Well, we blinked and missed spring.

In only the second week of May, Western Washington is soon to endure high temperatures close to averages typically expected in August.

An area of high pressure centered over southern Canada and stretching into the Pacific Northwest began to build Wednesday, supporting the development of dry conditions and unusually high temperatures in the days ahead.

Highs across the region will continue to climb upward through the 70s as pressure builds and are eventually expected to tip past 80 degrees — nearly 20 degrees above average for this time of year — by the weekend, according to the National Weather Service.

There’s “pretty much a 100% chance” Seattle will have temperatures in the 80s on Saturday, said Kayla Mazurkiewicz, a meteorologist with the weather service in Seattle.

The mercury will continue to rise as the ridge of high pressure remains anchored in place through at least Monday. High temperatures are expected to peak in the upper 80s to low 90s across the region on Sunday and Monday, the weather service said.

heat advisory is in effect for temperatures in the mid 80s to low 90s from Saturday afternoon through Monday evening for portions of northwest and west-central Washington. An excessive heat watch was initially issued, then upgraded to an advisory early Friday morning.

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In Seattle, there’s a 40% to 50% chance that highs will reach into the 90s on Mother’s Day, and an 85% chance of 90-degree temperatures in the southwest interior, according to the weather service.

Monday has the potential to be the hottest day in the upcoming heat wave, as well as the hottest day so far this year, but “there’s a little uncertainty to that,” Mazurkiewicz said.

A pool of cooler air drifting into Oregon and potentially a portion of Washington early next week may create an unstable atmosphere, opening the door to thunderstorms — especially east of Puget Sound — and cloud cover that could dampen temperatures.

Despite the presence of cooler air bumping up against the high-pressure system, hot temperatures on Monday seem to want to hold firm right now, the weather service said Thursday afternoon.

Temperatures are expected to begin to dance back down to the upper 70s by the middle of next week as the high pressure over the region loses its grip. There is some uncertainty about how fast a cooldown will occur, though, the weather service said.

The last time Seattle hit 90 degrees in May was in 2008, which also marked the earliest 90-degree day on record in Seattle. There have been only seven 90-degree days recorded in May — which typically has only two days with temperatures over 80 — in Seattle-Tacoma International Airport climate history.

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So, how exactly is an area of high pressure causing temperatures to soar this weekend?

In the Northern Hemisphere, the atmosphere is governed by winds that move from west to east, explained Carly Kovacik, another meteorologist at the weather service in Seattle.

These winds are disrupted by several factors, Kovacik said, like uneven heating of the Earth’s surface due to the planet’s tilt and topography like mountains or large land features.

These wind pattern disruptions create imbalances in temperature (and therefore pressure) both vertically and horizontally, ultimately creating wavelike patterns across the globe. These wavelike patterns are in the form of either troughs of low pressure — compact cold air — or ridges of high pressure, which are areas of higher atmospheric heights with warm and less-dense air, Kovacik said.

The atmosphere above us is always seeking equilibrium, Kovacik said — “so it is always trying to pull warm air poleward and cold air equatorward.”

When an area of high pressure moves into a region, like the ridge that has been building above us, air can do nothing other than sink toward the surface.

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“As this air sinks towards the surface, it is forced to compress, since there are more air molecules towards the Earth’s surface. Compression warms the air, resulting in warming temperatures,” Kovacik said.

The presence of the high-pressure ridge creating this weekend’s heat wave is similar to that of the infamous June 2021 heat dome, Mazurkiewicz said, but temperatures won’t spike as high or for nearly as long.

With increased heat also come increased chances of brush fires, plus fire danger and avalanche risk in higher terrains, the weather service warned.

As high temperatures make a run at 90 degrees this weekend, the weather service also warns of increasing risk of heat-related illnesses, especially in those sensitive to heat or who don’t have access to effective cooling and hydration.

Graphics to help you learn how to stay safe on the water, beaches or trails

People should also be aware that, despite warmer air temperatures, waterways may remain cold across the region.

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Snowmelt keeps the temperatures of most rivers and lakes in the upper 40s to low 50s this time of year. Puget Sound’s temperature is in the mid-40s, making cold-water shock a real concern for swimmers of all abilities.

The National Park Service has warned that rivers near Mount Rainier can turn to muddy torrents during heat waves as snow rapidly melts, which can lead to rapidly rising river levels.

Officials advise using caution during water activities to avoid hypothermia and water-related injuries for those seeking relief in area lakes, rivers and streams. Cold water can drain body heat up to for four times faster than cold air, the weather service said.

A person dives into the water from a pedestrian bridge at Lake Union Park into the water 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)