It feels like every year meteorologists introduce us to new terminology that was once just the purview of professionals and weather geeks. And this week in California, it's all about the "inside slider" — not the baseball pitch, but the slang term used for a northerly weather system that has an unusually steep southward trajectory.
Unlike the Diablo winds it triggers, an "inside slider" can happen here in Northern California at multiple times in the year — though offshore wind events here are becoming more common in odd months when they didn't used to occur.
This "inside slider" that began on Sunday is bringing cold air and a low pressure system down from the Pacific Northwest, creating a weather system — and wind — coming at us from the Sierra to the east, as opposed to from the ocean as normally happens. The air is literally sliding down "inside" the coastline, over land, while an area of high pressure continues to sit off the coast.
The National Weather Service says this pattern will cause "North to Northeast winds [that] will be 15 to 25 mph with gusts 35 to 45 mph, locally higher gusts up to 60 mph." And those winds are going to be mostly concentrated along the region's easternmost mountain ridges — hence PG&E's power shutoffs are concentrated this time in Solano County, eastern Napa County, and small pockets of far-eastern Contra Costa and Alameda counties.
It's safe to say the Inside Slider is living up to its name. Water Vapor Imagery 🛰️ is capturing the dry, northerly air that will continue to mix down into our neck of the woods over the next 24-26 hours. For the latest on our warnings/advisories: https://t.co/VsJ8NvGVs2 #CaFire pic.twitter.com/c2N6erEYdg— NWS Bay Area (@NWSBayArea) October 11, 2021
🚨 Science Alert! 🚨 If you've been reading our weather discussions, you may have noticed us reference this 'Insider Slider' weather pattern. Here's a breakdown of what that means! 🤓 #nvwx #cawx #azwx pic.twitter.com/dwvebrGrcY— NWS Las Vegas (@NWSVegas) October 11, 2021
Below is a video from Sacramento affiliate ABC10 from February 2020, explaining what an "inside slider" does in the wintertime with weather happening in the eastern Sierra, in contrast to what's happening in the Central Valley and Sacramento.
As has been illustrated before, Diablo and Santa Ana winds are also caused when an area of high pressure pulls winds over the Sierra and other mountains from the Great Basin. These hot, dry winds get sped up as they come across the Central Valley and then come rushing over the ridges around the Bay Area, creating times of high fire danger. The "Diablo" term began being used widely in the Bay Area after the 1991 Oakland Hills Firestorm to distinguish these winds from the Santa Ana winds in Southern California, and to suggest that they're coming from the direction of Mount Diablo, but they are part of the same weather phenomenon.
Today's "inside slider" is bringing increasingly high winds all over the Bay Area, as it did overnight in some locations. And as with previous Diablo wind events, these are often not felt down in the valleys, while extremely high winds can be gusting over nearby ridge tops — that was what occurred in the 2017 Tubbs Fire in Santa Rosa, when residents were caught by surprise by a surge in fire from the east being driven by winds they hadn't been feeling.
Anyway, don't park your car under any trees today if you can help it! That's the advice of ABC 7 meteorologist Drew Tuma, looking at the winds headed our way.