AgWeatherNet Weekly Outlook Monday Update for November 23 to November 29, 2020

A series of weak systems to keep conditions wet early this week with drier weather starting on Thanksgiving

Mark Ingalls, AgWeatherNet Intern
Joe Zagrodnik, AgWeatherNet Postdoctoral Research Associate

Note: There will be no weekly outlook on Friday, November 27. Outlooks will return Monday, November 30. Happy Thanksgiving!

Synopsis:

The trough currently in place over the West Coast will continue moving eastward, clearing the region overnight tonight and being replaced with a ridge. As it moves out, precipitation will decrease in most places statewide except for the mountains, Olympic Peninsula, and Northwest Washington. Shower activity picks up again Tuesday afternoon as a strong low moves toward Washington. Breezy conditions are also possible, particularly in the more typical windy locations around the state. Snow levels will be low enough that travel impacts look likely on the passes into Wednesday with a couple inches of snow expected there.

Some shower activity may linger into Thursday, but a strong ridge builds Thursday night into Friday. Most of the state will remain dry in response to this ridge with the exception of some shower activity north of US 2 west of the Cascade Crest. Saturday, an upper level trough skirts the region to bring shower activity primarily to areas north of I-90. Behind that, another ridge rebuilds to provide drier conditions for Sunday.

Discussion:

Shower activity in most lowland locations will taper off Monday afternoon, though some shower activity is likely to linger in the mountains and in the northwest interior. A weak ridge passes over in between the outgoing trough and one that is expected to come in Tuesday afternoon. More stable atmospheric conditions brought by the ridge combined with heightened surface moisture in Eastern Washington may produce patchy fog Monday night and Tuesday morning.

The next trough will be associated with a strong low advancing southeast from the southern Alaska Coast. It should be weakening as it slides south parallel to the British Columbia coast, but will still provide decent precipitation chances to most of the state as well as strong winds perhaps gusting as high as 40 mph in the Strait of Juan de Fuca and Columbia Gorge areas.

Precipitation around the state from this low will last overnight Tuesday and through most of the day Wednesday, especially in the mountains and west of the Cascades. Snow levels will drop from around 4000 to 4500 feet Tuesday evening to 2000 to 2500 feet by Wednesday morning. This will allow for a few inches of snow on all of the Cascade passes which could create significant travel impacts. Most of the Columbia Basin will remain dry during this event.

Showers (including mid- and high-elevation snow) will begin to taper off Wednesday night, but with northwesterly flow aloft some upslope showers are possible, particularly west of the Cascade crest. Otherwise, a ridge building Thursday after the passage of the low will allow for drying conditions through Friday. Northwestern Washington, including Bellingham and Port Angeles, look to be the exception here with a chance of rain showers continuing for that area.

Friday night into Saturday, a shortwave trough is expected to slide east from the Gulf of Alaska into British Columbia. Models are split on the exact position of this trough, but it seems that a more southern trajectory has a higher likelihood. This would bring increased shower activity to the state during that time period. This includes a renewed chance of snow on the passes. The shortwave proceeds east with the ridge rebuilding on Sunday for a return to drier conditions.


Important Points About Next Week's Weather

South Central Washington
Remainder of the Week
  • Wind: Generally S/SW. Breezy Tue night and Wed with gusts to 30 mph.
  • Precipitation: Light showers tapering off Mon. Chance of rain Tue night. Otherwise dry.
  • High Temps: Near 50 Tue & Wed, upper 40s Thu, mid 40s Fri.
  • Low Temps: Low 30s Mon night, mid 30s Tue night, low 30s Wed-Fri nights.
  • Sky Cover: Partly to mostly cloudy. Patchy fog Tue & Fri AM.
Weekend
  • Wind: Generally S/SW, breezy conditions possible Sat.
  • Precipitation: Dry conditions expected.
  • High Temps: Mid 40s Sat, low 40s Sun.
  • Low Temps: Near 30 Sat night & Sun night.
  • Sky Cover: Partly to mostly cloudy. Patchy AM fog.

North Central Washington
Remainder of the Week
  • Wind: Generally S/SW. Breezy Tue night and Wed with gusts to 30 mph.
  • Precipitation: Lowland rain showers Tue PM through Wed & Fri night. Mountain rain and snow showers through the week.
  • High Temps: Low 40s Tue, upper 40s Wed & Thu, mid 40s Fri. Cooler in higher terrain.
  • Low Temps: Near 30 Mon night, low 30s Tue night, near 30 Wed-Fri nights. Cooler in higher terrain.
  • Sky Cover: Partly to mostly cloudy. Patchy AM fog Tue & Fri.
Weekend
  • Wind: Generally S/SW, breezy conditions possible Sat.
  • Precipitation: Mountain rain and snow showers possible Sat.
  • High Temps: Mid 40s Sat, low 40s Sun. Cooler in higher terrain.
  • Low Temps: Upper 20s Sat & Sun nights. Cooler in higher terrain.
  • Sky Cover: Partly to mostly cloudy. Patchy AM fog.

Eastern Washington
Remainder of the Week
  • Wind: Generally S/SW. Breezy Tue night and Wed with gusts to 30 mph.
  • Precipitation: Rain/snow showers tapering off Mon PM. Chance of rain starting Tue, becoming rain/snow mix overnight and ending Wed AM.
  • High Temps: Low 40s Tue & Wed, near 40 Thu, low 40s Fri. Warmer in the Lewis & Clark Valley.
  • Low Temps: Low 30s Mon & Tue nights. Upper 20s Wed night, near 30 Thu night, upper 20s Fri night.
  • Sky Cover: Overcast Mon-Tue night, mostly cloudy to overcast Wed-Fri. Patchy AM fog Tue & Fri.
Weekend
  • Wind: Generally S/SW, breezy conditions possible Sat.
  • Precipitation: Low chance of rain/snow Sat.
  • High Temps: Near 40 Sat & Sun. Warmer in the Lewis & Clark Valley.
  • Low Temps: Mid 20s Sat & Sun nights. Warmer in the Lewis & Clark Valley.
  • Sky Cover: Mostly cloudy to overcast. Patchy AM fog.

Western Washington
Remainder of the Week
  • Wind: W on the coast, S along I-5 through Thu. Breezy Tue and Wed with gusts to 40 mph in more exposed locations. S Fri with strong winds possible on the Coast and along the Sound/Strait of Georgia north of Everett.
  • Precipitation: Lowland rain tapering off Mon PM, beginning again Tue lasting through Wed night, low chance Thu night & Fri, scattered showers Fri night. Mountain rain and snow showers through the week.
  • High Temps: Near 50 Tue, upper 40s Wed & Thu, near 50 Fri. Cooler in higher terrain.
  • Low Temps: Mid 40s Mon night, low 40s Tue – Fri nights. Cooler in higher terrain.
  • Sky Cover: Mostly cloudy to overcast.
Weekend
  • Wind: W and breezy through the Strait of Juan de Fuca Sat. Light and variable Sun.
  • Precipitation: Lowland chance of rain during the day Sat & Sun. Mountain rain and snow showers through the weekend.
  • High Temps: Upper 40s Sat & Sun. Cooler in higher terrain.
  • Low Temps: Upper 30s Sat & Sun nights. Cooler in higher terrain.
  • Sky Cover: Mostly cloudy to overcast.

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