It looks like nature is finally catching up with the calendar, as the southern and central portions of the United States are facing a risk for severe thunderstorms every day through Friday. Unfortunately for residents and vehicles alike, April promises to be more active than this underwhelming March.
Looking Back at March
March is usually the time of the year when severe weather picks up in earnest across the United States, as warm, unstable air filters in from the Gulf of Mexico and cool air leftover from the winter stays strong in the upper-levels of the atmosphere. This kind of an environment is ripe for instability, allowing explosive thunderstorms to develop and produce damaging winds, large hail, and tornadoes.
Up until last week, we hadn't really seen the ingredients for severe thunderstorms come together in any meaningful way. The record lull in severe weather was bound to break at some point, but unless there's a string of major severe weather outbreaks this year (which is always possible), the number of severe weather reports through this point in the year is the lowest we've seen in a long time.
Through Monday, we've only seen 37 (preliminary) reports of tornadoes, compared to the 10-year average of 222 through the same date.
We've only seen 194 reports of large hail through March 30, which is just 31.5% of the 10-year average.
Even more astounding is the fact that we've only seen 17% of the damaging wind reports that we typically see up to this point in the year.
Of course, that's not at all a bad thing. As I said a few weeks ago, the atmosphere doesn't build up potential energy like stress along a fault line; this lull in severe weather isn't going to cause the atmosphere to store energy and explode in some freakish, apocalyptic nightmare scenario. However, it doesn't mean that you should let your guard down. Last year got off to a quiet start, too, and 35 people died in an ugly tornado outbreak that occurred at the end of April.
Let's take a look at what you can expect this week.
The Storm Prediction Center has a pretty thick swath of the south painted under a slight risk for severe weather this afternoon, which is a two on a scale from zero to five. The predominant risks this afternoon are damaging winds and large hail (some larger than golf balls, as we've already seen), but a tornado or two can't be ruled out, especially towards Oklahoma and Texas.
Severe thunderstorms are firing up across the southern United States this evening, with severe thunderstorm watches (shaded in blue) in effect from Oklahoma to Georgia through the early nighttime hours. More watches are possible as unstable air spews forth and births vigorous convection. The above image is valid as of 4:30 PM CDT—check the Storm Prediction Center for the latest watches.
The storms are nasty hail producers—around 2:30 PM CDT, the National Weather Service received several reports of hail the size of baseballs (2.75 inches in diameter) in a nasty supercell in southeastern Arkansas. A three-dimensional radar image of the supercell that produced the baseball-size hail is visible in the image at the top of this post.
A strengthening low pressure system will briefly dip down into the Dakotas during the day on Wednesday, allowing warm, moist air to flow across the plains from the south ahead of a cold front approaching from the west. The Storm Prediction Center expects severe thunderstorms to develop in the warm sector ahead of and along the cold front as it swings through the area on Wednesday afternoon. Discrete storms will carry the risk for large hail, and the threat will transition to damaging winds once the storms start to form into one or more squall lines.
Second verse, same as the first. Thursday's severe weather will be similar to what's possible on Wednesday, with storms developing along the cold front as it stretches from the Great Lakes through northeastern Texas. Large hail and damaging winds are the main threats, with severe weather slightly more likely across areas that were battered by thunderstorms last week.
The golden egg of doom (a 15% risk for severe weather) threatens the western half of Dixie Alley on Friday. Provided there's enough instability and wind shear, the threat on Friday should be the same as it is/was on Wednesday and Thursday.
Once the novelty of seeing severe weather on a regular basis again wears off, you'll quickly come to see that low-end threats like this are tedious to cover (and read about!) since the threat is the same day in and day out—large hail, damaging winds, maybe a tornado or two. This will probably be the last time that I cover low-end threats in-depth like this unless there's a noteworthy threat, like hail the size of golf balls in Atlanta or New York City.
Even a regular ol' severe thunderstorm warning is nothing to sneeze at, as even a modest hailstone can inflict serious injury if it hits you or busts through your windows at home or in your car. Similarly, damaging winds are called "damaging" for a reason—it doesn't take much to down trees and power lines, and stronger winds can cause structural damage and launch loose objects (like branches or lawn gnomes) with little effort.
Even though it can get pretty routine, this is the time of the year where you should always pay attention to the risk for severe weather and listen for watches and warnings in your area.
[Images: Gibson Ridge, SPC, GREarth, author]