Last week’s storm system was mostly about the heavy rain and flooding, as Eric summed up nicely here. But the story that I think was most fascinating, meteorologically, was the hailstorm that hit some parts of the Houston area on Thursday night. The National Weather Service Houston office collected over 20 hail reports from the event, more than half of which were golf ball size hail or larger.
Put your car in your garage if possible or cover it with blankets. Hail pictured came down near Katy Freeway at Sam Houston toll road and the storm is headed straight to Houston. pic.twitter.com/f0prcLOuDf
— Arson (@txArson) May 10, 2019
@NWSHouston Hail from Clear Lake in last 15 minutes. Larger in the yard. Can't get to them pic.twitter.com/9EWFIjUhNI
— SETXWeather (@SETXWeather) May 10, 2019
https://twitter.com/VortexChasing/status/1126686637394518016
Houston doesn’t often get hail this big over this wide an area. So what happened here? Why did we have so much big hail last Thursday?
Houston doesn’t see a lot of hail
If you look at the map of annual average 1+ inch diameter hail days per year (this from 2003-2012), you’ll notice Houston is mostly on the outside looking in at significant hail reports.

Why is this the case? For one, thunderstorm updrafts are needed to allow for the water droplets that become hailstones to get above the freezing level. Houston is a warm place, and that freezing level is often too high and the storms not powerful enough to carry those droplets high enough for large hail to form. Our lower freezing levels occur in winter and spring, making hail more likely then. In fact, of the 62 hail reports of 2″ in diameter or larger in NOAA’s storm events database since 1950 in Harris County and adjacent counties, only 3 of those reports have occurred outside of January through May. The average hail maxima is also where it is because they simply get more powerful, supercell thunderstorms with violent updrafts in the Plains.