The weak upper low drifting offshore of SoCal will produce showers and thunderstorms across AZ for the next 48 hours and possibly a few thunderstorms across far south CA as well. For the most part, however, we will stay warm, sunny, and dry for the next few days. Model agreement…which was excellent for the past several days…has fallen apart. The GFS is not nearly as emphatic with the pattern change for next week…the longwave trough does not appears to be as deep as it once did. There is still the potential for a rather strong storm in NorCal about a week from now…and possibly further south…but the details are uncertain and the southern extent of the rainfall is seriously in question. There has been a rather disturbing trend by the models this winter to over-forecast the magnitude of troughs and storm systems over CA. Every promising system (though there have not been many) has fallen apart in the models’ projections by days 3/4 or even later. Confidence on the part of local forecasters has been degraded as a result…resulting in some pretty bad forecast calls this wet season. Not quite sure why this has occurred: could be the short-fused and rather unexpected El Nino event followed by our developing La Nina pattern…or there may be something else going on. As previously mentioned, inter and extra-decadal cycles in the Pac. are still poorly understood, especially those that operate on much longer timescales (potentially on the order of 20 years or more). We could be entering an as yet unkown…or at least unrecognized…long-term cycle. One must also at least consider the potential impact of global warming–climatological norms may very well be beginning to shift away from the weighted means programmed into our forecast models. This is only speculation, of course, but considering the rather impressive model performance in recent past years (2005-2006, for example) something has clearly perturbed confidence in these types of forecasts.
