Severe weather returned to Iowa on Thursday with afternoon thunderstorms firing along a cold front over western Iowa and slowly pushed east through the evening hours. The NWS issued a number of severe warnings for damaging wind, hail, and a few brief tornadoes. Polk County (Des Moines) received a few Tornado warnings during the early evening hours with the first being issued just after 7 PM. The timing of Tornado Warnings for Polk County is the subject of today's daily feature. The plot presents the frequency of the time of day when tornado warnings are active. Note that this is not the overall frequency, but plots the relative frequency to the total number of warnings issued for Polk County. Around 5 PM is the frequency winner with just over 10% of the total 98 warnings active about at that time. It is interesting to see the low frequencies during the early afternoon hours with a dramatic ramp after about 3:30 PM. Storms occurring later in the afternoon typically have more potential energy to tap into due to the additional daytime heating that adds instability to the atmosphere. Storms occurring earlier typically have less potent environments to work with to produce severe weather and even tornadoes.

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