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    Western US weather expert

    Pattern Change Coming, Eventually

    1/27/2014, 5:10:43 AM

    The huge, concrete barrier of an upper-level ridge that has given the bone-dry weather for over a month to California and well below-normal precipitation to much of the West may become history in a week.

    That is great news, right? Well, it is but I must temper things some. First, this pattern change will not begin until the middle of next week. Until then more of the same is coming. A couple of sub-tropical upper-level disturbances coming up the south from tonight to Sunday bring periods of middle and high clouds but no important precipitation. Then from Monday to Wednesday the big, strong ridge will pop up once more.

    The GFS and European have been advertising for a while now that the ridge breaks down allowing the westerlies to break through by the beginning of February. What they have not agreed upon is how that would happen and how wet it might get. For once the models today seem to be pretty close to one another.

    To show what happens across North America over the next week here are two maps from the GFS Ensemble model. They show the 500mb heights and how much above/below normal those heights are for each time period. The red is above normal and the blue below normal. The deeper the color the mode above or below normal the heights are.

    Wednesday, Jan. 29:

    Sunday, Feb. 2:

    Notice how the red in the West is replaced by blues and the deep blues in the eastern part of the nation turn to red.

    This change will finally mean the door is open for some rain and snow. The first storm comes next weekend with the possibility of some rain and snow spreading from north to south across California. There could be another storm, but the GFS spaces the two storms about a week apart.

    Now this is nice and any rain and snow is going to be welcomed. However, there is nothing showing, at this point, that either storm will bring heavy rain and snow and certainly will not be drought busters on their own. I also will remind everyone that our long-range computer models continue to show below-normal precipitation through the rest of the rainy season. There has been such a deep, deep hole dug in our rain and snow deficit that it is highly unlikely that over the rest of the season will be able to dig us out of this hole. It is not impossible, but it is higher unlikely.

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

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    Western US weather expert