AgWeatherNet Weekly Outlook for August 28 to September 4, 2020

Cold front to bring a change in weather pattern with temperatures rebounding midweek

Mark Ingalls, AgWeatherNet Intern
Craig Oswald, AgWeatherNet Field Meteorologist

Synopsis:

A cold front will begin crossing Washington form the west/northwest Saturday, bringing breezy conditions to the usual parts of the state. This event will be dry, with little-to-no precipitation in the forecast, even for windward sides of mountain ranges in the region, but will come with a modest drop in high temperatures. This will be realized Saturday west of the Cascades, with Eastern Washington having to wait until Sunday to cool down. A shortwave trough embedded in the mean flow may bring showers to parts of Western Washington, the Cascades, and the Olympics on Monday. A lower chance of rain extends east, primarily in the northern mountains. Precipitation values are expected to be light. Temperatures climb to above average statewide by midweek as a ridge builds over the Western United States.

Discussion:

The upper level low that was noted in last week's outlook looks to impact the Pacific Northwest as a strong trough, bringing a dry cold front across Washington on Saturday from the west/northwest. As it progresses east, winds will increase in many of the usual locations, such as the Strait of Juan de Fuca, the east end of the Columbia Gorge, and the Kittitas Valley. Somewhat lighter wind (though still breezy) can be expected in Eastern Washington lowlands outside of the lee of mountain gaps, on the Coast, and in the area west of I-5 and south of US 12. For the Columbia Basin and adjacent valleys, critical fire conditions are expected thanks to the wind and low relative humidity values. Areas of blowing dust can also be expected, primarily throughout regions of dryland farming.

For Western Washington, cooler high temperatures resulting from this cold front can be expected on Saturday. Highs along the I-5 Corridor will likely range from the upper-60s near the British Columbia Border to the mid-70s in the Greater Portland/Vancouver area. The drop will be most significant south of Seattle, where Saturday's highs represent a 5°-10° drop from those expected today (Friday). Eastern Washington will see the frontal passage later in the day Saturday, allowing temperatures to still reach well into the 80s with the coolest lowland temperatures being closer to the Cascades. In places like the Tri-Cities, Yakima, and Spokane, Sunday will be the coolest day during the forecast period with highs ranging from the mid-70s around Spokane to around 80° in the Columbia Basin and Yakima Valley.

Following the cold front, the trough will continue east, transitioning the Pacific Northwest to northwest flow aloft. This should be mostly dry, but a shortwave embedded within the mean flow may bring some rain showers to Western Washington, the mountains, and in the northern mountains of Eastern Washington Monday. Shower activity does not look to be widespread and precipitation values for those who see rain should be low. This will not be enough to make a dent in the drought that continues to grip Central Washington.

Following the passage of the shortwave, a ridge centered offshore will take hold over the region. With this, temperatures will climb to above average for the start of meteorological fall while generally northwesterly flow will keep the state dry. West of the Cascades, current expectations are that highs will range from the mid-70s in lower elevations of Whatcom County to the upper-80s in Clark County. Highs to around 70° may even extend out to the Coast. Temperatures may reach just into the triple digits in the Columbia Basin, Yakima Valley, and Okanogan lowlands, late in the week. It is possible that some parts of the state will break daily high temperature records during this upcoming heatwave.

Longer range guidance is indicating that this warmth will continue beyond the end of the forecast period and into the following weekend. At that time, the ridge may be focused in the general area of Vancouver Island with unusual strength. If this pattern verifies, well above average temperatures will be possible over the weekend with dry conditions.


8 to 14 Day Outlook, September 4 to September 10, 2020
  • Above average temperatures and below average precipitation are favored for the period.

Important Points about Next Week's Weather

South Central Washington
Weekend
  • Wind: Light and variable Fri. Becoming breezy and NW Sat PM with gusts to 35 mph in spots. W and light Sun.
  • Precipitation: No precipitation expected.
  • High Temps: Low 90s Fri, mid to upper 80s Sat (except 70s Kittitas Valley), upper 70s to near 80 Sun.
  • Low Temps: Mid 50s Fri Night, near 50 Sat Night, upper 50s Sun Night.
  • Sky Cover: Sunny to partly cloudy through the period.
Next Week
  • Wind: Generally W/SW wind. Breezy conditions possible Mon & Wed.
  • Precipitation: No precipitation expected.
  • High Temps: Mid 80s Mon, mid to upper 90s Tue-Thu.
  • Low Temps: Near 60 Mon & Tue Night, upper 50s Wed & Thu Night.
  • Sky Cover: Partly to mostly cloudy Mon, otherwise sunny to partly cloudy.

North Central Washington
Weekend
  • Wind: Light and variable Fri. Becoming breezy and NW Sat PM with gusts to 45 mph in spots. W and light Sun.
  • Precipitation: No precipitation expected.
  • High Temps: Near 90 Fri, low to mid 80s Sat, upper 70s Sun. Cooler in higher terrain.
  • Low Temps: Mid to upper 50s Fri Night, near 50 Sat Night, mid 50s Sun Night. Cooler in higher terrain.
  • Sky Cover: Sunny to partly cloudy through the period.
Next Week
  • Wind: Generally W/SW wind. Breezy conditions possible Mon & Wed
  • Precipitation: Low chance of mountain showers Mon, otherwise dry.
  • High Temps: Low 80s Mon, near 90 Tue, low 90s Wed-Thu. Cooler in higher terrain.
  • Low Temps: Mid 50s Mon Night, near 60 Tue Night, upper 50s Wed-Thu Night. Cooler in higher terrain.
  • Sky Cover: Partly to mostly cloudy Mon, otherwise sunny to partly cloudy.

Eastern Washington
Weekend
  • Wind: Light and variable Fri. Becoming breezy and NW Sat PM with gusts to 30 mph in spots. W and light Sun.
  • Precipitation: No precipitation expected.
  • High Temps: Mid 80s Fri, low 80s Sat, low 70s Sun. Higher in the Lewis and Clark Valley.
  • Low Temps: Low 50s Fri Night, mid 40s Sat Night, upper 40s Sun Night. Higher in the Lewis and Clark Valley.
  • Sky Cover: Sunny to partly cloudy through the period.
Next Week
  • Wind: Generally W/SW wind. Breezy conditions possible Mon & Wed
  • Precipitation: Low chance of mountain showers Mon, otherwise dry.
  • High Temps: Mid 70s Mon, low 80s Tue, mid to upper 80s Wed-Thu. Higher in the Lewis and Clark Valley.
  • Low Temps: Upper 40s Mon Night, low 50s Tue-Thu Night. Higher in the Lewis and Clark Valley.
  • Sky Cover: Partly to mostly cloudy Mon, otherwise sunny to partly cloudy.

Western Washington
Weekend
  • Wind: Mainly light and variable Fri. W and breezy with gusts to 30 mph in places Sat, calming for most Sun.
  • Precipitation: No precipitation expected.
  • High Temps: Mid 70s to mid 80s Fri, low to mid 70s Sat, mid to upper 70s Sun. Cooler in higher terrain and on the coast.
  • Low Temps: Low to mid 70s Fri Night, mid 40s to mid 50s Sat Night, low to mid 50s Sun Night. Cooler in higher terrain.
  • Sky Cover: Sunny to partly cloudy through the period.
Next Week
  • Wind: N wind, breezy conditions possible Tue & Wed.
  • Precipitation: Rain showers possible Mon, otherwise dry.
  • High Temps: Mid to upper 70s Mon, mid 70s to mid 80s Tue-Thu. Cooler in higher terrain and on the coast.
  • Low Temps: Low to upper 50s Mon Night, mid to upper 50s Tue Night, near 50 to mid 50s Wed-Thu night. Cooler in higher terrain.
  • Sky Cover: Partly cloudy to overcast Mon, otherwise sunny to partly cloudy.

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