AgWeatherNet Weekly Outlook for November 20 to November 26, 2020

Continued active pattern to give way to calmer conditions for Thanksgiving

Mark Ingalls, AgWeatherNet Intern
Joe Zagrodnik, AgWeatherNet Postdoctoral Research Associate
Craig Oswald, AgWeatherNet Field Meteorologist

Note: Because of the holiday, there will be no Friday outlook on November 27. There will, however, be Monday outlooks on November 23 and November 30 as usual. Happy Thanksgiving!

Synopsis:

The weekend will begin with a ridge over the Pacific Northwest, giving way to a weak cold front Sunday night into Monday that will bring generally light lowland rain and mountain snow. Under the ridge, patchy fog is expected in lower elevations in the mornings. Scattered showers are expected to continue in the mountains and west of the Cascades through Tuesday, but these will come with higher snow levels keeping precipitation as rain for the major passes. A stronger system Tuesday night into Wednesday will lower snow levels back down to around pass level, feature more widespread precipitation, and could produce gusty winds. As Wednesday's system moves out of the area, a ridge of high pressure will approach and amplify to become the dominant weather feature.

Discussion:

A ridge of high pressure building over Washington will keep conditions mainly dry statewide to start the weekend. Overnight and morning fog or freezing fog is possible Friday night into Saturday morning and again Saturday night into Sunday morning in lower elevations of the state, mainly in valleys and basins east of the Cascades where nocturnal temperature inversions can be particularly strong. Temperatures under the ridge are expected to be near seasonal averages for mid-November.

Sunday night, a cold front breaks through the ridge to bring rain showers and mountain snow. Look for snow levels to drop below pass level by Monday morning to produce a few inches of snow along the major Cascade travel corridors. This front will be weakening as it approaches the state, so rain will be limited in the more arid portions of the state. If isolated showers present themselves in the Kittitas or Yakima Valleys early Monday, these could produce a rain/snow mix or perhaps a brief period of freezing rain.

Tuesday evening, a gale-force low is expected to make landfall on Vancouver Island. Ahead of it will be a warm front that will keep shower activity in place through the day in Western Washington and the mountains. While there isn't a ton of moisture embedded within this front, it will be enough to raise snow levels to around 6,000 feet. As the low makes landfall, its' associated cold front will slide across the state from west to east beginning after nightfall Thursday. This is expected to bring in more moisture than the warm front earlier in the day, bringing a chance of precipitation to most of the state. Snow levels behind the front are expected to drop to around 3,000 feet. Snow in the passes may produce significant travel impacts.

Winds will also pick up in response to the cold front, with gusts being the highest in mountain gap regions such as the Strait of Juan de Fuca and Columbia River Gorge. This shouldn't be as strong as some of the wind storms the region has already experienced this fall, but gusts in excess of 35 mph do appear possible in some areas.

Light precipitation (with a snow level remaining around 3,000 feet) is possible Thursday in the mountains and Western Washington as the surface low moves east toward Alberta. Behind it, an upper-level ridge reaches Washington to allow for drying conditions. Models are in good agreement that this ridge will strengthen over the Pacific Northwest and Northern Rockies on Friday.

Sun angles this time of year are low enough that the stable conditions provided by the ridge may be enough for significant inversions in valley and basin areas, especially east of the Cascades. It is too early to determine how extensive this will be, but it is certainly possible to have widespread fog or freezing fog in and around the Columbia Basin while the ridge is in place. Outside of areas with strong inversions, above average temperatures can be expected.


8 to 14 Day Outlook, November 20 to November 26, 2020
  • Above average temperatures and above average precipitation are favored for the period.

Important Points About Next Week's Weather

South Central Washington
Weekend
  • Wind: Light and variable.
  • Precipitation: Isolated rain showers Sun night.
  • High Temps: Mid 40s Sat, low 40s Sun.
  • Low Temps: Upper 20s Fri night, near 30 Sat night, low 30s Sun night.
  • Sky Cover: Clear to partly cloudy through Sat night. Mostly cloudy to overcast Sun. Patchy fog.
Next Week
  • Wind: S/SW, breezy Tue & Wed.
  • Precipitation: Isolated wintry mix Mon AM. Chance of rain Tue & Tue night.
  • High Temps: Upper 40s Mon, low 50s Tue, near 50 Wed, upper 40s Thu.
  • Low Temps: Mid 30s Mon & Tue night, low 30s Wed & Thu night.
  • Sky Cover: Partly to mostly cloudy Mon-Wed. Decreasing clouds with patchy fog Thu.

North Central Washington
Weekend
  • Wind: Light and variable.
  • Precipitation: Scattered rain and mountain snow Sun. Scattered rain/snow mix and mountain snow Sun night.
  • High Temps: Mid 40s Sat, low 40s Sun. Cooler in higher terrain.
  • Low Temps: Low 30s Fri night-Sun night. Cooler in higher terrain.
  • Sky Cover: Clear to partly cloudy through Sat. Mostly cloudy to overcast Sat night-Sun night. Patchy morning fog.
Next Week
  • Wind: S/SW, breezy Tue & Wed.
  • Precipitation: Mountain rain/snow Mon, lowland rain mountain snow Tue, lowland rain/snow mountain snow Wed.
  • High Temps: Mid 40s Mon, upper 40s Tue & Wed, mid 40s Thu. Cooler in higher terrain.
  • Low Temps: Mid 30s Mon & Tue night, low 30s Wed night, near 30 Thu night. Cooler in higher terrain.
  • Sky Cover: Mostly cloudy to overcast. Patchy morning fog Thu.

Eastern Washington
Weekend
  • Wind: Light and variable.
  • Precipitation: Low chance of rain/snow mix Sun night.
  • High Temps: Mid 40s Sat, low 40s Sun. Warmer in the Lewis & Clark Valley.
  • Low Temps: Mid 20s Fri & Sat night. Near 30 Sun night. Warmer in the Lewis & Clark Valley.
  • Sky Cover: Partly to mostly cloudy.
Next Week
  • Wind: S/SW, breezy Tue & Wed.
  • Precipitation: Low chance of rain/snow mix Mon AM. Scattered rain Tue, scattered rain/snow Tue night, possible lingering rain/snow Wed.
  • High Temps: Near 40 Mon, mid 40s Tue, low 40s Wed, near 40 Thu. Warmer in the Lewis & Clark Valley.
  • Low Temps: Low 30s Mon & Tue night, upper 20s Wed & Thu night.
  • Sky Cover: Mostly cloudy to overcast. Patchy morning fog Thu.

Western Washington
Weekend
  • Wind: S wind mainly below 10 mph.
  • Precipitation: Rain and mountain snow showers Sun & Sun night.
  • High Temps: Near 50 Sat, upper 40s Sun. Cooler in higher terrain.
  • Low Temps: Low 40s Fri night, near 40 Sat night, low 40s Sat night. Cooler in higher terrain.
  • Sky Cover: Mostly cloudy to overcast.
Next Week
  • Wind: SW/W, breezy on the coast and along the strait Mon, widespread breeze Tue.
  • Precipitation: Rain showers Mon, rain and mountain snow likely Mon night-Tue night, rain and mountain snow showers Wed. Upslope showers possible Thu.
  • High Temps: Near 50 Mon, low 50s Tue, near 50 Wed, upper 40s Thu. Cooler in higher terrain.
  • Low Temps: Mid 40s Mon night, low 40s Tue night, near 40 Wed & Thu night. Cooler in higher terrain.
  • Sky Cover: Mostly cloudy to overcast.

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