Sabina Ehmann and her daughter Vivian, visiting Seattle from North Carolina, are prepared with umbrellas to shield the sun during a heat wave hitting the Pacific Northwest, Sunday, June 27, 2021, in Seattle. Yesterday set a record high for the day with more record highs expected today and Monday. (AP Photo/John Froschauer)
What is a 'heat dome'?
01:10 - Source: CNN
CNN  — 

As if hundreds of wildfires, crippling drought and a summer marked by a once-in-a-lifetime heat wave were not enough, more than 20 million Americans in the western US are on alert ahead of another historic heat wave.

“We’ve had two excessive heat watches this summer, I don’t remember ever having two in the same summer,” said Dana Felton, National Weather Service (NWS) meteorologist in Seattle.
It’s not just the Northwest that will have “feels like temperatures” skyrocketing past 100 degrees. Over half the US is under heat alerts this week.

Well over 100 million people are under heat alerts in more than 25 states across the country.

Get the forecast for your area

The Northwest braces for another round of record-breaking temperatures

A massive area of high pressure is strengthening along the Pacific Northwest and will set the stage for another classic “heat dome.” This will cause temperatures to soar 20 to 25 degrees above normal, possibly breaking more records.

The National Weather Service in Portland, Oregon, has issued an excessive heat warning for the event as temperatures in the city are forecast to reach the upper 90s by Wednesday and possibly eclipse 100 degrees both on Thursday and Friday.

Farther north, Seattle expects temperatures to surge as the usual 79-degree August afternoon is forecast to be in the mid to upper 90s from Thursday through Saturday.

In total, over 100 record temperatures could be set by late week.

According to Joe Zagrodnik, an atmospheric scientist at the Washington State University, the upcoming heat wave would be considered a “once in a decade” event if the decade was not the most recent decade, the 2010s.

A very high risk (magenta color) is issued when the entire population is due for long-duration heat, with little to no relief overnight.

In Seattle, climate records have been kept since 1894, but when it comes to the month of August, 15 of the 31 days this month have a daily record that has been set in the past 12 years (2009-2020).

Seattle’s record for the most 95-degree or more days is currently four, and if the forecast holds, they will reach five according to Felton, adding another record to the books.

Heat stretching across the country

Maximum temperatures will soar above 90 degrees for much of the US this week. Combine this with the humidity in some areas and it will feel much hotter.

It’s not just the West that will be baking in the August heat, much of the entire nation will be as well.

“Much of the Lower 48 will be mired in abnormally hot conditions through mid-week,” said the Weather Prediction Center (WPC). Heat Advisories have been issued from the central Plains and Mississippi Valley to the Lower Great Lakes and the Northeast.

“Daytime lows will be quite warm along the West Coast and east of the Mississippi River where numerous record warm minimum temperatures are possible on Wednesday and Thursday mornings,” said the WPC.

The warm temperatures combined with the high humidity will make temperatures feel as much as 15 degrees hotter than they actually are.

Near New York City, highs Thursday and Friday will be in the lower to mid-90s, with heat indices in the mid-90s to 104.

“In the urban corridor of northeastern New Jersey and into portions of New York City heat indices may briefly reach 105 on Thursday afternoon and possibly again on Friday,” said the NWS in New York City.

Fires and heat linked to climate change

Incredibly, some forecast models suggest the heat wave would potentially be more stifling if not for the tremendous amount of haze and smoke that currently blankets much of the Western skies.

“We don’t even really know if we are going to get smoke, or how much we will get, but if it is thick enough it will knock temps down a few degrees,” says Felton.

This will all be dependent upon wind direction.

With or without the addition of smokey skies, the heat will be dangerous. A harsh reality as climate change causes heat waves of this magnitude to occur more often.

This week, the Intergovernmental Panel on Climate Change released its latest findings further highlighting the unmistakable link between human-induced climate change and extreme heat events around the globe.

The landmark report concluded that it is “unequivocal” that humans have caused the climate crisis and confirms that “widespread and rapid changes” have already occurred.

Seattle’s summer to remember

Just 6 weeks ago, the region was under the grips of a heat wave for the ages. “When people look back at the summer of 2021 – they will remember the 3 days in June,” said Felton.

All-time record temperatures fell by the wayside as cities like Seattle soared to 108 degrees while Portland baked past 116 degrees.

An all-time record was set for Canada as a nation when Lytton, British Columbia, saw the mercury climb to a mind-numbing 121 degrees on June 29.

All of this in what has been one of the most destructive wildfire seasons on record as over 108 large fires burn across 15 different states in the US.