Analyzing Thursday’s severe weather
SPOKANE, Wash.– A severe thunderstorm carved a long path of destruction on Thursday afternoon that won’t be soon forgotten by those who experienced it firsthand. This storm caused severe damage in the town of Rockford, Washington and hail bigger than the size of golf balls in Liberty Lake, Otis Orchards, East Farms, and Hauser. Power outages and down trees were reported in Spokane and Whitman counties.
Hail of this size is more common on the high plains, but is rare in the Inland Northwest. Hail grows by staying stuck on the spin cycle, riding the winds moving up and down inside a thunderstorm. The stronger the updraft is (the winds rising in the storm) the longer the hail will stay suspended in the storm. The longer the hail stays in the storm, the larger it will grow. When hailstones start to collide and merge with other hailstones, you can get strange shapes like donuts or spiky balls like we saw with some of the hail Thursday.
That means the Thursday storm was exceptionally strong. Why was this the case?
The low pressure system off the Washington Coast brought us all the ingredients necessary for such a violent storm. In particular, winds out of the south over the past week brought in some of the wettest, most humid air we will probably see all year. This moisture provided fuel for the violent storm. The hot weather on Thursday led to unstable air, which rises quickly from the ground once the heat of the afternoon kicks in. In this case the unstable air carried this humid air upwards and into the clutches of thunderstorms moving north from Oregon. High above, strong jet stream winds pushed that rising air out from the core of the storm. Not only does this cause the storm to act like a chimney and strengthen it, it keeps the storm from collapsing on itself. Everything was favorable for dangerous storms that would be much stronger than a typical stormy day.
A final part of why the Rockford/Liberty Lake storm was so powerful is that there wasn’t much competition. It was the first and only storm to pass through that part of Washington and Idaho on Thursday. Any and all energy in the atmosphere got fed into one storm, a storm that showed up at the wrong place at the wrong time.
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