Well below average temperatures were observed throughout the Inland Northwest Friday as an upper level trough makes its way through British Columbia. The Tri-Cities recorded a high of 84° on Friday. The average for this time of year is in the mid 90s. Temperatures warm some Saturday, but will only be near average.
The bulk of the incoming heatwave falls Sunday through Wednesday as an upper level low moves closer to the coast and a ridge of high pressure builds inland. This pattern will draw warmer weather into the Pacific Northwest from California and Nevada. This contrasts from the heat wave that came at the end of July, which was driven by an anomalously strong ridge of high pressure dominating the weather pattern across the entire Western United States.
Because the larger weather pattern is different from the one that caused the recent heat wave, this round is not likely to be as hot or last as long. Highs in the Columbia Basin should peak Monday and Tuesday. As of Friday evening the National Weather Service was calling for a high around 105° in the Tri-Cities.
This matches well with model guidance. When taken together, models give a 50% chance of reaching at or above 105°, with most models coming in between 104° and 107°. Don’t expect new records out of the heat wave. Records currently stand at 112° and 109° for Monday and Tuesday respectively, both set in 1898.
As of early Saturday morning, no heat alerts are in place for the Tri-Cities, Yakima, or surrounding areas (though the National Weather Service in Spokane has issued some for their area). In their forecast discussion issued early Saturday, the National Weather Service in Pendleton indicated that these alerts are being considered. I wouldn’t be surprised to see something issued as early as during the day on Saturday. That said, regardless of what alerts the National Weather Service chooses to issue (if any), temperatures will probably be hot Monday and Tuesday.
From Wednesday into Thursday the upper level low pressure system morphs into an upper level trough as it gets absorbed into the general flow pattern. This change in the pattern is forecast to sweep it across the Pacific Northwest to bring another cool down to the region. Right now it seems that it won’t be as impressive as the cool down that brought highs in the 80s on Friday, but temperatures closer to average can be expected for the second half of the week.
It is important to note that models are struggling with several aspects of this metamorphosis. The low has been sitting offshore now for nearly a week, and early on weather models wanted to sweep it across the region as part of the current cool down. I am feeling increasingly confident that the low will become a trough and be swept across the Northwest sometime Wednesday to Friday, but exact details on timing and strength (which would make big differences in weather on the ground) are hard to come by.
Into the following weekend and beyond, there isn’t really a strong signal either way for what to expect. You can check what the models are saying by heading over to my Forecast Map page.
