The extreme heat that shattered records across the Pacific Northwest — and still has not abated in many areas — has no precedent in modern record-keeping, data analyses shows. This is also the case in British Columbia, where the temperature soared to an almost unimaginable 121°F in Lytton on Tuesday.

Why it matters: Heat of this magnitude is proving to be deadly, which is consistent with findings that heat waves are typically the deadliest weather phenomena in the U.S. each year.

The big picture: With the heat settling further inland in Washington, Oregon, Idaho, Montana and parts of Canada, it's possible to check the historical record to see how the approximately 60 all-time high temperature records stack up.

• Typically, all-time records are broken by fractions of a degree to one or two degrees most. But during this heat event — caused by an extraordinarily strong area of high pressure aloft, or "heat dome," and aggravated by drought and global warming — temperatures exceeded previous records by more than 10°F in some places.
• Studies getting underway now to examine how big a role climate change has been playing in this event are likely to find that heat of this magnitude, occurring so early in the summer in such a relatively cool region of the country, was virtually impossible without human-caused global warming.

By the numbers: A chart similar to the one above for Portland, except looking at Lytton, shows an even more pronounced temperature spike compared to the historical record, Berkeley Earth scientist Robert Rohde said on Twitter.

Stunning breakout far above all previously measured values to set a new national temperature record for Canada of 49.6 °C (121 °F).

This heatwave has reached further above historical means than any other summer heatwave previously recorded anywhere in North America. pic.twitter.com/aNURI7W8Yh

— Dr. Robert Rohde (@RARohde) June 30, 2021

Between the lines: While computer models accurately captured the likelihood of extreme heat, since they were projecting unprecedented outcomes, forecasters had some trouble mentally processing them. This was visible on social media, as forecasters shared their thinking, but also in official National Weather Service forecast discussions.

• One technical forecast discussion from the NWS office in Seattle on Tuesday evening stated: "As there is no previous occurrence of the event we're experiencing in the local climatological record, it's somewhat disconcerting to have no analogy to work with. Temperature records will fall in impressive fashion. Stay cool, stay hydrated."

What's next: With the Western U.S. in the grips of severe drought and unusually hot conditions, wildfire season has started early.

• In northern California, the Lava Fire grew to nearly 18,000 acres overnight.
• Smoky skies are spreading throughout British Columbia and spilling into Alberta as blazes ignite in that province, which usually features wildfires toward the end of the summer, when conditions are driest.
• On Wednesday, President Biden, together with Vice President Harris, members of the Cabinet and representatives from the private sector, are convening a virtual meeting with Western governors about the threat of a devastating fire season, and how best to prepare for it.
• “I ... know that we are in a different climate, as the president said, on every level than we were even 10 years ago,” Harris said.

Go deeper: Biden moves to raise federal firefighters' pay as wildfire season kicks off