IEM Daily Bulletin for May 22 2026

[daryl herzmann]

Iowa Environmental Mesonet Daily Bulletin for 22 May 2026

News

No news is good news

IEM Code Pushes <repo,branch> on Github

Timestamp	Repository	Message	Link
May 21 9:16 AM	iem,main	🐛 Fix 2025 shard location	Link
May 21 9:31 AM	iem,main	✨ Allow y-axis to scale to data https://mesonet.agron.iastate.edu/plotting/auto/?q=66	Link
May 21 10:37 AM	iem,main	⬆️ Update ruff precommit	Link
May 21 5:29 PM	iem,main	🎨 Rollup of msic PHP doc and bootstrap fixes	Link
May 21 5:42 PM	iem,main	💚 Address codereview	Link
May 21 5:54 PM	iem,main	💚 Revert aggressive str2int check	Link

Daily Feature

Precip near Severe Weather
Date: 21 May 05:30 AM
Votes: Good: 9   Bad: 0 Abstain: 0

After a very dry start to May, this past weekend saw numerous rounds of severe weather that also brought much needed rainfall. Such is the conundrum this time of year, needed and significant spring season rains often come with thunderstorms that are sometimes severe. The featured chart attempts to look into how much precipitation is associated with severe weather by totaling up one minute interval precipitation totals from the Des Moines airport when either a severe thunderstorm or tornado warning is activate for the airport. The left two panels report the precipitation partitioning percentages during, within an hour, and outside of severe warnings. The upper right panel shows the frequency of a given one minute intensity happening during a severe weather warning. The bottom right panel is a bit of a downer, but denotes how much of the one minute precipitation is likely missing within the one minute observations (long story, but NCEI's collection and distribution of one minute data has become very unreliable). So the overall percentages are not that large with precipitation totals near 10%, but it certainly accounts for a good portion of the most intense rainfall totals.

The featured media can be generated on-demand here

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NWS Watch/Warning Summary for 12 AM 21 May 2026 - 12 AM 22 May 2026 CDT

	Summary		By WFO					Watches
Type	US	IA	ARX	DVN	DMX	OAX	FSD	US
Tornado	12	0	0	0	0	0	0	0
Svr Tstorm	70	0	0	0	0	0	0	2
Flash Flood	26	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:  82 Verified:  20 [24.4%]
Polygon Size Versus County Size            [14.7%]
Average Perimeter Ratio                    [27.0%]
Percentage of Warned Area Verified (15km)  [10.9%]
Average Storm Based Warning Size           [1083 sq km]
Probability of Detection(higher is better) [0.61]
False Alarm Ratio (lower is better)        [0.76]
Critical Success Index (higher is better)  [0.21]

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