In a normal year, the southern United States would see severe weather on a weekly basis by the end of February. But that's a normal year, and this is 2015. For better or worse, severe weather across the United States is at an all-time low since records began nearly half a century ago.
If you were to picture weather in February, you would probably cringe at the thought of near-endless snow and cold. That's usually true for the northern United States, but the southeast is used to a much different idea of winter. Sure it gets cold (and even snowy!) on occasion, but February is about that time of the year when severe weather really starts to ramp up.
As the atmosphere slowly thaws out in the waning days of winter, warm and moist air begins to flow ashore into the southeastern United States. When a well-developed winter storm swings through the Midwest or Ohio Valley, it can tug the unstable air farther inland, allowing its cold front to crash into the instability and fire off some ugly bouts of severe weather. This process grows more common the closer we get to spring, as instability increases and upper-level winds grow more favorable for the development of severe thunderstorms.
As of this evening, the Storm Prediction Center has issued four* severe weather watches so far this year. That's all—four. All four products were tornado watches for areas of the Deep South that are supposed to see severe weather around this time of the year (Louisiana and Mississippi, Alabama, and the southeast coast from Florida to South Carolina).
Sure, four sounds like it could be a lot—especially in the winter months—but look how many watches we've seen through the end of February for the past 12 years:
Some years have been more active than others (remember the Super Tuesday tornado outbreak in 2008?), but this is the quietest January and February we've seen since 1970. The previous record-low year for watches was 1985, which saw just seven watches (two tornado, five severe thunderstorm) in January and February. The middle of the 80s set a really low bar, and this year managed to slither beneath it.
Why has it been so quiet? We can chalk it up to the configuration of the jet stream, which is the same factor behind the constant conga line of cold snaps pouring over the eastern United States. The sharp troughs in the jet stream that have brought cold, dry air to the eastern United States are also affecting the tracks of winter storms that move through the region.
Strong winter storms that have swung through the east have mostly stayed too far north or east (hi Boston!) to drag enough unstable air ashore from the Gulf of Mexico to create the instability needed for severe thunderstorm outbreaks. In other words, the jet stream and cold air are working together to save tiny towns from being wiped off the map.
There is a small irony in my writing this post today—a slight risk for severe weather exists across parts of northern Florida and southern Georgia this evening; the track of today's low pressure that's producing beaucoup snow across the Southeast is both strong and close enough to the coast that it's sucking unstable air north towards the cold front:
The cold front digging into the warm, humid air over northern Florida is allowing thunderstorms to fire up in what's turning out to be a pretty rare event this year. The main threat with today's severe weather would be damaging winds and an isolated tornado or two.
Other than that, the severe weather docket through the end of the month is empty as it can get. Let's hope this lucky streak continues through the spring months.
[Images: SPC, Tropical Tidbits | *Updated to add a new tornado watch issued by the SPC at 6:35 PM EST, an hour after this post's publication. This bumps the yearly total up to four from three—still a record low. ]