According to the Climate Prediction Center, the La Niña weather pattern that has persisted for nearly two years appears to be continuing through the summer months. Just as in winter, when La Niña can impact our snow and cold, in spring, La Niña can impact our weather and temperature extremes.
La Niña is part of the weather phenomenon known as ENSO, or El Niño Southern Oscillation. This refers to whether or not sea surface temperatures in the equatorial Pacific Ocean are colder (La Niña) or warmer (El Niño) than average – or near normal, which is known as the name of ENSO Neutral.
We have been in a La Niña state since mid-2020, and current forecasts show that La Niña conditions will persist this summer with a trend towards neutral conditions. It is possible that weak El Niño conditions will develop by the end of this year, but we are more likely to remain near neutral than anything else.
As we move deeper into the spring months, we will begin to see more severe weather conditions playing out nearby. Here’s a look at when all forms of severe weather (hail, tornadoes, damaging winds) start making their way through the state of Colorado.
At the end of April, extreme weather conditions are possible in far eastern Colorado. At the end of May we start to have more frequent severe thunderstorms and by mid-June we are in the height of severe weather season.
With the likelihood of La Niña continuing into July and August, what impact will this have on our weather extremes?
As we have already seen in parts of the Deep South, it has been a very active start to the inclement weather season. In the spring, in a La Niña pattern, what tends to happen is that the jet stream eventually crosses the northern third of the United States. In the spring, when temperatures warm southward, the temperature gradient of the air masses that are created turns into a recipe for bad weather.
Eventually the jet stream will begin to move further north, but due to La Niña it may not retreat as far north as it normally does at this time of year.
With the jet stream not retreating as far north as usual over the next few months, we will have cold air nearby which will allow stronger cold fronts to push into the warmer south and wetter. The collision of these air masses helps bring about outbreaks of severe weather and this configuration allows that to happen more often.
There is no drastic correlation when talking about the impacts of severe weather during a La Niña spring, but there are a few notable points that align with the thought mentioned above. Nationally, some of the most active severe weather seasons in the past 30 years have occurred during La Niña years: 2011, 2008, 1998, and 1995 all had significant severe weather impacts while La Niña was underway. .
Of the first 10 years with the most severe thunderstorm and tornado warnings in Colorado, seven of those years were La Niña years and three of them were El Niño years.
Also, something to note, some of our best severe weather years have all occurred since 2000. When we look nationally, during a La Niña, there is a severe weather target across Texas, l ‘Arkansas and Oklahoma.
For Colorado, there is no overwhelming evidence that we are going to have a significantly increased severe weather season due to the continued La Niña, but there are differences we can spot.
Severe weather events tend to be slightly suppressed statewide when an El Niño is present. Although Colorado is not several knots away from what is normal in a La Niña pattern, we tend towards the more frequent side of things when we talk about tornadoes. Mountainous regions and southern Colorado tend to have slightly more hail problems during a La Niña regime.
Temperatures and precipitation could also be affected by this continued La Niña, but the effects are not as noticeable as they are during the winter months. During the warmer months, ENSO tends to impact hurricane season more than anything else. That said, the long-term forecast for April through June shows signs of drought and warming across Colorado.
What the images above show is that the period between April, May and June should be half an inch to an inch drier than normal. At the same time, we might expect temperatures to be nearly a degree warmer than normal.
Of course, time will tell, but when looking at previous severe weather years, previous La Niña years and long-range forecasts, there is no reason to strongly doubt the possibility that this severe weather season is a little more active than normal in and around Colorado. This year.
Just as people do along the coast ahead of hurricane season, it’s time to prepare for the weather. Hail and tornadoes are no strangers to Colorado. The destructive winds too.
Preparing now for what these threats bring will make the action time much smoother.