This year's hottest day so far may end with a treat for Seattle: northern lights

Plenty of sunshine and highs in the 80s are on tap this July — err, May — weekend. 

Friday is expected to be the hottest day of the year so far across many locations in Western Washington, as the mercury heats to highs normal for peak summer, according to the National Weather Service. 

A high-pressure system — which causes air to descend rapidly, warming and drying along the way — began building over the region Wednesday, kicking off the warming trend.

On Friday, with the ridge of high pressure in place, temperatures will catapult up the thermometer another 5 to 10 degrees from Thursday, settling in the upper 70s to mid 80s, the weather service said.

Seattle’s average first 80-degree day is May 20. The earliest 80-degree day of a year recorded here was April 1, 1987, and the latest was July 21, 1980, according to the weather service.

Some of the lowest tides of year are also expected in Western Washington Friday, which means beachgoers enjoying the warm weather could see a lot of marine life.

Saturday is expected to remain warm in the Seattle area, but cooling winds will start blowing in from the Pacific, and the ridge above is expected to weaken. Highs in the Puget Sound interior will hold steady, while temperatures dip as much as 20 degrees along the coast, into the 60s.

The weather service is urging caution this weekend as many people likely take to the water, which remains cold despite the warmer air temperatures.

On Thursday, water temperatures were 54 degrees in Lake Washington, 56 degrees in Lake Sammamish and the lower 50s in Puget Sound, according to the weather service.

“It doesn’t matter what water you’re talking about, whether it’s the lakes, streams, or even Puget Sound, which is always cold,” said Dustin Guy, a meteorologist with the weather service in Seattle. 

That cooling ocean breeze will eventually blow into the interior, too, and by Sunday, the region will be uniformly cooler than at the start of the weekend. Highs on Mother’s Day will be in the 60s to lower 70s, which is slightly above seasonal levels, according to the weather service.

With the exception of a few possible showers in the mountains, warm, dry and sunny spring weather will linger at the start of next week.

Mother Nature will also grant us clear night skies this weekend as a solar storm whips through the upper atmosphere, lighting up the northern horizon in the faint red and green glow of an aurora borealis.

The National Oceanic and Atmospheric Administration Space Weather Prediction Center issued a G4 — severe — geomagnetic storm warning for the first time since 2005. 

The aurora is expected to be visible over much of the northern half of the country, and as far south as California to Alabama, through Sunday. 

NOAA in a statement Thursday warned of disruptions the solar storm could cause, including to the electric power grid, navigation, and radio and satellite operations.

The Kp-index, or planetary index, which is a system of measuring aurora strength running from 0 to 9, is expected to be at an 8 this weekend in North America, according to NOAA.

A Kp in the range of 8 to 9 means an aurora will move toward the equator and become “very bright and active,” if you’re in the right place, according to the weather service. Any occurrence above 5 is considered a geomagnetic storm.

The aurora typically stretches into only Alaska, Canada and Scandinavia, but an 11-year solar cycle expected to peak this year is making the glow visible in places farther to the south. Last spring, the light displays were visible in Arizona, marking the third severe geomagnetic storm since the current solar cycle began in 2019, according to The Associated Press.

The glow of the aurora is produced when particles from the sun’s magnetic field are blasted into space, eventually colliding with oxygen and nitrogen atoms and molecules in Earth’s upper atmosphere, according to the Space Weather Prediction Center.

Light pollution impacts the ability to see the aurora in action in Washington, so it’s best to get out of a city to view the lights. At less than 10% full, the waxing crescent moon won’t provide too much light disruption.

The Space Weather Prediction Center anticipates the best viewing times for those in range are between 10 p.m. and 2 a.m.