We’re getting way too caught up in terms, folks.
I wanted to keep Thursday’s forecast as clear and simple as possible: a line of severe storms possible during the evening into the early night.
It didn’t take long for the “D” word to start filling up my notifications Wednesday. Thanks to a Facebook post about a possible derecho Thursday in Virginia, I’m sure many other meteorologists in the area spent the day responding to someone else’s post. It’s annoying, but it’s the time we live in: the instant sharing of anything – true or untrue… as long as it gets our attention, right? Many Virginians now think of June 2012 when they hear “derecho”, and the “fear-sharing” (a term I’ve come up with to describe when you simply share a post because it scares you) starts.
So, allow me to clear things up.
Indeed, a line of very strong storms – possibly severe - is likely to drop south and east through Northern and Central Virginia and greater Lynchburg between 6-9 p.m. Thursday. Bands of storms may also extend south into the Roanoke Valley, NRV and Southside during this time as well.
The storms will develop just ahead of a very potent area of upper level energy – or spin – which will be dropping pretty far south for this time of the year. With temperatures in the lower 90s Thursday and plenty of wind and cold air aloft with the spin, the storms will have the potential to use that energy to become severe.
The upcoming pattern is more like something you would see in April, not mid June. (You’ll really enjoy the cool-off and very low humidity for Father’s Day weekend in the system’s wake, by the way.)
Any of the cells in the storms Thursday evening and night could produce damaging winds and large hail. That’s the case with ANY severe storm – derecho or not. A severe storm produces winds at or above 58 mph and/or hail 1” or larger and/or a tornado.
So yes, there is a threat of severe weather Thursday evening into early Thursday night. Whether the line of storms meets the general definition of a derecho, however remains to be seen and honestly should not matter.
Here is the how the Storm Prediction Center characterizes a derecho:
“By definition, if the swath of wind damage extends for more than 250 miles (about 400 kilometers), includes wind gusts of at least 58 mph (93 km/h) along most of its length, and also includes several, well-separated 75 mph (121 km/h) or greater gusts, then the event may be classified as a derecho.”
While I don’t feel it’s likely, no one knows for sure if Thursday night’s storms will meet the derecho criteria. Honestly, a lot of times, as was the case back in 2012, derechos aren’t really forecasted as much as they are simply observed once they form.
Even then, some derechos are stronger than others. Weaker derechos have passed through Southwest and Central Virginia in the past. To you, they were simply strong storms. The Mid Atlantic Derecho of June 2012 was particularly strong for this area. The likelihood of a repeat event similar in strength to that event is very low.
More than likely, the storms will take the presence of an MCS (Mesoscale Convective System) with a strong leading edge. An MCS is a cluster of organized storms common as we get into the summer months.
If you’re confused, I’ve made my point. It would have been nice to have simply alerted you to the possibility of severe weather late Thursday.
You can get wind damage without the storms being part of a derecho. So don’t let the official definitions get in the way of reality.