Violent Weather La Niña’s Fault? And What About Hurricane Season?

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Part II: Yesterday, I talked about the weird weather we’ve been having lately – record tornadoes, record floods, late season snows, late season record lows.  What’s going on? Does all this portend of more to come? Does it mean a more active hurricane season? Are there factors leading to the expected active hurricane season which are to blame for all of this unusually active/weird weather? ImpactWeather’s StormWatch Manager Fred Schmude helps shed some light on the situation.

“I think the main reason we’re seeing this active weather is the configuration of the main storm track which has been stuck over the same part of the country stretching from the Central Plains (Oklahoma and Kansas) eastward toward the Ohio Valley. Not only has it been nearly stationary over this region of the country, it has also been stronger that normal, more than likely due to the configuration of a weakening La Niña event over the eastern tropical Pacific. We saw a very similar pattern back in 2008 when we also had a weakening La Niña during the spring months resulting in a record number of tornadoes. The graphic below indicates we are near or slightly ahead of the 2008 pace…the big difference this year is unfortunately the tornadoes had made direct hits on urban areas resulting in an elevated number of fatalities, especially over Missouri (Joplin) and Alabama (Tuscaloosa and Birmingham).

Image: NOAA

“Since the storm track has been virtually stuck over about the same area of the country, we have also had a record amount of rain affecting the Mid Mississippi Valley through the Ohio Valley. Here’s another graphic highlighting precipitation anomalies over the past 90 days. The orientation of the storm is easily identifiable over the Ohio and Tennessee Valleys.

“Here’s another graphic showing how much rain has fallen over this region of the country during the past 90 days. Note the wide swath of 15 to 25 inches of rain extending from the Mid Mississippi Valley through the Ohio Valley, with isolated amounts up to 30 inches or more from northern Arkansas to Kentucky. This much rain falling over the same area of the country in such a short period of time has resulted in the widespread flooding we’ve seen across part of the Ohio and Mississippi River Valleys.

Image: NOAA

“On the other side of the coin, this same weather pattern has resulted in record drought conditions over a large part of the southwest U.S., including Texas, as the main storm track remains well north of the region. In essence, this rainfall pattern over the past several months should be more spread out, but in reality it’s been concentrated over the same area of the country.

“What does the forecast look like? I’m definitely beginning to see some changes in the atmospheric pattern that will weigh heavily on the long range outlook as we move into June. First of all, La Niña is quickly weakening and I think this will have a huge influence on the flow pattern resulting in more rainfall to the Gulf Coast and the drought-parched regions of Texas as tropical moisture returns during the summer months.  Secondly, we’re beginning to see signs the main storm track will be lifting a little farther north across the Northern Plains, Great Lakes and Northeast as we move into June and I think this will be the established pattern as we move into the summer months with the main threat of severe weather remaining over this region of the country. This of course does not mean areas farther to the south over the Deep South and Gulf Coast are out of the woods as far as severe weather is concerned, but it does indicate the frequency of severe weather events will decrease as we move into the summer months. However, before this happens we are going to see an enhanced risk of super cell thunderstorms and tornadoes over the next 48 hours stretching from the Ohio Valley to the northern Deep South as a strong upper level storm system clashes with unstable Gulf air.

“As far as the hurricane season is concerned, I definitely think we will see a very active season with several tropical cyclone threats on the Gulf Coast and Atlantic Seaboard due to a combination of a weakened La Niña to a “La Nada” (neither La Niña nor El Niño) and a stronger Bermuda High. Even though we will likely see fewer named storms compared to 2010, long range signals favor a flow pattern which is conducive to more tropical cyclone strikes across the U.S. coastline later this summer into the early part of fall.

In addition there could be some correlation to the current level of tornado activity and how active the season may be over the U.S. Back in 2008, we had a record number of tornadoes which also correlated to a very active tropical season with 16 named storms including Hurricane Dolly, TS Eduardo, TS Fay, Hurricane Gustav, Hurricane Hanna, and Hurricane Ike all directly affecting the Gulf Coast and Atlantic Seaboard.”

Even though large, violent tornadoes are pretty rare along the Gulf Coast, our main concern this time of year are tropical systems. The official start of hurricane season is less than a week away, although the peak of the season isn’t typically until August. I remember Ike all too well and let’s just say I don’t want history to repeat itself this year.

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