Dr. Daniel Swain Profile picture
Aug 21, 2020 5 tweets 5 min read Read on X
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) Image
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) Image
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) Image
Right now, I'd put the odds of dry lightning somewhere in NorCal Sun-Mon somewhere around 50/50. So there's a 50% chance this fizzles altogether. (Fingers crossed). But these storms, if they occur, would produce little/no rain as well as lightning & gusty winds.#CAwx #CAfire(4/n) Image
Given unprecedented number & extent of wildfires across NorCal & the firefighting resource drawdown already, this would be a very problematic weather outcome. But this kind of forecast is challenging, so follow @NWSBayArea & @NWSSacramento for details and updates. #CAwx #CAfire

• • •

Missing some Tweet in this thread? You can try to force a refresh
 

Keep Current with Dr. Daniel Swain

Dr. Daniel Swain Profile picture

Stay in touch and get notified when new unrolls are available from this author!

Read all threads

This Thread may be Removed Anytime!

PDF

Twitter may remove this content at anytime! Save it as PDF for later use!

Try unrolling a thread yourself!

how to unroll video
  1. Follow @ThreadReaderApp to mention us!

  2. From a Twitter thread mention us with a keyword "unroll"
@threadreaderapp unroll

Practice here first or read more on our help page!

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

Did Thread Reader help you today?

Support us! We are indie developers!


This site is made by just two indie developers on a laptop doing marketing, support and development! Read more about the story.

Become a Premium Member ($3/month or $30/year) and get exclusive features!

Become Premium

Don't want to be a Premium member but still want to support us?

Make a small donation by buying us coffee ($5) or help with server cost ($10)

Donate via Paypal

Or Donate anonymously using crypto!

Ethereum

0xfe58350B80634f60Fa6Dc149a72b4DFbc17D341E copy

Bitcoin

3ATGMxNzCUFzxpMCHL5sWSt4DVtS8UqXpi copy

Thank you for your support!

Follow Us!

:(