High Wind Warning
This is a warning issued for sustained surface winds greater than 40 mph/64 kph lasting more than an hour or winds over 58 mph/93 kph over land that are either predicted or occurring for an unspecified period of time.
High Winds Warning (Derechos)
Derechos are widespread, severe wind events resulting from persistent and violent a complex of thunderstorms that becomes organized on a scale larger than the individual thunderstorms-a Mesoscale Convective System (MCS)-but smaller than hurricanes. These winds normally persist for several hours or more. The type that forms during the warm season over land has been noted across North America, Europe, and Asia, with a maximum in activity noted during the late afternoon and evening hours.
The Derechos environment includes dry mid-level winds that are ingested into a squall line (a line of thunderstorms that have a common lifting mechanism) or just a segment of a squall line. The forward motion of the storm along with an intense downdraft (vertical movement of a very cool air mass ahead of the thunderstorm) produced by negative buoyancy via evaporational cooling. This brings down momentum from the middle levels of the storm to its surface.
A severe wind is one with wind speeds of 50 knots (58 miles per hour) at the surface. However, in a derecho, these severe winds encompass a distance of at least 400 km (250 miles) either out ahead of or along a squall line. The length of time the severe winds last can be particularly damaging. While a severe thunderstorm may produce severe convective wind gusts that last for several minutes at a point location, derecho winds can last 30 minutes or longer. Derechos can be tracked from radar and severe weather reports while they are occurring since severe weather reports will be given in sequence as the derecho traverses along.
High Wind Safety
If you are caught outside during high winds:
- Take cover next to a building or under a secure shelter.
- Stand clear of roadways or train tracks, as a gust may blow you into the path of an oncoming vehicle.
- Use handrails where available and avoid elevated areas such as roofs.
- Listen to the radio for changes in weather conditions that could create more dangerous driving.
In the event of a downed power line:
- Report downed lines to Dixie Electric or call 911.
- Avoid anything that may be touching downed lines, including vehicles or tree branches.
- Honk your horn, roll down the window and warn anyone who may approach of the danger. Ask someone to call the police.
- Do not exit the car until help arrives unless it catches fire. To exit, open the door, but do not step out. Jump without touching any of the metal portions of the car’s exterior, and quickly get to safe ground.
If you are driving:
- Keep both hands on the wheel and slow down.
- Watch for objects blowing across the roadway and into your path.
- If a line falls on your car, stay inside the vehicle. Do not touch any part of the metal frame of your vehicle.
- Keep a safe distance from cars in adjacent lanes, as strong gusts could push a car outside its lane of travel.
- Take extra care in a high-profile vehicle such as trucks, vans, SUVs, or when towing a trailer, as these are more prone to being pushed or flipped by high wind gusts.
- If winds are severe enough to prevent safe driving, safely pull over onto the shoulder of the road and stop; avoid parking near trees, power lines or buildings.