FastCast—Thursday, July 6 to Monday, July 10:
After the hottest day of 2023 so far (and first 90º+ day in Seattle) on Wednesday, another hot day is expected on Thursday, before some cooling brings temperatures down a bit with some additional cloud cover. In the lowlands, expect Thursday’s highs to reach the mid to upper 80s, with isolated highs in the low 90s and areas near the water remaining in the upper 70s to low 80s. Onshore flow will increase slightly late on Thursday, but it won’t be the heat-wave-ending marine push we’re used to. Instead, there will be a bit more cloud cover, with partly cloudy conditions on Friday and Saturday. High temperatures will drop to the upper 70s to low 80s in the lowlands, with locations close to the water staying in the mid 70s. By Sunday, temperatures will increase once more, with sunny conditions and highs back in the mid 80s. Monday looks to bring a marine push and highs dropping to the mid 70s to low 80s, with overcast conditions in the morning. Expect lows steadily in the low to mid 50s, except in the mid to upper 50s in the most densely populated areas. Additionally, smoke will remain with us through at least Thursday, with light surface smoke and smoke aloft that will bring moderate air quality (low risk to most everyone, except the most sensitive). Smoke will become more relegated to the mountains and areas downwind of local fires by Friday. There is no rain in the extended forecast, except a chance of mountain thunderstorms, which can have interesting cumulonimbus clouds that can frequently be seen across the lowlands!
(Check the bottom of the blog for a look at air quality during peak July 4th fireworks!)
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Continue reading the full blog below!
Hot weather will continue across the state on Thursday, after Seattle recorded its first 90º+ day of 2023 on Wednesday. Let’s take a look at the forecast.
Below is the European model forecast for Thursday’s highs.
Expect lowland highs in the mid to upper 80s, with isolated areas reaching the low 90s, and areas near the water remaining in the upper 70s to low 80s. The coast will drop to the low to mid 60s, Eastern WA will scorch in the upper 80s to low 100s, and the Portland area will be hot as well, in the upper 80s to low 90s.
The lowlands will see a noticeable cooldown on Friday, as seen in the European model forecast below.
The lowlands will cool to the upper 70s to low 80s on Friday, which will be noticeably less hot than Thursday. The coast will drop a bit more into the low 60s, but notice that Eastern Washington actually gets slightly hotter, increasing into the low 90s to low 100s. The Portland area will get a bit cooler as well, with highs dropping to the low to mid 80s on Friday.
Finally, let’s take a look at Saturday’s highs, also from the European model.
Saturday’s highs are almost a carbon copy of Friday’s, with the lowlands remaining in the upper 70s to low 80s (except in the low to mid 70s near the water), the coast remaining in the low 60s, and Eastern WA remaining in the low 90s to low 100s.
Overall, the lowlands will cool going into Saturday, as will the coast and the Portland area, and Eastern Washington will remain hot into the weekend.
Next, let’s take a look at forecast lows across the state, an important indicator of nighttime heat relief. Below is the European model forecast for lows on Thursday morning.
Expect lows in the lowlands to drop to the upper 50s to low 60s, except a bit cooler in outlying areas. Notice how warm it remains in Eastern Washington overnight, only cooling into the mid 60s to near 70º for most areas.
Let’s take a look at Friday morning’s lows as well, seen below from the European model.
Notice the lowlands are a bit cooler on Friday morning, with lows in the mid to upper 50s. Eastern WA is still quite warm, with lows only dropping to the low 60s in the north to the upper 60s to low 70s in the south.
Finally, let’s take a look at the smoke forecast. First, we’ll look at surface smoke, then smoke aloft (known as vertically integrated smoke). Below is the HRRR model forecast for surface smoke at 8 AM Thursday.
Notice light surface smoke across the entire state on Thursday morning, with the exception of the coast. Areas with surface smoke will have air quality degraded into the “moderate” category.
Below is surface smoke by 6 PM Thursday.
Surface smoke has thinned out a bit by Thursday evening, except downwind of local fires, as seen in the graphic. As onshore flow picks up, smoke from local fires will accelerate across the region from west to east. This will be most notable around the Tunnel 5 Fire just west of White Salmon, WA, in the Columbia River Gorge. Areas east of this fire will have degraded air quality. This same effect is possible, but to a lesser extent, for areas east of the McEwan Fire (NE of Shelton), with somewhat more degraded air quality possible for areas from Shelton to Enumclaw, including Gig Harbor, Tacoma, Auburn, and Federal Way.
Finally, let’s look at smoke aloft (vertically integrated smoke), which is what causes our deep blue skies to become hazy. Below is the HRRR forecast for smoke aloft at 8 AM Thursday.
Light to moderate concentrations of smoke aloft are expected across the entire state on Thursday morning. This type of smoke has no impact on air quality, except high up in the mountains, and is more notable for obscuring the skies and limiting visibility toward the horizon.
By 6 PM Thursday, smoke aloft remains mostly the same.
Concentrations are becoming lighter on the coast, but remain similar across the rest of the state, which means a hazy day is expected on Thursday.
Remember to stay cool, stay hydrated, and monitor air quality (links under “Helpful Weather Websites” on the right side of the blog). Updated information on the Tunnel 5 Fire in the Columbia River Gorge can be found by clicking here (or here: Tunnel 5 Fire InciWeb Page).
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Below is a screenshot from the PurpleAir air quality map around 11:50 PM on July 4th. Notice how nearly the entire region has unhealthy to hazardous air quality (140-500+) due to smoke from fireworks.
For more information on why air quality was so bad this year, be sure to read Cliff Mass’s most recent blog post on this topic:
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