We knew the storms that blew through on October 7th were not just typical severe thunderstorms. It was confirmed on Tuesday October, 11th by the National Weather Service that it was in fact a derecho.
Now, what is a derecho? It is classified as a long-lived straight line wind even that is associated with a fast moving line of severe storms that will have wind gusts 58 mph or greater and well separated wind gusts of 75 mph or greater. Of course, with the storms that moved through the Capital region there were several locations along the path that the winds met that criteria with a wind gust of 67 mph reported at the airport, the highest gust for any day in October. There were also microbursts along the path with winds between 80-100 mph, and there was a quick spin up tornado reported in Canajoharie which was rated an EF-0 with maximum winds of 85 mph, however, thankfully it was only on the ground for 75 yards.
One of the other criteria for a derecho is that is has a path of damage for at least 250 miles or more. In the case of the storm from October 7th, it traveled from the east end of Lake Ontario all the way to Nantucket Island, just over 400 miles!
There were over 250 reports of damaging winds along the path, slicing directly through the Capital region. No one was spared when it came to damage and of course at it’s height, hundreds of thousands were left without power. Many did not have their power restored for several days.
I believe the reason for the widespread damage we sustained was due, of course to the strength of the gusts, but also the duration of the strong wind gusts. In many cases the gusts lasted for several minutes.
This was not a very favorable setup for severe weather, temperatures that day were in the 60’s and dew point temperatures were mainly in the 40’s, the ingredients for widespread severe weather was not there! However, there were very strong winds above the surface and that was able to translate down to the surface with the leading edge of the line of storms.
Climatologically speaking when it comes to the frequency of derechos, here in the Capital Region we will see one every two years, also worth noting the National Weather Service says that 70% of all derechos that occur will typically happen during the warm season, whereas 30% of them will happen in the cooler months.