A very moist, unstable weather system is rotating around a low-pressure system in Southeastern Oregon will bring rain over Southeast Washington today and thick clouds for Northcentral Washington. We will be far enough away from the low to remain northwest of the unstable, wet air. The weather in this part of the region will be sunny and quite warm with highs this afternoon in the upper 80s to near 90.
On Tuesday, we will see clearing skies and warm temperatures with highs near 90 degrees. The atmosphere will be more unstable by Tuesday night compared to today with increasing clouds and increasing humidity as the area of low-pressure strengthens. The humidity will be unusually high for this neck of the woods with dew points commonly in the 50s, which will make the days feel rather muggy and hot.
On Wednesday and into Thursday, that moist and unstable air mass will remain over the forecast area bringing a 20% chance of thunderstorms on Wednesday and Thursday with high temperatures near 90. This energy appears to be focused over the western weather zones and Cascades and it may be a rather active afternoon and evening west of a line from Colville to Wenatchee. These storms will be slow moving rain producers and the threat of flash flooding will exist especially in the Cascades. We could also see breezy and gusty winds squeezing through the Cascade gaps during the afternoon and evening hours on Thursday.
Then Friday through Sunday there is reasonably high confidence that the region will enter more of a progressive westerly flow pattern with temperatures moderating back toward normal with light winds and sunny skies. Under sunny skies, high temperatures this weekend will generally be in the mid 80’s.