FastCast—Monday, Oct. 17 to Friday, Oct. 21:
After a truly historic day, weatherwise, on Sunday, a big cooldown is ahead on Monday, although smoke from local wildfires will remain through this week. Temperatures across the lowlands obliterated existing records, as easterly winds and strong offshore flow boosted highs into the mid to upper 80s, with some locations hitting the low 90s. Onshore flow briefly returned on Sunday night to bail us out of the strong offshore flow. Monday’s highs will be 10-30 degrees cooler than Sunday, reaching the low to mid 60s, with partly cloudy skies. Tuesday, Wednesday, and Thursday will be similar, with highs in the mid to upper 60s. Expect lows in the mid 40s to near 50º. The lingering effect of this weekend’s weather will be the increase in fire activity on both new and existing fires in the Cascades. With weak offshore flow expected, degraded air quality and surface smoke will continue this week, especially near wildfires. Stay tuned to each blog for information on smoke. A significant pattern change will arrive on Friday, with rain and highs dropping to the 50s. Stay tuned for more information on that later this week.
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Continue reading the full blog below!
Sunday brought strong offshore flow, increased wildfire activity, and temperatures obliterating previous records.
Seattle (Sea-Tac) reached 88º on Sunday, destroying the daily record (72º), and coming 1º shy of the all-time October record of 89º. Below are Sunday’s highs.
The number of locations that reached 80º+ degrees is extraordinary for October. Now, look at the map below, showing only locations that reached 85º+.
Many locations in the central lowlands eclipsed 85º, with some locations directly exposed to gap winds reaching the low 90s…in October!
Thankfully, a big cooldown is coming. Below is the NAM forecast, showing the temperature change from 1 PM Sunday to 1 PM Monday.
Notice that temperatures in the lowlands will be 15-30 degrees cooler on Monday. What will those highs be? Let’s take a look at the NAM forecast below.
Highs in the lowlands will drop to a much more seasonable low to mid 60s. Eastern Washington will still be warm, in the mid to upper 70s, along with the upper 60s to low 70s in the Willamette Valley.
Now for the smoke…let’s take a look at the upcoming conditions. Below is the HRRR smoke forecast for 8 AM Monday.
Surface smoke remains in the lowlands, especially north of Everett. The Cascades and the foothills will have heavier smoke.
By 4 PM Monday, smoke plumes from new and existing fires have grown.
It is possible that some of the thicker smoke will make its way into the lowlands, so stay tuned to PurpleAir (link on the right side of the blog) for rapid updates.
Smoke will remain on Tuesday, as seen in the 8 AM Tuesday forecast below.
Notice areas of heavier surface smoke encroaching into the foothills, and very heavy smoke in the Columbia River Gorge. It’s safe to say that degraded air quality will remain through Tuesday.
Below is the 4 PM Tuesday forecast.
By Tuesday afternoon, smoke has increased in coverage, especially in the Cascades and Willamette Valley, with heavy surface smoke in SW WA and the Portland/Salem areas.
It is important to note that this smoke forecast doesn’t reflect future changes in wildfire behavior. Continued light offshore flow will bring degraded air quality to the lowlands through this week, with areas downwind of wildfires having the worst air quality.
Stay tuned for more updates on the smoke situation and the significant pattern change — to rain and much cooler/stormier weather — expected to begin on Friday.
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