AgWeatherNet Weekly Weather Outlook Monday Update for December 7 to December 13, 2020

Areas of Widespread Fog and Freezing Fog to Clear by Tuesday Night

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

Synopsis:

Areas of fog and freezing fog that have taken hold in areas east of the Cascades look to dissolve by Tuesday night thanks to a weak disturbance expected to pass through the Pacific Northwest. Another disturbance looks to be in store for the state Thursday, and yet another but much stronger system for the weekend with statewide precipitation likely by Saturday night. Temperatures look to be seasonable for the period.

Discussion:

Weather conditions will continue to remain stagnant east of the Cascades through Tuesday while rain showers currently falling over the northern part of western Washington will slowly spread south and into mostly mountain areas of northern Washington just east of the Cascade crest. These showers are thanks to a tropical moisture plume flowing along a frontal boundary into British Columbia, and aren’t expected to wander east of the Okanogan.

By Tuesday night, a quick moving upper disturbance looks to pass through the state from the west. This is expected to bring enough forcing along with a surface boundary to mix out the lower levels of the atmosphere east of the Cascades, relieving the stagnant conditions and fog. A round of generally light and scattered low land rain and mountain snow showers is also expected. Showers are to move across the state from northwest to southeast beginning Tuesday night.

A transient ridge following Tuesdays disturbance will be the main weather influencer Wednesday as it passes over the Pacific Northwest prior to the next upper disturbance expected for Thursday. Showers are anticipated to linger across far eastern Washington near the Idaho border (particularly throughout higher terrain) and western Washington into Wednesday morning before slowly trending dry by the afternoon with a few stray showers likely lingering over the Cascades into Wednesday night.

More lowland rain and mountain snow showers are expected to move into the region from the west beginning Thursday. Low land snow also looks to be likely for areas of northern Washington east of the Cascades and the eastern Washington region. Showers should come to an end from west to east Friday with a few scattered showers lingering throughout western Washington and the Cascades throughout the day.

Conditions look to become much more active for the weekend with widespread precipitation likely by at least Saturday night. A deep and well occluded surface cyclone looks to move across the north Pacific draping a broad warm front over Oregon by Friday night. There is a bit of uncertainty as to the exact north to south position of the warm front but it is likely that the bulk of the precipitation associated with this boundary will impact Oregon with Washington remaining in the cool sector. It is expected that some lowland rain and mountain snow showers will impact the southern quarter of western Washington with a few stray showers making their way into the southern boundary of south central and to a lesser extent the eastern Washington region during the day Saturday, perhaps as even as early as Friday night in the far southwest corner of the state. Either way, expect widespread lowland rain and mountain snow by Saturday evening throughout western Washington and lowland rain/mixed precipitation and mountain snow throughout eastern Washington as showers move into the state form the southwest. Lowland snow is again more likely across lowland areas of northern Washington and the eastern Washington region Saturday night. Precipitation looks to continue statewide through Sunday, however becoming more scattered in nature throughout Washington east of the Cascades, especially throughout the Columbia Basin.


Important Points About Next Week's Weather

South Central Washington
Remainder of the Week
  • Wind: Calm to light and variable. S/SW and light by Tue, becoming breezy by Wed. Trending back to light and variable by Wed night. Breezy again Fri.
  • Precipitation: Scattered rain showers Tue night with greater activity to the east. Scattered rain/mixed showers Thu evening.
  • High Temps: Low 40s Tue, mid 40s Wed, low 40s Thu, near 40 Fri.
  • Low Temps: Mid 20s Mon night, low 30s Tue night, mid 20s Wed night, mid 20s Thu night.
  • Sky Cover: Mostly to partly cloudy. Areas of fog and freezing fog clearing Tue night.
Weekend
  • Wind: S/SE and generally light yet variable Sat. Breezy by Sun.
  • Precipitation: Chance for a rain/mixed shower Sat throughout the southern part of the region. Scattered rain/mixed showers Sat night and through Sun.
  • High Temps: Upper 30s Sat, near 40 Sun.
  • Low Temps: Mid 20s Fri night, mid 20s Sat night, mid 20s Sun night.
  • Sky Cover: Mostly cloudy to cloudy.

North Central Washington
Remainder of the Week
  • Wind: Calm to light and variable. S/SW and light by Tue night, becoming W/SW and breezy by Wed. Trending back to light and variable by Wed night. Light to breezy Fri.
  • Precipitation: Rain and high mountain snow showers to continue near the Cascade crest through Tue. Lowland rain and mountain snow Tue night, trending dry Wed with some lingering showers to the east. Snow showers Thu evening region wide with some rain/mixed in the Basin. Trending dry Fri.
  • High Temps: Upper 30s Tue, upper 30s Wed, mid 30s Thu, mid 30s Fri. Cooler in high terrain.
  • Low Temps: Low 30s Mon night, upper 20s Tue night, upper 20s Wed night, mid 20s Thu night. Cooler in high terrain.
  • Sky Cover: Mostly cloudy. Areas of fog and freezing fog clearing Tue night.
Weekend
  • Wind: SE and generally light yet variable Sat, breezier throughout the Basin. Breezy by Sun.
  • Precipitation: Widespread snow Sat night, trending toward scattered lowland rain and mountain snow showers Sun.
  • High Temps: Low 30s Sat, mid 30s Sun. Cooler in high terrain.
  • Low Temps: Low 20s Fri night, mid 20s Sat night, mid 20s Sun night. Cooler in high terrain.
  • Sky Cover: Mostly cloudy to cloudy.

Eastern Washington
Remainder of the Week
  • Wind: Calm to light and variable. S/SW and light by Tue, becoming breezy by Wed. Trending back to light and variable by Wed night. Breezy again Fri.
  • Precipitation: Lowland rain and mountain snow showers late Tue night and into Wed morning before trending dry by Wed afternoon. Snow showers Thu evening region wide with some lowland rain/mixed (primarily near Walla Walla). Trending dry Fri.
  • High Temps: Mid 40s Tue, upper 30s Wed, upper 30s Thu, upper 30s Fri. Cooler through the Blue Mtns.
  • Low Temps: Low 30s Mon night, low 30s Tue night, low 30s Wed night, upper 20s Thu night. Cooler through the Blue Mtns.
  • Sky Cover: Mostly cloudy. Areas of fog and freezing fog clearing Tue night.
Weekend
  • Wind: S/SE and breezy.
  • Precipitation: Low chance for a rain/mixed shower near the southern edge of the region Sat. Widespread rain/mixed showers and mountain snow Sat night, trending toward scattered lowland rain and mountain snow showers Sun.
  • High Temps: Upper 30s Sat, upper 30s Sun. Cooler through the Blue Mtns.
  • Low Temps: Mid 20s Fri night, upper 20s Sat night, mid 20s Sun night. Cooler through the Blue Mtns.
  • Sky Cover: Mostly cloudy to cloudy.

Western Washington
Remainder of the Week
  • Wind: Generally S and windy near the coast and sound, much lighter inland. Turning W/SW Tue night and trending light for Wed. S/SE and light to breezy Thu and Fri.
  • Precipitation: Lowland rain and high mountain snow showers continue to spread south through Mon night. Trending dry by Wed afternoon. Return of lowland rain and mountain snow showers Thu. Shower activity lessening by Fri with a few stray showers remaining throughout the region.
  • High Temps: Near 50 Tue, upper 40s Wed, mid 40s Thu, mid 40s Fri. Cooler through the Cascade and Olympic Mtns.
  • Low Temps: Mid 40s Mon night, low 40s Tue night, mid 30s Wed night, mid 30s Thu night. Cooler through the Cascade and Olympic Mtns.
  • Sky Cover: Mostly cloudy to cloudy.
Weekend
  • Wind: S/SE and windy Sat, especially near the coast and sound with gusts 50+ mph possible. Shifting SW and remaining windy Sun.
  • Precipitation: Some lowland rain and mountain snow showers in the southern quarter of the region Fri night. Widespread showers entering the region Sat and remaining through the weekend.
  • High Temps: Mid 40s Sat, near 50 Sun. Cooler through the Cascade and Olympic Mtns.
  • Low Temps: Mid 30s Fri night, mid 30s Sat night, upper 30s Sun night. Cooler through the Cascade and Olympic Mtns.
  • Sky Cover: Mostly cloudy to cloudy.

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