July 5, 2024
What To Expect During the Upcoming Heatwave
By Joseph Renalds
Yesterday high temperatures reached into the low 80s across much of western Washington with a few exceptions near large water bodies. However, now that July 4th has come and gone the summer heat is moving in. Over the next week, high temperatures will be above 80 degrees each day, some above 90, and struggle to get below 60 degrees at night.
What Is Causing the Heatwave?
This warmup is the result of an atmospheric setup that we typically see when temperatures get hot this time of year. Firstly, we need an upper level ridge that steers the storm track away from the Pacific Northwest. We can see the development of the ridge on this water vapor satellite image as the clouds are being pushed north of Washington and dry air dominates over the West Coast. 
Next we need to turn off the natural air conditioning we typically receive through onshore flow. While many heatwaves are associated with an easterly wind, this one differs slightly due to the thermal trough remaining more to our south in Oregon. Northerly winds can still warm us up quite a bit since they are not coming off the ocean, but not as strongly as easterly winds.
How Warm Will It Get?
Today we got into the mid-to-upper 80s across western Washington and it will get progressively warmer through Tuesday. With high temperatures expected to break the 90 degree mark on Sunday, Monday, and Tuesday daily records will be challenged at SeaTac Airport.
Temperatures will also remain warm overnight with lows not getting below 60 for several days. This will be exacerbated by the “urban heat island” effect which is caused by concrete and asphalt emitting heat energy long after the sun goes down.
We will get a break from the 90s by the middle of next week, but summery weather looks to continue. The National Blend of Models shows high temperatures reaching at least 80 degrees for the next 10 days as ridging continues to dominate the region. Were this forecast to verify, the streak of 80+ degree days would be the sixth longest streak since records began at SeaTac airport.
Conditions like this will lead to the drying out of vegetation so be aware of this if you are doing anything fire related. The National Weather Service has issued a Red Flag Warning for parts of the Cascades along with a Heat Advisory. Fires are already starting in eastern Washington and I think we all want to delay the fire/smoke season as much as we possibly can.
We will bring you any updates to the forecast as they come, but for now Huskies, make sure to stay safe and cool!
