Severe weather threat for Sunday, April 15
Damaging winds, tornadoes, heavy rain are all possible this afternoon and evening
We in the Charleston weather community are watching this afternoon’s weather with much interest as a sharp cold front approaches the area. Aided by energetic upper dynamics and what looks to be ample instability, the threat for severe weather will be with us from roughly 3pm-9pm.
This morning
Ahead of thunderstorms, we are finding partly cloudy skies and rather warm temperatures in the upper 60s to low 70s. Dewpoints are juicy in the mid-60s to almost 70, which is pretty substantial for this time of year. Instability is already building, and with additional sunshine we should be able to achieve 80 degrees easily, contributing to more than enough fuel to strengthen the squall line as it pushes into the area.
A few showers will be possible ahead of the front later this morning into early afternoon. Any premature instability release would be helpful ahead of the stronger storms this afternoon to help taper the severe weather threat, but it appears that widespread shower activity will be unlikely.
This afternoon and evening
Wind Advisory
Ahead of the front, winds will strengthen out of the south as the pressure gradient increases and we tap into a strong low-level jet. Gusts to 40 MPH will be commonplace especially on elevated surfaces such as bridges and overpasses. Please be careful when driving on the bridges today. Reduce speed and keep both hands on the wheel, especially if driving a high-profile vehicle.
Squall line approaches
By 2–3 PM, we should begin to see the squall line approaching the area from the west. High-resolution modeling suggests that there could be a broken band of supercell thunderstorms ahead of the line as they approach the I-95 corridor. While the threat this afternoon is primarily from damaging straight-line winds, tornadoes cannot be ruled out in broken portions of the line or from any standalone supercells that develop (though the likelihood of standalone storms appears to be small).
Squall line affects the Tri-County
By 4–5 PM, the leading edge of the squall line will be entering the Tri-County area from the west. Damaging straight-line wind gusts and very heavy rain will be possible. We need to watch the leading edge of the line for possible rotation and brief tornadoes as well. By 6PM, the line should be reaching the coast, and by 9 PM we should be starting to see things wind down somewhat.
Flooding threat this evening
1–2" of rain will be possible from the line as it swings through. While we need it, I’m concerned that the heavy rain combined with high tide at 8:31 PM may contribute to some flooding concerns in the streets of downtown Charleston. This will need to be watched closely. Be prepared for possible flood advisories.
Prepare for the weather
The best defense against severe weather is a good preparedness plan.
- Have flashlights ready and keep phones charged in case of power outages.
- Know your safe place in case severe weather threatens your location. If a tornado warning is issued, head to the lowest floor of your home or business and take shelter in an interior room, as far away from windows as possible.
- Outdoors? Be watching very closely for threatening weather. If you hear thunder or see lightning, head into a safe place quickly as you are in danger of being struck. Regardless of the “severe” status of thunderstorms — which is defined by NWS as having quarter-size hail, 58 MPH or greater winds, or a tornado — lightning is an ever-present hazard.
- Have multiple ways to receive watches and warnings. NOAA Weather Radio, smartphone apps from local TV stations, and broadcast radio/television are all good ways to listen for warnings. I’ll be tweeting warnings as they come in on @chswx on Twitter, but know that social media shouldn’t be your sole source of severe weather information.
Bottom line
- Severe weather is possible today, with damaging winds the primary threat. Tornadoes are a concern. Be prepared for that possibility. Have your severe weather plan ready to go in case a warning is issued.
- Not everyone will see severe weather. If you don’t see any severe weather today, count yourself as fortunate and don’t get mad that the weatherman got you worked up or interrupted your TV show for “nothing.” Your neighbors may not be as fortunate, and may actually really appreciate the heads-up and programming interruption.
- Flooding is a concern this evening for downtown Charleston. I don’t think this will be a widespread flooding event, but the timing of the line with high tide will need to be watched very, very closely.
I’ll be updating Twitter as needed today and will try to go live on Periscope for any imminent severe weather. Please stay safe, everyone!
