AgWeatherNet Weekly Weather Outlook Monday Update for October 26 to November 1, 2020

Unsettled weather through the week with a potent cold front by weeks end

Craig Oswald, AgWeatherNet Field Meteorologist

Synopsis:

A week of unsettled weather will start moving through the state from the west/northwest beginning tonight (Monday night). Precipitation will be mostly confined to western Washington including the Cascades and upland areas of northern Washington but also with chances elsewhere. Thursday/Thursday night will see the passage of a potent cold front from the northwest bringing a widespread surge of precipitation to western and northern Washington with rain showers expected across the Basin and south central parts of the state along with breezy and windy conditions. More widespread shower activity can also be expected on the Palouse and near the Idaho border. Cold air will settled over the state Friday and remain through the weekend. Temperatures that have been several degrees above average, and will continue to be through mid week, are expected to drop several degrees below average by Saturday. This will essentially effect a 20+ degree average temperature change between Thursday and Saturday for most of eastern Washington and approximately 10+ degrees throughout western Washington.

Discussion:

A pleasant weekend will give way to an active week of weather beginning tonight (Monday night). A modest disturbance, fed by a plume of moisture from the Pacific, looks to move in form the northwest bringing generally widespread rain showers and breezier winds throughout western Washington and the Cascades. Upland areas of northern Washington will also see rain showers, although lighter in nature, primarily Tuesday as showers make their way across the state. A few showers also stand reach low land areas of northern Washington and the Palouse. A low chance for a rain shower or two across the Basin and south central Washington is also acknowledged. Temperatures look to remain pleasant with mostly zonal flow aloft and air that looks to cool a few degrees yet remain warmer than average for this time of year. Chances for precipitation are expected to come to an end through the Basin, south central Washington, and the southeast corner of the state by Wednesday morning. Shower activity across the northern third of the state, east of the Cascades, likely won’t begin to trend drier until late Wednesday with showers likely even lingering through upland areas throughout Wednesday night thanks to an additional disturbance expected to enter southern British Columbia from the west on Tuesday night/Wednesday. Western Washington will continue to experience rain showers and scattered rain showers through Wednesday due to this. Totals for the first half of the week will be modest throughout eastern Washington with 0 to 0.25 inches likely. Smaller totals to be expected throughout the Basin, south central Washington, and the southeast corner of the state. With higher totals throughout the northern portion of the state and along the Idaho border north of Pullman, especially in the far northeast corner of the state. Totals across lowland areas of western Washington are indicated to be around 0.50 inches with more expected north of the Seattle metro area where totals stand to exceed 1 inch. The coast, Olympics, and Cascades will see higher totals as usual, again with greater totals to the north, some near 3 inches.

This one two punch of modest disturbances are but a teaser for a larger scale pattern change expected for the Thursday time frame. Zonal flow aloft will give way to a significant trough dropping in from the northwest from Alaska. A potent cold frontal boundary will begin to pass through the state Thursday, bringing a surge of rain and high mountain snow as well as breezy and windy conditions. By Friday night snow levels are expected to be around 3500 feet throughout western Washington and approach 2000 feet in eastern Washington as the coldest air will have settled into the region by this time. This event looks to bring wider spread precipitation to all areas of the state through Friday. Most of the state will likely trend dry Friday night with Far eastern Washington clinging to a few showers through Saturday before drying out. However there is some uncertainty as to whether the state will fully trend dry by Saturday or whether an upper disturbance or two will move into the Pacific Northwest from the north and initialize a few scattered rain/snow showers. This will likely be contingent upon how much moisture is available as dry and cold air is expected in conjunction with the trough. We will err toward the dry solution at this time and reevaluate in Fridays outlook. Precipitation totals for the latter half of the week in conjunction with the passage of the cold front look to be as much as a few tenths of an inch for Washington east of the Cascades with greater totals potentially to the south. Low land areas of western Washington may see between 0.50 and 0.75 inches with around 2 inches of snow water equivalent for high mountain areas possible.


Important Points About This Week's Weather

South Central Washington
Remainder of the week
  • Wind: Light and variable and becoming S/SW and breezy Tue. S/SW and windy by Thu with gusts 45+ mph. Trending lighter Thu night before switching N and windy Fri.
  • Precipitation: Low chance for a stray rain shower or two beginning Tue and lingering through Wed morning. Scattered rain showers likely Thu and lingering into Fri before trending dry Friday night.
  • High Temps: Low 60s Tue, mid 60s Wed, mid 60s Thu, low 50s Fri.
  • Low Temps: Low 30s Mon night, mid 40s Tue night, low 50s Wed night, upper 30s Thu night.
  • Sky Cover: Sunny and mostly clear early in the week with patchy overnight fog. Becoming mostly cloudy by Wed and remaining mostly cloudy to cloudy through the end of the week.

Weekend
  • Wind: Remaining N/NE and breezy through the weekend.
  • Precipitation: Dry conditions expected.
  • High Temps: Upper 40s Sat, mid 40s Sun.
  • Low Temps: Upper 20s Fri night, mid 20s Sat night, mid 20s Sun night.
  • Sky Cover: Mostly sunny to partly cloudy and becoming clearer by Sun.

North Central Washington
Remainder of the week
  • Wind: Light and variable and becoming S/SW and breezy Tue. S/SW and windy by Thu with gusts 45+ mph, particularly through the Basin. Trending lighter Thu night before switching N and windy Fri with strong gusts through significant N to S oriented valleys.
  • Precipitation: Upland rain showers with a few scattered low land rain showers Mon night through Wed night, drier across the Basin. Resurgence rain showers and high mountain snow beginning Thu, trending dry Fri night.
  • High Temps: Low 50s Tue, upper 50s Wed, upper 50s Thu, near 50 Fri. Cooler in high terrain.
  • Low Temps: Low 30s Mon night, upper 30s Tue night, mid 40s Wed night, mid 30s Thu night. Cooler in high terrain.
  • Sky Cover: Mostly cloudy early in the week. Mostly cloudy to cloudy by Thu, Partly cloudy Fri.

Weekend
  • Wind: Remaining N/NE and breezy through the weekend. Gusty through N to S valleys.
  • Precipitation: Dry conditions expected with some lingering rain/snow showers along the eastern boundary of the state in to Sat before trending dry.
  • High Temps: Mid 40s Sat, low 40s Sun. Cooler in high terrain.
  • Low Temps: Mid 20s Fri night, mid 20s Sat night, low 20s Sun night. Cooler in high terrain.
  • Sky Cover: Mostly sunny to partly cloudy and becoming clearer by Sun.

Eastern Washington
Remainder of the week
  • Wind: Light and variable and becoming S/SW and breezy Tue. S/SW and windy by Thu with gusts 45+ mph. Trending lighter Thu night before switching N and windy Fri.
  • Precipitation: A few scattered rain showers beginning Tue and lingering through Wed morning, drier toward the south. Rain showers likely Thu with mountain rain switching to snow Fri.
  • High Temps: Low 60s Tue, low 60s Wed, upper 50s Thu, mid 40s Fri. Cooler through the Blues.
  • Low Temps: Upper 30s Mon night, mid 40s Tue night, upper 40s Wed night, upper 30s Thu night. Cooler through the Blues.
  • Sky Cover: Becoming mostly cloudy Tue and mostly cloudy to cloudy Wed and remaining so through the end of the week.

Weekend
  • Wind: Remaining N/NE and breezy through the weekend.
  • Precipitation: A few rain showers and mountain snow showers lingering into Sat before trending dry.
  • High Temps: Upper 30s Sat, mid 30s Sun. Cooler through the Blues.
  • Low Temps: Upper 20s Fri night, mid 20s Sat night, low 20s Sun night. Cooler through the Blues.
  • Sky Cover: Mostly cloudy and becoming partly sunny by Sun.

Western Washington
Remainder of the week
  • Wind: Light and variable becoming S and breezy Tue. Gradually switching to W by Thu yet remaining breezy to windy, especially near the sound and coast.
  • Precipitation: Rain showers through the week, moderate at times. Mountain rain switching to snow Fri. Trending dry Fri night.
  • High Temps: Upper 50s Tue, low 60s Wed, upper 50s Thu, near 50 Fri. Cooler through the Cascades and Olympics.
  • Low Temps: Low 40s Mon night, low 50s Tue night, near 50 Wed night, near 40 Thu night. Cooler through the Cascades and Olympics.
  • Sky Cover: Mostly cloudy to cloudy. Becoming partly cloudy Fri.

Weekend
  • Wind: Becoming N yet variable and light Sat, yet breezy at times.
  • Precipitation: Dry conditions expected.
  • High Temps: Upper 40s Sat, upper 40s Sun.
  • Low Temps: Low 30s Fri night, near 30 Sat night, near 30 Sun night. Cooler through the Cascades and Olympics.
  • Sky Cover: Mostly sunny to partly cloudy. Becoming sunny by Sun.

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