Iowa Environmental Mesonet Daily Bulletin for 28 March 2024

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Daily Feature

TVS Heatmap
Date: 27 Mar 05:30 AM
Votes: Good: 11   Bad: 0 Abstain: 0

This week is Severe Weather Awareness Week in Iowa with Wednesday's topic focusing on Tornadoes. There will be a statewide Tornado Drill at 10 AM. The primary mechanism the National Weather Service uses to analyze possible tornadoes is their NEXRAD Doppler RADARs. One of the products these RADARs produce is something called a Storm Attribute Table. The IEM maintains an archive of these with a download interface available. RADAR algorithms can generate a Tornado Vortex Signature (TVS) alert within this table output when rotation is detected with appreciable depth. The featured map presents a heatmap of these TVS reports with the individual NEXRAD locations denoted by a "X". This algorithm only works on RADAR information relatively close to the RADAR location, so thus why you see no-data gaps. There are other algorithms that can help diagnose possible tornadoes at further away distances, so the NWS is not completely flying blind over these areas. It is certainly much "easier" to see tornadoes on RADAR when it is close to the RADAR location.

NWS Watch/Warning Summary for 12 AM 27 Mar 2024 - 12 AM 28 Mar 2024 CDT

Summary By WFO Watches
Type USIA ARXDVNDMXOAXFSD US
Tornado 0 0 0 0 0 0 0 0
Svr Tstorm 23 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:  23 Verified:  13 [56.5%]
Polygon Size Versus County Size            [31.9%]
Average Perimeter Ratio                    [17.2%]
Percentage of Warned Area Verified (15km)  [24.8%]
Average Storm Based Warning Size           [1436 sq km]
Probability of Detection(higher is better) [0.82]
False Alarm Ratio (lower is better)        [0.43]
Critical Success Index (higher is better)  [0.50]