Big Autumn Storm Moves In - NBC Connecticut
On Ryan's Radar

On Ryan's Radar

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

Big Autumn Storm Moves In

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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Forecast for Sat. Nov. 17

Powerful winds, flash flooding and even severe thunderstorms. There's a lot to talk about with the Tuesday storm. Let's start with the rain.

Nightly Weather Forecast for October 23Nightly Weather Forecast for October 23

(Published Monday, Oct. 23, 2017)

Flash flooding is a possibility in some areas with locally heavy rain totals expected. On average 1.5"-3.0" of rain is forecast but I would not be surprised to see a localized pocket of as much as 5" of rain! The most likely location for this is in western Connecticut in a handful of towns. Our high resolution models show the potential for some big totals including the RPM (pictured below) which prints out nearly 6" of rain parts of the Litchfield Hills.

The good news is our recent stretch of dry weather will mitigate the river flood threat. Smaller rivers and streams may see flooding but the bigger rivers such as the Farmington, Housatonic and Connecticut will stay in their banks.

While scattered showers and thunderstorms are possible through the day on Tuesday the heaviest rain will be centered on Tuesday evening and overnight.

Wind speed and direction about 2,500 feet above the ground. The bright red indicates winds of approximately 70 mph!

The other issue tomorrow will be strong and damaging winds. Something called a low level jet will develop across Connecticut during the day tomorrow. This occurs often. The question is how much of the strong winds in the low level jet will mix down to the ground. Hurricane force winds 3,000 feet above our heads can exist with barely a puff of wind at the ground! In this case there seems to be a bit more mixing than we typically see in these events which should promote strong and gusty winds across the state. Our forecast is for 45 to 60 mph wind gusts peaking Tuesday evening and night.

Forecast off the GFS model for 11 p.m. Tuesday. The wind is shown on the right with temperature and dew point in red and green, respectively. This shows the potential for 50 knot winds to readily mix to the surface with a shallow layer of instability near the ground.

The other thing we'll have to watch tomorrow is the possibility for severe thunderstorms. This is a setup known as a low CAPE/high shear setup. While these don't always produce with such strong low level shear any thunderstorm that does develop need to be watched closely. Damaging winds and an isolated tornado are possible.