AgWeatherNet Weekly Weather Outlook Monday Update for 17 May to 23 May 2021

Big pattern change with an upper level low moving over the region

Mark Ingalls, AgWeatherNet Intern

Synopsis:

Changes in the weather pattern were already being observed in Western Washington during the day Monday as a cold front began approaching the coast bringing with it showery and locally breezy conditions. It is forecast to move across the Cascades Monday night sending the wind and some rain into Eastern Washington. Behind the front temperatures will be much cooler as a closed low is likely to park over the northern Great Basin. Shortwave disturbances moving around the low are expected to bring repeated chances for rain and mountain snow showers through at least Thursday west of the Cascades and Saturday for some areas to the east. Ridging slowly builds into the region from west to east. This will cut off shower activity beginning Friday for Western Washington and spreading to along the Idaho border Sunday.

Discussion:

Cooler and wetter weather are on their way into the Pacific Northwest Monday afternoon with the arrival of a strong cold front. Cross-Cascade pressure gradients have already tightened to produce breezy conditions through the mountain gaps, spreading to become windy in much of Eastern Washington overnight and into Tuesday. Parts of Western Washington are not escaping strong winds, especially in typical windy spots. The initial pulse of shower activity is expected to move eastward, crossing the Cascades overnight with snow levels dropping to below pass level. Rain and snow from the front itself are likely to be limited to areas in or near the mountains.

The upper level trough associated with the cold front is forecast to produce a strong closed low pressure system that will track southeastward, stalling in the northern Great Basin region. This will keep unsettled and cooler weather in place over the Pacific Northwest with some areas seeing high temperatures up to 25 degrees cooler than what was seen during the recent hear wave. Rain and mountain snow showers continue west of the Cascades through Thursday. East of the Cascades, low chances of light rain are even present in the Columbia Basin beginning Thursday with higher chances in upslope areas. In all locations, precipitation values are not likely to make a positive impact on the ongoing drought.

A ridge of high pressure begins attempting to push into Washington on Friday bringing an end to rain chances for the west half of the state. Model guidance indicates that the low will be reluctant to move on as it attempts to stay put over the Great Basin. This gives continued chances of isolated rain showers for Friday and Saturday, mainly in the mountains, on the Palouse, and around Spokane, with lower chances in the Columbia Basin and Yakima Valley. The low finally gives in to the ridge, rapidly leaving Sunday to produce warmer and drier conditions to start the next work week.


Important Points About Next Week's Weather

South Central Washington
Remainder of the Week
  • Wind: W & windy Tue, W with breezy areas Wed, becoming N and breezy Thu, NE and breezy Fri.
  • Precipitation: Isolated rain showers Thu-Fri.
  • High Temps: Upper 60s Tue, mid 60s Wed, upper 60s Thu, near 70 Fri.
  • Low Temps: Low 50s Mon night, mid 40s Tue-Wed nights, upper 40s Thu-Fri nights.
  • Sky Cover: Partly cloudy Tue-Wed, mostly cloudy Thu-Fri.
Weekend
  • Wind: NE with breezy areas Sat, W and breezy Sun.
  • Precipitation: Isolated showers Sat.
  • High Temps: Low 70s Sat, mid 70s Sun.
  • Low Temps: Upper 40s Sat night, near 50 Sun night.
  • Sky Cover: Partly cloudy.

North Central Washington
Remainder of the Week
  • Wind: W with breezy areas Tue, N and light Wed becoming breezy Thu-Fri.
  • Precipitation: Upslope showers Tue, isolated showers Thu, upslope showers Fri.
  • High Temps: Mid 60s Tue-Thu, near 70 Fri. Cooler in higher terrain.
  • Low Temps: Near 50 Mon night, near 40 Tue night, low 40s Wed night, upper 40s Thu-Fri nights. Cooler in higher terrain and sheltered areas.
  • Sky Cover: Partly cloudy Tue-Wed, mostly cloudy Thu, partly cloudy Fri.
Weekend
  • Wind: NE with breezy areas Sat, W and breezy Sun.
  • Precipitation: Upslope showers Sat.
  • High Temps: Low 70s Sat, mid 70s Sun. Cooler in higher terrain.
  • Low Temps: Upper 40s Sat-Sun nights. Cooler in higher terrain and sheltered areas.
  • Sky Cover: Partly cloudy.

Eastern Washington
Remainder of the Week
  • Wind: W & windy Mon-Tue, W with breezy areas Wed, becoming N and breezy Thu, NE and breezy Fri.
  • Precipitation: Upslope showers Tue, isolated showers Thu-Fri.
  • High Temps: Low 60s Tue-Wed, near 60 Thu, low 60s Fri. Warmer in the Lewis & Clark Valley.
  • Low Temps: Upper 40s Mon night, upper 30s Tue night, near 40 Wed night, low 40s Thu & Fri nights. Warmer in the Lewis & Clark Valley.
  • Sky Cover: Partly cloudy Tue-Wed, mostly cloudy Thu-Fri.
Weekend
  • Wind: NE with breezy areas Sat, W and breezy Sun.
  • Precipitation: Isolated showers Sat.
  • High Temps: Mid 60s Sat, near 70 Sun. Warmer in the Lewis & Clark Valley.
  • Low Temps: Low 40s Sat night, mid 40s Sun night. Warmer in the Lewis & Clark Valley.
  • Sky Cover: Mostly cloudy Sat, partly cloudy Sun.

Western Washington
Remainder of the Week
  • Wind: SW with breezy areas Tue, generally W and breezy through the strait and on the coast Wed-Fri.
  • Precipitation: Rain and mountain snow Tue-Wed, isolated showers Thu.
  • High Temps: Upper 50s Tue, near 60 Wed, low 60s Thu, upper 60s Fri. Cooler in higher terrain.
  • Low Temps: Mid 40s Mon-Thu nights, near 50 Fri night. Cooler in higher terrain.
  • Sky Cover: Mostly cloudy to overcast Tue-Thu, partly cloudy Fri.
Weekend
  • Wind: W with breezy areas Sat & Sun.
  • Precipitation: Dry conditions expected.
  • High Temps: Near 70 Sat & Sun. Cooler in higher terrain.
  • Low Temps: Near 50 Sat & Sun nights. Cooler in higher terrain.
  • Sky Cover: Partly cloudy.

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