AgWeatherNet Weekly Outlook for April 23 to April 29, 2021

Active weekend, lasting into the week

Mark Ingalls, AgWeatherNet Intern
Craig Oswald, AgWeatherNet Field Meteorologist

Synopsis:

Clouds will continue to increase Friday night as a cold front moves from west to east across the state. Rain and mountain snow are expected periodically through the weekend, with the highest chance being in and west of the Cascades and the lowest chance in the Columbia Basin. Snow levels should remain high enough to not be an issue for cross-state travel. Lingering showers are possible Monday, but an upper level ridge building across the region is forecast to keep Eastern Washington dry through Thursday. Primarily northern reaches of Western Washington continues to have a chance for showers as a series of disturbances aimed at British Columbia through the week look spill into the area. Moist southwest flow aloft will also keep chances of rain in the forecast for the Cascades and Olympics, and to a lesser extent other Western Washington lowlands.

Discussion:

A cold front moving from west to east is bringing an end to warm and mostly sunny conditions for Washington State. It is forecast to reach the coast Friday evening, crossing into Eastern Washington by Saturday morning. Rain and mountain snow showers are expected with modest precipitation values for most of the state – the exception being the Columbia Basin and Yakima Valley where total rainfall is likely to remain below a tenth of an inch. Snow levels will start off around 6,000 feet, possibly dropping to around 4,000 feet behind the cold front. This will limit snow related impacts to cross-state travelers.

Behind the cold front lies its parent upper low that looks to come ashore by Saturday evening. Colder temperatures aloft and elevated moisture resulting from the low keeps a chance of rain showers in place for Western Washington, the Palouse, and mountainous parts of Washington Sunday and Monday with mostly cloudy skies elsewhere.

As the low continues its trek eastward, a ridge of high pressure is expected to begin building over the region from the west on Tuesday. For the eastern half of the state, this means a return to mostly clear to partly cloudy skies and warmer temperatures. Embedded within the southwesterly mean flow offshore, however, is a robust plume of subtropical moisture that is forecast to aim for coastal regions between Juneau and Tillamook with the focus primarily centered on British Columbia. A chance of rain showers will remain in place in and west of the Cascades under the influence of this plume through the end of the forecast period.

Toward next weekend, it appears that the ridge will flatten a bit as an upper level trough transits British Columbia. This trough may pull a cold front across Washington that would bring more widespread shower activity sometime Friday or Saturday.


8 to 14 Day Outlook, April 30 to May 06, 2021
  • Below average temperatures and near average precipitation are favored for the period.

Important Points About Next Week's Weather

South Central Washington
Weekend
  • Wind: SW with breezy areas Sat & Sun.
  • Precipitation: Chance of rain Saturday.
  • High Temps: Low 60s Sat, mid 60s Sun.
  • Low Temps: Near 50 Fri night, low 40s Sat-Sun nights.
  • Sky Cover: Mostly cloudy through Sat, partly to mostly cloudy Sun.
Next Week
  • Wind: Generally W with breezy areas during the afternoons.
  • Precipitation: Dry conditions expected.
  • High Temps: Upper 60s Mon, low 70s Tue, mid 70s Wed, upper 70s Thu.
  • Low Temps: Low 40s Mon night, mid 40s Tue night, low 50s Wed & Thu nights. Cooler in sheltered areas.
  • Sky Cover: Mostly clear Mon, partly cloudy Tue-Thu.

North Central Washington
Weekend
  • Wind: SW with breezy areas Sat & Sun.
  • Precipitation: Lowland rain showers Fri night, Sat, and Sat night. Upslope showers all weekend.
  • High Temps: Upper 50s Sat, low 60s Sun. Cooler in higher terrain.
  • Low Temps: Upper 40s Fri night, low 40s Sat-Sun nights. Cooler in higher terrain.
  • Sky Cover: Mostly cloudy.
Next Week
  • Wind: Generally W with breezy areas during the afternoons.
  • Precipitation: Chance of upslope showers Wed-Thu.
  • High Temps: Mid 60s Mon-Tue, upper 60s Wed, low 70s Thu. Cooler in higher terrain.
  • Low Temps: Low 40s Mon night, mid 40s Tue night, upper 40s Wed & Thu nights. Cooler in higher terrain.
  • Sky Cover: Mostly clear Mon, partly cloudy Tue-Wed, mostly cloudy Thu.

Eastern Washington
Weekend
  • Wind: SW with breezy areas Sat & Sun.
  • Precipitation: Rain showers Sat-Sun.
  • High Temps: Low 50s Sat, upper 50s Sun. Warmer in the Lewis & Clark Valley.
  • Low Temps: Mid 40s Fri night, near 40 Sat night, upper 30s Sun night. Warmer in the Lewis & Clark Valley.
  • Sky Cover: Mostly cloudy.
Next Week
  • Wind: Generally W with breezy areas during the afternoons.
  • Precipitation: Low chance of showers Mon & Thu.
  • High Temps: Near 60 Mon, low 60s Tue, mid 60s Wed, near 70 Thu. Warmer in the Lewis & Clark Valley.
  • Low Temps: Mid 30s Mon night, near 40 Tue night, mid 40s Wed & Thu nights. Warmer in the Lewis & Clark Valley.
  • Sky Cover: Mostly cloudy Mon, partly cloudy Tue, mostly cloudy Wed & Thu.

Western Washington
Weekend
  • Wind: Generally S and light Sat, becoming W and light Sun.
  • Precipitation: Rain and mountain snow showers.
  • High Temps: Near 50 Sat, upper 50s Sun. Cooler in higher terrain.
  • Low Temps: Upper 40s Fri night, mid 40s Sat & Sun nights. Cooler in higher terrain.
  • Sky Cover: Mostly cloudy.
Next Week
  • Wind: Generally W to SW and light.
  • Precipitation: Rain and mountain snow showers through the week.
  • High Temps: Upper 50s Mon, near 60 Tue-Wed, mid 60s Thu. Cooler in higher terrain.
  • Low Temps: Mid 40s Mon night, upper 40s Tue night, near 50 Wed & Thu nights. Cooler in higher terrain.
  • Sky Cover: Mostly cloudy.
Washington State University