Official hail records have been kept in Boston since 1950. On August 4th the largest hail recorded since that date fell in parts of the city and some of it did some significant damage. I don’t see any severe weather on the way, but there might be some thunderstorms Saturday, mainly north of Boston. Although many types of weather observation have been automated over the past several decades, hail measurement still generally relies on human monitoring and manual assessment.

There is now technology available which enables measurement of hail size. Meteorologists can use Doppler radar to see hail inside a thunderstorm and certain modes of the radar can even estimate the size of the hail. One issue with this method is although the Doppler radar can “see” the hail, it can’t know if it has reached the ground. In order to know if hail is impacting the surface, we need actual observations or some sort of sensor to tell us hail is actually reaching an area.


I recent became aware of a startup company called Understory Weather who is creating a network of weather stations, each with a very high tech hail monitor. The company’s vision is to have a nationwide network, which when deployed, gives an accurate depiction of where hail has fallen as well as incredibly precise data of wind, temperature and precipitation. Their stations also have wind and temperature data and they are working on other variables as well.

There are several of these systems deployed in New England, one of them is even in Sommerville. A picture below shows how the system is mounted. The silver ball is the hail sensor.

The data from Understory’s network of the August 4th storm is pretty remarkable.

This chart below shows the size of the hail estimated by the Doppler radar and then the size of the hail by the Understory network and/or NOAA. Notice how the Doppler estimates are not as accurate as the Understory observations.

Another chart I find fascinating is from Sudbury, Massachusetts. Notice how precise the hail report is, showing almost minute by minute when the hail was falling to the ground. This level of accuracy is going to revolutionize the way we understand the impact of hail.


Insurance Claims and Hail

Why does this matter? In reality the hail from a summer thunderstorm melts not long after it falls. However, damage can be long lasting and sometimes homeowners or property managers may need to file a claim. Obtaining an accurate picture of where hail actual fell during a severe thunderstorm helps with the claim process. Forecasters doing research on thunderstorms can also use this data to see how different storms manifest themselves in terms of their hail coverage.

The image below shows both actual reports and data from the Understory hail algorithm. During severe weather this data could be incredibly helping to warn homeowners and businesses in the path of storm containing large hail what’s on the way.

Here in the northeast large hail isn’t very common. We can go years or even decades without a hail event and even in the August 4th event, the majority of the land area didn’t see hail in spite of the fact a large percentage of the population did.

Severe weather definitely can impact our lives. I had a downburst fell two 50 foot pine trees on my own property in the past decade. Three years ago, hail actually ripped apart many of my larger leafed plants, but that was the extent of the damage. I knew there was a chance of hail and moved my car under the safety of the garage.

Many folks aren’t able to avoid the impact of hail, and the more technology can help us gain more insight and better prediction of risks.