Daniel Swain Profile picture
Feb 17 3 tweets 3 min read
October and December were extremely wet in parts of California (record wet in some parts of NorCal). But the most recent ~45 day stretch (Jan 1-Feb 17) has been among driest mid-winter periods on record most of CA, NV, UT, and portions of adjacent states. #CAwx #CAwater (1/3) Image
This has yielded in a seasonal "percent of average" precipitation map that is pretty misleading. Most of CA has slipped slightly below avg precip for the season to date--except for narrow swath along I-80 corridor that experienced the extreme Oct #AtmosphericRiver. #CAwx (2/3) Image
Yet hydrologic/landscape conditions--inc. surface reservoirs, soil moisture, streamflow, & vegetation aridity--are at extremely dry levels for mid-winter. This is due to 1) ongoing long-term drought and 2) the recent 6+ week record dry/warm & windy spell. #CAwx #CAWater (3/3) Image

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More from @Weather_West

Feb 19
Some mixed news on CA weather front over next couple of weeks. First, by Monday, another "inside slider" system will bring another burst of cooler & winder conditions statewide. Once again, some Sierra snow showers are possible, but most places stay dry. #CAwx #CAwater Image
Midweek, however, an even colder airmass and associated low pressure center will slide down the coast slightly farther to the west. This system, although still quite dry, stands a better chance of bringing convective activity (scattered showers/isolated thunder) statewide. #CAWx ImageImage
The biggest impact from this mid-week system, outside of some additional modest Sierra snow accumulations and a few pockets of accumulating small hail showers at lower elevations (like last week in SoCal), will be a dramatic shift toward much colder temperatures. #CAwx Image
Read 6 tweets
Feb 19
Very compelling and timely new analysis out in @Nature led by @DrBalch and featuring co-authors including @climate_guy, @_mikoontz, and @peedublya on how #climate warming is weakening the global barrier to nighttime fire. nature.com/articles/s4158…
They find a strong trend toward increased nighttime fire activity across most regions globally, driven primarily by increases in overnight vapor pressure deficit (VPD). In western U.S., number of flammable nights have increased by 45% in past 4 decades! nature.com/articles/s4158…
These quantitative findings strongly corroborate widespread anecdotes from wildland firefighters, who have reported remarkable increases in nighttime burning activity that seriously challenge historical fire management strategies--which assume fires usually "lie down" at night.
Read 6 tweets
Feb 7
Folks with self-described severe climate anxiety now reach out to me (& other climate scientists I know) essentially every week. It is often hard to know how to respond, since climate scientists are not trained clinical psychologists. (1/12)
The nature and volume of these requests can become overwhelming for those not professionally equipped to help people in that way. This is especially frustrating since many of these folks have actually sought professional help, yet those practitioners have been dismissive...(2/12)
...telling people that climate change won't affect them personally, or that it's "not as bad as you read about in the news," or that there's nothing they can do about it, so you need to "let it go." Well, as many folks who are paying attention realize, none of this is true.(3/12)
Read 13 tweets
Jan 5
Our new study on co-occurring air pollution extremes (ozone & PM2.5), led by @wx_statman & w/co-authors including @ClimateChirper, @climate_guy, & @Weather_West, is out today in @ScienceAdvances. We find large increases in co-occurrences in U.S. West.(1/n) science.org/doi/full/10.11…
Increasing air pollution co-occurrence trends are widespread across the U.S. West over the last ~20 years, and encompass almost all of the West's major population centers from the Rocky Mountain Front Range to the Pacific Coast. (2/n) science.org/doi/full/10.11…
This increasing trend in co-occurring high levels of two key classes of air pollutants, ozone (photochemical pollution; think smog) & PM2.5 (fine particulate matter; think smoke) is almost entirely due to increasing frequency of extreme PM2.5 events. science.org/doi/full/10.11… (3/n)
Read 14 tweets
Dec 31, 2021
Some photos, footage, and commentary from yesterday's devastating #MarshallFire in Boulder County. All photos and videos taken at various points along South Boulder Road (north side of the fire, looking south, on 12/30/21). Winds were gusting around 90mph at the time. #COwx (1/4)
Fire behavior was as you'd expect in grass/brush amid extreme wind & drought conditions: rapid rates of spread, continuous spotting and periodic sheeting fire. Fire jumped 6-lane Hwy 36 like it was nothing, and there was a 2+ mile long active fireline. #MarshallFire #COwx (2/4)
Behavior and dynamics of the fire plume were fascinating...and scary. A nearly horizontal plume, tilted by extreme westerly downslope winds, transitioned into a shallow pyroCu plume at the top of a hydraulic jump within a pronounced mountain wave. #MarshallFire #COwx (3/4)
Read 5 tweets
Dec 30, 2021
Conditions along South Boulder Road right now. #marshallfire #COwx
Unfortunately can confirm that numerous structures are now burning, many of them homes. This is an extreme/dangerous wildland-urban interface fire. Mainly Superior/Louisville. Gusts in excess of 80mph continue.
Read 4 tweets

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