A major severe thunderstorm outbreak could pummel parts of the Plains and upper Midwest Friday and Friday night.
The Storm Prediction Center (SPC), part of the National Weather Service (NWS), has placed portions of North Dakota, South Dakota and Minnesota under an “Enhanced” or “Moderate” risk. This means numerous to widespread severe storms could develop, and they may last a long time and be particularly intense in some spots. The risk zone includes an area struck by a deadly EF-4 tornado last week.
On a scale of one to five, with five being the highest risk category, “Enhanced” is a three and “Moderate” is a four. So, this is a potentially serious situation for truckers trying to drop off or pick-up before heading home for the weekend. They should expect at least minor delays due to occasional hard-falling hail and torrential rainfall, which will reduce visibility.
The biggest threat will be dangerous wind gusts, increasing the chance of rollovers for truckers who are deadheading.
The NWS classifies a thunderstorm as severe if it produces any of the following based on radar or eyewitness reports:
• Winds of at least 58 mph (50 knots).
• Hail at least 1 inch in diameter (quarter size).
• A tornado.
Some storms during this outbreak could produce winds of 70 mph or stronger in some spots, along with hail up to golf ball size (around 2 inches in diameter). The storms will likely come in waves from Friday afternoon until early Saturday, with relatively quiet weather between rounds.
Areas under the gun include Bismarck, Fargo, Grand Forks and Minot, North Dakota; Aberdeen and Watertown, South Dakota; as well as Minneapolis-St. Paul, Duluth, St. Cloud and Bemidji, Minnesota, impacting Interstates 29 and 94.
It’s not unusual for severe storms to hit these areas of the country in mid-July. On average, the peak of the season falls between July 7 and July 20.
The atmosphere will be prime for severe weather conditions, with plenty of heat, humidity and instability.
High temperatures will reach the mid-80s to lower 90s, with dew points — a measure of atmospheric moisture — in the mid-60s to lower 70s. This amount of heat and humidity will make the air very prone to vertical motion, creating strong updrafts and making the atmosphere very unstable. Also, temperatures aloft will be very cold, adding to the instability.
But whatever goes up must come down. The updrafts will eventually give way to powerful downdrafts of heavy, dense air that will crash to the ground, resulting in destructive straight-line winds.
By early Saturday, the last wave of severe thunderstorms from this outbreak will barrel through Sioux Falls, South Dakota; central and southern Minnesota, including Minneapolis-St. Paul; in addition to Green Bay, Milwaukee, Duluth and La Crosse, Wisconsin.
Severe storms don’t typically cause major/long-term disruptions in freight movement on the roads, unless they result in accidents, but drivers should expect at least minor delays when they run into these storms. Conditions can change quickly and may catch drivers off guard if they aren’t prepared.
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