17 May 2013
Guest Post from Bob Ryan Meteorologist for WJLA TV in Washington DC
(This post appeared on the WJLA Weather Blog)
Are cities changing summer thunderstorms?
This is a follow-up blog to a story I had on our 11PM news Tuesday May 14. You can see the actual story below but I wanted to expand a few things beyond 1 minute and 30 seconds. Here’s the tease :>). Do you live in a city? Marshall Shepherd, a leader in the increasing important field of urban meteorology (and current President of the American Meteorological Society) writes in a recent book that by 2030, 80% of the world’s population will live in an “urban environment” So you or you children, do or likely will live, in a city. Do you notice the city is warmer than the “countryside” or “rural area”? Yes cities are warmer, especailly on hot summer nights. It’s called the urban heat island or UHI. We can see it.
The concrete, buildings, streets, ashphalt absord heat in the day and just like a hot pot of water are slow to cool at night. I think everyone living in a city, during a summer heat wave knows cities are hotter. Is the city weather different than the “rural” weather? I hope you think yes-at least on summer nights cities are warmer. Also warmer on winter nights-which helps the heating bills. OK is the “climate” (think average summer temperaturers) of the cities different? Is the climate of the cities changing? Yes, I know slipperly slope and not going there. But let’s just agree that on a small scale (let’s call it a microclimate) the climate is changing. So now what about summer thunderstorms? Here is a series of radar images that Marshall Shepherd thinks shows were started in part by the Atlanta urban area in a northeast flow of unstable air.
- The story I did via Skype is with one of the leading researchers in urban meteorology Dr. Robert Bornstein. His ideas about cities affecting thunderstorms came about by talking with NWS forecasters who observed thunderstorm lines that seemed to “split” as they moved into New York City. He wonded why and thought that maybe cities can by either the heat island or the city structure/buildings can change the motion or flow of thunderstorms or even lines of storms.
He set out to test his idea/theory by experiemts. He and students made physical/mathematical simulations of the city and the atmopshere and found in some special cases thunderstorms do split around NYC.
Also his ideas that cities, as Marshall Shepherd has found in Atlanta, Georgia, under certain conditions may even be the starting point of individual storms. And here Washington-Baltimore area may indeed change lines of thunderstorms in the Washington area as some researchers have suggested. So here is the short story. See what you think. Are cities changing our weather?
FYI: Bob Ryan is the only meteorologist in broadcasting who served as President of The American Meteorological Society, and has forecasted Washington’s Weather for over 3 decades.