NYSSA – The thunderstorm that would barge through Nyssa and trigger millions in damages was already gaining power when it moved into Malheur County early on the afternoon of Wednesday, June 26.
A thunderstorm needs several key ingredients to thrive, according to meteorologists. First the storm itself must pack cold air and moisture. Next a blanket of dry, hot air ahead of the squall is needed. Then it needs lift produced by warm or cold air or mountains.
That day, the storm rolled into Malheur County it was still only a run-of-the-mill thunder squall with lightning, thunder and some rain.
But as the storm moved, it hit a layer of hot, dry air over the county, according to Sophia Adams, a meteorologist for the National Weather Service in Boise.
Like an engine revving, the storm began to recharge itself as it gobbled up more hot, dry air. That warmer air created what is known as convection, where strong upward motion sucks the heat into the heart of the storm.
“That warm air we understand it to be the fuel for the storm,” said Adams.
The storm then gained “sheer” – high winds that change speed and direction.
“The whole concept here is the atmosphere is trying to balance itself. You have the warm, hot air rising, attempting to balance the environment out,” said Josh Smith, a meteorologist for the National Weather Service in Boise.
The storm continued to gain power as warm, dry air climbed toward cold moist air that was falling.
“Cold air sinks because it is heavy and dense. Gravity pulls it to the surface,” said Smith.
As the cold air falls it creates an imbalance in the atmosphere and it begins to accelerate.
“That’s where you get the stronger winds to develop, in the cold moist area. The great imbalance promotes stronger winds,” said Smith.
All of the key factors merged in moments over Nyssa.
“Everything was meeting at the same time,” said Smith.
The storm then lashed Nyssa with rain and winds between 60 and 70 mph. The wind tore off roofs, knocked down trees and ripped out power lines.
A storm survey by the weather service concluded the damage to the town and outlying areas was “consistent with a wet micro-burst. The direction of downed trees, toppled crops, and strewn debris was indicative of straight-line winds from the west and the northwest caused by an outflow from the micro-burst.”
According to the report, the most “extensive damage occurred in areas south and east of the storm, where the wind was coming out from the north and west.”
The storm summary reported one person was injured with a broken arm from a tree limb.
Smith said the storm did not create a tornado.
“In this case, based on what we saw on the radar, we didn’t see any low-level spinning. It never worked its way down to the surface,” said Smith.
The storm continued to feed off warm, dry and cold air as it moved west, toward the Sawtooth Mountains in Idaho.
“Once it gets to that strength it takes over its own environment until it runs out of moist or warm air,” said Smith.
Once it reached the Sawtooth Mountains, said Smith, the sun began to set, depriving the storm of warm air.
Smith said the storm was unusual for the local area.
“The storm did produce, in Garden Valley, two-inch hail and that does not happen in our part of Idaho often. 1998 was the last time we recorded two-inch hail,” he said.
“This particular storm had all the right ingredients at the right place to allow it to happen,” he said.
News tip? Contact reporter Pat Caldwell at [email protected]
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