ROANOKE, Va. – A Tuesday tweet by Andrew Freiden, a meteorologist at the NBC affiliate in Richmond, got my wheels turning.
We've seen this happen a few times in Roanoke too. Even though we're a smaller city than Richmond, this effect has given rise to pop-up storms occasionally. https://t.co/YMMoVYeKiB— Chris Michaels (@WSLS_Michaels) July 27, 2021
How can cities influence summertime thunderstorms?
While Roanoke or Lynchburg may not be an enormous metropolis like New York or Chicago, the urban infrastructure can play a role in day-to-day weather. Roanoke was one of only 13 cities across the U.S. studied for the urban heat island effect last summer.
It’s possible that a city like Roanoke could develop its own storms, though we know that’s not always the case in the summer.
Urban Heat Island
Here’s how it works. The buildings, concrete and asphalt (among other things) absorb heat more efficiently than rural areas.
In a case like Richmond, summers can be several degrees higher than surrounding rural locations (according to data from Climate Central).
A few suggested ways to combat this effect include (but are not limited to): planting more trees along streets and whitewashing asphalt.
In order for storms to form, you have to have heat and humidity at the surface. Hot and humid air is more buoyant, so it rises into relatively cooler air. That process of cooling and condensing allows clouds to form. As the air continues to rise, it reaches its fullest potential (Convective Available Potential Energy) and storms can form.
The increased heat from urban infrastructure and, in some cases, increased lift from very tall buildings can give rise to pop-up summertime thunderstorms more efficiently than surrounding areas.
This is something that was brought to light by many researchers, one of them being Dr. Marshall Shepherd. He studied this phenomenon using a series of NASA satellites in the early 2000s.
At night, this heat/warmth isn’t released as quickly as it might be in a more rural location. So while most ordinary cell thunderstorms tend to dissipate after sunset, a city center could delay that process due to the increased warmth.
In recent winters, there have been times when we’ve seen surrounding suburbs of Roanoke receive an icy glaze from freezing rain. However, the city stays just above 32°F, leaving precipitation to fall as a very cold rain.
Again, that’s not to say this happens all the time. But there are examples we’ve seen as recently as February 2021 where something like that has happened.