AgWeatherNet Weekly Weather Outlook for September 13 to September 19, 2021

Wetting rain in the forecast for this weekend

Mark Ingalls, AgWeatherNet Field Technician

Synopsis:

A generally dry start to the week is forecast with temperatures near average Monday and Tuesday. Tuesday night, a weakening cold begins to move through the state, bringing light rain to Western Washington, the Cascades, and Okanogan Highlands. These will generally taper off from west to east on Wednesday. Thursday, will be another dry day for most. The first strong cold front of the season is likely to begin impacting Washington Thursday night with rain spreading eastward through the day Friday. The entire state has a chance of rain out of this system with lingering showers through the weekend as smaller disturbances move through.

Discussion:

A transitory ridge of high pressure is forecast to build across the Pacific Northwest Monday, bringing mostly clear skies and dry conditions statewide. Temperatures Monday and Tuesday are forecast to be near seasonal averaged. In Western Washington, clouds increase Tuesday ahead of a weakening cold front as the ridge moves eastward. Rain showers will move from west to east with a chance of precipitation for all of Western Washington, the Cascades, and the Okanogan Highlands Tuesday afternoon through Wednesday morning. The urban area along the Puget Sound is likely to be shadowed significantly by the Olympic Mountains thanks to zonal flow but should still see as much as a tenth of an inch of rain (higher closer to the mountains).

Most of the moisture will be focused on Vancouver Island, keeping the Inland Northwest dry. Despite this, the pressure gradient should tighten across the Cascades and Eastern Washington leading to breezy conditions through mountain gaps (like the Columbia Gorge and Kittitas Valley) and in the Columbia Basin on Wednesday. A few isolated gusts to 40 mph are possible in the mountain gaps and in the Palouse along the Idaho border. Otherwise, busts in the 20 to 30 mph range should be common.

Mostly cloudy skies remain in place in and west of the Cascades through Thursday. In Eastern Washington, look for high clouds to start moving in as a strong cold front approaches the coast. Rain may begin as early as Thursday afternoon along the coast, spreading eastward Thursday night through Friday.

The cold front is likely to have an atmospheric river behind it, providing approximately 24 hours of decent moisture for the region. While the most likely case is that this will be aimed in a southwest-northeast direction, bringing decent wetting rains to the whole state, there is a small chance that it will have a more zonal component to it which would limit rainfall values in Eastern Washington. Aside from rain, gusty winds are also possible on Friday and Saturday. Current indications are that the strongest winds will be along the coast generally south of Aberdeen and through Cascade mountain gaps. It is still a ways out and the wind forecast is highly susceptible to change, but it is something to take note of in the meantime.

Scattered rain showers, mostly in Western Washington and mountainous areas, are likely to continue through the remainder of the weekend as an upper level trough remains parked over the region. When all is said and done, some areas of Western Washington may receive close to an inch of rain with higher values on the coast and in the mountains. In the Columbia Basin and adjacent lowlands, the current consensus is for rainfall to remain below a half an inch. This won't be enough to cure the current drought situation, though modest improvement is possible.

Central Washington Heat Stress:
Note: This is an experimental forecast product that may undergo changes over the coming weeks. For questions or comments, please email Mark Ingalls. This will be the last week for the heat stress product in 2021.

Heat stress concerns are minimal this week in Central Washington. Tuesday will be the warmest day of the week with highs near or just above 80. Under this temperature with mostly sunny skies, light winds, and a dew point near 45, the wet bulb globe temperature should peak in the low 70s. This is below the threshold where precautionary actions relating to heat stress for workers is advised. Temperatures only cool after Tuesday. The highest fruit surface temperatures should remain below 105 on Tuesday and below 100 for the remainder of the week.


8 to 14 Day Outlook, September 20 to September 26, 2021
  • Below average temperatures and near average precipitation are favored for the period.

Important Points About This Week's Weather

South Central Washington
Remainder of the Week
  • Wind: S and light Tue, W with breezy areas Wed, light and variable Thu, SW and breezy Fri.
  • Precipitation: Scattered showers Fri.
  • High Temps: Near 50 Mon night, near 60 Tue night, low 40s Wed night, near 50 Thu night, mid 50s Fri night. Cooler in sheltered areas Mon-Wed nights.
  • Low Temps: Near 60 Tue-Wed nights, mid 50s Thu-Fri nights. Cooler in sheltered areas.
  • Sky Cover: Partly cloudy Tue-Wed, increasing clouds Thu, mostly cloudy Fri.
Weekend
  • Wind: SW with breezy areas Sat & Sun.
  • Precipitation: Rain showers.
  • High Temps: Upper 60s Sat, mid 60s Sun.
  • Low Temps: Low 50s Sat & Sun nights.
  • Sky Cover: Mostly cloudy.

North Central Washington
Remainder of the Week
  • Wind: S and light Tue, W with breezy areas Wed, light and variable Thu, SW and breezy Fri.
  • Precipitation: Low chance of mountain rain Tue night, rain Fri.
  • High Temps: Near 80 Tue, low 70s Wed, near 70 Thu, upper 60s Fri. Cooler in higher terrain.
  • Low Temps: Mid 50s Mon-Tue night, upper 40s Wed night, near 50 Thu night, low 50s Fri night. Cooler in higher terrain.
  • Sky Cover: Partly cloudy Tue-Wed, increasing clouds Thu, mostly cloudy Fri.
Weekend
  • Wind: SW with breezy areas Sat & Sun.
  • Precipitation: Rain showers.
  • High Temps: Mid 60s Sat & Sun. Cooler in higher terrain.
  • Low Temps: Near 50 Sat night, upper 40s Sun night. Cooler in higher terrain.
  • Sky Cover: Mostly cloudy.

Eastern Washington
Remainder of the Week
  • Wind: S and light Tue, W with breezy areas Wed, light and variable Thu, SW and breezy Fri.
  • Precipitation: Chance of rain Fri.
  • High Temps: Mid 70s Tue, low 70s Wed, upper 60s Thu, mid 60s Fri. Warmer in the Lewis & Clark Valley.
  • Low Temps: Mid 40s Mon night, upper 50s Tue night, upper 30s Wed night, mid 40s Thu night, upper 40s Fri night. Warmer in the Lewis & Clark Valley.
  • Sky Cover: Partly cloudy Tue, mostly cloudy Tue night, partly cloudy Wed, increasing clouds Thu, mostly cloudy Fri.
Weekend
  • Wind: SW with breezy areas Sat & Sun.
  • Precipitation: Rain showers.
  • High Temps: Low 60s Sat-Sun. Warmer in the Lewis & Clark Valley.
  • Low Temps: Mid 40s Sat night, low 40s Sun night. Warmer in the Lewis & Clark Valley.
  • Sky Cover: Mostly cloudy.

Western Washington
Remainder of the Week
  • Wind: W and light Tue, NW with breezy areas Wed, W and light Thu, S with breezy areas Fri.
  • Precipitation: Rain showers Tue & Thu-Fri night.
  • High Temps: Near 70 Tue, mid 60s Wed-Thu, near 60 Fri. Cooler in higher terrain.
  • Low Temps: Low 50s Mon night, mid 50s Tue night, near 50 Wed night, low 50s Thu night, mid 50s Fri night.
  • Sky Cover: Mostly cloudy to overcast.
Weekend
  • Wind: SW with breezy areas Sat, SW and light Sun.
  • Precipitation: Rain showers.
  • High Temps: Near 60 Sat & Sun. Cooler in higher terrain.
  • Low Temps: Low 50s Sat & Sun nights.
  • Sky Cover: Mostly cloudy to overcast.

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Washington State University