There is a chance of showers for the Tri-Cities in place through Wednesday thanks to a deep low pressure system that is lazily moving across the Western United States. Rain chances drop off significantly Sunday night, but we can expect to see periodic light rain and drizzle for the next several days.
The presence of the low itself is enough to allow some vertical movement in the atmosphere, which will be aided by daytime heating. Dew points will remain right around 50° through Tuesday, so there will be plenty of moisture available to be transported up creating convective shower activity. Because one of the main drivers will be daytime heating, much of this will occur in the afternoon and evening, dying off after sunset.
Most of the activity for Eastern Washington and Eastern Oregon will be around mountainous areas thanks to orographic lift, which is the term used to describe when terrain forces air to rise. Storms whose formation is aided significantly by orographic lift will likely dissipate as the enter the Columbia Basin since moving into flatter areas removes that source of vertical motion
There is strong agreement between models for the general pattern in place over the Pacific Northwest early this week (the presence of the large upper-level low), but there is a lot of variability between models when it comes to where and when storms will develop.
An example of this uncertainty is the image above. They represent what these two models think doppler radar imagery will look like at 2pm Monday, and they are clearly not on the same page. The NAM (on the left) has an area of strong showers moving into the Columbia Basin with light rain over Central Idaho. The HRRR (on the right), however, has a small number of isolated and weaker showers in the Columbia Basin with copious amounts of rain in the Hell’s Canyon region. The HRRR also has more activity in the Cascades and Okanogan.
This is not surprising given the meteorologic setup in place over the region. The science just isn’t to the point where I (or anyone else) can say who will get rain out of this system, when they will get it, and how much they will get. For now, we will have to be satisfied with knowing that there will be showers and thunderstorms wandering about Eastern Washington and Eastern Oregon.
One thing that would help improve weather forecasts is a new radar site in Central Oregon. This is the area where a we can expect a decent number of showers and thunderstorms to form before moving toward the Tri-Cities and they are almost completely out of range for our existing network. Good low-level radar data there would improve the models, something which I discussed at length in this post.
Looking at Wednesday and Thursday, our friendly neighborhood low pressure system will interact with a new one as it heads northeast into Alberta and Saskatchewan. This should help to keep temperatures on the cooler end of things, but current indications are that rain showers will be confined to in and near mountain areas. This is still a little ways out, but I’ll be keeping tabs on it and will be sure to keep you updated over on Tri-Cities Weather on Facebook as well as on Twitter. You can also check current radar and lightning data right here on my website by clicking this link.
