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]

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] 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]

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] 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]

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

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]

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] 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]

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]

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…
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…

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]

If you've been wondering why I've been somewhat less visible here, that's partly because of the "shifting winds" of social media. But also, I've been spending much effort scrambling to find some way to support my climate scientist-communicator role moving forward. Thus far, I have not yet been successful in these efforts--& if nothing changes, the time left in my current role may unfortunately be limited. A great number of individuals & organizations have voiced support--and I'm hugely grateful for that!--but ultimately a large gap looms.

Some additional thoughts regarding the still strengthening #ElNiño and its implications for western U.S. hydroclimate during winter 2023-24. (Brief thread!) #CAwx #ORwx #WAwx #HIwx #CAwater #CAfire International dynamical models ensemble is now unanimous in predicting strong to very strong #ElNiño event that will peak sometime this winter. This is a remarkably strong signal, so I'm reasonably confident that the oceanic signature of a strong EN will actually occur.

Confirmed human toll from wildland-urban interface #MauiFires is terrible (already second deadliest wildfire in modern American history), but grim reports from residents on the ground suggest actual toll is even greater & that there is still minimal outside assistance. #MauiFire

https://twitter.com/nohea_d/status/1689570022530965504

As previously discussed: #Lahaina was town that was unfortunately quite vulnerable to a wind-driven fire from precisely the direction in which this one originated (due to surrounding extensive grasslands and brush, prevalence of wood structures, & relatively isolated location).

One thing I keep reflecting on, especially in context of recent events (CA's winter storm onslaught & dramatic increasingly dramatic hydroclimate whiplash), is how high societal need is for scientist-communicators & others who offer critical context as events unfold in real-time. There is much public demand for such roles, but there continues to be a (frankly) bewildering refusal by institutions (academic, public, private, and otherwise) support these kinds of roles in any broad sense.

Brief thoughts on likely return to active weather pattern in CA after a much-needed several day break right now. There is *high* confidence that wet and cool conditions will return next week, but right now there is *low* confidence in strength of storms. #CAwx #CAwater (1/4) Ensembles suggest that there is very high likelihood that unsettled and occasionally stormy conditions return to most of CA by early next wk. But vast majority of ensemble members suggest this will involve series of weak to moderate systems vs. major storms. #CAwx #CAwater (2/4)

Brief thread about...snow. As of this weekend, the Southern Sierra now appears to have largest snowpack in recorded history (as measured by snow water equivalent, or SWE). Not just for the calendar date, but for *any* date! #CAwx #CAwater [1/n] As I earlier noted was plausible, the "warm" atmospheric river storm on Fri actually *increased* net watershed SWE substantially--partly because it still snowed at high elevations, but also because lower elevation snowpack absorbed a lot of rainwater! #CAwx #CAwater [2/n]

A few storm updates following my session Wed PM:
Event still largely on track, but two modest shifts that could affect impacts:
1) Storm may not be quite as warm across central & northern Sierra; could see some very heavy snowfalls above 6,500 ft once again.
#CAwx #CAwater [1/5]

https://twitter.com/Weather_West/status/1633616991067185153

2) Rainfall may be a bit heavier and more concentrated across the northern portion of central CA (but slightly less to north). This means flood risk in Monterey County (including Big Sur Coast), as well as southern Sierra & foothills, has increased somewhat. #CAwx [2/5]

Lot of hype right now regarding supposed potential for widespread "sea level snowfall" later next week NorCal.

That almost certainly isn't going to happen (for variety of reasons). But some unusually low elevation snowfall (to 1000-1,500 feet or so) is certainly possible. #CAwx Yes, I know that the coarse-resolution ensemble models are showing accumulating sea level snowfall for SF/Sacramento. They are very likely wrong--and the same models' *own thermal profiles* are not supportive of snow in these areas with this pattern! #CAwx

Additional widespread precipitation is likely over the next 8-9 days over the northern 2/3 of CA, and it will be heavy at times (especially northern third of CA). Strongest storm, with some more heavy rain, wind, and thunderstorms, is due in on Sat. #CAwx #CAwater [1/4] However, these are primarily areas that have not been nearly as wet as central CA recently. Also, these will generally be colder storm systems, bringing a greater balance of snow (vs rain) in mountains & somewhat limiting higher elevation runoff. #CAwx #CAwater [2/4]

Okay, folks. Starting to look like it's going to be a rough 10+ days from a flood risk perspective in Northern California, with a series of very wet & high-impact storms. Brief thread now; blog post late this PM; YouTube live Q&A Tue. [1/n] #CAwx #CAwater The next inbound storm looks like it will be quite strong. A rapidly deepening surface low (i.e., meteorological "bomb cyclone") will remain well offshore, but the associated warm and cold fronts will bring widespread heavy rain and strong winds to NorCal later Wed. #CAwx [2/n]

Some thoughts on impacts from ongoing and likely prolonged very wet spell in NorCal. (Short thread). TL;DR: widespread heavy precipitation is likely, with mostly minor flood issues becoming more widespread this weekend & *possibly* more significant next week. [1/n] #CAwx #CAwater Lighter precipitation continues today, but the next significant storm will be this weekend. This will come in the form of a moderately strong low pressure system coupled with a robust, warm, and relatively slow-moving atmospheric river. #CAwx #CAwater [2/n]

Still not seeing many images of damage, but based on anecdotes from folks in quake zone it does sound like there was damage to some structures & especially to infrastructure. I suspect that ongoing widespread regional power outages are reason we haven't heard more yet.#earthquake

https://twitter.com/Weather_West/status/1605219834391941122

This points to an emerging paradox in media reporting on disasters that's become really apparent in recent years: the more severe the damage, the less news initially makes it out (because power is out and telecoms are down) and the less coverage they receive.