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22 Oct, 4 tweets, 3 min read
This is the fire weather forecast I was hoping wouldn't come to pass, given all that has already transpired in 2020: Very strong offshore winds, coupled w/exceptionally low humidity & record-dry vegetation, will bring extremely critical wildfire risk Sun/Mon. 1/3 #CAwx #CAfire Image
This will likely be strongest & most widespread offshore wind event of season, & is reminiscent of extreme events in 2019 & 2017. Hardest-hit areas appear to be west slopes of Sierra Nevada (gusts of 70+mph) & SF Bay Area (widespread gusts 40-50mph; higher in hills). #CAwx Image
Exceptionally low atmospheric humidity (relative humidity of 5% or less and dewpoints below zero F) will accompany these strong winds. This will be a *cold* offshore wind event, and temperatures will drop precipitously (especially in mountains). #CAwx ImageImage
These truly extreme upcoming fire weather conditions, combined with record-dry vegetation for time of year, portend a dangerous period ahead. I would anticipate fairly widespread Public Safety Power Shutoffs by electrical utilities on Sun/Mon to prevent ignitions. #CAwx #CAfire

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More from @Weather_West

Daniel Swain Profile picture
7 Oct
New research led by @ggpersad & featuring @PabloWater. Using downscaled climate model simulations, we show that there is unexpectedly high inter-model agreement re: increasing extremity of California hydroclimate due to #ClimateChange. (1/n) link.springer.com/article/10.100… #CAwater
In general, climate models agree than an increasing fraction of California's overall precipitation will become concentrated into the most intense events--and that the most extreme precip events will themselves be substantially more intense. (2/n) link.springer.com/article/10.100… #CAwater
There is also agreement that CA's already pronounced precipitation seasonality will become even sharper--with more rain concentrated into winter months at expense of the autumn & spring. Consider the wildfire season implications... (3/n) link.springer.com/article/10.100… #CAwater #CAfire
Read 8 tweets
Daniel Swain Profile picture
21 Sep
Fire weather update: relatively mild (near avg) temps will continue for a few more days across California. Calmer winds will result in poor air quality, as visible this AM. A weak cold front with a few light North Coast showers possible mid-week. But then... #CAwx #CAfire (1/n)
There is unfortunately multi-model ensemble agreement that a very strong ridge will build near CA and the West Coast by end of Sept., bringing yet another major heatwave by early October to CA, OR, and adjacent states. #CAwx #ORwx #CAfire (2/n)
Early indications is that this early Oct event will have potential to bring record heat to CA and possibly other areas. This will coincide with weak offshore flow, so should spread all the way to coast and bring extreme wildfire burning conditions once again. #CAwx #CAfire (3/n)
Read 4 tweets
Daniel Swain Profile picture
7 Sep
You could write an entire meteorology textbook just based on the phenomena visible from this afternoon's wild satellite imagery looking down at the American West. (Thread) #CAwx #WAwx #ORwx #COwx #UTwx #MTwx #IDwx
Most prominent is incredibly strong early-season cold front plunging southward from Canada and currently stretching along a roughly east-west axis from Eastern Washington to North Dakota. Clouds are rapidly developing behind the front as cold air replaces a very hot airmass.
Next, there are numerous large wildfire smoke plumes visible in nearly every state not covered by clouds--including Washington, Oregon, California, Utah, Idaho, and Colorado. The total smoke volume is massive, and extends across most of the continental U.S.
Read 7 tweets
Daniel Swain Profile picture
21 Aug
Okay, time for a NorCal fire weather update. First, good news: fire activity decreased overnight due to development of shallow marine layer along immediate coast, and cooler temps inland. Next 24 hours, fire activity will be strongly diurnal (i.e.,like normal).#CAwx #CAfire (1/n) Image
The bad news: this is as good as things are going to get for a while. This wknd, ridge builds back in once again from east, suppressing marine layer and bringing hot/dry conditions inland (though will *not* be as hot as last record heatwave over past week). #CAwx #CAfire (2/n) Image
Then, slightly disconcerting news. Remnant moisture & instability from former Hurricane #Genevieve will approach CA from south on Sunday. Uncertainty remains, but right now it appears there is a real risk of *another* dry lightning event in NorCal Sun/Mon. #CAwx #CAfire (3/n) Image
Read 5 tweets
Daniel Swain Profile picture
21 Aug
Just did some rough math. It appears that we're closing in on 600,000 acres burned by lightning-sparked wildfires in Northern California *in just 7 days.* Nearly all such fires are still spreading rapidly. I'm truly at a loss for words. #CAwx #CAfires #CaliforniaWildfires
And there haven't even been any offshore winds driving these fires! Just absolutely stunning.
There is so much fire activity, include several *new* large fires today, that I think very few people have had the bandwidth to process the magnitude of what is going on in NorCal right now. It's no wonder that CalFire and local firefighting agencies are so overwhelmed.
Read 4 tweets
Daniel Swain Profile picture
16 Aug
Absolutely incredible footage of #LoyaltonFire #pyrovortex ("Fire Tornado") earlier today. Pretty sure this validates @NWSReno's Tornado Warning--which is, I believe, the first ever issued by @NWS specifically for a wildfire-generated pyroconvective event. #CAwx #CAfire #NVwx
To be clear: this is *not* first documented instance of a large-scale fire vortex. Devastating #CarrFire in 2018 near Redding, CA produced one of the strongest such events in recent memory, outside of a couple of previous events during Australian firestorms. (1/3) #CAwx #CAfire
Such events are not a new phenomenon--they have probably occurred during particularly intense wildfires under the right atmospheric conditions since...well, time immemorial. But I suspect these recent events have been more noticeable for two key reasons: (2/3) #CAfire
Read 4 tweets

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