After an extended quiescent period over California, a dramatic and sudden change in the weather is in the works. This huge pattern shift is being driven by an active MJO signal in the West Pacific and the remnants of former Supertyphoon Nida, which are currently being absorbed by the westerlies. The models have been struggling profoundly with this pattern shift, unlike during the major storm event in October where there was remarkable consensus. Right now, the GFS is not really capturing the expected evolution of this pattern, though it does track the early (very cold) system fairly well. I do think it is likely that the GFS is simply dropping the ball in this instance, and the ECMWF (or almost any other global model) seems to be the better indicator here. If the ECMWF is to be believed, significant rainfall will be possible almost statewide for almost every day next week. This would be a fairly remarkable event. Here’s a chronological breakdown:
A cold to very cold upper low retrograding southwest from Canada is expected to drop down into California by Sunday, bringing much colder temperatures both at the surface and aloft. 850 mb temps are progged by the GFS to fall to impressively low values–below -6 C in parts of NorCal. The 0 C isotherm is expected to make it all the way down to SoCal at some point, too. While it is likely that temps will modify once precipitation begins, there remains a small chance that precipitation-type will not be rain over some lowland parts of NorCal on Sunday or Monday, especially if some deeper convection can get going. Meanwhile, a slug of subtropical moisture interacts with the southern boundary of the cold air in SoCal to produce some potentially significant rainfall. Even at day 5, the prognosis remains uncertain, but it does appear that even the first system may now be fairly notable in several respects.
Then…we move on to the parade of powerful Pacific storms that appear likely to slam into California from the west, bringing the potential for heavy rainfall and strong winds for much or all of next week. The ECMWF solutions are actually fairly ominous, even with dry antecedent conditions, because of the relentless and widespread nature of the rainfall it foresees (with snow levels >8000 feet). As mentioned before, the GFS has been really unreliable thus far with this pattern shift, though it does serve as a reminder that almost anything could still happen (though the very wet scenario is looking increasingly likely). I do expect the GFS to come in line by this time tomorrow, or we may have to consider its alternate solution more seriously. In any case, the GFS still brings moderate to heavy rainfall to much of the state; it just isn’t as apocalyptic as the other models at the moment. At the very least–there is high confidence that we will have an incredibly dynamic pattern in the next week–with snow levels in CA starting out near (or below?) 1000 feet on Sunday/Monday and rising to 8000+ (maybe 10000 feet?) by later in the week, with significant precipitation at times. Again, I will update once or twice before Sunday, and keep an eye on the comments section, as well. Side note: the advertising scheme has more or less reached its final form. If you have any complaints or comments, please let me know!