The National Weather Service had not issued a tornado warning or watch anywhere in the United States this year as of Friday, making it the longest beginning of a year without the threat of tornadic activity on record, officials with the weather service's Climate Prediction Center said.
A colder winter -- especially in the eastern half of the nation -- combined with drought conditions in the west have created the mild tornado season so far, said meteorologist Mike Halpert with the center in College Park, Md.
"We had the jet stream going through the middle of the country," he said, referring to a current of cold, arctic air that blasted from Canada, dipped deep into Arkansas and then headed back to the northeast. "The upper-level conditions conducive for the formation of tornadoes were not able to form as well. They are more dependent on the warmer weather."
But the year's mild tornado period may end soon, forecasters said, and Arkansas could again be a target.
The Climate Prediction Center announced last week its discovery of an El Nino, a warming of the southern Pacific Ocean that alters weather patterns across the United States. Since 2000, the center identified several weak El Nino events in 2002, 2004, 2006 and 2010.
The 2010 El Nino was blamed for unseasonably high temperatures during the Winter Olympics in Vancouver. Large Gulf of Mexico hurricanes have been more apt to develop during years with El Ninos, too.
In September, the Climate Prediction Center issued an El Nino "watch," when El Nino conditions appeared to be forming. Forecasters retracted that watch when the El Nino died out, but then early this month, the conditions formed again.
It's late for the discovery of one, Halpert said. They normally appear in late fall.
The El Nino is possibly responsible for lifting the jet stream out of Arkansas, Halpert said. The jet stream brought unseasonably cold air to the state during the past few months and provided the ingredients for sleet and snowstorms in February and March, Halpert said.
Now, as temperatures rise, heavy rain has soaked most of Arkansas, and a pattern more apt to produce severe weather has formed.
National Weather Service meteorologist Jeff Hood of North Little Rock said the jet stream "retreated back" to the northern United States.
"We're not going to see that deep, diving cold air anymore," Hood said. "We're getting a southwestern flow now that's bringing moisture from the southwest. When that happens, it can lead to severe weather.
"When you've got cool air from the west meeting warmer air to the east, it's a true collision, and that's what brings the tornadoes."
January and February are generally the least-tornadic months in Arkansas because of the colder weather, said National Weather Service meteorologist Chris Buonanno of North Little Rock.
But the state isn't immune to twisters early in the year. In January 1999, Arkansas recorded 107 tornadoes during the month, and on Feb. 5, 2008, 12 tornadoes ripped through the state, including one that traveled 122 miles from Atkins to Highland and killed 13 people.
Mild weather early in the year also doesn't always translate into mild springs. In 2004 -- one of the quietest starts to tornado season in the United States -- a record 1,819 tornadoes were reported by the end of the year, according to the Climate Prediction Center.
"We're getting into the time of year in Arkansas where severe weather is expected," Buonanno said. "It picks up in late March and April, and peaks in the first week of May, usually. It begins declining in June, but severe weather can happen anytime."
Last year, after a wet winter and early spring, an EF4 tornado with winds up to 200-mph struck April 27 in central Arkansas, killing 16 people.
"A prime signal for severe weather in the spring is having cold air in the west and warm in the east," Halpert said. "Last month, it was cold in the east. It was the opposite configuration of what is needed.
"But that's beginning to change now," he said. "Things need to warm up to get storms going, and that's happening."
The cold, wet winter hindered business at Arkansas Storm Shelters, a Russellville company that installs storm shelters across the South, said owner Jared Gray.
"When it snows, we shut down," he said, referring to the snowfalls in mid-February and early March. "People focus their attention on immediate needs. Lately, they've been thinking of fuel sources, generators, their roofs -- all emergency purchases.
"It will switch, though, as it warms up."
Gray said storm shelter businesses have increased sales during the past 10 years because of the proliferation of tornado pictures and videos on social media sites such as Facebook and YouTube.
"Shelters are a lot more popular than before," he said. "Sales spiked after the Vilonia tornado. People see how tragic tornadoes can be."
State Desk on 03/15/2015