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Dr. Daniel Swain Profile picture
Dr. Daniel Swain
@Weather_West
Weather and climate scientist focused on extreme events like floods, droughts, & wildfires on a warming planet.
14 subscribers
Jul 16 • 19 tweets • 4 min read
The discourse surrounding precipitation changes in a warming climate (both public discussion and even scientific one at times) is complicated by widespread conflation of changes in averages vs extremes (and also actual vs *potential* evaporation/evaporative demand). [Thread] Increased temperatures rapidly raises "ceiling" on both precipitation & evaporation intensity--but same is *not* true for typical/average values of either! Regional mean precip can increase or decrease with warming, and actual evaporation is constrained by local H20 availability.
Jul 13 • 30 tweets • 5 min read
And now: A thread regarding my thoughts on "1.5°C"--not only as a Paris Agreement target, but also re: relevance to recent #climate events & overlaps (or not) w/geophysical realities. (This was originally written as a response to a journalist, who used excerpts in their article.) Time series of Earth's global average temperature over time, between 1850 and 2024, as calculated by the Berkeley Earth research group. It depicts the Earth's average temperature as having risen to near or above 1.5C above the late 1800s average by 2023-2024. First and foremost, it's absolutely true that every tenth of a degree matters; each increment of global warming will bring a relatively larger increase in adverse societal and ecological impacts than the last.
Jul 5 • 14 tweets • 3 min read
There have been claims that NOAA/NWS did not foresee catastrophic TX floods--but that's simply not true. This was undoubtedly an extreme event, but messaging rapidly escalated beginning ~12 hrs prior. Flood Watch mid PM, "heads up" outlook late PM, flash flood warnings ~1am. As always, this is not to blame the victims! Quite the opposite; this truly was a sudden & massive event and occurred at worst possible time (middle of the night). But problem, once again, was not a bad weather prediction: it was one of "last mile" forecast/warning dissemination.
Jun 16 • 9 tweets • 3 min read
Some perspective on recent warmth over past month in California. Many folks, most of whom live within ~20 miles of the coast, have been asking: where's all this hot weather I keep hearing about? Well...the short answer is inland & across hills/mountains. [Thread] #CAwx #CAfire Map from climatetoolbox.org depicting observed temperature departures from average over the past 30 days. In this map, departures from average for daily average temperatures are plotted across the western U.S. (with dark red colors depicting record/near-record warmth and blue colors depicting below average temperatures). In fact, the past ~30 days have actually been near record-warm (yes, yet again!) across a substantial portion of the foothills & higher mountains ringing Central Valley, plus the Imperial Valley (which is a very hot place to begin with!) However... #CAwx #CAfire
Apr 17 • 8 tweets • 2 min read
Amer. Meteorological Soc. (@ametsoc) just issued a (fully justified) dire statement regarding rapidly accelerating & potentially disastrous efforts to decimate weather & climate enterprise in U.S. If implemented, this would cost many lives & cause major/ long-term economic harm. @ametsoc "In effect, the scientific backbone and workforce needed to keep weather forecasts, alerts, and warnings accurate and effective will be drastically undercut, with unknown — yet almost certainly disastrous — consequences for public safety and economic health."
Feb 28 • 11 tweets • 2 min read
The mass firing of both new hires and recently promoted senior staff within #NOAA, including mission-critical and life-saving roles at the National Weather Service (#NWS), is profoundly alarming.
1/11 It appears that staff fired today include meteorologists, data scientists responsible for maintaining weather predictive models, and technicians responsible for maintaining the nation’s weather instrumentation network (among many others).
2/11
Feb 21 • 5 tweets • 2 min read
A period of very warm mid-winter conditions appear likely for much of California and portions of the interior West in late Feb. A strong ridge will form during this period, with large-scale subsidence & warm air advection allowing for a genuine winter "heat wave" next week. #CAwx Snapshot from ECMWF ensemble for next week, which depicts a narrow-ish but strong ridge centered along the West Coast that will bring a period of mild weather/anomalous winter warmth. Temps in 80s will be widespread in SoCal, & even 90s are possible. T-shirt and shorts weather will also extend into NorCal and beyond (well into 70s), as well as desert SW (where late spring-like temps in 90s are likely). Late Feb records may be broken in some places. #CAwx #AZwx Temperatures will be far above average, and in some cases record warm for late February, across portions of the West Coast next week. This ECMWF ensemble snapshot of temperature anomalies captures that, highlighting southern CA and the Desert SW as particularly anomalous hotspots.
Feb 7 • 8 tweets • 3 min read
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.
Jan 17 • 23 tweets • 4 min read
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.
Jan 11 • 16 tweets • 6 min read
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...
Jan 9 • 23 tweets • 7 min read
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…
Jan 1 • 10 tweets • 2 min read
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]
Dec 14, 2024 • 7 tweets • 2 min read
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]
Nov 18, 2024 • 7 tweets • 3 min read
A strong, prolonged, very moist, and relatively warm #AtmosphericRiver event, in conjunction with rapidly-strengthening #BombCyclone (yes, that's the term!), will bring major rain (and, locally, wind) impacts to OR/NorCal this week. Flooding is likely. #CAwx #ORwx #CAwater [1/6] Snapshot of 3-day accumulated IVT (integrated vapor transport) along the West Coast of North America from the GFS model. It depicts extremely high 72-hr accumulated IVT values aimed at far northern California coast. First, a low pressure system west of OR and WA will undergo explosive deepening (rapid strengthening, known as "bombogenesis") over the next 2 days. It may become one of the strongest low pressure systems on record in this region. (~940mb) #CAwx #ORwx #CAwater [2/6] A map plot depicting the relative anomalousness of surface pressures over the northeastern Pacific Ocean later this week. There is a region of red west of WA and OR, indicating that the upcoming storm may bring some of the lowest surface pressures on record in this region.
Nov 16, 2024 • 6 tweets • 3 min read
Signs of some "big time" weather for TBD portions of U.S. West coast over next 10 days. A major #AtmosphericRiver, & perhaps a short sequence of very wet ARs, will affect some section of coast between NorCal & WA--perhaps bringing very heavy rain accumulations. #CAwx #ORwx [1/6] Map of ECMWF ensemble average precipitation accumulated over the next 10 days in the U.S. West. Heavy accumulations are depicted from far NorCal into Oregon and Washington. First, it's important to consider the broader context. This autumn to date has been very (anomalously) dry across most of CA (except for far northern parts of state), but much less so in PacNW. It has also been broadly warmer than average across the West. #CAwx #ORwx [2/6] Map of temperature anomalies for the past 60 days across the U.S. from climatetoolbox.org. Nearly all areas are depicted as being warmer than average.
Map of precipitation anomalies for the past 60 days across the U.S. from climatetoolbox.org. Nearly all areas in California are depicted as being drier than average except for the northenrmost part of the state.
Oct 8, 2024 • 9 tweets • 2 min read
We are witnessing a genuinely extraordinary, and regionally quite deadly and destructive, period for extreme #weather in the United States. And, quite frankly, the fingerprints of #ClimateChange are all over what has transpired in recent weeks and may yet occur in coming days. An incredible, ongoing, & increasingly record-shattering heatwave has plagued much of Southwestern U.S. for *weeks* now. Phoenix has now seen *2 consecutive weeks* with record temperatures *every day.* Many other locations have set new Oct and/or "heat streak" records.#CAwx #AZwx
Sep 28, 2024 • 19 tweets • 3 min read
The images and stories just beginning to emerge from eastern TN and western NC in the aftermath of widespread catastrophic flooding wrought by #Helene are genuinely horrifying, and the full scale of the disaster is likely as yet untold. #TNwx #NCwx [Thread: 1/n] 20-30 inches--and perhaps locally 40+ inches--of rain fell along highest ridges of the Southern Appalachians due to 1-2 punch consisting of extreme "predecessor rain event" (PRE) that was historic in its own right followed by further extreme rain directly from #Helene. [2/n]
Aug 19, 2024 • 4 tweets • 2 min read
For the first time since June in many parts of California and the broader Southwest, *cooler* than average temperatures can be expected for the next week, thanks in part to arrival of a *second* anomalously deep August low pressure system over NorCal Thu/Fri. #CAwx [1/4] ECMWF weather model depiction of anomalously low GPH near California later this week, representing an unusually deep summer low pressure center. Another round of widespread rain & possible t-storms will occur in western WA & OR. In far NorCal, esp. northern mtns (Shasta region), some decent showers & t-storms are possible. Few showers/isolated thunder may reach farther south than last event--locally to I-80 corridor. #ORwx #WAwx #CAwx [2/4]ECMWF weather model depiction of cumulative precipitation across the American West this week, which shows a widespread wetting rainfall across the Pacific Northwest with more limited precipitation across portions of the northern third of California.
Apr 7, 2024 • 23 tweets • 4 min read
For folks in Colorado wondering what the heck is going on with #Xcel's large-scale pre-emptive power line de-energization to avoid wildfire ignitions during high wind events, I wanted to share a some thoughts as a scientist who studies climate/weather/wildfire. #COwx [1/n] The first utility-scale "Public Safety Power Shut-offs" (#PSPS) in response to fire risk of which I'm aware began in 2010s in California in response to catastrophic wildfire events in urban interface sparked by power infrastructure during extreme fire weather/wind events. [2/n]
Feb 5, 2024 • 10 tweets • 4 min read
I wanted to reiterate some recent findings from our own research specifically addressing extreme #AtmosphericRiver storms in a warming climate.

1) CA will more extreme ARs in a warming climate, mainly (~80%) due water vapor increases. #CAwx #CAwater science.org/doi/10.1126/sc…
Image 2) Extreme CA ARs in a warming climate will not only be more intense, but they may also have preferentially more southerly (deep subtropical) origins (like present one!). #CAwx #CAwater science.org/doi/10.1126/sc…
Image
Dec 5, 2023 • 13 tweets • 3 min read
Scientific institutions must create--and sustain--new kinds of roles so that researchers can provide the deep public engagement necessary to respond effectively to the escalating impacts of #climate change. The status quo isn't working. [Thread: 1/n] nature.com/articles/d4158… My own role as a climate scientist-communicator is highly unusual in the academic world: I'm a practicing scientist who spends a large fraction (now over half) of my time engaging the public, and the rest of my time actually conducting research and writing papers. [2]