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Finally, More ‘Normal’ Summer Weather Arrives

Rains with little flooding and a cool down are ahead

A summer weather pattern with more normal popup showers and larger storms of two the three inches of rain are ahead through about mid-July. That follows above normal temperatures that put a dent if a deficit of growing degree units that retarded crop growth.

That’s the latest weather outlook from Dale Mohler, a senior meteorologist who specializes in commodity weather forecasting for Accuweather.com.

“If I would draw what I would call a normal summer pattern, this would be pretty close to it,” Mohler told Agriculture.com Tuesday.

That nonexistent normal is really just an average of the chaos that is weather. But the recent pattern has included the hallmarks of summer.  They offer humid air drifting north from the Gulf Coast, which spawns popup showers with small amounts of rain and cold fronts moving from west to east that push underneath the warm humid air, creating a line of showers the produce heavier rains of about an inch. And finally, we’ve seen examples of “mesoscale Convective Complexes” or MCCs.

These are fast-moving storm systems as big as the state of Iowa. They produce about 60% of the rainfall in summer.

“They can cover a pretty big area with one to three inches of rain,” says Mohler. Such storms have recently formed in North Dakota, them moved southeast across Minnesota and Wisconsin to the Chicago area.

Although they can bring hail and tornadoes, they’re generally beneficial. They form in the Plains, move at about 30 miles an hour, and can travel several hundred miles before losing energy. They rarely reach the East Coast.

Because they move quickly, they cause less flooding, although a series of such storms can bring at least localized flash floods.

“It’s different than what we saw earlier when we had a stalled front,” Mohler says.

Some areas of the western Corn Belt had higher than normal temperatures late last week and early this week, which will help lower the deficit in growing degree days, a measure of heat needed for growing crops.

Sioux City, Iowa, for example, had four days in the upper 90s.

“That will catch you up in a hurry,” Mohler says.

It’s not quite enough to make up for a long stretch of cool temperatures in June. That might take a week of those above average temperatures, Mohler says.

But one measure, temperatures from Iowa State University’s Iowa Environmental Mesonet, shows an almost normal average of growing degree days in some locations. Waterloo, Iowa, for example, tallied 947 growing degree days between May 1 and July 1. That’s just 12 behind the 959 growing degree days that is the normal climate observed back to 1951. Mason City, to the north and west in the state, was more than 100 days behind at 822 vs. the climate of 924 by July.

ISU-GDD-Precip-Temp-Chart
Iowa Environmental Mesonet

Mohler says two cold fronts will bring rain to the Corn Belt. The first arrives Friday in the west end and Saturday further east. The second arrives in the middle of next week. It will also bring slightly cooler temperatures that are about five degrees below normal, in the 70s.

“It all adds up to being pretty favorable for the Midwest,” Mohler says.

Today’s Weekly Weather and Crop Bulletin also shows some progress in regaining growing degree days in the western Corn Belt. Using a longer time frame going back to April 1, last week’s bulletin showed all of Iowa to be between 100 and 200 days behind normal. This week’s map shows the deficit gone in the southwest corner of the state, with nearly all of the rest of the state 100 days behind normal. Most of Minnesota remains 200 days below normal while parts of southern Ohio and Indiana are ahead of normal in growing degree days.

Departure-from-Normal-Growing-Degree-Days
Climate Prediction Center, NOAA

            

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