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Agriculture Weather Forecast - Explaining a Year’s Worth of Weather

published: May 14th 2010
by: Weather Wise by Brian Bledsoe

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Well folks, one column a month leaves us a lot to talk about.  I am all about giving you too much information, then you can take it a step further and research more about it if you like.  Or, you can always ask me questions.  I love talking about what makes the weather tick…
 

Here we go…  What is El Nino?  El Nino is the abnormal warming of the equatorial Pacific Ocean that can drastically alter global weather patterns.  El Nino occurs about every 2 to 7 years and can last 6 to 14 months.  El Nino has been awesome for the Southern Plains, erasing a tremendous multi-year drought.  Below is the Drought Monitor from early May 2009:

All that yellow, brown, and red shading is indicative of the wide reaching drought that Texas was enduring.  Check out the most recent Drought Monitor early May 2010:  Notice how the drought has been completely erased from the state of Texas

Bottomline, El Nino was an agricultural savior to much of the Southern Plains.  An active storm track got going late in 2009 and still hasn’t quit.  Below is map of North America and the prevailing pattern during an El Nino:

An El Nino usually leads to the intensification of the Southern Branch of the jet stream, which usually roars  across the southern tier of the United States.  Not only does this increase the storm frequency, but the storms are usually loaded up with juice (moisture) from the Pacific Ocean.  History is a very useful weather tool, and history proved to be spot on with how the Winter and Spring forecast shook out.  In the early Spring of 2009, I began talking about how the drought for Texas would not only come to an abrupt end in late 2009 and early 2010, but it would go from one extreme to the other.  Simply put, that’s just how El Nino works.  However, all good things usually come to an end…
 

La Nina:  La Nina is the abnormal cooling of the equatorial Pacific Ocean, that can dramatically alter global weather patterns.  La Nina occurs about every 2 to 7 years and can last 10 to 24 months.  Below is an graphic representing the weather pattern that dominates the US, during a La Nina:

Notice how the pattern is completely different.  The jet stream is consolidated into one stream that usually runs along the northern tier of the US.  This means less frequent storms, plenty of wind, and the likelihood of drought increases greatly.  The problem with La Nina, is that once established, it can be very tough to erase.  That big blocking high pressure that centers itself in the western Pacific Ocean, becomes a monster that most farmers and ranchers fear.  And, rightly so…
 

Computer models not only forecast what type of weather we may see in the near term, but they can also forecast what phase the Pacific Ocean may hold.  El Nino or La Nina.

 

The above graphic shows how strong El Nino developed from last Summer through early January.  Positive numbers equal El Nino, while negative numbers equal La Nina.  The dotted line shows how El Nino intensified in the late Fall and especially during the Winter.  It peaked out during late December and early January.  The red lines are the model forecast of the trend that will occur during the next several months.  Notice how this particular forecast called for El Nino to pretty much come to an end ( line approaches 0 ) early in the Summer.  Then possibly entering La Nina territory ( lines going below 0 ) sometime during the Summer.  At the time this forecast was made ( January ), I could tell that the trend was correct, but the timing was still a bit uncertain.

 

The above model forecast was made in February.  Notice how the trend is still heading toward La Nina, but even more so.  Look at all the lines below zero starting later in the Summer and notice how closely they are packed together.  This simply means that the computer model is confident that we will likely be slipping into a La Nina at sometime later in the Summer.  Strength, still to be determined.

 

 The March forecast is even more telling.  El Nino ends completely by June at the latest, and La Nina looks like a certainty.  Not just a La Nina, but possibly indicating a fairly strong La Nina developing by late Summer.  You can see where this is going…

The April forecast is pretty much in line with the March forecast, indicating strong confidence that La Nina is right around the corner late this Summer and Fall.  Most of the lines have this La Nina entering moderate to strong intensity right away.  This means that while we may be ok in the moisture department for early Summer, it may shut off abruptly by late Summer.
 

The graphic below shows the temperature anomalies for the various oceans around the world. 

 

Notice that there is still some areas of the Pacific Ocean that are near the equator are still about 1 to 1.5 degrees C above normal.  However, the lingering El Nino is a shell of what it was back in December and January.  Like we’ve just talked about, it will continue to rapidly disappear.
 

Here is a look at that La Nina pattern again:

Not only may we dry out in the Southern portion of the country, but it may turn quite hot.  Double whammy for sure…  The one thing that may be a wild card for the late Summer, is what type of tropical activity may impact the Gulf Coast.  La Nina’s are usually favorable for an uptick in tropical storms and hurricanes.  Usually the problem with relying on tropical activity for good moisture, is that it usually ends up being way too much and does more harm than good.  Granted, this may save some parts of the south late in the Summer, it won’t be around to help in the Fall and Winter.  Like I always tell farmers and ranchers, plan ahead, plan ahead, plan ahead…