Seattle recorded 0.76 inches of rain, breaking the previous record of .54 inches for the date, set on July 23, 1949.
Lightning strikes were first recorded over the Cascades of Snohomish County at around 2 a.m., then moved into the Puget Sound region.
By 11 a.m., 683 cloud-to-ground lightning strikes had been recorded in Western Washington between Lewis County and the Canadian border. In one hour alone, from 8 to 9 a.m., there were 236 lightning strikes.
At the same time, heavy rainfall began moving into the Puget Sound region, slowing the morning commute and triggering a number of crashes and fender-benders across the region. In King County alone, state troopers responded to 39 collisions between 4 a.m. and 11 a.m.
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Standing water was reported earlier on northbound Interstate 5 near 145th Street.
The forecast calls for more rain and lightning through Wednesday evening in Western Washington. Rain is expected to taper off Thursday and some sunbreaks are possible over the lowlands by Thursday afternoon.
The storm also is expected to dump heavy rain on the east slopes of the north Cascades. The rain could cause flash floods in the areas scarred by wildfires in Chelan and Okanogan counties.
At 1:45 p.m., the Washington State Patrol reported a half-inch of hail on the ground at the Twisp fire camp and 50-mph winds.
Meanwhile, lighting from thunderstorms could spark new wildfires in the southeast corner of the state, around the Tri-Cities and Walla Walla.
Dry, hot weather is expected to return to the state over the weekend.