A broad atmospheric river event is delivering heavy precipitation and high winds to much of the western U.S. over the next 48 hours, but there's a unique little tornado risk tucked into California's Central Valley on Thursday afternoon and evening.
As of early Thursday morning the risk for any low-topped supercells across California's Central Valley seems pretty darned low, limited by extensive cloud-cover. Some destabilization is expected, with early morning guidance suggesting around 500 j/kg of surface based instability and 0-3 km cape values around 50-100 j/kg. Similarly, there's some low-level turning present but not a ton when looking at forecast soundings across the area.
I don't necessarily expect a string-of-pearls with numerous mini-supercells across the Central Valley today, but it'll be interesting to watch and see if any robust updrafts can spin a little bit as we head through the late afternoon and evening hours along the I-5 corridor.
The Storm Prediction Center has outlined the area in a marginal risk (level 1 out of 5) with a 2% tornado probability area. You can read the latest discussion here.
...Central Valley of California...
Recent satellite imagery depicts an intense cyclone off the West
Coast, with a strong shortwave trough moving through its southern periphery towards central CA. This shortwave is forecast to reach the coast later this afternoon, with the ongoing warm-air advection shower activity moving to the east/south as it does. As these showers clear out, temperatures should warm into the upper 50s/low 60s while mid-level cold-air advection results in 500-mb
temperatures in the -22 to -25 deg C range. This will support weak airmass destabilization, with modest buoyancy anticipated during the afternoon. This could result in some deeper, more sustained
convection. Vertical shear will be strong enough to support
transient rotation within any deeper updrafts, yielding a localized
wind/brief tornado risk during the late afternoon.