Vicious Storms: Some Answers to Your Questions

Wednesday evening's storms were powerful and created some incredible displays of clouds, lightning, and hail. Over the course of the evening we had tons of questions about the storms that were moving through so I wanted to take some time to answer some of them here. 

Why was there a tornado warning issued? Did a tornado touch down?

The tornado warning issued for Fairfield and Litchfield Counties last night because of strong rotation indicated on radar. The picture above shows a powerful rotating wall cloud near Poughkeepsie as the storm moved through. 

While there was strong rotation with the storm visible from the ground and on radar at least as of now there are no reports of a tornado touchdown. While there was very strong wind shear in the atmosphere - there wasn't a whole lot in the lowest 5 to 10,000 feet which is critical for tornado development. The National Weather Service in Albany is surveying damage in Wappinger's Falls, NY to see if a tornado did indeed touch down.

By the time the storm got into Connecticut the storm began to weaken substantially and as I said on air last night the tornado threat was diminishing over Sherman and New Milford.

Why was there so much hail? 

Last night's storms were prolific hail producers in some spots. Quarter size hail (or even a bit larger) in New Milford with many pea to dime size hail reports elsewhere. 

All thunderstorms contain a fair amount of ice in their clouds way above our heads. The more powerful the storm the larger this ice grows as the storm's updraft is able to keep these ice particles - also known as hail stones - suspended. As a piece of hail in the clouds (where it's below freezing) comes in contact with super cooled water it keeps growing and growing until gravity ultimately wins. These ice chunks then accelerate from the cloud down to the ground. 

Model sounding for Poughkeepsie, NY around the time of the tornado warning shows plenty of instability but relatively weak wind fields (<30 mph) in the lowest 10,000 feet of the atmosphere which is hostile to tornado development - even if a thunderstorm itself is rotating. The winds above that level are much stronger which allows rotation or a supercell to develop. Also seen here is an unusually low wet bulb zero height - 8,500 feet which means hail only has a shallow depth of melting to fall through before reaching the ground.

Frequently, this hail melts on the way to the ground in Connecticut. Hot summer days can produce a 15,000 foot thick layer of warmth that's just too much for the hail to survive. What initially could have been a golf ball size chunk of hail in a cloud will be reduced to a mere pea size stone as it melts rapidly while falling through warmer and warmer air. Last night was a little different. 

The 32 degree wet bulb temperature was only about 8,500 feet above our heads. This means the hail only had a relatively short distance to fall to survive melting. The unusually cold environment allowed hail produced in the storm to make it to the ground more readily. 

Normally when we get thunderstorms it's warm and humid - but yesterday was sort of cool. What's the deal?

Thunderstorms thrive off instability. You want a really warm and humid air mass near the ground (think 95 degrees and sweltering humidity) and unusually cold air aloft. 

Unusually cold temperatures around 18,000 feet up allowed instability to develop for storms even without high heat and humidity at the ground which is typical for our summer storms.

Obviously yesterday wasn't 95 and humid! What we did have yesterday was a really cold pocket of air about 18,000 feet up - which is our favorite place in the atmosphere to look. The temperature at this level approached -19C which is unusually cold. So cold in fact we didn't need big heat and humidity in  order to produce instability. It's a balance between the low level warm and upper level chill - as you want the biggest difference between the two. 

Those clouds were nuts! What were they?

The clouds we saw in many towns last night right around and just after sunset are known as shelf clouds. You get shelf clouds as cool thunderstorm outflow rushes away from a storm and forces air up on the leading edge of a storm. These shelf clouds can be beautiful - but can also be a signature that's associated with damaging winds. Thankfully, the winds in Connecticut remained below severe limits and we didn't receive any reports of wind damage.

Thank you!

On another note - a big thank you to our viewers for sending in pictures and reports all night. We really appreciate the help in these storms. You can view some of those pictures here.

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