Ag Weather Forum

The ingredients have come to the table for a major severe weather outbreak on Monday afternoon and evening, April 28. However, there are some questions on whether or not storms will initiate or be widespread.

A low-pressure center is moving through the Northern Plains and will traverse the Upper Midwest here on Monday. A band of heavy rain and thunderstorms is already occurring on the leading edge of that low as it moved from the Dakotas into Minnesota early this morning. These thunderstorms were not severe, but they do showcase the amount of lift that this system will be producing later today as it moves eastward.

A cold front extends southwest from the low center across the Central Plains and will be a focal point for additional showers and thunderstorms as well, especially this evening and overnight into Tuesday morning.

But back to the north, the major ingredients that forecasters look for will all be there to fuel potential severe storms. Warm weather and plenty of widespread moisture near the surface, shifting and strengthening winds with height (wind shear), and sharp frontal boundaries are all enticing the Storm Prediction Center (SPC) to issue a moderate risk (four out of five on their risk chart) across portions of Iowa, Minnesota, and Wisconsin. This setup favors very large hail and long-track tornadoes for any storms that can tap into this environment. Damaging wind gusts are a significant threat as well.

The SPC has had this risk in their extended outlooks since early last week as this setup has been forecast for a long time now. Those living in the area have probably been seeing this risk on their local news for many days and should be well aware of the risks today.

But has this event been hyped up? Will storms occur? Models aren't so sure. Though some of the larger models have precipitation moving through the region this afternoon and evening, those that allow for convection and thunderstorm generation are producing very limited and spotty thunderstorms. That's not really enough to produce widespread impacts across the region, but more spotty areas of damage. Small lines and clusters could evolve rather quickly, reducing the tornado threat somewhat and increasing the wind threat. The SPC notes in its Day 1 Outlook issued at 1 a.m. CDT: "Uncertainty remains regarding the evolution of diurnal convection across the warm sector. Guidance generally suggests that surface-based storms will develop near the surface low and along the prefrontal trough/dryline across southern MN, which could evolve quickly into a cluster or linear mode, though the environment would still support embedded supercell potential with all severe hazards possible. If development in this area can remain semi-discrete, then a couple of long-track tornadic supercells could occur.

"Farther south into IA, stronger heating/mixing is expected near the dryline, though large-scale ascent and low-level convergence may be somewhat weaker compared to areas farther north. While guidance varies regarding the potential for development across IA during the afternoon, any supercell that can initiate and be sustained could become long-tracked within the expanding and very favorable warm sector, posing a threat for strong to intense tornadoes and very large hail."

In other words, this event does have some "bust" potential, because even great setups don't always produce the expected outcomes. But for those that do see thunderstorms approaching your area, there is a significant risk that it would be severe and damaging.

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

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