You may remember Summer 2011. It was the hottest on record in OKC, with 63 triple-digit heat days. During that summer, our climate was under a neutral phase of the ENSO cycle. What is ENSO?
El Niño Southern Oscillation is a climate pattern that can have influences on our daily weather. It changes every several years from either a La Niña, El Niño, or neutral phase where neither one exists. During La Niña, high pressure sets up south of Alaska, allowing the equatorial Pacific waters to cool. This typically allows for drier and warmer than average conditions across much of the south.
The effects are more pronounced during the winter months. La Niña has been with us since Winter 2011.
Temperatures in April of this year in OKC have been very warm; 4.6 degrees above average. Rainfall has also been above average by a little over two inches.
Another element that influences our weather is the NAO, or North Atlantic Oscillation. It has a positive and negative phase.
During the positive phase, the south and eastern part of U.S. tend to see warmer than average temperatures. This has been our pattern throughout Winter 2011-2012.
So what will our climate pattern be like by May? Turns out, La Niña is fading.
Sea-surface temperatures have been warming in the equatorial Pacific Ocean and are expected to continue to warm through May. The NAO should become more negative too. Here’s a graphic to explain the NAO:
Look at that curvy black line, which represents the NAO index. Over the past several months, it’s been positive. However, so far in April, we’ve seen it a bit more negative. Through May, NAO may become more negative. What does all of this mean? If NAO becomes negative, and/or an El Niño develops, which is quite a possibility, we could be looking at a cooler and wetter next several months, including the potential for more severe weather.
By: Danielle Dozier