A "historic" and potentially deadly heat wave is on tap for the Pacific Northwest into southwestern Canada this weekend into early next week, with never-before-seen temperatures possible in cities like Portland, Ore., and Spokane, Wash.

Why it matters: The heat wave will affect a region where many people lack central air conditioning, raising the likelihood for public health impacts. In addition, power demand is likely to spike at a time when hydropower resources are running relatively low due to drier than average conditions.

The background: This heat wave is related to the same weather pattern that brought record heat to the Southwest last week, and is proving to be remarkably persistent.

• As in the Southwest, the heat will raise the risk of wildfires, too, in Oregon, Washington, northern California, and British Columbia, among other areas.

Driving the news: Computer models are unanimous in showing a highly unusual weather pattern moving into place over the Pacific Northwest beginning this weekend, with an extraordinarily strong high pressure area aloft, colloquially known as a "heat dome," anchored over the region.

• The jet stream will take a detour around this high, bulging northward toward Alaska, and allowing mild air to surge northward.
• Heat waves such as this one are one of the clearest manifestations of human-caused global warming, with studies showing that climate change boosts the odds of their occurrence and heightens their severity.
• Some recent studies have found that extreme heat events could not have occurred in the absence of global warming.

Details: In Seattle, where the average high temperature for this time of year is in the low-to-mid 70s, the National Weather Service (NWS) is predicting a high of 97°F on Sunday, which would break the record for the hottest temperature on record there during the month of June.

• The Weather Service stated that Sea-Tac Airport has a 75% chance of exceeding 95°F on Saturday, and an 85°F chance of exceeding 95°F on Sunday.
• The heat will be most intense in inland areas of Washington and Oregon, away from any cooling influences of the Pacific Ocean. There, temperatures are forecast to soar to between 100°F and 114°F on Saturday and Sunday, and remain extremely hot through much of next week.
• Portland, Ore. is forecast to be in the low triple-digits on Saturday and Sunday, likely breaking their June temperature record and getting within striking distance of smashing their all-time high temperature record of 107°F.

What they're saying: The NWS is not mincing words about the severity of the heat event that is coming: "Triple digit heat arriving this weekend and persisting well into next week could rival some of the longest lasting and extreme heat waves in the recorded history of the Inland Northwest," agency forecasters in Spokane wrote Wednesday.

• Forecasters noted that multiple hot days will increase the likelihood of heat-related illness, particularly because overnight low temperatures won't drop below the 60s and 70s, preventing people from recovering from the heat at night.
• In a typical year, heat kills more people in the U.S. than any other weather-related hazard.

Of note: In addition, the drought is likely to worsen in interior portions of the Pacific Northwest, as the high temperatures dry out soils, and make the region more prone to wildfires during this period as well.