IEM Daily Bulletin for May 1 2026

[daryl herzmann]

Iowa Environmental Mesonet Daily Bulletin for 01 May 2026

News

No news is good news

IEM Code Pushes <repo,branch> on Github

Timestamp	Repository	Message	Link
Apr 30 10:10 PM	iem,main	⚡️ Refactor AFOS retrieve service - Add additional schema validation - Use chunked database query for increased performance - Non-functional change	Link

Daily Feature

Reason for Freeze Alerts
Date: 30 Apr 12:41 AM
Votes: Good: 11   Bad: 0 Abstain: 0

The forecast has chilly and even freezing low temperatures possible over the next few days. Typically, this would not necessarily be a big deal as the calendar is only at the end of April and climatology says we have a week or two to go before freeze risks substantially subside. This spring has been a bit different with plenty of very warm days and the growing season has gotten off to a very fast start. When this happens, the NWS will issue such alerts like Frost Advisories and Freeze Warnings even though climatology says freezing temperatures are more common than not. The featured chart presents an IEM estimate of the number of growing degree days since March for an Iowa statewide estimate. The 2026 total certainly stands out and comes in fifth largest since 1893.

The featured media can be generated on-demand here

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NWS Watch/Warning Summary for 12 AM 30 Apr 2026 - 12 AM 1 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	9	0	0	0	0	0	0	0
Flash Flood	3	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:   8 Verified:   2 [25.0%]
Polygon Size Versus County Size            [25.2%]
Average Perimeter Ratio                    [30.0%]
Percentage of Warned Area Verified (15km)  [13.4%]
Average Storm Based Warning Size           [1385 sq km]
Probability of Detection(higher is better) [0.50]
False Alarm Ratio (lower is better)        [0.75]
Critical Success Index (higher is better)  [0.20]

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