2007

Another major and damaging Santa Ana-driven wildfire occurred this weekend near Malibu. Temperatures were not particularly high with this Santa Ana event, but the low humidities  and strong wind gusts in excess of 60 mph  were more than enough to fuel the flames. These conditions have since abated, and the weather across the state has returned to the seemingly perpetual state of “sunny and dry.” There is some moderate hope that this may change over the course of the coming week. Several cold but moisture-starved troughs will slide to the NE of CA over the next 7 days, bringing more gusty offshore winds and some fairly cold air aloft. At the surface, these troughs will translate to cold overnight low temperatures across inland parts of the state and possibly some snow showers over the Sierras. Brisk winds could develop at times as well, and there remains the possibility that a slightly more westward track of these “inside slider”-type systems could bring some light convective precipitation to NorCal. Almost certainly, however, these systems will be dry and cold for the state.  The pattern may begin to undergo some significant changes beginning in the 5-10 day period. A significant undercutting of the mean Eastern Pacific ridge complex will begin to occur, potentially dragging a very moist plume across the West Coast all the way from the West Pacific. This is the classic setup for major West Coast rainfall events, though what part of the coast is impacted most greatly remains to be seen. At this point, the GFS and ECMWF are indicating that some significant to heavy precipitation could fall in NorCal and CentCal up through Oregon, though this is likely to vacillate between now and when the potential rain event actually takes  place. La Nina would tend to favor a more northerly track of these systems, so we will have to see how that pans out. The MJO is currently active, but is being hampered in its eastward progression by the lack of tropical forcing (decrease in equatorial convective activity due to cooler SSTs). It is possible that the MJO will not be able to influence the pattern over the eastern half of the Pacific Ocean as much as it would have otherwise. There is also a large cold pool of unmodified Arctic air that remains stuck over Siberia through the Canadian Northwest Provinces, which has the potential to spill southward at the very first opportunity given some northerly flow aloft. La Nina does favor this type of cold northerly flow pattern, as so we need to keep an eye on that potential over the next few weeks. There is still some indication that La Nina (currently moderately strong) will peak early in the season. More on that as the situation evolves…