Record Warmth and Some Storms - NBC Connecticut
On Ryan's Radar

On Ryan's Radar

First Alert Meteorologist Ryan Hanrahan Gives You His Take on Connecticut's Weather

Record Warmth and Some Storms

On Ryan's Radar

NBC Connecticut First Alert meteorologist Ryan Hanrahan gives you the science behind the forecast and shares with you an in-depth look at the weather impacting Connecticut.

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Afternoon Forecast for September 19
Courtesy: Ben Gebo

It's not the earliest heat wave on record but it was pretty darn impressive. 94, 96, and 91 (at least) over the last 3 days makes this the first heat wave of 2017. The earliest heat wave on record occured back in 2002 when the mercury exceeded 90F for three consecutive days April 16-18.

With record warmth we managed a few loud storms last night. While the storms remained sub-severe with limited, if any, damage reports in the state they did wake many people up!

Many storms around here tend to weaken after the sun goes down. As the sun sets the atmosphere cools and instability wanes. Thunderstorms need an unstable atmosphere to form! Last night was different in that several clusters of storms actually strengthened around midnight. We actually expected this to happen as there were a few ingredients in place that were a bit unusual. The biggest was the unususally steep mid level lapse rates.

Evening weather balloon launch from Long Island plotted as a skew-t. The red line (temperature) juts to the left fairly quickly between 10,000 feet and 20,000 feet which indicates temperatures are falling rapidly with height. This "steep lapse rate" was the key ingredient to keeping thunderstorms strong through the overnight.

Lapse rates are easy to understand. It's simply the temperature difference between two levels of the atmosphere. We express lapse rates in degrees per kilometer - so the larger the value (or steeper the lapse rate) - the faster temperature decreases with height. This helps promote instability in the atmosphere. Last night the lapse rates were steep (in excess of 7C/km) and there was a surge in moisture a few thousand feet up after dark. The combination of increasing moisture underneath the steep mid level lapse rates helped fueld storms that lasted well into the night.