At about 330 PM Eastern Time today, I posted a radar image to my DailyKos account's Facebook page warning Connecticut residents of a strong line of severe thunderstorms that was making its way ashore. Here was the image:
Weatherdude from DKosOver the next few hours, something meteorologically amazing happened -- the storm seemed to turn into a mini hurricane over land, reportedly causing extensive damage near Hartford, CT, including a storm spotter reporting a wind gust to 100 MPH:
65-75 MPH winds about to move ashore in Middlesex and New Haven Counties in Connecticut. Be prepared for very strong winds as this line of storms moves inland.
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Just In..Skywarn spotters reporting wind gust to 100 mph @ S. Glastonbury! Hundreds of trees down. Extremely dangerous storm-— WBZ Boston Weather (@wbzweather) August 10, 2012
What the heck happened? Let me explain...
Even though it's rapidly been nicknamed a "mini hurricane" on social media, it wasn't a tropical system. It was something called a "mesolow."
In the strongest part of the storm, there was a narrow but intense jet of winds one or two thousand feed above ground level. This 65-75 MPH jet of winds surged forward, causing surrounding parts of the storm to curl back due to friction. Think about when you run your hand through a swimming pool -- this is the same process that causes the little tiny whirlpool/vortices along the edge of your fingers.
As the severe thunderstorm's winds continued to strengthen, they caused the storm to spin more. After about 30 minutes, the Coriolis effect took over. Coriolis is the perceived force caused by the rotation of the Earth that causes moving objects to deflect to the right of their motion. As the winds and Coriolis effect took over, it turned the rotation in the thunderstorm into very tiny low pressure system called a mesolow.
Mesolows can be as small as a thunderstorm (as we saw today) and they can be as big as a few counties. They can last for a day or more, and if they move over the ocean, they can serve as the nucleus for tropical storm development.
The rotation of the Connecticut mesolow enhanced the winds in the storm, causing the low to spin faster, and giving the storm a very ominous almost hurricane-like appearance on the radar, complete with a center of circulation that was almost like the "eye" of the storm:
You can even see a very defined wind shift in Hartford, CT as the mesolow went by -- shifting the winds from due south to due north in just two hours:
As the storm moved into more stable air, it started to dissipate and weaken a bit, taking on a less-ominous (but still pretty awesome) appearance on radar:
Mesolows occur on a semi-regular basis in strong lines of thunderstorms, and they're pretty cool to look at on radar. Unfortunately, however, the storms that produce them can (and did, in this case) produce a lot of damage. Below is a map of wind damage reports (blue W) and tornado reports (red T) as of 750 PM EDT. The number will likely increase a bit as more reports trickle in.
If you experienced the storm in New England today, let us know how you fared.