Today will be a pretty interesting weather day across some of the most heavily-populated sections of the East Coast, as there’s a heightened risk for large hail, damaging winds, and tornadoes in major cities like Atlanta, Charlotte, D.C., Baltimore, and Philadelphia. Here’s what you need to know to stay safe.
The three-dimensional radar image above shows a powerful tornado-warned supercell just north of Atlanta, Georgia, as it dumped golf-ball-size hail along the city’s northern suburbs around 2:15 PM EDT. There was some wind damage, but no reports of tornadoes with this particular storm as of the publication of this post.
The above map shows severe thunderstorm and tornado watches as of 3:30 PM EDT. The number and location of watches will shift and evolve throughout the day as the risk for severe weather grows and dissipates in different areas. The counties shaded in red are under a tornado watch, while the counties shaded in blue are under a severe thunderstorm watch. The watches are in effect until the storms move out or the threat diminishes—whichever comes first.
While we’re focusing here mostly on the severe weather happening from Georgia through Pennsylvania, there are also some pretty hefty thunderstorms firing up over Florida. Severe thunderstorm watches cover most of the peninsula this afternoon, as storms bring the risk for large hail and damaging winds. An isolated tornado or two can’t be ruled out in areas where storms interact with sea breezes or boundaries from previous storms.
The Storm Prediction Center has issued an enhanced risk for severe weather across most of the Mid-Atlantic region, which means today’s risk for severe thunderstorms is a three on a scale from zero to five. The upgrade from the always-common “slight risk” is due to the 30% probability of damaging winds in excess of 60 MPH and hail the size of quarters or larger within 25 miles of any point in the enhanced risk area.
The enhanced risk just shows the area where the most widespread risk for severe thunderstorms exists—areas in the marginal and slight risk zones have to pay attention to the weather today, as well.
Large hail and damaging winds are always dangerous, especially if you’re caught outside or in your vehicle when a storm approaches, but the threat that makes people hyperventilate the most is tornadoes.
The above map shows the risk for tornadoes today as forecast by the Storm Prediction Center in their afternoon update. A 5% risk for tornadoes exists across the I-85 corridor between Atlanta and Charlotte—this means that there’s at least a 5% probability of seeing at least one tornado within 25 miles of any point within the shaded area. That seems like it’s low, but the climatological risk for tornadoes in this region on April 20th is about 0.30%. Any tornadoes that develop should be on the weaker side, but even the smallest EF-0 tornado is life-threatening if you’re in its path.
Folks who live near the Mason-Dixon line should pay a little closer attention to the threat for tornadoes. There’s a stationary front sitting along a line stretching from just south of State College, Pennsylvania, southeast through Philadelphia and extreme southern New Jersey, and any thunderstorms that form along or near this boundary have an increased risk of producing tornadoes. The shifting winds around a stationary or warm front make these features a common focus for tornado activity.
As always, make sure you’re never more than a few hundred feet from safety on a severe weather day. Don’t park under an overpass during a hailstorm. Keep an eye on the radar so you know what’s coming and you’re not scrambling to take action if a severe thunderstorm or tornado warnings is issued.
[Images: Gibson Ridge, GREarth, author]