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Date: 9/25/2013

Title: El Nino or La Nina this Winter?

It is that time of year when we take a very close look at water temperatures in the subtropical Pacific Ocean as water temperatures can play a large role on how the last part of fall and the winter season will unfold.

A little refresher. El Nino is when water temperatures in the subtropical Pacific are warmer than normal. La Nina  is the opposite, water temperatures are a bit colder than normal.

Even very small water temperature changes (+/-0.5 to 1.5C) can play a large role where the jet stream develops during the winter and spring seasons, can make areas warmer or colder, etc.

Most of the time during the winter of 2012/2013 we were in a La Nina weather pattern. La Nina played a large role in the mild and dry start to the winter season last year (especially November and December). As water temperatures warmed slightly late last winter in the subtropical Pacific, winter got a lot more interesting with more storms and increased snowfall across many areas of the USA late in the winter season.

The El Nino and La Nina phenomenon impact the weather patterns across the USA differently based on locations. The impacts of El Nino are felt more along the west coast and southern areas of the USA while La Nina impacts the Pacific Northwest, Rockies and Plains states.

But what happens when there is no El Nino or La Nina when water temperatures are close to normal averages? We may find out this winter as odds are that we are going to be in what is called an ENSO neutral situation (ENSO stands for El Nino Southern Oscillation).

See plot below that shows the odds of an ENSO neutral winter look higher than having an El Nino or La Nina.

Being in an ENSO neutral pattern does make a winter forecast a little more tricky as the known weather patterns that are associated with El Nino or La Nina may not come into play this winter. 

If we do end up in a winter season where water temperatures in the Pacific are close to normal or just slightly above normal, then we do have an increased risk of some real cold periods this winter as the northern latitudes may dominate the weather pattern this winter as opposed to the Pacific.

So, some of the long range forecasts for this winter you have heard calling for some cold weather this winter may be on to something!