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  • Writer's pictureMeteorologist Joseph Cooper

Late May Warmth Comes With Possible Severe Threat For Some.

Updated: Oct 18, 2023

We are already into the second week of May 2020, but for many across the Ohio Valley and Great Lakes it still feels more like Winter. In the past few days snow has occurred in central Wisconsin (just last night 5/9/20) and in northeastern Ohio Friday night (5/8-9/20). The latter of which was just one day shy of breaking the latest date for accumulating snowfall in Cleveland, OH set back in 1907! However, if you are tired of below average temperatures and lingering wintry weather, I have some good news for you.

After the warm March across the region, April brought a rapid flip in the upper-level pattern leading to a trough and cooler than average temperatures across much of the Ohio Valley and Great Lakes region, a far cry from the March temperatures that felt more like May. However, we have been watching another pattern change for roughly 30-45 days that was forecast to occur the end of May into June. As data has continued to come into the shorter range (next 7-10+ days) model data has become much more consistent with more seasonal temperatures arriving mid-May lasting through much of the month. This looks to take us from temperatures running from 10-25° below average today across IN/IL to 5-10° above average next weekend!

This warm up will be thanks to a flip in the Jetstream in which the troughiness will set up to the west and ridging will occur across the nations mid-section and then spread to the east. While some waves of troughiness will move through (that should occur normally in the Spring) leading to periods of “cooler” temperatures, this is expected to become more of the anomaly than the norm.

However, the warm up across the central and eastern US may come with a bit of a price. With large troughs moving on board the west coast, then spreading into the Great Plains, the threat for severe weather is expected to increase through the latter half of May and perhaps in the first part of June. While it is far too early to pinpoint threats and areas where those threats could occur, the overall look to the pattern suggests uptick in severe weather across the nation’s heartland.

The CIPS Severe Weather Analog Guidance shows the increased severe weather potential in the short-term forecast. You can see probabilities of strong to severe storms increase and become more widespread over the next 5-8 days.

The CFS Severe Weather Dashboard shows the increasing SCP (Supercell Composite Parameter) values of >= 1 across the US. The warmer colors show more locations registering that value across the CONUS, thusly supporting the idea of more widespread and favorable conditions for supercells and severe weather.


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