than that could fall this week alone! Let’s take a look at what’s ahead.

Below is the HRRR model forecast for rain through 11 PM Monday, in the first (weak) system moving through overnight Sunday into Monday.


Rain with this system will be modest, with 0.2 to 0.4 inches around the lowlands (possibly higher in some places). The mountains will receive the most rain, with up to 1.25 inches south of Snoqualmie Pass.

A nice break in the rain (though it will still be cloudy) is expected on Tuesday and Wednesday. As seen in the European model below, a brief ridge (red colors) will build over the area on Wednesday.


This ridge will bring some warmer temperatures on Wednesday (though it may feel “muggy” since it’s on the cloudy side). Expect highs on Wednesday to reach the mid to upper 60s in the lowlands and the low to mid 70s in Eastern Washington.

However, the dry weather won’t last for long. Rain returns on Thursday as troughing re-establishes itself over the Pacific Northwest. This means that a steady stream of weather can move in, bringing lots of rain. Take a look at the difference between the model above (Wednesday) and the model below (next Saturday).


This is a total shift from Wednesday, with significant troughing established by Saturday. This troughing will help bring systems from Thursday into the weekend.

The European model below shows total rain through Saturday evening (including the rain on Monday).


From Thursday to Sunday, expect 1-1.75 inches of rain in the lowlands, 1.5 to 4 inches in the mountains/on the coast, and 0.4 to 0.8 inches in Eastern Washington.

Notice that totals in the lowlands are between 1.5 and 2 inches for the first 7 days of May. This means that it’s possible that we will receive over 75% of this month’s average rainfall in one week!

There is also a chance of some Convergence Zone activity and breezy conditions on Saturday.

Stay tuned…although it is spring, the active weather hasn’t gone away!

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The Pacific Northwest Weather Workshop (the annual conference about Pacific Northwest weather) is on Zoom from 8:45 AM to 12:30 PM on May 7th, and it is free!

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