Friday, November 30, 2012

Is This the Long-Awaited Pattern Change? With Saturday Update.

Those of us living in the drought-striken areas of the United States and those that depend on moisture for a living or shipping have, for nearly two years, been anxiously watching for signs of rain. I may have found one.

Meteorologists know that "teleconnections" -- what is occurring in one part of the atmosphere that can affect other parts of the atmosphere -- are an important element of long-range forecasting. One of the most important teleconnections for significant moisture in the central U.S. is the development of a high pressure system in the upper atmosphere in the Pacific around 130°W. Today's European model shows just that (arrow) in ten days. Once the high forms, storms are guided into the West then Central parts of the U.S.


The United States' NWS Global Forecast System (GFS) which forecasts farther into the future than the European, shows exactly that occurring.

Storm 1's forecast location on December 10.


Storm 2's forecast location on December 12.


Storm 3's forecast location on December 16. 

So, how much rain (and snow) might result? Here are the forecast totals for storms 1 and 2 in the central U.S. (the quantitative precipitation forecast doesn't go far enough to capture the moisture from storm 3)
click to enlarge, from NWS GFS model
The light orange area from southeast Missouri through the northern Ohio Valley is five inches of moisture!

Keep your fingers crossed.

Update, at 5:30pm Saturday. My commenters below express skepticism and the same is true on Facebook. Let me give you a little secret from an experienced central U.S. forecaster. As I said on Facebook yesterday, the long range models, until we get about 72-84 hours from the actual start of the event, start the precipitation too far east. Over time, the models start moving the precipitation west. That happened on the latest version (18Z Saturday) of the U.S. GFS model.

Look how the heavier precipitation starts farther west (arrow) than on the identical graphic above which is from the 12Z Thursday run. This is exactly the behavior of the models I would expect based on years of central U.S. forecasting. I'm still feeling good about moisture in the central U.S. the middle third of December.

6 comments:

  1. If this were to actually come together, does it signal a possible long term pattern change, that may bring with it more normal rain fall for a while, or is this just another short term thing that brings a day or two of rain here and there (even if heavy in some places) and then is gone again for months? Or is it even possible to guess that?

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    1. It's not possible to guess. Odds are that nothing resembling this storm will even occur in the first place. Just something fun to look at in the long range...

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  2. Steve, my friend Rob and I disagree on this one.

    I think the odds are quite good for a pattern change that might eventually lead us out of the drought.

    Why? Because the European, the GFS and teleconnections all point to the same thing.

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    Replies
    1. Well, you'll forgive me when I say that I'll believe it when I see it ;-)

      Thanks for the update.

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    2. The good thing about weather forecasting is that you get to find out who is right in the end :)

      The GFS at 240 hours looks MUCH more amplified on the west coast than the ECMWF. Much more. I believe the EC until given strong evidence otherwise, and the EC says this pattern shift isn't even a blip on the butterfly's radar...

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  3. @Steve: You are forgiven!

    Just remember to write back when the forecast turns out to be correct? :-)

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