Monsoon moisture is surging into the Inland Northwest Tuesday evening as an upper level low spins off the coast of Oregon. On Monday, I reported that Wednesday was likely to see thunderstorm activity pushed eastward into Idaho and Utah because of how close the low was expected to be to the Washington coast.
Updated models (thanks to more recent observations) have shifted the Wednesday storm activity a little bit to the west, resulting from the low now expected to run a little further offshore. This is likely to keep the dry slot close to the low a little bit further to the west allowing for thunderstorm activity again during the day.
Most of the storm activity looks like it will be focused closer to the Blue Mountains with places like Walla Walla and Pendleton seeing a higher chance of thunderstorms. This is thanks to a mixture of things – being further from the low’s center, being a little bit cooler, and better uplift aided by the terrain.
Severe thunderstorms are defined as having 58+ mph winds and/or 1″+ diameter hail. Under a marginal risk event, it is expected that a few of these will occur but they certainly aren’t likely to be widespread. Strong, but not severe, thunderstorms will be more common. The marginal risk area runs about 50 miles on both sides of a line from La Grande in the southeast to Omak in the northwest.
Cloud cover from Tuesday’s storms may inhibit storm growth by limiting daytime heating in the morning hours. This didn’t stop the heat on Tuesday with the Tri-Cities Airport in Pasco reaching 90° just after noon but the ridge moving further east should lead to less heat in the region. Model guidance keeps the storms east of the Tri-Cities, but small differences in the low’s position, temperature, and individual storm strength may lead to big changes in where storms end up hitting.
𝓛𝓲𝓰𝓱𝓽𝓷𝓲𝓷𝓰 𝓢𝓽𝓪𝓻𝓽𝓼: Central Oregon has seen over 800 lightning strikes today. These strikes have ignited at least 70 fires resources from @DesNatlForest @OchocoNatForest @ODF_COD and Prineville District @BLMOregon have responded to.
— Central OR Fire Info (@CentralORFire) August 9, 2022
As of writing (18:00 Tuesday), thunderstorms have already made their mark in the region. One tracked from the Blue Mountains to Pendleton and Walla Walla, lowering the temperature in Walla Walla from 99° to 79° in half an hour and dropping 0.11″ of rain. In Central Oregon, lightning had sparked 70 small fires by 16:30. Fire starts may be seen overnight and into Wednesday as well. Despite heavy rain in many of the thunderstorms, lightning on the edges or in front of the storm may be enough to generate new fire events.
