Breakdown: Heat Dome - Why Northwest experienced a historic heat wave

MEMPHIS, Tenn. (WMC) - The most extreme heat wave ever recorded in the Pacific Northwest continues to bring sweltering heat to the region. Millions of people are currently under excessive heat warnings — many areas baking under triple-digit temperatures without air conditioning in a region that usually enjoys mild summers.

Behind the misery is a weather phenomenon known as a heat dome.

What is a heat dome? A heat dome occurs when the atmosphere traps hot ocean air like a lid or cap, according to the National Oceanic and Atmospheric Administration (NOAA):

High-pressure circulation in the atmosphere acts like a dome or cap, trapping heat at the... — High-pressure circulation in the atmosphere acts like a dome or cap, trapping heat at the surface and favoring the formation of a heat wave.(NOAA)

A team of scientists funded by the NOAA MAPP Program investigated what triggers heat domes and found the main cause was a strong change (or gradient) in ocean temperatures from west to east in the tropical Pacific Ocean during the preceding winter.
Imagine a swimming pool when the heater is turned on — temperatures rise quickly in the areas surrounding the heater jets, while the rest of the pool takes longer to warm up. If one thinks of the Pacific as a very large pool, the western Pacific’s temperatures have risen over the past few decades as compared to the eastern Pacific, creating a strong temperature gradient, or pressure differences that drive wind, across the entire ocean in winter. In a process known as convection, the gradient causes more warm air, heated by the ocean surface, to rise over the western Pacific, and decreases convection over the central and eastern Pacific.
As prevailing winds move the hot air east, the northern shifts of the jet stream trap the air and move it toward land, where it sinks, resulting in heat waves.
https://oceanservice.noaa.gov/facts/heat-dome.html

All-time high temperature records were broken across Washington and Oregon.

Morning, W WA! ICYMI....several stations set new ALL-TIME records on Monday:

Bellingham 99°F (previous 96°F 7/29/2009)
Sea-Tac 108°F (104°F set 6/27/2021)
NWS Seattle 107°F (105°F set 7/29/2009)
Olympia 109°F (105°F set 6/27/2021)
Quillayute 110°F (99°F set 8/9/1981)#wawx
— NWS Seattle (@NWSSeattle) June 29, 2021

If the triple digits weren’t enough, this type of heat is so rare in that part of the world that many homes and businesses don’t have air conditioning. So imagine suffering through multiple days of triple digit heat without AC! While it is usually a drier heat in that part of the country, 116 degrees is still 116 degrees... it’s hot for even the most seasoned folks in places like Las Vegas and Phoenix. But again, other areas that get this warm have widespread air conditioning.

The Portland Airport officially hit 116°F shortly after 5pm this evening making this the warmest temperature on record. This breaks yesterday's warmest temperature on record of 112°F. 3 days ago the warmest temperature on record was 107°F set twice in Aug '81 & once in Jul '65.
— NWS Portland (@NWSPortland) June 29, 2021

NWS forecasters in Seattle said Friday they “have never seen Pacific Northwest data like this.”

HEAT WAVE
This is expected to be unprecedented event. Those of us at the office have never seen PNW forecast data like this. We encourage everyone to make plans now to check in on and ensure their loved-ones, neighbors, pets, and the entire community remain safe and healthy #WAwx pic.twitter.com/xfKtw7IICR
— NWS Seattle (@NWSSeattle) June 25, 2021

The unprecedented heat wave has proven to be deadly, is impacting salmon migration, and agriculture. Additionally, it’s fueling wildfires.

Meteorologists from the National Weather Service in Medford, OR say, “Although temperatures aren’t as hot as they were, high temperatures will remain well above normal through the [July 4th] weekend. Heat Advisories remain in effect for most of the area through Saturday (July 3rd) when high temperatures are expected to peak again. Afterwards, temperatures will gradually lower into next week, but will remain 10 degrees above normal through much of next week. Make sure to stay hydrated and avoid strenuous activities during the hottest part of the day. Never leave children or pets in closed vehicles.”

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