2009

Well…there is actually a considerable amount to discuss at the moment. First things first, the upcoming week:

A parade of relatively weak systems will affect CA this week, mainly the northern part of the state. Since air aloft will become progressively colder through the weekend, some precipitation will become convective by Wednesday or Thursday, and although the setup does not look particularly favorable for thunderstorms, the potential for brief intense showers, local small hail, and lower snow levels (perhaps with a rumble of thunder) will increase. Rainfall will not be particularly heavy–probably not more than 0.5 inches in any one location, and SoCal will see even less (if anything). The most noteciable change will be the plummeting temperatures through the week, with 850 mb temps dropping as low as -3 C over NorCal. This will likely bring the coldest weather of the season thus far to CA by Friday and Saturday.

The models are having a difficult time ascertaining the pattern right now more than a couple of days in advance. There now appears to be a reason in addition to the mere changing of the seasons (which itself can be enough to inject even more chaos than usual): the MJO signal in the West Pacific is very strong. This MJO wave has been percolating for a while, but the magnitude of the signal has really spiked in recent days and begun to shift eastward (two good signs that it will soon affect zonal flow over the Pacific). In fact…the signal is currently stronger than at any point in at least 14/15 months. As such, and given the favorable time of year, I would expect a period of active weather for the West Coast, including CA, over the next 1-3 weeks. The models seem to be starting to pick this up in recent runs, and have amplified the flow over the Pac.  Stay tuned, and don’t be surprised if the models change their tune frequently in the coming days.

As illustrated clearly in the above loop of SST anomalies over the past month or so, El Nino rapidly strengthened in October, and that trend has continued into November. The most recent frame–which is not included in the loop–is even warmer. As recently mentioned, a very strong Kelvin wave is propagating eastward and contributing to this pretty incredible rate of temperature anomaly increase. If the current anomalies were to flatten off and remain constant at this point, we would already be nearing a strong event–and we just hit moderate levels a couple of weeks ago. The overall heat content anomaly in the Nino regions has nearly doubled in the past month–which is a pretty fantastic statistic. Also of note is the very large and very warm pool of water just under the surface–the most recent T-Depth anomaly plots show an area of 6+ C degree readings, effectively maxing out the scale on the graph (see below). The fact tha the MJO is extremely active so early in the season also indicates that El Nino is having an effect on global circulation–MJO events are often much more pronounced during significant El Nino  years. Stay tuned…I have delayed the Seasonal Outlook for a week or so because we will have a better idea of whether this El Nino will be by then. Hopefully this post will suffice in the meantime…