An area of high pressure over the southwestern U.S. will be sending warmer temperatures our way in the next few days, particularly in the inland parts of the Bay Area. And meteorologists are closely monitoring the situation as some more monsoonal moisture moves our way.
This whole thing with monsoonal moisture in the summer, coming from the southwest, seems to be a new thing the media discovered this year — given the devastating impact of one lightning storm on our region last August, caused by some similar moisture. But this happens seasonally in many parts of the world, and the National Weather Service says this has been a particularly "robust" monsoon season for the Desert Southwest, which is why there have been seemingly biweekly scares about dry lightning here around the Bay for the last couple of months. (We also saw some of this in August of 2017, in addition to last August.)
But it takes unstable air combining with that moisture to create thunderstorms, and so far that doesn't appear to be happening this week, but it still might, as National Weather Service Bay Area forecaster David King say in the briefing seen below.
"As of right now, the instability needed to create a storm [is] staying a little bit further separated from the moisture," King says. "So there's no fire [warnings] issued currently. But we are watching this very closely."
King says we will see the moisture move into the Bay Area by Thursday morning in the form of high clouds, and temperatures will begin to rise and reach the 90s in some locations — though probably still just the 70s in SF.
As the NWS explained on Twitter yesterday, "Thankfully, the setup for this upcoming monsoonal moisture return does not remotely come close to last year's setup in terms of moisture content, instability, and source of lift. Nonetheless, all it takes is 1 lightning strike over a dry fuel environment to trigger a fire start."
You can see the mass of moisture in the GIF below moving over Las Vegas, where it already is causing a cluster of storms.
This monsoonal moisture will move in from the Desert Southwest, which has experienced a robust monsoon this summer. Note that even this afternoon, we're observing a cluster of storms screech their way south of @NWSVegas and along the CA/NV/AZ Border. pic.twitter.com/0z4bZOLKZi— NWS Bay Area (@NWSBayArea) August 11, 2021
The NWS says that we're very likely not to see much of this moisture head into our region at all.
"While most of this moisture won't make it here, some of it will get picked up by southerly winds aloft and [get] lodged here," the weather service says on Twitter.
Fingers crossed we just have a brief heatwave and no storms!!
Below is an explainer about how lighting happens, from the NWS Los Angeles bureau.
Previously: Monsoonal Moisture Brings Small Chance of Lightning and Rain to Bay Area