Why blizzards, heat waves, tornadoes and floods are hitting the US this week

What’s up with all the weather this week?

By Andrea Thompson edited by Claire Cameron

Heavy rain has brought flooding to Hawaii. Parts of the upper Midwest are covered in more than two feet of snow, with flakes still falling. Hail, strong winds and tornadoes threaten the eastern United States. And the West is in for record-breaking heat. Why is all the weather apparently happening right now?

The short answer: it’s March. Early spring is a transitional time of year, weather-wise. Cold air from the north lingers even as warm, moist air pushes up from the south, leading to collisions over the contiguous United States that set favorable conditions for unstable weather and large snowstorms. “March and April is the time of year we get these collisions in air masses,” says Brian Hurley, a meteorologist at the National Weather Service’s (NWS’s) Weather Prediction Center.

Let’s dig a little more into the details, starting with the snow in the Midwest. A storm, or low pressure system, developed over the area, with cold air coming down from Canada meeting moist air flowing up from the Gulf of Mexico. That means the storm “has a lot of moisture to work with,” Hurley says, so snowfall is high. The snow is also very wet compared to what usually falls in the region in January or February. This is quite normal for March and April snow there, says Hurley. However, because this storm is quite strong, it is producing blizzard conditions and snowfall rates of up to three to four inches per hour in some locations. Some places can see record snowfall for this time of year.

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Next, the low pressure system has a feature associated with it which, in meteorology, is called a QLCS, or quasi-linear convective system. Basically, this means a long, wavy line of thunderstorms – which can be seen trailing down from the low pressure area in a classic comma shape on weather maps. The waves happen when “the winds blow out faster” ahead of the main line, Hurley says, an arrangement that looks like a tight arc. The wind occurs due to large pressure differences, and in this case, winds could gust up to 60 to 70 miles per hour in parts of the Mid-Atlantic on Monday. Abundant moisture creates an unstable atmosphere that will cause thunderstorms to develop, which together with the strong winds can create tornadoes.

Now let’s go west. Upstream of a low pressure area you will find a high pressure area, which is exactly what will settle and strengthen over the Southwest this week. That will usher in a major heat wave that is expected to send temperatures well above 100 degrees Fahrenheit (38 degrees Celsius) in some places. This also happens in the summer and is often called a heat dome — temperatures won’t get as high as they would if this were, say, July, “but are very warm compared to what (they) should be,” Hurley says. The heat wave could set all-time March records unusually early in the month.

Moving west and further upstream again, on the other side of the high pressure system is another low pressure area. This one, called the “Kona low,” brings southerly winds “that pull a lot of deep moisture up over the islands,” said Thomas Vaughan, a meteorologist at the NWS’s Honolulu office. The Hawaiian Islands usually see a few of these systems a year, he says, but this one was intense. Several places saw rainfall totaling 15 inches or more over five days, leading to flash floods and mudslides. These rains “far exceeded normal rainfall values ​​for the entire month of March,” says Vaughan. Further rain is expected this week, although not on the same scale, he adds.

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