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Daniel Swain

@Weather_West

26 Oct

https://twitter.com/psuweatherman/status/1320737633782263809

First, some good news: NorCal seems to have made through initial (extreme wind) phase of this critical fire weather event relatively unscathed. Few new small fires, but nothing unmanageable. A few thoughts as to why this was the case: #CAwx #CAfire

https://twitter.com/psuweatherman/status/1320737633782263809

Very strong to extreme winds and exceptionally low humidity did materialize, despite an initial delay. A peak Bay Area gust of 89mph (with fairly widespread gusts above 50-60 mph), and peak Sierra Nevada gusts well over 100mph, were recorded. #CAwx #CAfire

In some spots, extreme winds did indeed mix down to low elevations (interior North Bay Valleys; Oakland Airport; San Francisco; Half Moon Bay). But some locations closer to sea level saw little wind,so sea level gusts were somewhat less widespread than initially anticipated.#CAwx

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Daniel Swain

@Weather_West

22 Oct

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

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

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

Read 4 tweets

Daniel Swain

@Weather_West

7 Oct

@ggpersad

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

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Daniel Swain

@Weather_West

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)

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Daniel Swain

@Weather_West

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

@Weather_West

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)

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)

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)

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