Dr. Daniel Swain Profile picture
Sep 21, 2020 4 tweets 4 min read Read on X
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)
Seasonal outlook for Oct-Dec continue to suggest an elevated risk of lower than avg precip & warmer than avg temps for the rest of autumn in CA. I wish I had better news on wildfire front, but there's currently not much on horizon at the moment. #CAwx #CAfire (4/end)

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More from @Weather_West

Feb 7
Out today in @GlobalChangeBio is our (brief!) rapid-response piece on the broader context surrounding the January 2025 Southern California wildfires & relevance of wet-to-dry hydroclimate whiplash to fire both locally and globally on a warming Earth. [1/8] onlinelibrary.wiley.com/doi/full/10.11…
@GlobalChangeBio Coastal Southern California experienced an exceptional wet-to-dry "hydroclimate whiplash event" between May/June 2024 (following a second anomalously wet winter) and Dec/Jan 2024/5 (characterized by the driest start to season on record in many parts of the region). [2/8]  Figure panel from Swain e al. 2025. The relevant portion of the caption reads:  Map depicting the geographic scope and magnitude of the June 2024–December 2024 wet-to-dry hydroclimate whiplash event in southern California as measured using 6-month Standardized Precipitation and Evaporation Index (SPEI6) differences. The black rectangle region encompasses the region that experienced the most extreme fire weather conditions on January 7-8 2025, and the white open star depicts the approximate location of Los Angeles, CA.
@GlobalChangeBio This whiplash event caused a pronounced vegetation accumulation-then-desiccation cycle, adding more fuel for (potential) fires to come then drying it out to record levels for time of year--setting stage for destructive fires when strong winds arrived.[3/8]
onlinelibrary.wiley.com/doi/full/10.11…
Read 8 tweets
Jan 17
After becoming increasingly enmeshed in the wildfire world, you start to notice things about the way we've systematically altered our relationship with the natural environment in a way that has increased the risk of destructive fires. And then you stop being able to unsee them.
I've always lived in the American West, in different parts of California and on the Colorado Front Range. I've traveled throughout the West extensively; even as a child, fire was always there in the distance--a companion on family roadtrips, a backdrop to summer afternoons.
One of my earliest memories (fuzzy though it is; I was very young) was ash falling from the sky while out at a San Francisco park. The date? October 20, 1991--the day the devastating Oakland Hills fire tore through around 3,000 structures and killed 25 in the Berkeley Hills.
Read 23 tweets
Jan 11
Our paper on "Hydroclimate volatility on a Warming Earth" is out in Nature Reviews Earth & Environment. We assess existing scientific literature & conduct new analysis--concluding that "#HydroclimateWhiplash" is increasing due to #ClimateChange. [Thread] nature.com/articles/s4301…
"Hydroclimate volatility" refers to rapid transitions between unusually wet & dry conditions relative to local baseline. For quantitative analysis, we define a new "hydroclimate whiplash" metric using Standardized Precipitation & Evaporation Index (SPEI). nature.com/articles/s4301…Figure 1 from Swain et al. 2025. Caption: Location, date and impacts of select hydroclimate whiplash events from 2016 to 2023, and the corresponding magnitude of changes in the Standardized Precipitation Evapotranspiration Index (SPEI; shading). The brown shades represent wet-to-dry events and green shades dry-to-wet events. The events do not represent a comprehensive catalogue of all whiplash events but are illustrative of the breadth and diversity of geographies subject to such rapid transitions. Societally and ecologically consequential hydroclimate whiplash events can occur in virtually...
One key aspect of the framework for understanding such volatility is that it encompasses both "supply" & "demand" side of water balance--that is, not only precipitation (or lack thereof), but also evaporation (or evaporative demand). Precipitation doesn't tell the whole story!
Read 16 tweets
Jan 9
Is there a link between #ClimateChange & increasing risk/severity of #wildfire in California--including the still-unfolding disaster? Yes. Is climate change the only factor at play? No, of course not. So what's really going on? [Thread] #CAfire #CAwx #LAfires iopscience.iop.org/article/10.108…
There is rarely, if ever, a singular cause of complex disasters--so don't be fooled by disingenuous "straw man" binaries! For wildfire, encroachment into high risk areas, historical land management, & climate all matter (to contextually varying degrees). theguardian.com/environment/20…
What is the primary link between #ClimateChange and wildfire, both in CA specifically and more broadly globally? Vegetation moisture, and therefore its flammability (which includes propensity to ignition, combustion intensity, rates of spread, and etc.). nature.com/articles/s4155…
Read 23 tweets
Jan 1
Apropos of recent, ah, speculation...a few thoughts about #fog.

Fog is, simply, a shallow cloud that extends all the way to the ground. It's usually composed of condensed water droplets--though "ice fog," composed of ice crystals, can occur if it's cold enough. [Thread: 1/10]
#Fog usually forms when air cools to its dew point (i.e., when temperature decreases & relative humidity reaches 100%, causing air to become saturated,) and the air can no longer "hold" additional water vapor, which condenses out as (visible!) liquid droplets. [Thread: 2/10]
There are several processes that can cool air to its dew point & create #fog, including warm, moist air moving over a cool surface ("advection fog"), cold air moving over warm water ("steam fog"), and rapid cooling of the Earth's surface at night ("radiation fog"). [Thread: 3/10]
Read 10 tweets
Dec 14, 2024
A few notes on this morning's #Tornado Warning for San Francisco from @NWSBayArea (I am still traveling, so my live interactions are still somewhat limited):

1) Yes, a formal warning was issued by NWS for San Francisco this AM based on a suggestive radar signature. #CAwx [1/7]
@NWSBayArea 2) So far as I know, this was indeed first such warning ever issued for SF proper (but not first tornado in SF!). Other similar warnings have been issued elsewhere in Bay Area under similar conditions (i.e., offshore waterspout potentially moving ashore as tornado). #CAwx [2/7]
@NWSBayArea In 2005, for example, an EF1 tornado occurred in South Francisco, causing some notable damage. Other more significant tornado events have occurred elsewhere in the Bay Area and NorCal; although rare, they are not unprecedented. #CAwx [3/7]sfgate.com/bayarea/articl…
Read 7 tweets

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