Heat dome to challenge record highs in northwestern US beyond Fourth of July
As the true "dog days of summer" get underway, AccuWeather forecasters say Mother Nature is poised to crank up the thermostat across the northwestern United States and portions of southwestern Canada.
High temperatures soared to levels well above the historical average during the holiday and will continue to do so in the following days. Intense summer heat will also elevate the risk for heat-related illnesses, especially as folks host outdoor parties, head out to cool off at the pool or lake, or take part in other outdoor activities.
"The heat is due to a northward bulge of the jet stream that will allow a heat dome to remain over the northwestern U.S. and western British Columbia, Canada," AccuWeather Meteorologist Nicole LoBiondo explained.
A large area of the U.S. from Northern California through Washington state will bake under intense heat through midweek.
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"High temperatures through at least Wednesday are setting up to run 10-20 degrees Fahrenheit above the historical average for this time of year," said LoBiondo. "Record high temperatures will be challenged from Medford, Oregon, to the southwestern Canadian coast."
Even though temperatures are expected to throttle back a bit on Thursday, they will remain above historical average.
AccuWeather forecasters say the Interstate 5 corridor will be the zone that receives some of the most intense heat from this event.
Wednesday morning, heat advisories and excessive heat warnings were in effect from parts of Northern California to south-central and southwestern Washington, according to the National Weather Service.
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For cities like Portland, Oregon, high temperatures in early July typically top out in the upper 70s to near 80. This week, 90s will be common, and the City of Roses may even reach the century mark on Wednesday, according to the latest forecast.
Record high temperatures of 97 from 1972 and 96 from 2015 are in jeopardy on Tuesday and Wednesday, respectively, in Portland.
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Farther north, Seattle can also challenge its daily record high of 91 on Wednesday that was set in 2015. Currently, temperatures are expected to peak in the low 90s.
"With the holiday, residents who are planning to be outside for extended periods of time should pack plenty of water and even an umbrella to provide some shade," said LoBiondo.
As the heat builds, another factor that could further worsen outdoor conditions is wildfire smoke. AccuWeather forecasters say some wildfire smoke is expected to linger on Wednesday, though some improvement may be possible.
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This smoke is from western Canadian wildfires, some of which were sparked earlier this year by Mother Nature's own fireworks display: lightning.
Near-surface smoke arrived in parts of Washington and Oregon late Monday and Tuesday and will shift into parts of the northern Plains by midweek.
In the smokiest areas, high temperatures may not soar quite as high, given the limited nature of the sunshine. However, air quality will take a significant hit in these areas, likely reaching unhealthy or dangerous levels for some individuals.
In addition to the record-challenging heat in the Northwest, conditions will remain quite hot across the Southwestern states this week.
On Sunday, Phoenix experienced its highest temperature reading so far in 2023 when the mercury reached a sizzling 115.
In fact, Phoenix hasn't recorded a high temperature below 110 since the end of June. Historical average temperatures for the city in early July hover around 107, so any measure of heat above that threshold is significant.
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AccuWeather forecasters say almost no relief is on the way as temperatures in Phoenix are expected to climb above the 110-degree threshold daily through at least early next week.
It's a similar story in Las Vegas. After Sin City set a new record for the latest date that a 100-degree reading was observed in a calendar year on Friday, temperatures soared to 111 and 112 degrees on Sunday and Monday, respectively. The region will continue to have highs in the triple digits into next week.
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