Get ready for a weather phenomenon that will leave you in awe and maybe even a little confused! An unusual weather pattern has emerged, bringing a unique contrast to California's Central Valley.
Under a stubborn ridge of high pressure, the Central Valley has been shrouded in a prolonged episode of tule fog, creating cold and damp conditions. But here's where it gets controversial: this dense fog is a stark contrast to the warm and dry weather experienced elsewhere in the region. It's like Mother Nature is playing a game of weather hide-and-seek!
The recent autumn season has been a real head-scratcher for meteorologists. While some parts of Central California experienced their wettest fall on record, with patchy areas drenched from the Central Coast to the Great Basin, it wasn't just about the rain. The temperatures were a surprise too! Despite the wet conditions, it was anomalously warm across California and even warmer in the interior West. So, autumn 2025 was a wet and wild ride, but with a mild to warm twist.
And this is the part most people miss: the stable weather pattern that allowed the tule fog to persist has also brought an unexpected gift to the broader West. An anomalously warm and dry air mass has settled in, creating a remarkable temperature contrast. While the Central Valley remains cool and damp under the fog, just a couple of thousand feet higher, in the nearby hills and mountains, it's a whole different story - warm and sunny skies prevail!
The early-season snow drought across nearly the entire West is a direct result of this temperature-driven phenomenon. And it's not just about the lack of snow; it's the warm storms that are bringing flooding rainfall to the Pacific Northwest, with freezing lines near or above mountain peaks. A real contrast in weather extremes!
For the next couple of weeks, California can expect more of the same. The persistent ridge will keep temperatures warm and skies sunny in the hills and mountains, while the Central Valley and parts of the SF Bay Area continue to battle the cold and damp conditions under the tule fog. It's a stagnant pattern, and it's here to stay for now.
Meanwhile, the Pacific Northwest is bracing for a potential widespread flood event. Strong atmospheric rivers will bring very wet and warm conditions, causing flooding from small creeks to mainstem rivers. The warm, moist subtropical air will ensure that almost all precipitation falls as rain, even in the mountains, increasing the immediate runoff.
As we look ahead to mid-late December, the North Pacific flow pattern becomes a bit uncertain. While the ensembles suggest continued ridging over California, bringing dry conditions to the south and central regions, there's a glimmer of hope for some precipitation, especially in NorCal. However, the most striking feature is the high confidence in very warm conditions across the entire West, including California. This means the Central Valley may slowly see reduced fog coverage as the warm and dry air mass takes over.
The winter seasonal outlook continues to lean towards a warmer and drier tilt, especially for Southern California and the Southwest. Despite the recent feedback questioning the promised wet winter, it's important to remember that winter predictions are typically for Dec-Feb, and we're still in the early stages. So, while December may turn out drier and warmer than average, the winter story is far from over!
The latest ECMWF seasonal outlook suggests a tilt towards drier and warmer conditions for southern and central California, influenced by the ongoing La Niña event and a persistent warming pattern in the Pacific. The warm ocean temperatures along the California coast and offshore could add an interesting twist, potentially bringing warmer and wetter storms. As for the long-term, the current La Niña conditions are expected to fade, possibly transitioning to El Niño by early summer 2026. But ENSO predictions are tricky, so we'll have to wait and see!
If you're interested in learning more about the fascinating world of weather and its impact on our planet, join me for a live virtual event on Wednesday morning. We'll be discussing the increase in rapidly-intensifying tropical cyclones in a warming climate, a topic that's rare along the West Coast but crucial on a global scale. It's a chance to explore the science and practical implications of these extreme weather events. So, mark your calendars, grab your coffee, and let's dive into the world of atmospheric science together!
