Yeah it would have to be something highly anomalous. Probably a combination- record high h5 heights, very dry conditions, good mixing via westerly winds. This area is the antitheses of UHI. 'Corn sweat' can contribute to somewhat higher DPs in mid to late summer, but that also would tend to keep temps a bit lower.
I don't think I have seen a temperature higher than 98 on my weather station, and that is pretty rare. Nice to have the mesonet stations just to my SW and NE to validate my obs.