The first sign of the storm will likely be a clap of thunder, said National Weather Service meteorologist Steve Reedy on Wednesday afternoon.
Heavy rain, large hail, visible lightning and severe winds could take five to 30 minutes to follow and could last for about two hours, he said.
The incoming thunderstorm was expected to pelt parts of Western Washington with hail as big as golf balls, severe winds and potentially a tornado.
National Weather Service forecasters expected the storm to start rolling into Seattle around 6 p.m.
“When thunder roars, go indoors,” Reedy said. “When you hear the thunder, that’s kind of your clue that conditions are going to deteriorate from that point.”
Seattle Public Schools announced all after-school events were canceled and buildings would close after 5 p.m. Wednesday.
All sports practices and after-school activities would end early enough to let families pick up students in time to avoid the storm, the district’s statement said.
The district shared its announcement with families and staff as patches of blue sky started dwindling Wednesday afternoon across Seattle.
“We apologize for the short notice but want to prioritize the safety of our community and staff,” the district said.
National Weather Service forecasters expect the storm will roll into Seattle around 6 p.m., with a 15% to 19% chance of hail greater than an inch in diameter and a 10% chance of hail larger than 2 inches.
Forecasters expect heavy rainfall Wednesday night in Seattle, with up to three-quarters of an inch of rain before Thursday morning. Typical “springlike weather” is expected to return Thursday, Reedy said.
The weather agency issued a severe thunderstorm watch through 9 p.m. Wednesday in King, Clark, Thurston, Lewis, Cowlitz, Pierce and Skamania counties.
Residents of King, Pierce, Lewis and Thurston counties have between a 5% and 9% chance of seeing a tornado during the storm. That risk falls to between 1% and 4% for residents of Clark, Cowlitz and Skamania counties, Reedy said.
“This is not the time to go outside and work with anything metal,” Reedy said. “Stay inside and stay informed.”
