Thursday, May 10, 2012

La Nina's gone. Now what?

NOAA's scientists made it official this week, burying the La Nina conditions that have been in control for about two years.

Meteorologists say water temperatures in the eastern Pacific basin have warmed, and the La Nina has become what is called Enso-Neutral. What that means is we're in between El Nino and La Nina.

La Nina was one of the factors in our incredibly mild winter, and it played a role in the very mild late February and March in 2011. It also was considered a factor in the above-average number of hurricanes in the Atlantic and Caribbean last summer, although nearly all those storms never hit the United States.

So now what?

NOAA's forecast is for Neutral conditions to continued through September, although meteorologists say a few of the computer models predict an El Nino could form by late summer.

And beyond that? The forecast is for an equal chance of Neutral or El Nino conditions for the end of the year, taking us through autumn and into next winter.  La Nina conditions are not expected to develop again in the near future.

So here's what that means:

HURRICANE SEASON ... Just about all scientists expect fewer tropical storms and hurricanes in 2012 than in 2011. In La Nina seasons, the low-level winds from the Pacific to the Atlantic are weak. That allows thunderstorm clusters to develop in the Atlantic and Caribbean, which helps tropical systems develop.

There are plenty of other factors at work, such as Atlantic Ocean surface water temperatures. But La Nina is one player involved.

This season, those winds across the United States won't be as weak. That means conditions won't be quite as ripe for tropical storms and hurricanes to form.

Of course, only one storm -- Hurricane Irene -- affected the United States last year, even though there were an above-average number of systems.  If there are only two hurricanes in all of 2012, and both of them hit the U.S. mainland, we'll consider 2012 worse than 2011.

NEXT WINTER ... In La Nina winters, conditions in the South tend to be warm and dry. That's pretty much what happened this past winter.  Once again, however, there are other factors involved.

La Nina was in place for the winter of 2010-11, but there also was a Greenland block -- strong high pressure over Greenland, sending cold air funneling southward into the eastern United States. The result: a very cold December and January, and then a warm mid and late February when La Nina took control from the Greenland block.

But with no La Nina next winter, it's safe to say we won't have it as mild as in the winter of 2011-12. Then again, few winters are as mild as 2011-12.  You can pretty much count on using the heat at home a lot more, and we'll probably be at least looking at the chances of snow and ice more than we did last winter.