Ag Weather Forum

After a busy severe weather day on Sunday, another day of active severe weather is unfolding for Monday, May 18. Widespread areas of extremely large hail, damaging winds and strong tornadoes are forecast for portions of the Plains and Midwest.

A frontal boundary remains draped from the Texas Panhandle northeast through central Kansas, Iowa, and western Wisconsin on Monday morning. That frontal boundary will be the focal point for a major severe weather event for this afternoon and evening. Very warm and moist air east of the boundary clashes with much cooler air behind it with a temperature difference of about 40 degrees Fahrenheit. Such extreme changes in temperature are a good spot to develop thunderstorms, especially if we can see a catalyst ride along that boundary. Indeed, we will as a low-pressure center develops over Kansas midday and rides northeast along the front through the evening hours. This will produce areas of strong-to-severe thunderstorms for late this afternoon and evening.

With how dynamic this system is, all hazards will be on the table. But the threat for very strong tornadoes is the most concerning, from south-central Kansas into south-central Iowa. The Storm Prediction Center (SPC) has put out a large "enhanced" risk of severe weather (level three out of five on their threat index) from extreme northern Oklahoma northeast through much of southern and central Iowa. Within that zone, a "moderate" risk (level four out of five) has been placed over portions of south-central Kansas into extreme southeastern Nebraska and northwestern Missouri as of the 11:30 a.m. CDT issuance.

It is in this area that the strongest tornadoes and largest hail are most likely. Storms are likely to start out as small supercells before forming into clusters and lines along the cold front this evening. The transition of storms to lines will result in more of a wind threat as the evening persists, getting into Missouri, southern Wisconsin, and possibly Illinois.

The severe threat extends east through the Midwest where storms that were severe on Sunday have continued for Monday. Storms currently extend from central Missouri through Illinois and into western Indiana as of 11:30 a.m. CDT and the SPC has issued a severe thunderstorm watch for the northern extent of these storms in Indiana and far southern Michigan and northwestern Ohio through the afternoon. Large hail and damaging winds are the largest threats with these storms.

These storms continue from the major severe weather outbreak that occurred on Sunday. As of Monday morning, at least 27 tornadoes, including some massive ones near Saint Libory and Palmer, Nebraska, and Salix, Iowa. Nine recorded hurricane-force wind gusts of more than 75 mph and 19 reports of hail over 2 inches in diameter were reported.

To go along with the severe weather threat today, heavy rainfall could produce areas of flooding, especially for those that have recently seen heavy rainfall.

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John Baranick can be reached at john.baranick@dtn.com

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