AgWeatherNet Weekly Outlook for October 02 to October 08, 2020

Upper level ridging remains the dominant factor this week, hint of fall weather beyond

Mark Ingalls, AgWeatherNet Intern
Craig Oswald, AgWeatherNet Field Meteorologist
Joe Zagrodnik, AgWeatherNet Postdoctoral Research Associate

Synopsis:

Upper level ridging will remain the dominant weather pattern over Washington during the period. For the weekend, the ridge will weaken somewhat and shift east, allowing for more (but still weak) onshore flow in Western Washington resulting in areas of low clouds and fog there in the mornings through Sunday. A dry cold front is expected to cross the state Sunday, slightly cooling temperatures and increasing winds in the lee of the Cascades. Monday through Wednesday, a new ridge will build over the region, causing temperatures to rebound before it moves east on Thursday in the leadup to a strong trough for the following weekend.

Discussion:

The ridge of high pressure over the region Friday is fostering relatively calm conditions, which should continue until Sunday. Freezing levels in this mornings atmospheric soundings were around 14,000 to 15,000 feet at Quillyute, Spokane, and Salem. In fact, upper level temperatures in this ridge were so high Friday morning that one would have to travel to the Yukon Territory or Alaska to find freezing levels below 10,000 feet  a very anomalous situation for this time of year.

Despite high freezing levels, relatively calm conditions at the surface are allowing for localized overnight temperature inversions. A number of AgWeatherNet sites in Eastern Washington were at or below 40° Friday morning, with the coldest being Curlew (north of Republic) which reached 37°. Lows in Western Washington lowlands were moderated by low clouds and fog. The sun angle is still high enough to clear nighttime inversions, allowing for above average highs statewide Friday with the exception of on the coast, where low clouds and fog will remain through most of the day.

This general pattern of morning inversions (with low clouds west of the Cascades) and afternoon warm temperatures will continue through Sunday as the upper pattern briefly becomes more zonal, allowing for a weak dry cold front associated with a modest upper disturbance to cross the state. Winds will pick up behind the front as is crosses the Cascade Mountains, but this is not expected to be a major wind event. Breezy conditions are expected through the Gorge, Kittitas Valley, and Columbia Basin, but gusts will likely only peak around 35 mph in the most exposed locations.

The front will moderate temperatures somewhat. In Western Washington, highs Sunday will be about 5° cooler than on Saturday. The front will cross into Eastern Washington after much of the daytime heating has occurred, so residents there will have to wait until Monday for highs that will be a few degrees cooler than on Sunday. Overnight lows will not see much impact except in sheltered valley locations where nighttime inversions may be weaker Monday morning.

A new ridge builds over the Pacific Northwest for the first half of the week, bringing a rise in high temperatures and an expected return to morning inversion conditions. By Tuesday, highs west of the Cascades should be 5°-10° above seasonal averages, while areas east of the Cascades will be 10°-15° above average. Some isolated frost is possible in valley locations north of Spokane Tuesday morning, but other than that temperatures aloft should remain high enough to keep lows above freezing, even where inversion conditions persist.

The ridge begins to degrade for the second half of the week as a strong trough develops offshore and begins to move toward the region. It does not seem likely that this will have much impact during the forecast period, which ends Thursday, beyond a low chance of showers in Western Washington north of about Everett (with the highest chance along the Cascade Crest. That said, it does signal a possible return to fall-like conditions for the following weekend. There is still uncertainty with this system, and more information will be given in subsequent outlooks.


The National Drought Monitor image showing conditions in Washington for September 29. (Source: Univ. of Nebraska/NDMC)

The National Drought Monitor has been updated to place a narrow section of Central Washington under extreme drought conditions (D3 on the scale from D0 to D4). This includes Goldendale, Yakima, Mattawa, and Wenatchee. Severe drought (D2) conditions extend to include the Tri-Cities, Moses Lake, and Omak, with Spokane, Pullman, Ritzville, and Walla Walla experiencing moderate drought (D1) conditions. The dry conditions are mostly limited to Eastern Washington, though there is some concern along the Columbia Gorge and I-5 corridor south of Kelso. The Washington Cascades are not experiencing drought conditions, except isolated areas south of Mount Adams and Mount St. Helens.

The monthly drought outlook from the Climate Prediction Center indicates that improvement to drought conditions are expected to be seen throughout Washington, with drought removal even being possible outside of the hardest hit areas listed above. This improvement is possible because longer range models are indicating a more active period in our weather pattern in the coming weeks. Since most of the precipitation in Central and Eastern Washington come in the fall and winter months, this period will be critical for drought improvement or removal. On average, about 45% of Yakimas annual precipitation falls between November 1 and January 31.


8 to 14 Day Outlook, October 09 to October 15, 2020
  • Above average temperatures and above average precipitation are favored for the period.

Important Points about Next Week's Weather

South Central Washington
Weekend
  • Wind: Calm to light and variable. Becoming W/SW and breezy by Sun afternoon, particularly through the Cascade mountain gaps. Trending lighter through Sun night.
  • Precipitation: Dry conditions expected.
  • High Temps: Low 80s Sat, upper 70s Sun.
  • Low Temps: Near 50 Fri night, upper 40s Sat night, mid 40s Sun night.
  • Sky Cover: Sunny and mostly clear, yet hazy.
Next Week
  • Wind: Generally light and variable. Slightly breezier by late afternoon before trending calmer through the overnight.
  • Precipitation: Dry conditions expected.
  • High Temps: Upper 70s Mon, near 80 Tue, low 80s Wed, upper 70s Thu.
  • Low Temps: Mid 40s Mon night, upper 40s Tue night, upper 40s Wed night, upper 40s Thu night.
  • Sky Cover: Sunny and mostly clear. Haze expected to ease early in the week.

North Central Washington
Weekend
  • Wind: Calm to light and variable. Becoming W/SW and breezy by Sun afternoon, particularly through the Basin. Trending lighter through Sun night.
  • Precipitation: Dry conditions expected.
  • High Temps: Low 80s Sat, upper 70s Sun. Cooler in high terrain.
  • Low Temps: Low 50s Fri night, near 50 Sat night, upper 40s Sun night. Cooler in high terrain and deep valleys.
  • Sky Cover: Sunny and mostly clear, yet hazy.
Next Week
  • Wind: Generally light and variable. Slightly breezier by late afternoon before trending calmer through the overnight, particularly through the Basin.
  • Precipitation: Dry conditions expected throughout the week except for a few light scattered rain showers along and near the Cascade crest Thu. Trending dry Fri.
  • High Temps: Upper 70s Mon, upper 70s Tue, upper 70s Wed, mid 70s Thu. Cooler in high terrain.
  • Low Temps: Upper 40s Mon night, near 50 Tue night, upper 40s Wed night, upper 40s Thu night. Cooler in high terrain and deep valleys.
  • Sky Cover: Sunny and mostly clear through the first half of the week with haze expected to ease. Skies becoming partly cloudy Thursday and Friday.

Eastern Washington
Weekend
  • Wind: Calm to light and variable. Becoming SW and breezy by Sun afternoon, trending lighter through Sun night.
  • Precipitation: Dry conditions expected.
  • High Temps: Upper 70s Sat, mid 70s Sun. Cooler through the Blues.
  • Low Temps: Upper 40s Fri night, upper 40s Sat night, mid 40s Sun night. Cooler through the Blues.
  • Sky Cover: Sunny and mostly clear, yet hazy.
Next Week
  • Wind: Generally light and variable. Slightly breezier by late afternoon before trending calmer through the overnight.
  • Precipitation: Dry conditions expected.
  • High Temps: Low 70s Mon, mid 70s Tue, mid 70s Wed, low 70s Thu. Cooler through the Blues.
  • Low Temps: Mid 40s Mon night, mid 40s Tue night, mid 40s Wed night, mid 40s Thu night. Cooler through the Blues.
  • Sky Cover: Sunny and mostly clear through the first half of the week with haze expected to ease. Skies becoming partly cloudy Thursday and Friday.

Western Washington
Weekend
  • Wind: Calm to light and variable. Becoming W/SW and slightly breezier by Sun afternoon, trending lighter through Sun night. Sea breeze near the coast.
  • Precipitation: Dry conditions expected.
  • High Temps: Near 70 Sat, mid 60s Sun. Cooler through the Cascades and Olympics.
  • Low Temps: Upper 40s Fri night, upper 40s Sat night, upper 40s Sun night. Cooler through the Cascades and Olympics.
  • Sky Cover: Sunny and mostly clear, yet hazy. Areas of fog in low lying and coastal regions through the overnights and mornings.
Next Week
  • Wind: Generally light and variable. Slightly breezier by late afternoon before trending calmer through the overnight. Sea breeze near the coast.
  • Precipitation: Dry conditions expected through the first half of the week. A few light scattered rain showers to begin moving in from the NW Thu. Showers to be relegated to the northern half of the region with slightly more activity along and near the Cascade crest. Trending dry Fri.
  • High Temps: Upper 60s Mon, low 70s Tue, low 70s Wed, mid 60s Thu. Cooler through the Cascades and Olympics.
  • Low Temps: Upper 40s Mon night, mid 40s Tue night, near 50 Wed night, mid 40s Thu night. Cooler through the Cascades and Olympics.
  • Sky Cover: Sunny and mostly clear through the first half of the week with haze expected to ease. Skies becoming partly cloudy Thursday and Friday. Areas of fog in low lying and coastal regions through the overnights and mornings continuing until mid week.

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