AgWeatherNet Weekly Weather Outlook for September 7 to September 12, 2021

Temperatures moderating later this week but remaining dry for most

Mark Ingalls, AgWeatherNet Field Technician

Synopsis:

Well above average temperatures are forecast for the next few days but the upper air pattern shifts to generate wind flow out of the west. This is forecast to bring temperatures down to below average for this time of year starting Friday in Western Washington and toward the end of the weekend in Eastern Washington. Conditions look mainly dry through the weekend, though a few isolated showers are possible Tuesday night and Thursday in the mountains and west of the Cascades. Otherwise, watch for generally mostly cloudy skies to the west with clear to partly cloudy skies east.

Discussion:

A ridge of high pressure centered over the West Coast states is responsible for the current heatwave. A shortwave trough embedded within the mean flow should cross the state Tuesday night, bringing with it a low chance of showers in the mountains and west of the Cascades. Wednesday, breezy conditions are likely in typical windy spots such as the Strait of Juan de Fuca, Cascade mountain gaps, and Columbia Basin.

By Thursday, the ridge will sift to be centered over a line from Gallup, New Mexico to Regina, Saskatchewan. As it pushes eastward, the ridge will be replaced by another shortwave trough. This again brings low chances of rain to the mountains and western lowlands. Unfortunately, even with these two disturbances total precipitation over the next week looks to remain below a quarter inch statewide with the most drought-stricken regions likely to miss out on wetting rains.

With more westerly flow, temperatures are expected to begin cooling statewide with Western Washington also benefiting from mostly cloudy skies. Average highs for this time of year are around 73 for Seattle, 78 for Portland, 76 for Spokane, and 83 for Pasco. By Friday, high temperatures should be below average in Western Washington lowlands though mostly cloudy skies should keep nighttime lows above average through the weekend.

For Eastern Washington lowlands, highs near average are forecast Friday and Saturday before cooling more Sunday. As usual, the Cascades will block the marine clouds from reaching Eastern Washington, allowing for some chilly nights on the Palouse and in the northern mountains. Typical cold spots stand a chance of getting near or below average Friday night and beyond.

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.

The highest risk for heat stress to both workers and fruit comes in the first half of the week with a few places getting close to 90. Still, with dew points near 50, wet bulb globe temperatures are forecast to peak in the upper 70s bringing low risk to outdoor workers. Cooler temperatures in the low to mid 80s with dew points down around 45 on Friday bring this value into the low 70s, further limiting risk of heat-related illnesses.

Peak daytime solar radiation for this week in September is about the same as early April. Still, with a warm start to the week fruit skin temperatures may approach 120 Tuesday. This will be the only day with FST values that warm. Wednesday, the breeze picks up and temperatures moderate somewhat so that FST values should remain below 105, where they are likely to stay through the end of the week.


8 to 14 Day Outlook, September 6 to September 12, 2021
  • Below 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
  • Wind: Light and variable Tue, W with breezy areas Wed, W and light Thu-Fri.
  • Precipitation: Dry conditions expected.
  • High Temps: Low 90s Wed, upper 80s Thu, low 80s Fri.
  • Low Temps: Near 60 Tue-Wed nights, mid 50s Thu-Fri nights. Cooler in sheltered areas.
  • Sky Cover: Mostly clear. Hazy.
Weekend
  • Wind: Generally W and light.
  • Precipitation: Dry conditions expected.
  • High Temps: Low 80s Sat, near 80 Sun.
  • Low Temps: Mid 50s Sat night, low 50s Sun night. Cooler in sheltered areas.
  • Sky Cover: Mostly clear. Hazy areas.

North Central Washington
Remainder of the Week
  • Wind: Light and variable Tue, W with breezy areas Wed, W and light Thu-Fri.
  • Precipitation: Isolated showers Wed, best chances near the mountains. Isolated mountain showers Thu.
  • High Temps: Near 90 Wed, upper 80s Thu, low 80s Fri. Cooler in higher terrain.
  • Low Temps: Upper 60s Tue night, mid 60s Wed night, upper 50s Thu-Fri nights. Cooler in higher terrain and in sheltered areas.
  • Sky Cover: Mostly clear. Hazy.
Weekend
  • Wind: Generally W and light.
  • Precipitation: Dry conditions expected.
  • High Temps: Low 80s Sat, near 80 Sun. Cooler in higher terrain.
  • Low Temps: Mid 50s Sat & Sun nights. Cooler in higher terrain and sheltered areas.
  • Sky Cover: Mostly clear. Hazy areas.

Eastern Washington
Remainder of the Week
  • Wind: Light and variable Tue, SW with breezy areas Wed, SW and light Thu-Fri.
  • Precipitation: Isolated mountain showers Tue & Thu.
  • High Temps: Mid 80s Wed & Thu, near 80 Fri. Warmer in the Lewis & Clark Valley.
  • Low Temps: Mid 50s Tue-Wed night, low 50s Thu night, near 50 Fri night. Warmer in the Lewis & Clark Valley.
  • Sky Cover: Mostly clear. Hazy.
Weekend
  • Wind: Generally W and light.
  • Precipitation: Dry conditions expected.
  • High Temps: Near 80 Sat, mid 70s Sun. Warmer in the Lewis & Clark Valley.
  • Low Temps: Near 50 Sat night, upper 40s Sun night. Warmer in the Lewis & Clark Valley.
  • Sky Cover: Mostly clear, hazy areas.

Western Washington
Remainder of the Week
  • Wind: N and light Tue, W and light Wed, W with breezy areas Thu, NW with breezy areas Fri.
  • Precipitation: Isolated showers Tue night & Thu.
  • High Temps: Upper 70s Wed, mid 70s Thu, near 70 Fri. Cooler in higher terrain and along the coast.
  • Low Temps: Near 60 Tue night night, upper 50s Wed-Fri nights. Cooler in higher terrain.
  • Sky Cover: Partly cloudy Wed, mostly cloudy Thu-Fri.
Weekend
  • Wind: W and breezy on the coast Sat, NW and breezy on the coast Sun.
  • Precipitation: Dry conditions expected.
  • High Temps: Near 70 Sat & Sun. Cooler in higher terrain.
  • Low Temps: Mid 50s Sat & Sun nights. Cooler in higher terrain.
  • Sky Cover: Mostly cloudy Sat, partly cloudy Sun.

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Washington State University