IEM Daily Bulletin for Sep 24 2025

[daryl herzmann]

Iowa Environmental Mesonet Daily Bulletin for 24 September 2025

News

No news is good news

IEM Code Pushes <repo,branch> on Github

Timestamp	Repository	Message	Link
Sep 23 8:25 AM	iem,main	📝 Sundry updates per review	Link
Sep 23 2:13 PM	pywwa,main	📝 Denote pyWWA 1.7.1 release	Link

Daily Feature

Waiting after first sub 39°F
Date: 23 Sep 05:30 AM
Votes: Good: 11   Bad: 0 Abstain: 0

The chilly start to September has been replaced by persistently mild temperatures without return to such chilly weather to speak of. For Ames, the low back on the 7th of September was 38°F with no values cooler since. The featured chart looks into the interval each fall season between the date of first sub 39°F to the date of first sub 32°F temperature for Ames. The dashed line provides a reference to associate the number of days with a given subsequent date. The linear fit line is an attempt to fit the two dates and the relatively poor correlation shows that having such a cool temperature does slightly increase the earliness of the second temperature, but not by much. Values shown around the 7th of September range from about a week to over 50 days!

The featured media can be generated on-demand here

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NWS Watch/Warning Summary for 12 AM 23 Sep 2025 - 12 AM 24 Sep 2025 CDT

	Summary		By WFO					Watches
Type	US	IA	ARX	DVN	DMX	OAX	FSD	US
Tornado	1	0	0	0	0	0	0	1
Svr Tstorm	92	0	0	0	0	0	0	2
Flash Flood	32	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:  93 Verified:  16 [17.2%]
Polygon Size Versus County Size            [23.9%]
Average Perimeter Ratio                    [31.4%]
Percentage of Warned Area Verified (15km)  [6.7%]
Average Storm Based Warning Size           [1451 sq km]
Probability of Detection(higher is better) [0.75]
False Alarm Ratio (lower is better)        [0.83]
Critical Success Index (higher is better)  [0.16]