Even though Friday was the official start to spring, severe weather season across the U.S. typically ramps up much earlier. This year, however, has been quiet. Extremely quiet. In fact, we're on track to see the quietest start to the year we've ever recorded. That's probably going to change pretty soon.
Severe thunderstorms usually begin to pick up in coverage and intensity across the southern and central United States in late February and early March, marking the beginning of a fairly boisterous severe weather season that lasts through the summer months. The most volatile time of the year is from late March through early June, when the atmospheric setup is most favorable for supercells, which are the leading cause of the country's infamous tornado outbreaks.
"We are in uncharted territory with respect to lack of severe weather", said Greg Carbin, SPC's warning coordination meteorologist. "This has never happened in the record of SPC watches dating back to 1970."
Since the beginning of 2015, the SPC has issued only four tornado watches and no severe thunderstorm watches, which is less than 10 percent of the typical number of 52 tornado watches issued by mid-March. The approximately 20 tornadoes reported since January 1 is well below the 10-year average of 130 for that time period.
There is no one clear reason to explain the lack of tornadoes, Carbin said. "We're in a persistent pattern that suppresses severe weather, and the right ingredients — moisture, instability, and lift — have not been brought together in any consistent way so far this year."
A severe thunderstorm or tornado watch is issued when conditions are favorable for the development of these dangerous phenomena. Warnings, on the other hand, are issued when large hail, damaging winds, or a tornado is imminent or occurring. We can look at the number of warnings and severe weather reports to further visualize this year's (lack of a) severe weather season.
The above map shows all of the severe thunderstorm and tornado warnings issued between January 1 and March 21; compared to previous years, there have only been a handful of warnings this year over the areas that usually see severe weather during January and February. This map should be lit up like a Christmas tree by now.
Warnings just show us where thunderstorms had the imminent potential to produce damaging winds, large hail, or tornadoes—while the National Weather Service is getting better at cutting down on the number of false alarms, not every warned storm produces severe weather. Reports sent to the NWS give us ground truth as to where severe weather has occurred so far this year.
Through March 21, we've only seen 35 tornado reports, 66 hail reports, and 209 reports of wind damage or gusts of 58 MPH or greater. Such a calm atmosphere is almost unprecedented seeing that we're a week and a half away from April.
Not that this is a bad thing, of course. Severe weather doesn't work like earthquakes; unlike the potential energy stored along a fault line as stress builds up, the lack of severe weather isn't causing the atmosphere to build up pressure that will lead to an explosive outbreak. We could go ten years without another tornado outbreak, and that fact alone wouldn't mean that the next outbreak would be "the big one," so to speak.
The only downside to this lull is that it breeds complacency; the longer we go without a major severe weather event is a longer time that people haven't had to seriously pay attention to forecasts, make plans for what to do in the event of an emergency, and take action because of an approaching storm. The one good thing about active severe weather is that it gets people in the habit of safety.
Our luck is on borrowed time, unfortunately. The pattern's going to change at some point, and it looks like the lull is nearing its end.
During the day on Monday, there's a marginal risk for severe weather across parts of central and northern Florida as well as a portion of the central Plains. A marginal risk is a one on a scale from zero to five.
Any thunderstorms that form across the risk area in Florida have a chance to produce damaging winds (58+ MPH), and communities across parts of Oklahoma and Kansas should be on the lookout for supercells that could drop large hail along with some gusty winds.
The models are hinting at a slightly more interesting severe weather event on Tuesday.
The Storm Prediction Center has issued a slight risk—two out of five—for severe weather across the Ozarks on Tuesday, with a marginal risk buffering this zone that includes St. Louis, Kirksville, and communities just east of Tulsa and Kansas City.
A low pressure system is expected to develop over the northern Plains and Upper Midwest on Monday and Tuesday, which could bring enough unstable air into the region that any thunderstorms that form could tap into wind shear and turn severe. The SPC warns that any supercells that form carry the risk for large hail and damaging winds. This forecast can and likely will change over the next couple of days as models get a better idea of what will happen and forecasters can narrow down the impacts, so anyone in and around the Ozarks should prepare for their first bout of severe weather since last year.
Always stay tuned to your local forecast if you live in an area that typically sees severe weather around this time of the year. Patterns can change on a dime, and an end to your streak of nice, calm weather could surprise you if you're not staying up-to-date. The Storm Prediction Center is responsible for issuing severe weather outlooks and severe thunderstorm/tornado watches, while local National Weather Service offices issue local forecasts and individual warnings.
[Satellite Image: MODIS Today from March 16, 2015 | Maps by the author | Updated information for Monday and Tuesday around 6:30 PM EDT on Sunday for visitors coming over from io9. Thanks for reading!]