March 23, 2016 Dallas Storm Report: A Case Study
Hail in Dallas
On the evening of March 23, 2016, a large weather system passed over the Central US, bringing warm, moist air ahead of a strong cold front. The conditions were ripe for severe weather in the Dallas area. This fostered the development of vast numbers of hailstones, many of which had sizes exceeding 2” in some areas. Our analysis indicates that this storm affected 1 million homes in the Dallas area. Other sources expect an estimated $700M in insurance claims.
Understory’s weather station network detected this storm in real-time as it moved west to east over the Dallas area. Our revolutionary weather stations recorded each individual hailstone impact, providing an unprecedented dataset with which to understand the nature of this storm. Our proprietary algorithms used those data to provide ground-truth measurements of the damage potential of this storm to homeowners in the Dallas area.
Unlike radar-based methods for hail estimation that are limited to locating hail in the cloud, our ground-based stations measure where it actually falls! This post discusses the value added by Understory weather analytics, especially compared to radar-only methods. We’ll start with a focus on the damage potential from the March 23 hailstorm to homeowners in Dallas. After that, we’ll walk you through two ground-breaking observations: a time trend of hailstone size and hail angle of impact.
Damage Potential to Homeowners
The analytics team at Understory has developed a method to correct radar-based hail estimates using data directly measured by our stations. This “radar fusion” approach provides a direct assessment of the potential for hail-related damage across the entire Dallas area. Higher damage potentials imply a higher incidence of property damage as well as more costly repairs.
In Figure 1, we show a snapshot of Understory’s interactive map of hail damage potential in the Dallas area as revealed by our radar fusion approach. Measurement points from our weather stations, local spotter reports, and National Weather Service hail reports are indicated on this map and are color coded by green (meaning hail did occur) and red (hail did not occur).
This figure shows that the Plano and Garland neighborhoods had the highest potential for significant hail damage. In contrast, radar-only estimates showed no hail falling near northern Plano or Garland. Photos from western Plano (top left) and from northern Plano (top right) show hailstones with sizes of 1.5” to 2”. In Garland, photos from the next day show significant property damage (bottom right). Together, these local spotter reports confirm that Understory weather analytics gives a more accurate picture of where damaging hail fell in the Dallas area. Since our stations provide data in real-time, this allows property insurance agencies to prioritize their response efforts and proactively reach out to their customers almost immediately following a major storm.
Unprecedented Real-time Storm Tracking
Figure 2 shows individual hailstone strikes at all 7 of our Dallas stations where hail fell. We easily detect hailstones arriving within fractions of seconds of each other. This level of time precision has never before been available! We have discovered that larger hailstones often arrive before smaller ones. This likely reflects the fact that larger hailstones have higher terminal velocities than smaller ones. Examples of this phenomenon can be seen in Figure 2, especially at our Richardson and Garland stations.
For the First Time Ever, Hailstone Impact Trajectories
Intuitively, it makes sense that a direct hit is more impactful than a glancing blow. This concept can help insurers better understand the potential for property damage from hailstones. For example, a flat roof is particularly susceptible to vertically falling hail, while a steeply sloped roof is more susceptible to wind-driven hail that is falling nearly horizontally. Until now, there was no data available to address this issue.
Understory’s weather analytics provides, for the first time ever, a measurement of the incoming trajectory of hailstones. Property insurers can access this information by pulling a precision hail report from our database at a given address associated with a new claim. They can then compare the incoming hailstone trajectory with the angle of the roof in question to obtain additional information on the validity of the claim.
In Figure 3, we demonstrate the validity of our trajectory measurements. We give an example of the angle of impact from horizontal for the hailstones that fell at two of our stations: Garland and Plano. Here, 90 degrees is straight down, meaning hail falling completely vertically. In contrast, 0 degrees means horizontal hail moving perfectly parallel to the ground.
This figure shows that at Garland (blue histogram), most hailstones were impacting at shallow angles, with almost nothing coming straight down. This indicates large winds and wind-driven hail. Video and photo evidence from Garland (image on the left) confirm this, showing massive winds blowing hailstones from right to left across the image. Contrast this with Plano (green histogram), where our measurements indicate more vertical hail. Again, video and photo evidence show vertically falling hail that is consistent with our measurements.
The Final Word
In summary, the Understory weather station network in Dallas recorded hundreds of hail strikes with unprecedented accuracy and precision. This type of hail data has never been observed before, and is providing completely new insights into the nature of extreme hailstorms. We use these insights to give insurance companies a real-time understanding of the true impact of hail storms. Insurance companies can then use this information to prioritize their response efforts and better understand the claims they receive from their customers following a major storm event.