IEM Daily Bulletin for May 20 2026

[daryl herzmann]

Iowa Environmental Mesonet Daily Bulletin for 20 May 2026

News

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Daily Feature

Six Hour Dew Point Changes
Date: 19 May 05:30 AM
Votes: Good: 9   Bad: 0 Abstain: 1

Storms developed along a frontal boundary over southwestern Iowa on Monday afternoon with muggy air ahead of the front helping to fuel the storms. Cooler and less humid air has worked into the state overnight with dew point temperatures 10 to 15 degrees cooler. The featured chart looks into six hour dew point temperature change based on hourly data from the Des Moines airport. The data is partitioned by one degree Fahrenheit and by week of the year with the frequency units being average number of hours per week per year. Certainly values near zero are the most common as dew point fluctuations are less than air temperature. It is interesting to denote the largest frequencies at values just above zero during late June into late August. Some of this is the effect of evapo-transpiration processes adding moisture to the air during daytime hours, but it is also a tightening of the possible distribution of dew point temperatures during the most humid time of the year.

The featured media can be generated on-demand here

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NWS Watch/Warning Summary for 12 AM 19 May 2026 - 12 AM 20 May 2026 CDT

	Summary		By WFO					Watches
Type	US	IA	ARX	DVN	DMX	OAX	FSD	US
Tornado	0	0	0	0	0	0	0	0
Svr Tstorm	145	0	0	0	0	0	0	4
Flash Flood	27	0	0	0	0	0	0	---

ARX = LaCrosse, WI DVN = Davenport, IA DMX = Des Moines, IA OAX = Omaha, NE FSD = Sioux Falls, SD

IEM Cow Report

SVR+TOR Warnings Issued: 142 Verified:  58 [40.8%]
Polygon Size Versus County Size            [26.4%]
Average Perimeter Ratio                    [28.4%]
Percentage of Warned Area Verified (15km)  [17.3%]
Average Storm Based Warning Size           [1677 sq km]
Probability of Detection(higher is better) [0.74]
False Alarm Ratio (lower is better)        [0.59]
Critical Success Index (higher is better)  [0.36]

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