Widespread drought conditions, long summer days and an intense heat dome will force temperatures to soar to monthly and possibly all-time record high temperatures across the Northwest in the coming days.
"This event will likely be one of the most extreme and prolonged heat waves in the recorded history of the Inland Northwest," said the National Weather Service office in Spokane, Washington.
This heat event will stretch across Washington, Idaho, Oregon and even northern California, and it could last through the July 4th weekend. Over 20 million people live in areas with heat alerts that will last through the weekend.
"This won't just be one day in the 100s. Multiple days in a row of triple-digit highs will make heat illness all the more likely if precautions aren't taken, because the heat will continue to stress the body each day," the NWS in Spokane said.
Heat is one of the leading weather-related killers in the United States, according to the NWS, resulting in hundreds of fatalities each year.
"High temperatures are expected to increase each day this weekend and top out near 20 to 30 degrees above average on Saturday and Sunday over Washington and Oregon," the WPC in Spokane said.
It's predicted to be so hot that some airlines are waiving fees for travel changes for those who consider the temperatures too uncomfortable to visit the region.
The latest Risk of Hazardous Temperatures product from the Climate Prediction Center (CPC) shows the region in a high risk of excessive heat through next Friday, July 2nd.
"Don't be surprised by future outlooks extending this out further," the Spokane NWS wrote in a blog Friday.
The CPC's long-range forecast shows above-average temperatures lasting through the July 4th weekend, prolonging the misery for those without air conditioning.
The Northwest's natural air conditioning won't get cool enough
"Our natural nighttime A/C of temperatures in the 50s and low 60s will instead be in record territory of the upper 60s and 70s, posing a problem for those who don't have an A/C system to cool their home ... which many Inland Northwest residents don't," the NWS in Spokane said.
Hot days and warm nights don't allow the body time to cool down, making people more susceptible to heat illness with each additional day.
"In this area, not many people have A/C, so we don't have the relief that we can get in other places that get this hot," said Mary Butwin, a meteorologist for NWS in Seattle.
This could make the heat lethal in Seattle and Portland, which rank first and third, respectively, for major US cities with the fewest air-conditioned households. A US Census Bureau study in 2015 found that only 33% of Seattle-area homes were air conditioned.
The lack of A/C in Seattle -- a city known for its tepid summers -- has not historically been a problem. Between 1971 and 2000, the city averaged only three 90-degree days each summer. However, from 2015 to 2018, the average number of 90-degree days increased to 10 each summer.
Not surprisingly, the Census Bureau updated its findings in 2019, revealing that A/C adoption in Seattle had risen to 44%, an 11% increase in A/C units installed since 2015.
The city has eclipsed the 100-degree mark on only three days in the last 100 years of record-keeping. It's forecast to hit 100 three days in the next few days alone.
"What makes this heat wave unique from others we've had in the area is the lack of a marine influence in the overnight hours," said Samantha Borth, a meteorologist at NWS in Seattle.
With its proximity to Puget Sound and the Pacific Ocean, overnight temperatures can fall into the 50s, even on the hottest summer days.
Since record-keeping began at Seattle-Tacoma International Airport in 1945, there has been only one night in which the temperature failed to drop below 70 degrees: the morning of an infamous 103-degree afternoon in July 2009. Come Sunday and Monday, the record books could include two additional 70-degree mornings. The 103-degree record could also be in jeopardy.
The drought is making the heat hotter
Much like the Southwest heat wave last week, a massive ridge of high pressure -- colloquially referred to as a heat dome -- will be responsible for the torrid heat.
In a heat dome, high pressure acts as a lid on the atmosphere, and as hot air attempts to escape the lid forces it back down, warming even more as it sinks.
This ridge is also responsible for the unrelenting drought, as it directs rain away from the region.
Another factor to keep in mind: Dry soils heat more efficiently than moist soils, contributing to the higher temperatures near the ground. As the air warms, soils dry out more quickly, reinforcing the heat and making droughts worse.
"Dry weather plus the heat surely does not help drought conditions," Miles Higa, a meteorologist with NWS in Portland, told CNN.
This heat wave and the exceptional drought in the West are part of a damaging feedback loop enhanced by climate change, experts say. The hotter it gets, the drier it gets. And the drier it gets, the hotter it gets.
Over 90% of areas in western states are in drought, with over 55% in the highest two categories ("extreme" and "exceptional").
"Unfortunately, it is not good. We are already in exceptional drought across the region, and it can only get so much worse," said Mary Wister from the NWS in Pendleton, Oregon. "My heart goes out to everyone who is in the agricultural community, because it is going to be a tough week without a doubt. It is going to get worse, unfortunately, before it gets better."
Records in jeopardy in major cities
By Sunday high temperatures could be 25 to 35 degrees above what's normal for this time of year in Seattle and Portland.
Seattle's average high in late June is 73 degrees, while Portland typically enjoys 76-degree afternoons this time of year. Forecast models suggest high temperatures could reach above 100 degrees for the two cities from Saturday through Monday.
Portland is particularly susceptible to extreme heat this weekend because of easterly winds rushing through the Columbia River Valley, warming the air as it descends towards the city.
The hottest June temperature ever felt in the city was 102 degrees on June 30, 1942. The all-time maximum temperature the city has endured was a notch higher, at 107 degrees on July 2, 1942.
From Saturday to Monday, forecasts are pointing to high temperatures in the range of 100 to 110 degrees in Portland, likely breaking the all-time June mark and threatening the overall maximum temperature.
"With all three days, we would be breaking the June highest temperature record, and if we do reach the 107, we would be tying the all-time warmest day ever recorded in Portland," said Lisa Kriederman, a meteorologist at NWS in Portland.
As the massive dome of high pressure strengthens, the air will compress and heat up, like the warmth felt on a bike pump while pumping a tire. That, combined with dry winds from the deserts of eastern Washington and Oregon, will potentially send the mercury to near all-time records in both states.
Away from the Pacific Coast
In Spokane, temperatures are likely to top 100 degrees well into next week.
"We haven't seen anything like this in a while," said Rocco Pelatti, a meteorologist at the National Weather Service in Spokane. "For the Spokane area, we are forecasting 108 for Monday and Tuesday. Even after Tuesday, it still looks like it will stay hot, with temperatures in the 100s."
The last time Spokane experienced consecutive days over 100 degrees was in 1928.
"Saturday, Sunday, Monday, Tuesday we have temperatures exceeding 100 degrees," Pelatti said. "Guidance suggests that the temperatures still stay above 100 after Tuesday for a number of days, so it could possibly exceed six."
Similar to Washington and Oregon, Idaho will see blistering record heat well into next week.
"Right now, we're looking at 105 to 110 in snake basin of Idaho and the Treasure Valley," said Korri Anderson, a meteorologist with NWS Boise. "We could be breaking all-time records in Boise on Tuesday and Wednesday of next week."
The all-time record at Boise is 111 degrees and Ontario is 113 degrees, Anderson said.
"For the state of Washington, the all-time record is 118 degrees and that was set in south-central Washington, and then for Oregon, 119 degrees is the all-time state record, and that was here in Pendleton and in Prineville, Oregon," said Wister, the meteorologist with the NWS in Pendleton. "It's hard to imagine us getting that hot, but those temperatures are going to be pretty close as we get into Monday and Tuesday."
These temperatures will also be within striking distance of the 118-degree state record for Washington, set in August 1961.
Extreme heat to become the norm in the Northwest
Parts of the Northwest could see the average number of 105-degree days increase from 0 to 2 in as little as 15 years, according to a recent study.
Without any intervention, that number would increase to an average of five days by late century, while 90-degree days would increase from roughly six days to 37 days each year in that same period.
"We always have a chance of extreme heat, particularly in the summer," Katharine Hayhoe, a scientist with the Nature Conservancy, previously told CNN. "But as the world warms, we see that summer heat waves are coming earlier, lasting longer, and are becoming hotter and more intense."