Supercells with large hail possible around Seattle, Portland on Wednesday
Supercell thunderstorms with very large hail could develop across parts of the Pacific Northwest on Wednesday afternoon. While severe thunderstorms usually happen in Washington and Oregon every year, the severity of the storms expected on Wednesday could rival the upper bounds of what folks in this area are used to seeing.
Warm temperatures at the surface, combined with a strong upper-level trough swooping ashore, will lead to widespread instability across much of Washington and Oregon by Wednesday afternoon.
Thunderstorms bubbling up amid the instability will find enough wind shear throughout the atmosphere to turn severe. Some of these thunderstorms could develop into supercells, which are storms with rotating updrafts that allow the storm to grow stronger and last longer than a ‘regular’ thunderstorms.
Damaging winds, large hail, and an isolated tornado or two are possible in the strongest storms that develop on Wednesday. While all modes of severe weather are possible, the greatest threat by far will be the potential for large hail, especially along the I-5 corridor between Seattle and Eugene.
Forecasters with the Storm Prediction Center painted a 15% risk for significant hail across the region. Hail is considered “significant” when it’s about the size of a hen egg (2.00 inches in diameter) or larger.
The SPC says that supercells here could produce hailstones 2.00 to 2.50 inches in diameter. This is more than enough to cause serious injury, smash up cars, and do serious damage to homes.
Hail this large is exceptionally rare in the Pacific Northwest.
Since 2003, we’ve seen 16,642 reports of hail 2.00+ inches in diameter across the United States. Just 15 of those reports came from Oregon, and only 5 of those instances were reported in Washington.
Including reports of golf ball size hail (1.75 inches in diameter) brings the total number of significant hail reports in Oregon up to 94, and raises that number up to 24 in Washington. Despite the jump in numbers, all of those significant hail reports came in east of the Cascades—none within the I-5 corridor itself.
Please take this threat seriously if you’re under a risk for severe thunderstorms on Wednesday.
Falling hail can seriously injure or kill you. Hailstones the size of golf balls and hen eggs typically fall at 70 mph—and they often travel faster if there are high winds involved.
Try to avoid getting caught in a vehicle during a severe thunderstorm. If you’re in a vehicle when hail starts to fall, cover up with anything available—coats, blankets, sunshades, anything that may protect you from shattered glass, flying debris, and the hail itself.
If you’re at home when a severe thunderstorm arrives, stay away from doors and windows no matter how tempting it may be to watch the storm. Hailstones blowing in the wind and bouncing around can easily shatter windows, send debris into the air, and even hit you.
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