Determining Hail Size Using Radar
Hail size is key for damage assessment, but radar tools often miss the mark when creating an accurate estimate. Accurate hail size relies on expert meteorologists who use radar data and ground reports to provide reliable information for insurance claims and legal issues.
Hail size is important for determining the extent of damage from severe storms, but current radar tools like the Maximum Expected Hail Size (MEHS) algorithm often show inaccurate estimates, sometimes overestimating or underestimating the actual size. Accurate hail size assessment remains dependent on HailTrace's expert meteorologists who use a combination of radar data and ground reports to provide reliable information for insurance claims and legal purposes.
Hailstorms are Costly!
Hail size has been one of the main pieces of evidence used by the restoration industry. Larger hailstones can produce extensive damage to buildings, crops, and animals.
This can be quite costly for the homeowners and businesses affected by the severe hail event. Many hailstorms have cost over $1 billion in property damages and are given the nickname “billion dollar hailstorms”.
For properties with hail damage, they will need to file an insurance claim and provide proof of damage. This proof may include verifying the size of hail that fell at their location. Without a ground truth report of hail size, how can this be shown?
Finding Hail Size using Radar
At HailTrace, we can determine hail size using a variety of different radar tools. This includes more than just high reflectivity on radar, we also look at products including correlation coefficient and differential reflectivity.
A case study in progress by Forensic Meteorologists Daniel Schreiber and HailTrace's Matthew Amory looks into many different examples of storms using carefully selected reports all over the United States. These points were selected from the Storm Prediction Center (SPC) Storm Reports and Community Collaborative Rain, Hail, and Snow Network (CoCoRaHS).
What did the study find?
For this particular study, they looked into a product called Maximum Expected Hail Size (MEHS).
MEHS is an algorithm product that gives an estimate of the largest hail size within an area. Below is a graph of the measurements found using radar derived MEHS compared to the hail size reported at the location:
The numbers of MEHS must be the same as the hail size on the graph for the algorithm to be reliable. This is shown on the graph by the orange line, meaning the closer a point is to the line, the more accurate MEHS is on that measurement. However, the MEHS algorithm show many different hail sizes from what is measured. The most extreme examples of error include a 1” hail MEHS estimate for a 5.25” hail report (circled in purple) and conversely a 3.75” MEHS estimate for a 1” hail report (circled in red).
The mismatch between MEHS and reported hail size can also be a major issue for smaller hail sizes as many sub-severe (<1”) hail reports are overestimated. The same goes for underestimating severe hail to sub-severe sizes.
Takeaway: Trust Your Meteorologist
No radar product has shown to be a 100% accurate in estimating hail size. That leaves it up to the meteorologist to determine the hail size using any available resources including radar and reports. This study has shown that MEHS is unreliable in determining hail size when compared to surface ground truth.
This issue highlights the importance of having a real meteorologist when trying to determine the size of hail that has fallen at a location. They are equipped with the knowledge to conduct a forensic analysis and make a sound estimate of hail size. HailTrace has an entire team of meteorologists to ensure that we employ state of the science techniques to create our hail size estimates.