Current State of The Tropical Pacific Ocean: El Nino and La Nina

If you read this blog with regularity, you know we focus a lot on long range weather patterns and prediction of said patterns.  We've been under the influence of an El Nino, for the past several months.  However, this is rapidly changing.  Below is a map that shows current sea surface temperature anomalies:

As you can read from the legend, the yellow, orange, and red colors indicate warmer than normal sea surface temperatures.  That small yellow stripe across the equatorial Pacific Ocean is what is left of our El Nino.  After two really dry Winter's here in Southern Colorado, El Nino blessed us with adequate snowfall and more than adequate snowfall for some places.  This was courtesy of the southern branch of the jet stream being active.  The typical El Nino pattern is pictured below:

Notice how it keeps the southern tier of the country pretty wet and cool.  Southern Colorado was on the northern fringe of the active storm track and reaped some of the benefits.  Now some would say that it didn't benefit us at all.  Colorado Springs only picked up 32" of snow for the Winter and Pueblo only 29".  Granted, those totals are below normal, but not as below normal as last Winter.  Plus, we have seen some decent rain this Spring, and that has helped to keep the drought away.

In fact, the only droughty spots in the state reside in parts of the northern mountains and the northwest part of the state.  Otherwise, we are in pretty good shape.  Good news, as we continue to head through Spring...

However, I am afraid of what may happen later in the Summer and into the Fall and Winter season of 2010.  El Nino is going to go away, and be replaced by the drought producing La Nina.

The graph above illustrates how quickly and dramatically El Nino is likely to come to an end.  Notice how all of the red lines drop to below normal sea surface temperatures and in a pretty noticeable fashion.  If the above model forecast is correct, we should slip into La Nina conditions somtime in July.  I believe the above model forecast to be correct.  Why?  If you go back and read my previous post on the PDO and AMO, you will understand:  Simply put, the current state of the PDO supports more frequent and long lasting La Nina's.  Not good for Southern Colorado.

As you can see, the La Nina favored pattern includes a big blocking ridge of high pressure, that sends most of the good storms to our north.  We see a lot of downsloping wind, dry air, and subsequent drought is easy to achieve.  The Winter's of 2005-06, 2007-08, and 2008-09 were influenced by La Nina conditions and our snowfall totals sufferred.  Unfortunately, I see La Nina coming back and bringing the potential for a dry and hot late Summer, dry and windy Fall and Winter.  Can we get enough early monsoon moisture to offset this trend?  That is the wildcard, in which I am not yet sure.  Should know in the next month or so though...  Stay tuned.

Chief Meteorologist Brian Bledsoe


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