IEM Daily Bulletin for Dec 18 2025

[daryl herzmann]

Iowa Environmental Mesonet Daily Bulletin for 18 December 2025

News

No news is good news

IEM Code Pushes <repo,branch> on Github

Timestamp	Repository	Message	Link
Dec 17 11:03 AM	iem,main	🎨 Improve time parameter validator for service	Link
Dec 17 9:46 PM	iem,main	✨ Add snowfall variables to output	Link

Daily Feature

Nice December Tuesday
Date: 17 Dec 04:35 AM
Votes: Good: 11   Bad: 0 Abstain: 0

Temperatures warmed nicely on Tuesday and provided some needed melting of recently accumulated snow and ice. The featured map presents high and low air temperatures from the ISU Soil Moisture Network. Most of Southwest Iowa started the day without any snow cover, so temperatures were able to reach the upper 40s and even lower 50s. A general weather forecasting rule of thumb is that high temperatures will be capped at about 43°F when the day starts off with at least four inches of snow on the ground. You can see this rule hold for the stripe of Iowa from the NW to SE corners of the state which had the deepest snow cover.

The featured media can be generated on-demand here

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NWS Watch/Warning Summary for 12 AM 17 Dec 2025 - 12 AM 18 Dec 2025 CST

	Summary		By WFO					Watches
Type	US	IA	ARX	DVN	DMX	OAX	FSD	US
Tornado	0	0	0	0	0	0	0	0
Svr Tstorm	10	0	0	0	0	0	0	0
Flash Flood	0	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:  10 Verified:   7 [70.0%]
Polygon Size Versus County Size            [31.9%]
Average Perimeter Ratio                    [40.5%]
Percentage of Warned Area Verified (15km)  [10.8%]
Average Storm Based Warning Size           [8142 sq km]
Probability of Detection(higher is better) [0.56]
False Alarm Ratio (lower is better)        [0.30]
Critical Success Index (higher is better)  [0.45]