Picture this: a Golden State split down the middle – one side blanketed in a chilly, damp mist that harkens back to bygone eras, while the other side sizzles under unseasonably sunny skies. It's a weather paradox that's gripping California right now, and it's got everyone talking. But here's where it gets controversial – is this just a quirky weather fluke, or a sign of bigger changes brewing in our climate? Let's dive in and unpack what's happening, step by step, so even beginners can follow along.
We've got the final data now, and it's confirming what folks in Southern California have been buzzing about: this past fall was genuinely soaked in some spots, marking a historic deluge. From September through November 2025, parts of Central California saw their wettest autumn on record – and we're talking records dating back to the late 1800s! This included scattered areas stretching from the Central Coast northeastward into the San Joaquin Valley, across the Southern Sierra, and even into bits of the Great Basin. In Southern California, most places experienced an autumn that ranked in the top 10% for wetness, with a handful breaking records that hadn't been touched in decades. And this is the part most people miss – it wasn't just rainy; it was surprisingly mild overall, with temperatures running warmer than average across the state, and even hotter in the interior West, where Nevada and neighboring areas notched their warmest fall ever against our climate-shifted norms.
So, for much of California, autumn 2025 was a rare combo: soaking wet but comfortably warm. The rainfall caught forecasters off guard, as seasonal outlooks didn't predict it. Digging deeper, it's tough to pinpoint the exact trigger without a full study, but the widespread ocean warmth across the Pacific storm paths leading up to California likely amped up the storms that did hit, making them more potent. Think of it like a runner fueled by extra energy – those warm waters 'juiced up' the systems, leading to heavier downpours.
Fast-forward to the last couple of weeks, and the scene has shifted to a calmer, steadier vibe as a strong high-pressure system, or ridge, has taken hold aloft. That means dry skies and warmth for most of the state – except in the Central Valley, where a stubborn blanket of radiation fog, famously called tule fog, has been the rule rather than the exception. This fog varies in density and spread from day to day, but it's been a near-constant companion in parts of the Valley for over two weeks, often persisting all day. It's reminiscent of times decades ago when such fog events were far more frequent and lingering. I chatted about this recent tule fog spell, plus some broader science and history of fog, in a recent YouTube session – check it out here: (https://youtube.com/live/P-FTpZdpNOA). For newcomers, tule fog forms when cool, moist air gets trapped near the ground under a layer of warmer air above, creating a dense haze that reduces visibility and chills the air below.
But here's the fascinating twist: this same stable pattern fostering the fog has ushered in unusually warm and dry conditions for the rest of the West, including most of California outside the fog zone. In fact, the temperature difference is striking – chilly readings under the fog in the Valley contrast sharply with balmy highs just a short drive up into the hills or mountains. Southern California has been enjoying the warmth too, for the most part. This autumn warmth, paired with the ongoing dry spell in many areas, has sparked early 'snow drought' across nearly the entire West (barring some lucky basins along Arizona's Mogollon Rim that got drenched). Don't get me wrong, it's not completely parched; there's been some rain or quick-melting snow in most mountain spots, and the season's still young – snow deficits can often rebound. Yet, it's noteworthy that this deficit is mostly driven by heat, with expectations of it lasting awhile, even as heavy, warm rains flood the Pacific Northwest. For example, storms there will be so mild that snow lines hover near or above mountaintops, turning most precipitation into rain that rushes downhill fast.
Looking ahead, the East Pacific ridge is set to stick around for at least another 1-2 weeks, with a very warm and moist atmospheric river – that's a narrow band of concentrated water vapor in the atmosphere, like a river in the sky – poised to bring serious flood risks to the Pacific Northwest by curving around the ridge's northern edge. We could see flooding from small streams to major rivers, with the subtropical warmth exacerbating the issue by pushing snow levels high, so nearly all precipitation falls as rain instead of accumulating as snow.
As we approach mid-to-late December, the North Pacific weather pattern gets a bit murkier. On average, models show the ridge persisting over California, boosting dry chances especially in the south and central parts. There's a slight uptick in odds for some rain sneaking through, particularly in Northern California, but it's not a sure thing. One eye-opener in the forecasts is the high certainty of anomalously warm conditions across the whole West, including California, even where rain might arrive. For the state, this means two key takeaways: first, building meaningful snowpack in the Sierra is unlikely for the next 2+ weeks, even if storms return later. Second, the Central Valley's fog might gradually ease as the dry, warm air draws out moisture from the lower atmosphere. How long that takes is uncertain, but with another couple of weeks of ridging, I expect the fog to lift as surface dampness diminishes, per the ECMWF model ensemble.
Shifting gears to the winter outlook, I've heard plenty of feedback like, 'What happened to that promised wet winter?' Let me address that in two parts. First, no reputable forecaster ever guarantees outcomes from seasonal predictions; we only spot 'tilts' in probabilities. Sub-seasonal shifts, especially in transitional seasons like fall and spring, can flip the script entirely. If someone assured you otherwise, I'd say it's time for a refund! Second, winter hasn't even started yet – forecasts typically cover December-February or January-March. So far, December looks poised to be drier and warmer than average for most of California. We'll see how the rest pans out, but the bulk of winter is still ahead.
And speaking of that: the newest ECMWF seasonal outlook, released last week (with others coming next), leans toward drier and warmer conditions in southern and central California plus the lower Colorado basin this winter, thanks to the ongoing La Niña and that V-shaped Pacific warming. That still checks out to me. There's a wildcard, though – those unusually warm coastal waters stretching offshore, which could make any storms that do hit warmer, wetter, and more volatile, potentially boosting rainfall like we saw in fall. Where we land by season's end is still up in the air, but it's a mix we've seen a lot lately. And this is the part most people miss – but here's where it gets controversial: some argue this pattern is purely natural variation, while others see it as amplified by climate change, with warmer oceans acting like steroids for storms. What side of that debate are you on?
Peering farther out, current La Niña conditions seem set to weaken soon and vanish by late winter or early spring. Models like ECMWF and others are eagerly predicting a swift switch to El Niño by early summer 2026, backed by a strong westerly wind burst in the West Pacific now, which might spread tropical warming eastward. But ENSO predictions this far ahead are tricky – models have improved but can overreact to starting conditions. I'll keep an eye on it!
Last week, I shared a global climate update in a live session, covering long-term trends in temperatures and greenhouse gases, plus recent ENSO shifts and the next six months. Give it a listen!
As a friendly heads-up: Join me for a live virtual chat on Wednesday morning about hurricane trends in a warming world! Hosted by Reask (https://reask.earth/), with Steve Bowen (https://www.linkedin.com/in/stevebowenwx/), we'll explore the science and impacts of rapidly intensifying tropical cyclones – hurricanes – in a heating climate. These are rare on the West Coast, but vital globally. I'll tie in how similar trends fuel wildfires and thunderstorms too, and who knows what else might pop up in our conversation. It's early U.S. West Coast time for an international crowd, but for you early birds with your coffee ready, mark it: 7-8am Pacific on Dec. 10. Free sign-up here (https://reask.earth/webinar-hurricane-intensification).
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What do you think – should we brace for a foggy future, or is California's weather just keeping us on our toes? And on the broader climate front, how do you feel about the potential El Niño shift? Is it a relief or a worry? Drop your thoughts in the comments – I'd love to hear your take!
