Summer Storms

by Anna Cavallo

We’ve had a very stormy week here in Minneapolis. This map shows observed precipitation over the Midwest from Tuesday morning to Wednesday morning, although I think it mainly reflects 9 p.m. Tuesday to 3 a.m. Wednesday. Look closely and you’ll notice that the left tip of the top red (heaviest rain) section is right over Minneapolis—downtown was drenched with more than 4 inches of rain overnight. Parts of the city were swimmable, with flash floods resulting from a downpour of 1.25 inches in just half an hour. In retrospect, I wish I had braved the rain for just a minute to run down the block and witness the people who apparently were frolicking in waist-deep water. But I was content to sit inside, listening to my neighbors whoop at the crashing thunder while the sky lit up with giant, picture-perfect bolts of lightning. Even from the sky at sunset, you knew something big was coming, as purplish-orangish-gray replaced the daytime blue. The whole event was stunningly beautiful—if also dangerous and damaging.

Last night we had another bout of storms, and more are on the way later today. Tornado watches and warnings have been scattered around the state.

None of this stormy weather should be surprising, given that we’ve also had high temperatures in the 90s with stifling humidity nearly every day for a week. After working on Lerner’s new Weatherwise series this past year, I’m well aware that heat (energy) + moisture in the air + low-pressure systems moving through = an easy recipe for storms. But I’m more fascinated than ever with the intricacies of the atmosphere. For instance, how is it possible that we’ve continued to have such humid days even after storms have released so much moisture from the atmosphere? Is the source of this endless moisture a weather event halfway around the world, or something right here in Minnesota?

Perhaps I’m still most baffled by weather forecasting, and particularly the advanced technology that is crucial to our detailed, down-to-the-minute forecasts. Meteorologists use computer models, or programs, that interpret and synthesize weather data from all over to predict how weather will change over the next period of time. Short-term forecasts are the most accurate. Even those are sometimes off. But given the amount of data that is processed to generate detailed modern forecasts, it’s incredible that they’re ever accurate. Find out all about it in Doppler Radar, Satellites, and Computer Models: The Science of Weather Forecasting. For a more general introduction to the science of weather, check out Gases, Pressure, and Wind: The Science of the Atmosphere. And to feed your atmospheric curiosity a little more, the Weatherwise series also includes titles on storms and clouds and precipitation. Each book features enlightening diagrams, lots of striking photos, and text by science author Paul Fleisher that makes these complex subjects accessible.

Even if the forecasts aren’t always right, on Tuesday I appreciated the warning that it was not the night for an outdoor movie. Thanks to meteorologists and forecasts for a night spent reading inside, marveling at the powerful storms striking and soaking the world outside my windows.

Top image courtesy of NOAA/National Weather Service.