IEM Daily Bulletin for Apr 25 2026

[daryl herzmann]

Iowa Environmental Mesonet Daily Bulletin for 25 April 2026

News

No news is good news

IEM Code Pushes <repo,branch> on Github

Timestamp	Repository	Message	Link
Apr 24 9:02 AM	iem,main	🔥 Remove now-defunct mention of ECMWF MOS data	Link
Apr 24 9:03 AM	iem,main	⬆️ Update eslint precommit	Link
Apr 24 2:34 PM	iem,main	📝 Add color for DS	Link
Apr 24 6:11 PM	iem,main	✨ Add KML export to python watchwarn backend The legacy PHP service remains, but python now services the frontend. https://mesonet.agron.iastate.edu/cgi-bin/request/gis/watchwarn.py?help	Link
Apr 24 6:41 PM	iem,main	💚 Address eslint lint	Link
Apr 24 10:21 AM	pyiem,main	🎨 Account for XTEUS without value set	Link
Apr 24 8:42 PM	pyiem,main	🐛 Support with_sqlalchemy_conn to wrap generator	Link

Daily Feature

Polk Co. Tornado Warning Timing
Date: 24 Apr 05:30 AM
Votes: Good: 13   Bad: 0 Abstain: 0

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.

The featured media can be generated on-demand here

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NWS Watch/Warning Summary for 12 AM 24 Apr 2026 - 12 AM 25 Apr 2026 CDT

	Summary		By WFO					Watches
Type	US	IA	ARX	DVN	DMX	OAX	FSD	US
Tornado	17	0	0	0	0	0	0	1
Svr Tstorm	117	1	0	1	0	0	0	1
Flash Flood	2	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: 128 Verified:  52 [40.6%]
Polygon Size Versus County Size            [26.9%]
Average Perimeter Ratio                    [28.6%]
Percentage of Warned Area Verified (15km)  [19.9%]
Average Storm Based Warning Size           [1344 sq km]
Probability of Detection(higher is better) [0.75]
False Alarm Ratio (lower is better)        [0.59]
Critical Success Index (higher is better)  [0.36]

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