Cold storm for the upcoming week

This is certainly shaping up to be an active fall in CA. Another strong storm system is becoming increasingly likely by the end of the work week, with the potential for significant precipitation and wind once again over NorCal. This storm will also have a much higher potential of bringing measurable rainfall to all of CA than the previous one, given its colder origins and meridional path.

Once again, it appears that the basis for this storm will be the remnants of a tropical system–this time, it’s Hurricane Nekki in the Central Pacific. Energy from this system will amplify the jet over the far E Pac this week and help spin up a deep surface low near the Washington coast. It’s also possible that some extra moisture will become entrained in the system, but it’s a bit early to tell at this time. Regardless, it does appear that this system will be a strongly baroclinic weather-maker, and there will be quite a bit of cold air aloft over CA by the time the trough axis swings over the state late next weekend. Given the relatively strong sun angle this time of year, and strong curved jet over and just west of CA, I do expect a fair bit of thunderstorm activity. 850 mb temps will approach 0 C  over NorCal, so snow levels will probably be below all the major passes in the Sierras (perhaps as low as 4000 feet in post-frontal convection).  Very early rainfall estimates are actually rather high–as much as 4-5 inches in the mountains, and a very healthy 1-2 inches in the valleys. On top of all the very heavy precipitation earlier this month, some flooding issues more characteristic of winter could ensue. Also, since this will all fall before the end of the calendar month, many locations in NorCal that haven’t already been pushed over their all-time records may very well be after this storm dumps a few more inches.

All in all, pretty impressive for October–if this keeps up, we’ll be in good shape water-wise by the spring…