August 18, 2023

Heat Moves Out, Smoke Moves In

Last updated 3:50 PM, Friday, August 18th, 2023 

By Joseph Renalds

Happy Friday Huskies!

The heatwave finally being over is perfect for a Friday. This last week added four more 90 degrees or higher days to the 2023 tally bringing the total up to six. We can now put this heat in the past as our natural air conditioning, courtesy of the Pacific Ocean, moves back in.

Now that the much welcomed morning clouds have burned off, we will see temperatures only getting into the upper 70s this afternoon. The onshore flow that is bringing us relief from the heat is also increasing fire danger on the eastern side of the state as it pushes through the mountains. Westerly sustained winds of 15-25 mph, gusts up to 40 mph, and low relative humidity have prompted a Red Flag Warning to be issued for much of eastern Washington through late Friday night.

Our weather this weekend on the westside has its own twist and is also related to wildfires. Starting around midnight tonight, winds will shift northeasterly as seen in this morning’s run of the UW-WRF. This offshore wind will bring in smoke from wildfires in the Cascade mountains and British Columbia that has for the most part stayed away from the Seattle area.

A model that is very helpful when it comes to smoke prediction is the HRRR (High Resolution Rapid Refresh). Let’s use this morning’s 18z (11am) run to see how the smoke progresses. The blue colors represent light smoke while the yellows, reds, and purples depict higher concentrations of smoke. 

At 12AM on Saturday, most of the smoke is still on the eastside of the state.

By 8AM, the smoke is pushing into the Cascades from the east. This may be your last chance to cool your homes down by letting cool air in through the windows before air quality will be impacted.

At 12PM, you will see the sun start to turn that eerie red color we have all sadly gotten used to as smoke first moves in over head. The HRRR smoke model cross section, shown in the second image below, models what a vertical slice of the atmosphere would look like at noon. The jagged features are the Olympic (left) and Cascade (right) mountains. You can see pretty clearly that there will be a layer of smoke around two-thousand feet above the surface.

Now I wish I could say that the smoke would just stay above us, but I cannot. By 4PM, smoke will be mixing down to the surface and impacting air quality. The smoke looks to worsen through the night and will be the worst during the daytime on Sunday.

How much mixes down is what will determine the impact on our air quality. The Puget Sound Clean Air Agency is predicting “the air quality will likely reach MODERATE or UNHEALTHY FOR SENSITIVE GROUPS on Saturday; and UNHEALTHY or worse at times on Sunday.” The National Weather Service Seattle has also issued an Air Quality Alert for most of the west side which goes into effect at 9AM tomorrow and goes through noon on Monday.

The good news is that this smoke event does NOT look to be a long lasting one. Winds look to switch back onshore from the SW through the lowlands late Sunday night. There will likely be smoke around on Monday, but it will clear out as the day goes on.

Aside from smoke, the weekend looks nice temperature wise. The lows will be in the upper 50s and highs in the low 80s. The high temperature on Sunday is a bit tricky to pin down because the smoke could keep it a few degrees cooler than it otherwise could be. 

The other big story on the west coast right now is of course Hurricane Hilary, which is currently a Category 4 storm churning to the south of Cabo San Lucas. It is heading toward southern California where a Tropical Storm Watch is currently in effect for the first time ever in that area. The last time a tropical storm made landfall in California was 1939. While the storm will not be as strong as it is now when it reaches the coast, it will still bring a massive amount of moisture and flooding into the desert southwest. Its remnants will also cause flooding concerns into Idaho and portions of eastern Washington and Oregon early next week. 

I hope you have a good and safe weekend Huskies!

 

Reach forecaster Joseph Renalds at theuwdawgcast@uw.edu, on Twitter @TheUWDawgcast, or on Instagram @uwdawgcast.