IEM Daily Bulletin for May 27 2026

[daryl herzmann]

Iowa Environmental Mesonet Daily Bulletin for 27 May 2026

News

No news is good news

IEM Code Pushes <repo,branch> on Github

Timestamp	Repository	Message	Link
May 26 1:47 PM	iem,main	📝 Link to MRMS monthly plot (iowa only) https://iem.local/current/index.phtml/precipitation/month_mrms_iowa	Link
May 26 2:03 PM	iem,main	📝 Rollup misc php/bootstrap5 fixes	Link
May 26 2:19 PM	iem,main	🗑️ Deprecate legacy COOP periods app replaced with https://mesonet.agron.iastate.edu/plotting/auto/?q=107	Link
May 26 3:17 PM	iem,main	🐛 Fix autoplot select menu CSS	Link
May 26 10:22 PM	iem,main	🎨 Improve parsing robustness	Link

Daily Feature

Briefly above average
Date: 26 May 05:30 AM
Votes: Good: 15   Bad: 0 Abstain: 0

For most of the state, rainfall amounts over the Memorial Day weekend were rather meager. Much of the state continues to "run on fumes", so to speak, after the wet April and heavy rains mid May. The featured chart shows the fickle rainfall story for Ames this May with the blue bars showing observed daily rainfall with the red bars indicating the month to date departure from average. The observed and climatological accumulation are plotted as well. Those aforementioned mid May rains are about all there is to speak of for Ames during May. The big rainfall on the 18th put the month-to-date departure barely above average and the departures are again grown since. The bad news is that the next week and perhaps even the next two weeks look very dry with warmer temperatures and reduced humidity, which will quickly escalate the drought situation during what should be the wettest portion of the year.

The featured media can be generated on-demand here

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NWS Watch/Warning Summary for 12 AM 26 May 2026 - 12 AM 27 May 2026 CDT

	Summary		By WFO					Watches
Type	US	IA	ARX	DVN	DMX	OAX	FSD	US
Tornado	13	0	0	0	0	0	0	0
Svr Tstorm	95	1	1	0	1	0	0	3
Flash Flood	33	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: 104 Verified:  31 [29.8%]
Polygon Size Versus County Size            [18.4%]
Average Perimeter Ratio                    [18.6%]
Percentage of Warned Area Verified (15km)  [9.0%]
Average Storm Based Warning Size           [1784 sq km]
Probability of Detection(higher is better) [0.64]
False Alarm Ratio (lower is better)        [0.70]
Critical Success Index (higher is better)  [0.26]

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