Short-lived pattern change over CA

The warm and dry weather that has persisted in CA as of late will quickly come to an end over the next 24 hours.  A weak area of low pressure is currently generating an area of mid-level clouds over the state, possibly leading to a light shower or two overnight. A splitting system will then move in overnight, bringing some light rain to much of CA tomorrow. Rainfall totals should be less than 0.25 inches across the board, and snow levels won’t drop much below 3000-3500 feet, even in the north. A somewhat stronger system will move in by Thursday, bringing more rainfall (0.50-1.5 inches in the north; 0.25-0.75 in. in the south) and lower snow levels (2500-3000 feet in the north), but generally nothing too impressive. The intensity of the third and apparently final system in the series, however, has been increased dramatically over the past 24 hours by virtually all of the models. The GFS and ECMWF are both currently insistent that the Saturday storm will be very imprssive, esp. in NorCal. The low center will be developing rapidly as it approaches the CA coast from the west, riding a powerful 180 kt jet with an exit region over central/northern CA. It currently appears that the low may undergo a period of rapid intensification as it approaches the coast on Saturday, bottoming out below 990 mb (per GFS) and below 980 mb (per ECMWF). Given that the low center will be passing directly over the San Francisco region, this is quite impressive. The benchmark for strong/damaging winds in NorCal from these types of systems is generally 995 mb, so this system certainly has the potential for strong/damaging winds (if the ECMWF is to be believed, rivaling the winds of the January storm). Intense heavy rain and embedded thunderstorm activity would also be a concern, but that would be secondary to the magnitude of the winds. Snow levels would be near to slightly below average–3000-4500 feet in the north. Given that this is a very new development, the forecast is liable (and even likely) to change quite a bit as we get closer to the event. I cannot say at this time what impact this storm will have on SoCal. At the moment, it looks like the focus will be on areas north of Santa Barbara, but again, this could change. It does appear that the pattern will begin to revert to a warmer and drier one after this weekend–recent GFS depictions of a very cold pattern have vanished altogether. Stay tuned, in any case…

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