Interesting developments?

Filed in Uncategorized by on December 11, 2006 0 Comments

This past weekend’s “storms” were not particularly impressive, though they were not expected to be. The second–on Sat. PM–did bring a wind gust of 44 mph to my SR gauge, which is the strongest speed since last winter. 3 day total rain accum. in SR was 2.15 in.–certainly not incredible, but it did help the water situation. More light to moderate rains are on tap next 48 hrs. from about South San Francisco northwards along the coast, w/ a few light showers as far south as Monterey. Otherwise, some brief ridging will take place before the next wave of wet weather begins to approach on Thurs. This is where things get interesting. Or strange, at least. 18z run of the GFS along w/ the ECMWF and the Canadian models all indicate a deep trough will be carved in the mean flow somewhere to the west of CA by days 4/5. All the models also indicate there will be a howling 160-180 kt jet stream aimed squarely at the CA coast near the Bay Area for over 48 hours. The GFS does not develop ANY precipitation over the Bay Area until the last 6 hours of this period, and even then, it indicates that precip would stay on the light side. I feel that the models may be significantly underestimating the rainfall potential of the Fri/Sat./Sun. system, given the powerful jet perpendicular to the Coastal Range, deep lifting associated with the jet, and baroclinic instability. Also, the current systems have a very impressive subtropical/even tropical moisture tap going all the way back past the dateline. The models could be missing the potential for this powerful jet to entrain copious tropical moisture and bring heavy rain to CA this wknd. Neither scenario is a sure thing, but the potential certainly exists for a much stronger storm than the GFS is currently indicating. Regardless of the strength of the original storm, it appears that a very cold and unstable airmass will dive down from the Gulf of Ak. after the main cold front passes through. This will give rise to convective showers and possibly some isolated thunderstorms. Snow levels have the potential to be quite low with this event, as well…perhaps below 2000 feet. Assuming the moisture moves east and the skies clear by the middle of next week, some very cold nights could be on tap again, perhaps colder than during the November cold snap. Certainly stay tuned these next few days!