CHICAGO — CBS Chicago’s Emmy-winning Meteorologist, David Yeomans, offered a presentation on current and future weather patterns affecting agriculture for members of the Illinois Soybean Association on May 21. Yeomans dove into how tornado alley is shifting, damaging thunderstorm wind events are happening more often and temperatures are becoming more variable. 

Yeomans began his webinar presentation by noting that a variety of weather patterns have recently come through Illinois, from floods to near-drought conditions, increased tornadoes and rare wind-driven dust storms. He also offered moisture projections for the rest of the season, displaying a weather map showing that most of northern Illinois is currently about 40 percent short of normal precipitation levels, while southern Illinois remains around 20 percent bereft of average rainfall for the year. 

“Over the past 45 days it has been super dry from Springfield to Peoria, up to Rockford and especially in the Chicago area, where we have had half to one-third of our normal rain. This is a significant amount of rain that is missing,” said Yeomans. “If we change that percentage to actual inches on the ground, over much of our growing area in northern Illinois we are 3-to-5 inches short. That has done an incredible number on our soil moisture.”

Soil moisture is at two percent of normal or less in parts of Illinois, “which can have a huge impact on your operation,” according to the Chicago meteorologist. He displayed satellite imagery illustrating near record-low subsoil moisture levels in areas including Dekalb County, where 4 inch-deep soil is very dry and 8 inch-deep soil is completely dry. In Champaign the numbers are similar, while in St. Charles soil moisture levels are also crossing into record-low territory. Record-dry soil levels have also been reported in Freeport. 

Rainfall that fell in north-central Illinois and Chicagoland on May 20 and 21 was “not a drought-buster,” according to Yeomans, with only around ½-⅓ of an inch recorded from Rockford east to Chicago. Northwestern Illinois, however, enjoyed more than 3 inches of rain, helping to close the precipitation in that area. “From Chicago out to Rockford we’re still showing less than half of our normal weekly rainfall for this time,” he said. “Drizzle and light rain is not very beneficial to 8-inch and 20-inch soil moisture levels, which are still suffering.”

Shifting to his summer weather outlook for farmers, Yeomans said the current “La Nada” weather pattern — sort of a neutral, less predictable pattern that is neither an El Nino or a La Nina — doesn’t offer much in the way of clues as far as long-range summer and autumn weather prognostications. 

“There is also a less often-discussed multi-month cycle called the MJO, which has to do with global weather patterns; it’s also in a neutral phase. With these not influencing us one way or the other, the NOAA Climate Prediction Center says that local soil moisture is what they’re weighing most heavily when they produce their map,” Yeomans said. 

“Using soil moisture as one of their most important factors moving forward this summer, (NOAA is) projecting hotter than normal weather in Illinois and really across the country for June-July-August. They are hopeful for normal summer rainfall.”

The warming climate is having an impact on precipitation, with 36 inches or so usually falling in Illinois each year. However, fewer overall days of rain are being recorded, with longer dry stretches in between. The heaviest rainfall days of the year are now producing as much as 45 percent more precipitation per event than in previous years, a trend which Yeomans expects to continue to increase. 

Farmers can expect to have to contend with tornadoes, derechos and even the occasional haboob (a thunderstorm-driven straight line wind burst that can produce dust storms such as the one that hit northern Illinois and Chicago on May 16) in increasing frequency, according to Yeomans. The forecast that Illinois and the Midwest may be in line for a greater frequency of tornado events is based on recent climate observations, he said. 

“Tornado alley was always Texas, Oklahoma and Kansas, but there is data that tornado alley is shifting eastward. This is according not to an analysis of tornado occurrences, but the atmospheric variables that cause tornadoes. They’re becoming less common in Texas, and those favorable days for tornadoes are going up sharply in the deep south and the upper Midwest,” said Yeomans. 

Yeomans’ presentation was titled “Facing the Future: Tornado Alley Shifts & Their Impact on Illinois Farming.”