A particularly strange and rare event has unfolded over the past 24 hours off of the southern and central California coast. A complex of strong to severe thunderstorms developed over the near-shore waters off of Los Angeles County yesterday evening and moved northwest through the night, affecting immediate coastal areas and producing one of the best light shows this part of the state has seen in quite some time. Nearly 2000 cloud to ground lightning strikes–with many more in-cloud strikes–are thought to have occurred through the course of the event. Radar reflectivities reached over 65 dbz over water, which is indicative of large hail. Some rainfall did occur over the immediate coast, where up to 0.25 inches fell. The complex of storms morphed by about 3 AM into a very unusual formation–a swirling doughnut of showers and thunderstorms clustered around a center that was rain (and at times even cloud) free. This “eye” has been clearly visible on satellite and radar imagery for hours, and continues to be evident as the mesoscale circulation churns off the Monterey County coast. I personally have never seen anything like this in CA before. The vorticity maximum at the core of the cyclonic feature is fairly strong, so this may account for some of the atmospheric spin, but the rest appears to have come from sources that many of us may be more familiar with–the Catalina Eddy and other low-level terrain-induced atmospheric currents that commonly direct the marine layer to spin around during the summer months. Certainly, it’s worth a look at the satellite imagery just to get a look at this incredible convective circulation over CA.
For the next 24-48 hours, I think the models are handling the current situation extremely poorly, so a forecast based on satellite trends is probably most prudent. There is a lot of moisture and instability out there, so some more unexpected thunderstorm activity is certainly possible. A surge of clouds is currently about to enter the San Joaquin Valley from the southeast, so it is possible that these could develop further.
The longer-term is interesting, as well. Briefly: GFS and ECMWF both bring precip to NorCal during this period from an unseasonably deep eastern Pacific storm system. This would be rather unheard-of, and there would probably be a convective threat associated with any such system. Stay tuned…
