Lightning and hail comes with the storms moving across Puget Sound on Thursday afternoon and evening.
KIRO 7 Meteorologist explain ingredients appear to be coming together for stronger thunderstorms around parts of Western Washington Thursday afternoon and evening.
Time-stamped updates: Storm coverage, damage in Puget Sound
[10:15 p.m.] The National Weather Service Seattle said there was about 2,500 cloud to ground ligtning strikes from Lewis County to the Canadian border on Thursday.
[8:50 p.m.] Storms are slowly weakening but heavier rain and lightning is expected for some areas.
[8:35 p.m.] Rainbows were spotted Lake Washington after the thunderstorms that rolled through Western Washington.
[8:00 p.m.] Lacey battalion chief told KIRO 7 there's widespread damage. Wires down, widespread damage and countless trees on homes and cars.
[7:58 p.m.] Small hail, lightning and gusty winds are expected for parts of the South Sound after 8 p.m.
[7:43 p.m.] Power lines are down and blocking 14th Avenue Southeast in Lacey.
[7:02 p.m.] KIRO 7 Meteorologist Morgan Palmer reports since the National Weather Service started archiving warnings in 1986, there has not been a day as active as this one.
[6:56 p.m.] More non-severe storms rolling north toward Seattle on busiest severe weather day in decades. Reports from Lacey - Olympia - Grand Mound area of downed trees and power lines continue.
[6:42 p.m.] Flooding becoming a problem for traffic across Puget Sound. Video in Lacey shows people driving through water over the Tacoma Narrow Bridge. Closer to Seattle, water is gathering along the side of southbound I-5 near Boeing Field.
[6:27 p.m.] Crews are working to restore power to a Lynnwood fire station. A lightning strike caused a power outage.
[6:20 p.m.] Video shows flooding on part of NB I-5 north of Olympia, creating traffic delays.
[6 p.m.] Drivers in a number of cars are sheltering in place after power lines were knocked down across a long stretch of Yelm Highway in Lacey. The power lines are live and could electrocute someone.
[5:15 p.m.] In Lacey, video and photos show major street flooding and wires down on Yelm Highway.
[5 p.m.] Lightning strikes reported from South Sound to Seattle.
[4:30 p.m.] Olympia Airport reports a gust to 50 MPH with the storm.
[4 p.m.] Up to 600 lightning strikes in Western Washington in the past half hour.
[3:30 p.m.] Chopper 7 captures lightning over Lake Washington. Meanwhile, lots of thunder and small hail spots pop up in Pierce and Kitsap counties.
Areas most at risk
Morgan agrees with the Storm Prediction Center (a division of the National Weather Service) that the greatest threat will extend from southern Washington northward to the South Sound and central Puget Sound region as well as the foothills of the Cascades.
Thunderstorms will be likely higher up in the mountains and on the eastern slopes, too.
West of Puget Sound, across the western/northern Olympic Peninsula and north/west of Everett: Your atmosphere is likely to stay more stable as cooler air begins to flood in from the Pacific Thursday afternoon. Thunderstorms aren't ruled out in these parts, but they're more likely to stay fairly modest.
After 10 p.m., the threat for thunder will have passed most areas as cooler, more stable air overspreads the area. The exception will be in central and northern Washington east of the Cascades where thunderstorms could continue into the early overnight hours.
What to expect if a storm develops near you
Most of these thunderstorms will have lightning (possibly a lot of lightning!), so you'll want to make sure you get inside if you hear thunder or see lightning.
Of the impacts that can cause damage: We're really looking at a few storms that could produce hail to the size of nickels or even quarters. Isolated wind gusts to 50-60 miles per hour could accompany the strongest storms.
This isn't thunderstorm damage like those monster storms in Tornado Alley, but quarter-size (one inch diameter) hail can still cause minor roof damage, especially on older roofs.
It's important to note that if we have this sort of larger hail or stronger wind from thunderstorms, it's likely to impact a very small part of our region. Most of us will not see these sorts of more serious impacts. We'll be hopeful we don't see them at all!
The tornado threat is minimal.
Outside of the few areas that might see strong storms, we can still expect scattered to numerous thunderstorms with small hail and lightning -- the more typical thunderstorms for springtime in the Northwest.
It's a good idea to download our KIRO 7 Pinpoint Weather App as it will immediately notify you if any weather warnings or alerts are issued for your area. You can also track the storms with the Pinpoint Doppler Radar within the app.
Why are meteorologists making this such a big deal?
Meteorologists look at many different factors to determine if thunderstorms will develop. One of the critical variables is atmospheric instability.
Normally, here in the Pacific Northwest, the airmass in place is cool and dreary as we're so close to the cool Pacific Ocean.
Thursday, however, you'll notice the air is unusually muggy and by afternoon temperatures will be well into the 70s in many areas on their way to near 80 in some spots. This is unusual for us!
In addition, above us in the atmosphere, temperatures will be rapidly cooling.
This difference between warm, muggy air at the surface and colder air aloft will allow thunderstorms to grow higher in the sky -- much like how a hot air balloon rises higher the hotter the air inside the balloon!
The taller the thunderstorm, generally the more fierce the weather.
There are other factors in place like differences of wind speed with height and the incoming push of cool Pacific air that will make for a volatile environment.
We have not seen these thunderstorm ingredients coming together like this in the Western Washington region for years.
The good news is that the thunder threat will be gone by Thursday night and we'll be back to more typical Northwest springtime weather for the beginning of boating season this weekend: cool and mainly cloudy.
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