Published April 27, 2013
Tornado season has been off to a slow start compared to an amped up season last year. AccuWeather.com Meteorologists talk about why the season has been on a slow start, but may pick up as the months progress.
The daily count and running annual trend of tornadoes in the United States is significantly lower this season compared to last. According to NOAA, last year in the months of January through April 25 saw 592 tornadoes. This season between the same months, the U.S. has only experienced 226 tornadoes. The average per year is 492.
Henry Margusity, an AccuWeather.com expert senior meteorologist said that there are two main key points as to why there has been a decrease in tornadoes this year compared to last. The first is, last year, tornadoes were active during the first half of the season between Jan. 1 through April 25.
"Last year we had gangbusters to start out the year, and this year we haven't had any," he said.
The second reason Margusity gives is the warmer weather has been delayed.
"Last January was very warm. As the warmth continued there were more outbreaks," he said.
This January and the remained of the winter was very cold.
AccuWeather.com Expert Senior Meteorologist Dan Kottlowski said the cold pattern that has occupied the United States is due to a major change in the upper levels of the atmosphere above the Arctic Circle. A pattern change that occurred in February allowed cold air from Canada to dip down into southern states. This pattern occupied much of the U.S. into April.
With the cold air pattern sticking around for a longer period of time, the conditions were not favorable for tornado formation, Margusity said.
Harold Brooks, senior scientist at the National Severe Storms Laboratory in Oklahoma also agrees that cold weather has a played a significant role in deterring tornadoes from forming.
"Final counts in March will be close to the lowest mark on record," he said.
This tornado season is abnormal and Brooks said it is in the lower 10 percent of tornado activity over the past 60 years.
The reason that we witnessed more tornadoes last year is because January through March was very warm compared to this year.
Cold fronts were going down into the Gulf of Mexico and would disperse dry air all across the southern states, according to Margusity. This is unfavorable to tornado formation, because the Gulf of Mexico is a key suppler of humid, moist air to produce tornadoes. Another factor in the Gulf of Mexico that was prohibiting humid air was the sea temperatures aren't that warm yet. Although, Kottlowski said temperatures are starting to rise.
With cold air lasting into the later part of spring and the lack of deep tropical moisture, this has contributed to the lack of tornado formation.
"The atmosphere is not unstable," Kottlowski said.
Margusity said that this is just a weather pattern we are in. The tornado season in 2004 was similar to this one, however Margusity pointed out that we are not in a La Nina or El Nino that would be driving this colder weather pattern.
However, AccuWeather Meteorologists think that the months of May and June could be active when it comes to tornadoes.
"Our fear is that there will be more severe weather in June," Kottlowski said.
According to Kottlowski, severe weather will happen in May, but a better question to ask is how much.
Harold Brooks, a scientist at the National Severe Storms Laboratory said that even though we got off to a slow start, that there is no way to really tell what the rest of the season will be like.
"This means nothing for May. Anything that happens between Jan. 1 to April virtually tells us nothing about how the rest of the season will be," he said.
As far as predicting when and where tornadoes will form, meteorologists are still working and researching.
Predicting exactly where a tornado will strike is hard to do because tornado are unpredictable. However, Margusity said that eventually meteorologists will be able to predict 6-12 hours in advance which areas are likely to have tornadoes and the severity.
Brooks also expressed the challenge of predicting tornadoes.
"Maybe 10 years, between five and 10 years from now depending on time of year and what type of system we are looking for. It is a hard research problem," he said.
The decline in tornadoes compared to last year is not a bad thing.
"This is a good thing," Margusity said.
Margusity said that with a lack of tornadoes, there is not massive destruction and people are not getting hurt or killed from severe weather.
For all of your up to date and local severe weather, be sure to check out AccuWeather.com Severe Weather Center.