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    Ken Clark

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    Big Changes and at Least Some Rain

    January 23, 2013; 1:30 PM ET

    On Monday, I showed dramatic differences in the models for late this week and weekend in California. One model was pretty dry and the other was very, very wet. So how are things looking now two days later?

    Neither of Monday's models are going to end up right. In reality, something in between is most likely to occur, but even today there are differences on how much rain will fall and when.

    We still have two main features in the rather short-term. A northern branch progressive trough just off the Northwest coast and to west of northern California that is moving east. In the south, we have a closed low siting around 25N and 129W that is nudging a little to the east right now.

    While the northern branch system will not DIRECTLY impact the weather except in northern California, it will serve one purpose. That is to continue to bring copious moisture from the southern latitudes northeast and across the rest of the state into tomorrow. Precipitable water (the measure of how moist the whole column of air is in inches) is 1.00 to 1.50 inches to the west and south with this moist plume right now.

    The air mass is very dry still in the low levels from all the warm, offshore flow of late, but showers have been occurring all day just offshore though they certainly are still only falling aloft from central California on south. However, it looks like one piece of energy breaks off from this southern low and moves toward south-central and Southern California tonight into tomorrow. While it may take a little time to moisten up the whole column of air, a few scattered showers seem likely at some point tonight into tomorrow. Most models have the greatest threat sometime later tonight into tomorrow morning. Rain in the north tonight will taper off and end tomorrow. There very well may be a time later tomorrow into tomorrow night it does not do a lot, but I can't sit here and say there can't be a shower or two around.

    Friday into Saturday, the low latitude low will get kicked east and northeast as another northern branch trough starts to develop and head south off the Northwest coast. This is likely to bring some rain to Southern California and maybe a little rain to portions of the central part of the state. However, models disagree quite a bit on amounts. In fact, the European model takes the low so far south, it brings NO rain to central and much of Southern California. I don't like that solution right now because of all the moisture that is present ahead of the low. I think southern sections at least pick up 0.25 to 0.50 of an inch (with the caveat that the GFS is bringing over 1.00 inch). Less rain seems likely in central portions of the state. Snow levels in the south will remain high, above 8,000 feet.

    After this goes east, another big change will take place as a colder trough drops down from the north. This can bring showers Sunday and Monday to just about anywhere and noticeably lower temperatures and snow levels. Snow levels by Monday could be down to 3,500 feet in the Sierra and 4,500 feet in the south. More on that later this week.

    The views expressed are those of the author and not necessarily those of AccuWeather, Inc. or AccuWeather.com

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