AgWeatherNet Outlook for November 29 to December 5, 2021

Warmer weather coming to an end with a cold front midweek

Mark Ingalls, AgWeatherNet Field Technician

Synopsis:

Ridging in the Southwestern United States will continue to be the dominant player in the forecast for Washington this week. The strength and position of this pattern is expected to drive another atmospheric river into Northwest Washington and British Columbia Tuesday and Wednesday, bringing rain there with a chance of showers in mountains statewide. Unseasonably warm temperatures will come to an end for many Thursday and Friday as a colder airmass moves in for the weekend. Under a westerly to northwesterly flow pattern, several disturbances are likely to move across Washington during this period, but timing and strength are uncertain. Still, look for a chance of rain and mountain snow to remain in place for many to end the week.

Discussion:

Another round of flooding is being observed in Northwest Washington thanks to a series of atmospheric river events that impacted that area over the last few days. Another moisture plume is forecast to come in Tuesday into Wednesday. This will be weaker, but rainfall totals near to above one inch can be expected in Whatcom and Skagit County lowlands with higher amounts in the North Cascades and windward Olympics. Elsewhere, a chance of showers is in place for mountain areas not listed. Given the trajectory of this moisture, the core Puget Sound urban area will see significant shadowing from the Olympics leading to lower rainfall values with much of Eastern Washington remaining dry.

The upcoming as well as recent atmospheric rivers have been aimed at the Lower Mainland of British Columbia by a strong upper level ridge in the Southwestern United States. This influence is keeping temperatures warmer than average in many parts of Washington, with snow levels expected to peak this week around 8000 to 9000 feet before a cold front crosses the Pacific Northwest on Thursday.

Aside from bringing much cooler temperatures into the region, the cold front will initially push moisture out. Dry weather statewide is not likely to stick around, however, as a series of disturbances are forecast to cross Washington Friday through the weekend. There is a modest level of uncertainty on the strength and timing of these systems, but it looks like the general weather pattern will be showery with rain and mountain snow in the mountains and western lowlands. There is also a chance of rain and mid-elevation snow along the Palouse, but models are not enthusiastic about giving rain to the Columbia Basin and Yakima Valley.


8 to 14 Day Outlook, December 6 to December 12, 2021
  • Above 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
  • Precipitation: Rain ending Mon.
  • High Temps: Upper 50s Tue, mid 60s Wed, upper 50s Thu, upper 40s Fri.
  • Low Temps: Mid 40s Mon night, near 50 Tue night, mid 40s Wed night, mid 30s Thu-Fri nights.
  • Sky Cover: Mostly cloudy.
Weekend
  • Precipitation: Low chance of rain showers.
  • High Temps: Upper 40s Sat, mid 40s Sun.
  • Low Temps: Near 30 Sat night, low 30s Sun night.
  • Sky Cover: Partly to mostly cloudy.

North Central Washington
Remainder of the Week
  • Precipitation: Low chance of rain Tue, possible mountain showers Wed-Thu, low chance of rain and snow Fri.
  • High Temps: Mid 50s Tue, low 60s Wed, mid 50s Thu, mid 40s Fri. Cooler in higher terrain.
  • Low Temps: Low 40s Mon-Wed nights, mid 30s Thu night, low 30s Fri night. Cooler in higher terrain.
  • Sky Cover: Mostly cloudy.
Weekend
  • Precipitation: Low chance of rain and snow.
  • High Temps: Mid 40s Sat & Sun. Cooler in higher terrain.
  • Low Temps: Near 30 Sat & Sun nights. Cooler in higher terrain.
  • Sky Cover: Mostly cloudy.

Eastern Washington
Remainder of the Week
  • Precipitation: Rain ending Mon.
  • High Temps: Near 50 Tue, upper 50s Wed, low 50s Thu, low 40s Fri. Warmer in the Lewis & Clark Valley.
  • Low Temps: Low 40s Mon night, mid 40s Tue-Wed night, near 30 Thu night, low 30s Fri night. Warmer in the Lewis & Clark Valley.
  • Sky Cover: Mostly cloudy to overcast.
Weekend
  • Precipitation: Low chance of rain and snow.
  • High Temps: Low 40s Sat, near 40 Sun. Warmer in the Lewis & Clark Valley.
  • Low Temps: Mid 20s Sat & Sun nights. Warmer in the Lewis & Clark Valley.
  • Sky Cover: Mostly cloudy.

Western Washington
Remainder of the Week
  • Precipitation: Rain Tue-Thu, resuming again with mountain snow Fri PM.
  • High Temps: Mid 50s Tue, upper 50s Wed, near 50 Thu, mid 40s Fri. Cooler in higher terrain.
  • Low Temps: Near 50 Mon-Tue nights, mid 40s Wed night, near 40 Thu night, upper 30s Fri night. Cooler in higher terrain.
  • Sky Cover: Mostly cloudy to overcast.
Weekend
  • Precipitation: Chance of rain and mountain snow.
  • High Temps: Mid 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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