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Dr. Daniel Swain Profile picture
@Weather_West
Mar 8, 2020 • 3 tweets • 3 min read • Read on X
A low pressure system off coast will move inland on Tuesday, bringing a widespread rain event to SoCal. This will be a warm/moist system with only modest dynamics, so almost everyone from Central Coast southward will see moderate rainfall of 0.5-2 inches. #CAwx ImageImage
However, this system does have plenty of moisture (associated w/an #AtmosphericRiver focused to the south and east of CA) and some respectable atmospheric instability. As a result, there's actually a decent chance of thunderstorms w/brief heavy downpours on Tues in SoCal. #CAwx Image
NorCal, unfortunately, will only see scattered showers from this system. A slightly more promising chance of colder showers (& maybe some Sierra Nevada snow) comes about a week from now--but in general, ensembles continue to suggest below-average precipitation in long range.#CAwx ImageImage

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More from @Weather_West

Dr. Daniel Swain Profile picture
Apr 17
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."
@ametsoc "If you believe in the importance of NOAA research for maintaining and improving NWS forecasts and services to the nation then *THE TIME TO ACT IS NOW*. Reach out to your elected representatives and share your concerns."
Read 8 tweets
Dr. Daniel Swain Profile picture
Feb 28
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
The U.S. NWS is a truly world-class meteorological predictive service, perhaps singularly so. Its cost of operation is only ~$3-4/yr per taxpayer—equivalent to a single cup of coffee—and yields a truly remarkable return on investment (at least 10 to 1, and perhaps 100 to 1).
3/11
Read 11 tweets
Dr. Daniel Swain Profile picture
Feb 21
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.
Looking ahead to the end of winter and spring, the California/U.S. West precipitation dipole (i.e., unusually wet in the north and unusually dry in the south) appears likely to continue. The dryness may expand to include more of CA/West Coast later in spring, too. #CAwx #CAwater Spring precipitation prediction for the United States from the C3S superensemble. It suggests a relatively high likelihood of drier than usual conditions across the interior SW (lower Colorado River basin) as well as southern California, with an increased chance of above-average precipitation in the Pacific Northwest.
Read 5 tweets
Dr. Daniel Swain Profile picture
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
Dr. Daniel Swain Profile picture
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
Dr. Daniel Swain Profile picture
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

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