AgWeatherNet Weekly Weather Outlook for Aug 14 to Aug 20, 2020

Hot temperatures expected for the weekend and early next week

Craig Oswald, AgWeatherNet Field Meteorologist
Mark Ingalls, AgWeatherNet Intern

Discussion:

The main weather story this outlook period is the excessive heat expected primarily for Sunday through Tuesday. An amplification of the upper wave pattern looks to continue through the weekend as an upper trough digs south from Alaska into the North Pacific. This is expected to place Washington state under the western portion of a ridge resulting in much warmer temperatures by Saturday, putting an abrupt end to the recent stretch of milder temperatures many of us have enjoyed over the last few days. Temperatures can be expected to climb through the weekend and reach as high as 105°F for parts of the Columbia Basin with some inland portions of the southern half of western Washington reaching into the upper-90s by Sunday. Weather conditions are also expected to be dry with sunny and mostly clear skies statewide through the weekend.

As the trough digs south through the weekend, upper level flow is expected to shift from northwest to southwest. By Monday morning it is expected that the ridge axis will lie to the east across western Montana with a robust upper trough set up over the north Pacific. This set up will provide strong southwest flow over the Pacific Northwest, helping to direct moister air from the tropics into the region. An upper disturbance currently situated offshore from southern California is indicated to become entrained in the upper, southwest flow downstream from the trough axis creating a shortwave disturbance embedded in the mean flow. This disturbance is expected to move into southwest British Columbia Sunday night/Monday giving the chance for a few thundershowers and scattered light rain showers to form over the northern portions of the Cascade crest. Lowland portions are likely to remain dry with only an increase in cloud cover expected. There is also the low chance for a thundershower or two to impact portions of eastern Washington, primarily southern parts of the Palouse and the area around the Blue Mountains, Sunday night. Other areas in eastern Washington are expected to remain dry, however, a stray thundershower cannot be completely ruled out, especially with some of the latest high-res model guidance hinting at such. Temperatures across the state look to remain hot east of the Cascades early in the week while beginning to trend cooler west of the Cascades.

The Tuesday night/Wednesday time frame will again see a chance for rain showers and a stray isolated thundershower or two (primarily over higher terrain) as the upper trough weakens while progressing east into the Pacific Northwest. The bulk of this activity will again mostly be confined to northwest and far southeast portions of the state. The length of the Cascade crest will stand to see a few light showers Tuesday night through Wednesday. Lowland portions of the northern half of western Washington also stand to see a few scattered light rain showers during this period. The Blue Mountains and areas immediately around the Blues have about the same chances of seeing shower activity during this time frame.

Conditions look to trend dry for the remainder of the week statewide as Washington regains residence under the western edge of an upper ridge. However, it appears that the upper trough over Alaska and the North Pacific will remain in place into the following weekend. There is model disagreement this early, but it is possible that some form of precipitation will come around again the following weekend. Whether this is in the form of more widespread frontal passage type rain showers or simply a few scattered high terrain rain showers will be determined by next weeks outlook. Climatologically speaking however, the more likely scenario is the latter.


8 to 14 Day Outlook  Aug 21, 2020 to Aug 27, 2020
  • Warmer than average temperatures and near average precipitation are expected during the 8 to 14 day time frame.

Important Points about Next Week's Weather

South Central Washington
Weekend
  • Wind: Calm to light and variable during the day, becoming breezier by the evening, and returning to calm through the overnight.
  • Precipitation: Dry conditions expected with the low chance for an isolated thundershower Sunday night.
  • High Temps: Upper 90s Sat, low 100s Sun.
  • Low Temps: Near 50 Fri night, upper 50s Sat night, mid 60s Sun night.
  • Sky Cover: Sunny and mostly clear through the weekend with mostly cloudy skies building in Sunday night.
Next Week
  • Wind: Light and variable winds turning SW and breezy Monday, especially during the evening hours. Winds trending back to mostly light and variable through Wednesday yet remining breezy during the evening hours before trending calm to light during the overnights.
  • Precipitation: Dry conditions expected.
  • High Temps: Near 100 Mon, upper 90s Tue, low 90s Wed, low 90s Thu.
  • Low Temps: Mid 60s Mon night, near 60 Tue night, upper 50s Wed night, upper 50s Thu night.
  • Sky Cover: Mostly sunny during the day Monday and Tuesday with partly cloudy skies at night. Becoming sunny and mostly clear Wednesday.

North Central Washington
Weekend
  • Wind: Calm to light and variable during the day, becoming breezier by the evening, especially through the Basin. Returning to calm through the overnight.
  • Precipitation: Dry conditions expected with the low chance for an isolated thundershower Sunday night, primarily through upland and mountain areas.
  • High Temps: Mid 90s Sat, low 100s Sun. Cooler in high terrain.
  • Low Temps: Mid 50s Fri night, mid 60s Sat night, mid 60s Sun night. Cooler in high terrain and deep valleys.
  • Sky Cover: Sunny and clear, becoming partly cloudy Sunday night.
Next Week
  • Wind: Light and variable winds turning SW and breezy Monday, especially during the evening hours. Winds trending back to mostly light and variable through Wednesday yet remining breezy during the evening hours (mostly through the Basin) before trending calm to light during the overnights.
  • Precipitation: Low chance for an isolated thundershower/rain shower near the Cascade crest Tuesday night/Wednesday, otherwise dry conditions expected.
  • High Temps: Near 100 Mon, upper 90s Tue, low 90s Wed, low 90s Thu. Cooler in high terrain.
  • Low Temps: Mid 60s Mon night, mid 60s Tue night, low 60s Wed night, low 60s Thu night. Cooler in high terrain and deep valleys.
  • Sky Cover: Mostly sunny during the day Monday and Tuesday with partly cloudy skies at night. Becoming mostly sunny and mostly clear Wednesday.

Eastern Washington
Weekend
  • Wind: Calm to light and variable during the day, becoming breezier by the evening, and returning to calm through the overnight.
  • Precipitation: Dry conditions through the weekend with an isolated thundershower/rain shower possible near the Blue Mtns. and southern portions of the region Sunday night.
  • High Temps: Upper 80s Sat, upper 90s Sun.
  • Low Temps: Upper 40s Fri night, mid 50s Sat night, mid 60s Sun night.
  • Sky Cover: Sunny and mostly clear through the weekend with mostly cloudy skies building in Sunday night.
Next Week
  • Wind: Light and variable winds turning SW and breezy Monday, especially during the evening hours. Winds trending back to mostly light and variable through Wednesday yet remining breezy during the evening hours before trending calm to light during the overnights.
  • Precipitation: Chance for a few isolated thundershowers/rain showers over the Blue Mtns. and the surrounding area Tuesday night/Wednesday. Otherwise dry conditions expected.
  • High Temps: Mid 90s Mon, mid 90s Tue, upper 80s Wed, mid 80s Thu.
  • Low Temps: Low 60s Mon night, upper 50s Tue night, mid 50s Wed night, mid 50s Thu night.
  • Sky Cover: Mostly to partly sunny during the day Monday and Tuesday with partly cloudy skies at night. Becoming Sunny and mostly clear Wednesday.

Western Washington
Weekend
  • Wind: Generally calm to light and variable yet becoming breezier by the evening, especially near the coast with onshore winds. Trending calm through the overnight.
  • Precipitation: Dry conditions through the weekend with a few thundershowers/rain showers along the northern half of the Cascade Crest Sunday night.
  • High Temps: Near 90 Sat, upper 90s Sun. Slightly cooler to the north. Much cooler through the Cascades and Olympics.
  • Low Temps: Mid 50s Fri night, upper 50s Sat night, mid 50s Sun night. Slightly cooler to the north. Much cooler through the Cascades and Olympics.
  • Sky Cover: Sunny and clear, becoming partly cloudy Sunday night, mostly cloudy to the north.
Next Week
  • Wind: Mostly W/SW and light yet variable, breezier Wednesday.
  • Precipitation: Chance for a few thundershowers/rain showers along the Cascade crest Tuesday evening through Wednesday. Chance of a few light rain showers throughout lowland areas of the northern half of the region Tuesday night/Wednesday. Otherwise dry conditions expected.
  • High Temps: Upper 80s Mon, mid 80s Tue, low 80s Wed, low 80s Thu. Much cooler through the Cascades and Olympics.
  • Low Temps: Mid 50s Mon night, mid 50s Tue night, mid 50s Wed night, low 50s Thu night. Much cooler through the Cascades and Olympics.
  • Sky Cover: Mostly to partly sunny during the day through the week. Partly cloudy during the overnight.

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