Call it the silver lining in last winter’s polar vortex: This year has so far seen fewer twisters than any similar period in at least six decades and possibly a century or more.
The U.S. has so far seen zero tornado deaths –- the safest start since 2002.
The start of 2014 is definitely the slowest in terms of tornadoes since 1953, when the most detailed database was started, Harold Brooks, a senior researcher at the National Severe Storms Laboratory in Norman, Okla., told NBC News.
Slightly less reliable records dating back to the 1870s suggest “this is likely the slowest start to a tornado season since 1915,” he adds. “1900 is possibly slower and, prior to that, we're looking at the late 1870s and early 1880s for challengers.”
For Greg Forbes, the severe weather guru at The Weather Channel, the most striking data is that the start of 2014 marks “the longest that we have gone at least since 1950” without a tornado at 3 or stronger on the Fujita scale. Tornadoes are rated from 0-5, with 5 being the most powerful.
So how did the Arctic polar vortex play into this? Cold blasts coming down with the upper-level jet stream last winter prevented warm air from coming in off the Gulf of Mexico. That stalled the creation of storms from the clashing of cold and warm weather fronts.
“The cold winter weather systems drove cold, dry air even across the Gulf Coast states such that the instability was not adequate for severe storms even across the Gulf Coast states on most occasions."
“The cold winter weather systems drove cold, dry air even across the Gulf Coast states such that the instability was not adequate for severe storms even across the Gulf Coast states on most occasions,” said Forbes.
Another way to look at it, said Brooks, is that “the lack of warm, moist air at low levels of the atmosphere have meant there have been fewer than normal thunderstorms this winter and, as a result, fewer than normal tornadoes.”
So is there a chance that 2014 will go down as a season with no twister deaths? The odds are heavily against that: On average, twisters kill about 60 people each year in the U.S., and no year on record has ever been free of tornado deaths.
Moreover, late April and May have traditionally been the more active times for twisters. For Wednesday, areas from northern Nebraska to northern Texas face a “slight risk” of twisters, the Storm Prediction Center warned.
After a slow start in spring, Forbes warned, the jet stream pattern “is beginning to get more favorable” for twisters.
Indeed, some activity could develop as soon as Wednesday. “A small tornado outbreak (is) likely” in some central states tomorrow, Forbes predicted on his tornado watch page.