Warm; winter; then warm again?

California continues to bask in unseasonable warmth and dryness this weekend. Temperatures will approach 90 degrees in SoCal on Sunday, and even NorCal will likely see some 70s. And then…high clouds and cooling afternoon temperatures will occur as the very long-advertised pattern change approaches. It does now appear that the subtropical jet stream will undercut the mean high over the Eastern Pacific this week. As this occurs, storm systems will be able to make it progressive further east. By midweek…NorCal should see a weak to moderate cold frontal passage, and SoCal could see a few showers. The big event is currently progged for Thursday and Friday. The GFS indicates a large gyre, with multiple centers of circulation, moving E/NE towards the OR/CA coast later in the week, drawing a significant amount of subtropical moisture up from the south. Current indications are that the low center closest to CA may be rather potent…perhaps as deep as 986 mb or so. Depending on its proximity to the coast, high winds could result in NorCal and CentCal. An extended period of moderate to heavy rain may also occur, esp. in NorCal, as a 100 kt jet pushes very moist air against the coastal ranges ahead of and along the cold front. This system…although lacking slightly in jet dynamics…could still be quite impressive. The models still have a lot to resolve over the next few days…especially given the complex interaction between the three low centers (Fujiwara Effect with a twist)…so I would expect the details to change significantly as we come closer to the event. Still…given the very dry antecedent conditions…any rain at this point will be beneficial. Going forward, CA would need to see at least 200% of average rainfall for the rest of the season in order to approach average rainfall for the season. This is extremely unlikely, so it certainly looks like we will be at least somewhat below average when our as yet rather dismal wet season comes to a close in May. And…perhaps we should not be suprised…the GFS is quite insistent that this wet and active pattern will not stick around for long. By day 10, a strong ridge may build back in behind the departing storm systems. If this is the case, we had better hope that we can accumulate some hefty rainfall totals during this week’s briefly rainy interlude. We’re going to need it. 

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