Warm and dry weather to end by this weekend

The weather over the holiday weekend was nothing short of spectacular across the entire state of California. Mild temperatures occurred statewide–as warm as the low 80s in parts of Southern California and well into the 60s even for foothill location in the northern part of the state. Warm and dry conditions will continue for at least another 48 hours as the ridge maintains its strength overhead. By Friday, however, the Pacific jet will begin to undercut the ridge over the West Coast and bring a more active pattern back to California.

Current Pacific water vapor imagery (NOAA)

As the mean ridge breaks down and gets pushed up towards British Columbia, a respectable subtropical jet will begin to focus an increasingly active storm track over NorCal starting on Friday. The first system will be rather weak and centered on the northern half of the state, though there may be the chance of a few thunderstorms as lapse rates increase (especially on Saturday). After that, there is still considerable disagreement in the models as to how the pattern will evolve. The GFS and ECMWF have both (at times) indicated the potential for a very wet pattern to develop over the next week or so, powered by a strong subtropical jet rounding the base of a mean trough off of the CA coast. There is little consistency on this front, though, and it would not be the first time in the recent past that model prognostications of an strong undercutting jet fail to come to fruition. In any case, it certainly does appear that our pleasant mid-winter warm spell will soon come to an end, with more seasonable temperatures and precipitation patterns prevailing.


GFS depiction of a fairly robust subtropical jet undercutting the West Coast ridge

Finally, as a side note: it does appear that the magnitude of SST anomalies in the tropical Eastern Pacific are decreasing, and have been doing so for several weeks. A new Kelvin wave may be propagating across the Pacific at present, but it certainly does not appear to be as strong as the ones experienced earlier in the season. The main effect of the present wave may simply be to slow the decline of El Nino conditions. Dynamical models from the CPC and other international climate monitoring agencies all indicate that El Nino conditions will persist in some form for at least the next couple of months before falling below the El Nino threshold this summer (much as would be expected during a typical event).


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