Early morning thunderclaps elicit no applause.

Byline: Tim Christie The Register-Guard

A classic midsummer thunderstorm cracked down on parts of Eugene and Springfield early Friday, knocking out power to a few hundred homes and awakening an untold number of sleepers with concussive, cacophonous power that would have made Thor proud.

The meteorological pyrotechnics hit first about 12:40 a.m. and rocked on for more than an hour, according to officials at the National Weather Service.

Utilities reported scattered outages in the area.

About 300 customers of Eugene Water & Electric Board lost power, most in north and west Eugene and in the River Road area, spokesman Lance Robertson said.

All but about 50 customers had their power restored by midmorning; the remainder waited while crews replaced transformers fried by lightning, he said.

The Emerald People's Utility District reported scattered outages affecting only about 50 customers, including some along Sears Road in Cottage Grove, where four or five transformers were struck by lightning.

Tens of thousands of lightning strikes occur each day in the United States; according to one Web site that counts strikes (thunderstorm .vaisala.com), more than 57,000 bolts hit the United States between 1 p.m. and 3 p.m. Friday.

Thunderstorms are not uncommon in Oregon, but the Willamette Valley does not get the frequent electrical storms that are seen and heard in the Midwest and East.

To understand why that is, a person first needs to understand how thunder and lightning work.

Lightning originates about 15,000 to 25,000 feet above sea level, when raindrops are carried upward until some turn to ice, according to the weather service.

Cloud-to-ground lightning originates up in that water and ice region, then the charge moves downward in 50-yard steps until it encounters something on the ground that provides a good connection - a tree, a farmer's tractor, a golf club.

That connection completes the circuit and the charge is delivered from a cloud to the ground, then the current flows back up the same path, lighting the sky.

Thunder occurs as the energy in the lightning bolt heats the air around it to about 50,000 degrees in a microsecond.

That hot air is at very high pressure, causing it to expand outward and compress the surrounding air.

That compression causes a disturbance that starts out as a shock wave for the first 10 yards, then turns into an ordinary sound wave, or thunder.

"The lightning rapidly expands the air, sort of like a sonic boom like thing," said Russ Willis, a meteorologist with the National Weather Service in Portland.

We don't get as many thunderstorms as the Midwest because it's not hot enough and the air isn't wet enough, weather experts say.

"In the Midwest, you have this tremendous source of moisture" from the Gulf of Mexico, said George Taylor, state climatologist. "Moisture is the fuel that strengthens thunder storms."

While it rains a lot here, the actual amount of water vapor in the air is less than it is in the Midwest and East, according to Taylor.

Friday's storm was set off by monsoon moisture that moved up from Arizona, said Willis of the weather service.

A weak upper low off the coast pushed the moisture up to destabilize the air mass and create thunder storms.