How can drivers determine if dark clouds on the horizon may signal severe thunderstorms capable of producing tornadoes, hail or powerful winds? Detecting severe storms often requires sophisticated equipment, but truckers can use their senses to make a close prediction while on the road.

Cloud configurations

Not all dark clouds are the same. A severe storm that could lead to life-threatening weather will often have clouds that look very dark or even have a sickly green tint. They’re usually very large cumulonimbus clouds with low-lying bases. Additionally, drivers would see the storm clouds develop vertically at a rapid pace. Watch for any rotation in the clouds.

Rain-cooled air rushes ahead of a storm, plowing under warm, moist air and forming a flat “shelf cloud,” a type of cloud often associated with severe thunderstorms. (Photo: NOAA)

Temperature transformations

If a trucker is standing outside, he or she should pay very close attention to the temperature. A rapid drop from warm to much cooler, brisk conditions may indicate the approach of a severe storm.

Wavering winds

Drivers should be on their toes if the weather suddenly gets very windy under dark skies, or if there’s an abrupt calm during or right after a thunderstorm. That eerie calm doesn’t necessarily indicate the end of a storm, but rather could be a sign of dangerous weather to come.

Precipitation patterns

Be aware of hail or heavy rain followed by either dead calm or a fast, intense wind shift. This could mean that a tornado is coming, especially if the hail is large.

Related: 4 ways heat waves can scorch truckers

Bottoming out barometer

When it’s safe to do so, drivers can use their favorite mobile weather apps to track the atmospheric pressure over the course of a few hours. A rapid drop in pressure is a sign that a possible severe storm is approaching.

Listen intently

As drivers see storms, they should try to eliminate any unnecessary sounds and listen very closely. A loud roar or an intense noise similar to a freight train is typically the sign of a tornado getting close. Drivers should pull off an exit as quickly as they can and take shelter.

Tornado watch versus warning. (Image: NOAA)

Storms that fall below severe limits can certainly be dangerous simply because of the lightning or heavy rain. But to be classified as severe by the National Weather Service, a storm has to be producing one or more of the following based on radar or eyewitness reports:

• Winds of at least 58 mph.
• Hail at least 1 inch in diameter (quarter size).
• A tornado.

Drivers should set their weather apps to “location” or “GPS” mode to ensure they will receive severe weather alerts no matter where they are.

Click here for more FreightWaves articles by Nick Austin.

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