AgWeatherNet Weekly Weather Outlook for September 20 to September 26, 2021

Dry weather returns for the Fall Equinox

Mark Ingalls, AgWeatherNet Field Technician

Synopsis:

Mainly dry conditions are expected in Washington this week with. A building ridge of high pressure is forecast for Monday and Tuesday for near average temperatures. Look for a weak cold front on Wednesday that may produce some rain showers along and west of the Cascades with breezy conditions in the Cascade mountain gaps and the Columbia Basin. Thursday through Saturday, dry and seasonally warm weather returns with a new ridge building in the Western U.S. Into the weekend, flow shifts to a more zonal regime to provide increased clouds and a few showers west of the Cascades, with a low chance of rain extending to parts of Eastern Washington on Sunday.

Discussion:

Over the past couple days, an atmospheric river brought rainfall to nearly all of Washington. West of the Cascades, values of around one to three inches were observed in the lowlands, with the exception of the Olympic Mountain rain shadow (Sequim, the San Juan Islands, and the North Sound) which generally saw around one half to one inch of rain. Eastern Washington had lower values, with the mountains north of Spokane coming in with around three quarters of an inch. Unfortunately, only a few hundredths were observed in the Columbia Basin, and many rain gauges within about 25 miles of Brewster (including Omak) didn't record any rain.

To start the week, a ridge of high pressure is likely to build over the region, resulting in drier and warmer weather. This pattern is interrupted by a weak cold front and shortwave trough that are forecast to transit the Pacific Northwest. This will result in extra clouds statewide. A chance of rain exists in and west of the Cascades, with the highest chances in mountain regions. Still, the highest rainfall values will likely remain below a tenth of an inch. Otherwise, look for temperatures to drop by a few degrees with breezy conditions through Cascade mountain gaps and the Columbia Basin.

A new ridge moves in behind the cold front to resume Washington's warm and dry trend for Thursday and Friday. Into the weekend, an upper level trough is forecast to track through Yukon and northern British Columbia, leading to more zonal flow in the Pacific Northwest. This may bring a few rain showers, mainly to mountain areas with a low chance for Western Washington lowlands. Another period of breezy winds through the mountain gaps and Columbia Basin is also possible.


8 to 14 Day Outlook, September 20 to September 26, 2021
  • Near average temperatures and above average precipitation are favored for the period.

Important Points About This Week's Weather

South Central Washington
Remainder of the Week
  • Wind: Light and variable Tue, W with breezy areas Wed, light and variable Thu-Fri.
  • Precipitation: Dry conditions expected.
  • High Temps: Near 80 Tue, upper 70s Wed-Thu, near 80 Fri.
  • Low Temps: Upper 40s Mon night, low 50s Tue-Thu nights, mid 50s Fri night. Cooler in sheltered areas.
  • Sky Cover: Mostly clear to partly cloudy.
Weekend
  • Wind: Generally W with breezy areas.
  • Precipitation: Dry conditions expected.
  • High Temps: Low 80s Sat, near 80 Sun.
  • Low Temps: Mid 50s Sat & Sun nights. Cooler in sheltered areas.
  • Sky Cover: Mostly clear.

North Central Washington
Remainder of the Week
  • Wind: Light and variable Tue, W with breezy areas Wed, light and variable Thu-Fri.
  • Precipitation: Dry conditions expected.
  • High Temps: Mid 70s Tue, upper 70s Wed-Thu, near 80 Fri. Cooler in higher terrain.
  • Low Temps: Near 50 Mon night, low 50s Tue night, low 50s Wed night, mid 50s Thu night, upper 50s Fri night. Cooler in higher terrain and sheltered areas.
  • Sky Cover: Partly cloudy Tue, mostly cloudy Wed, mostly clear to partly cloudy Thu-Fri.
Weekend
  • Wind: Generally W with breezy areas.
  • Precipitation: Low chance of mountain showers.
  • High Temps: Mid 80s Sat, near 80 Sun. Cooler in higher terrain.
  • Low Temps: Upper 50s Sat night, mid 50s Sun night. Cooler in higher terrain and sheltered areas.
  • Sky Cover: Partly cloudy.

Eastern Washington
Remainder of the Week
  • Wind: Light and variable Tue, W with breezy areas Wed, light and variable Thu-Fri.
  • Precipitation: Dry conditions expected.
  • High Temps: Mid 70s Tue-Wed, low 70s Thu, mid 70s Fri. Warmer in the Lewis & Clark Valley.
  • Low Temps: Low 40s Mon night, mid 40s Tue-Fri nights. Warmer in the Lewis & Clark Valley.
  • Sky Cover: Mostly clear to partly cloudy.
Weekend
  • Wind: Generally W with breezy areas.
  • Precipitation: Low chance of mountain showers north of Spokane.
  • High Temps: Near 80 Sat, mid 70s Sun. Warmer in the Lewis & Clark Valley.
  • Low Temps: Near 50 Sat night, upper 40s Sun night. Warmer in the Lewis & Clark Valley.
  • Sky Cover: Partly cloudy.

Western Washington
Remainder of the Week
  • Wind: Light and variable Tue, W and light (except breezy on the coast and through the strait) Wed, light and variable Thu-Fri.
  • Precipitation: Low chance of rain Wed.
  • High Temps: Low 70s Tue, upper 60s Wed-Thu, near 70 Fri. Cooler in higher terrain.
  • Low Temps: Near 50 Mon night, mid 50s Tue night, low 50s Wed-Fri night. Cooler in higher terrain.
  • Sky Cover: Partly cloudy Tue, mostly cloudy Wed, partly cloudy Thu-Fri.
Weekend
  • Wind: Generally W, breezy periods through the strait.
  • Precipitation: Low chance of rain Sun.
  • High Temps: Near 70 Sat, upper 60s Sun. Cooler in higher terrain.
  • Low Temps: Mid 50s Sat & Sun nights. Cooler in higher terrain.
  • Sky Cover: Partly cloudy Sat, mostly cloudy Sun.

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Washington State University