AgWeatherNet Weekly Weather Outlook for July 31 to August 6, 2020

A welcome cooling trend through the weekend into early next week

Mark Ingalls, AgWeatherNet Intern
Michelle Daughtrey, AgWeatherNet Intern
Joe Zagrodnik, AgWeatherNet Postdoctoral Research Associate

Discussion:

The recent heat wave is coming to an end as a shift to westerly, onshore flow is underway. Friday will be the last day of widespread 100°+ temperatures east of the Cascades and areas west of the Cascades are already back to more comfortable temperatures. Temperatures will still be hot in Eastern Washington lowlands through the weekend, but a cold front Monday should cool things further with highs in the 70s for the I-5 Corridor and upper-80s to low-90s for lowlands in the east side of the state. This cold front is not expected to bring much moisture into the Pacific Northwest, with shower activity expected to be limited to Western Washington and the Cascades Sunday night into Tuesday morning. Otherwise, dry conditions are expected with temperatures climbing from near average conditions.

This week's heatwave is the result of an upper level ridge centered over the Western United States and a robust low pressure system offshore near 140°W (the Washington Coast is at 124°W). Southerly flow resulting from the low has been driving extreme heat from the deserts of California, Nevada, and Arizona into the Inland Northwest. The ridge will begin a slow trek eastward Friday or Saturday, allowing the low to move closer to the coast. At the surface, this will result in stronger flow out of the west bringing cooler air from the Pacific across the state for the weekend. The strength of this influence will wane as it gets further from the coast, but even in Spokane high temperatures stand to drop 10°-15° on Saturday. Western Washington won't see as abrupt of a change because the marine influence is already in place there. Breezy conditions can be expected Friday and Saturday in parts of Eastern Washington, particularly in the mountain gaps on the leeward side of the Cascades.

For much of the state, conditions on Sunday will nearly match Saturday with mostly sunny skies and similar temperatures. The Olympic Peninsula will be the exception to this as a cold front will bring shower activity to that region as early as that afternoon. This continues inland through Monday, when most of Western Washington and the Cascades can expect scattered showers. This front is not expected to have enough moisture embedded in it to bring precipitation to Eastern Washington, but it will nudge temperatures down somewhat. As the cold front traverses the region, winds will pick up both along the Strait of Juan de Fuca and in Eastern Washington.

Some lingering showers might remain in and along the margins of the Cascades Tuesday, but for the rest of the state Tuesday through Thursday looks to be sunny to partly cloudy with temperatures rebounding midweek, except on the coast. A weak ridge crossing the Pacific Northwest on Wednesday will provide the heating mechanism for this warm up, but it won't be nearly as strong as what we had this week. Model guidance indicates that only the lowest spots of Eastern Washington stand a chance of reaching 100°. Beyond the forecast period, conditions appear favorable for a large trough to develop offshore. This would bring a return to southerly flow across the Pacific Northwest, bringing a return to hot temperatures.

This last Thursday (July 30), several locations in Eastern Washington broke daily temperature records. The Tri-Cities Airport in Pasco was the highest climate site in the state with a maximum temperature of 111° (beating the old record of 107°). This was the first time in five years that the airport in Pasco reached 110°. Other locations that broke or tied records were Ephrata (107°), Omak (106°), Walla Walla (108°), Wenatchee (105°), and Yakima (105°). The hottest AgWeatherNet site was Benton.E located at the foot of Red Mountain east of Benton City. That location reached 110° (the only station to do so). A station within our network that is operated by Boise State University near Caldwell, Idaho recorded a high of 112°.

Climatologically, the Pacific Northwest has reached its driest stretch of the year. On top of this, hot temperatures, low humidity, and intermittently breezy periods will also enhance the need to be fire aware this week. Arid portions of the state are well within their fire season, but the forests of Western Washington are drying out from this spring's precipitation. Fuels are becoming more susceptible to burning, with the highest concern being on the east slopes of the Cascades, in the Blue Mountains, and the Okanogan. Fire threats aren't limited to Eastern Washington, though. A small fire that was started Wednesday is burning west of Port Angeles in Olympic National Park.


8 to 14 Day Outlook, August 7 to August 13, 2020
  • Above average temperatures and below average rainfall are favored during the 8 to 14 day time frame.

Important Points about Next Week's Weather

South Central Washington
Weekend
  • Wind: SW flow through the weekend. Breezy Fri & Fri Night with gusts to 30 mph in spots.
  • Precipitation: Dry conditions expected.
  • High Temps: Low 100s Fri, upper 90s Sat, mid 90s Sun.
  • Low Temps: Upper 60s Fri Night, mid 60s Sat & Sun Nights.
  • Sky Cover: Clear to partly cloudy.
Next Week
  • Wind: W/SW flow Mon & Thu with breezy conditions possible those days. Otherwise light and variable.
  • Precipitation: Dry conditions expected.
  • High Temps: Near 90 Mon, upper 80s Tue, low to mid 90s Wed & Thu.
  • Low Temps: Low to mid 60s Mon Night through Thu Night.
  • Sky Cover: Clear to partly cloudy.

North Central Washington
Weekend
  • Wind: Light S flow Monday shifts W Monday night. This pattern continues throughout the weekend. Gusting not to exceed 20 mph.
  • Precipitation: Dry conditions expected with some scattered showers potential coming from the Canadian border and W from the Cascades Friday night and Saturday morning.
  • High Temps: Upper 110s Fri, low 100s Sat, around 100s Sun.
  • Low Temps: Low 70s Fri night, upper 60s Sat night, mid 60s Sun night.
  • Sky Cover: Partly cloudy Fri. Mostly cloudy Saturday. Mostly clear Sunday.
Next Week
  • Wind: Light W/NW flow Monday. Transitions to S/SW Tuesday through Thursday. N/NW flow Friday.
  • Precipitation: Showers expected Monday. Dry conditions Tuesday and Wednesday. Scattered showers possible Thursday.
  • High Temps: Mid 90s Mon, mid 90s Tue, upper 90s Wed, upper 90s Thu.
  • Low Temps: Low 60s Mon night, low 60s Tue night, low 60s Wed night, low 60s Thu night.
  • Sky Cover: Mostly cloudy Monday. Mostly sunny Tuesday and Wednesday. Mostly cloudy Thursday.

Eastern Washington
Weekend
  • Wind: W flow through the weekend. Breezy in areas Fri with gusts to 25 mph.
  • Precipitation: Dry conditions expected.
  • High Temps: Low 100s Fri, low to mid 90s Sat & Sun.
  • Low Temps: Mid 60s Fri Night, Low 60s Sat & Sun Night.
  • Sky Cover: Clear to partly cloudy.
Next Week
  • Wind: W/SW flow Mon & Thu with breezy conditions possible those days. Otherwise light and variable.
  • Precipitation: Dry conditions expected.
  • High Temps: Mid 80s Mon & Tue, upper 80s to low 90s Wed & Thu.
  • Low Temps: Upper 50s Mon Night through Thu Night.
  • Sky Cover: Clear to partly cloudy.

Western Washington
Weekend
  • Wind: Light and generally S/SW yet variable Friday and Saturday. Increased flow Sunday but still light and gusts not to exceed 20 mph.
  • Precipitation: Scattered showers Friday morning dissipate by the afternoon. Saturday expected to remain dry. Showers expected Sunday on the Peninsula, otherwise dry in the region.
  • High Temps: Upper 70s Fri, upper 70s Sat, upper 70s Sun. Much cooler through the Cascades and Olympics.
  • Low Temps: Upper 50s Fri night, mid 50s Sat night, upper 50s Sun night. Much cooler through the Cascades and Olympics.
  • Sky Cover: Partly to mostly cloudy Fri and Sat. Partly sunny Sun. Mostly cloudy Sun night moving into Mon.
Next Week
  • Wind: Onshore flow produces continued W/SW pattern into Monday, while calm two lightly breezy conditions continue. Winds shift Tuesday to primarily N flow through Wed. Gusts Tuesday and Wednesday evening could reach 30 mph. Thursday gusts could reach 40 mph.
  • Precipitation: Scattered showers throughout the region Monday. Dry conditions expected Tuesday and Wednesday. Light scattered showers Thursday and Friday.
  • High Temps: Upper 70s Mon, low 80s Tue, mid 80s Wed, upper 70s Thu. Much cooler through the Cascades and Olympics. Cooler near the coast.
  • 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 cloudy Monday. Partly cloudy Tuesday and Wednesday. Mostly cloudy Thursday.

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