Dangerous winds could accompany record-breaking Wednesday heat

Temperatures in parts of Iowa are expected to eclipse 70 degrees on Wednesday, which might set new record highs for the day and the entire month of December, according to the National Weather Service.

But the winds that will carry that warmth are expected to be severe, with sustained speeds of up to 40 mph and gusts of up to 70.

“It’s not going to be a pleasant day,” said Roger Vachalek, a Weather Service meteorologist in Johnston.

There’s a chance for thunderstorms as the day progresses, but total rainfall is expected to be somewhat limited because the storms will be moving quickly. No tornadoes are expected like the ones that killed dozens on Friday in six states that were also partially fueled by unseasonable heat from the southern plains.

Still, the Weather Service warns that travel might be difficult for taller vehicles, and the winds might topple trees and power lines.

‘Extreme temperature swings’

The start of December has been about 9 degrees warmer than normal statewide, but that pales in comparison to the same time period in 1939, which averaged 15 degrees warmer, State Climatologist Justin Glisan said.

That year, the city of Thurman in southwest Iowa set the state’s highest December temperature of 74 degrees.

“I don’t think we’re going to break that statewide record,” Glisan said of this week’s warmth. “But 30 and 40 degrees above average we don’t see that often. Those are extreme temperature swings.”

The high temperature in Des Moines is predicted to reach 71 degrees on Wednesday, whereas the normal high is 36. The previous record high for December in Des Moines is 69 degrees.

A lack of snow on the ground — which can reflect up to 90% of solar radiation — and increased soil moisture are aiding the unseasonably warm temperatures.

“All the little things are coming together,” Glisan said.

What remains of the first snow of the season, which fell late last week, is expected to mostly melt on Wednesday, Vachalek said. That includes the snowpack in the far northwestern part of the state that had a foot of snow.

However, temperatures are expected to be closer to normal starting Thursday.

Glisan said the current colder surface temperatures of the equatorial Pacific Ocean — which he described as a “weak La Niña” — portend a snowy remainder of this winter.

Don’t worry about your daffodils

The recent streaks of warmth won’t likely fool early blooming plants into thinking it’s spring.

“Most plants are pretty well adapted to these warm spurts that we have from time to time throughout the winter,” said Aaron Steil, consumer horticulture extension specialist for Iowa State University. “We may see a few unusual things, like the foliage of some spring blooming bulbs poke out of the ground if it’s warm enough, but it’s easier for plants to deal with it this time of the year because they’re going into dormancy.”

Most of Iowa’s topsoil isn’t frozen, according to Iowa State data, and some plants will continue to grow underground until it does.

“If we get a week or a week and a half of really warm temperatures, that pulls plants out of dormancy, and if it’s followed by really cold temperatures, we could see some dieback,” Steil said. “But there’s nothing you can do about that anyway. You just have to let that weather out, so to speak.”