Wild Monday of Weather Expected Across CT (Monday, April 13, 2020)

A vigorous weather system across the south combined with an eastward advancing cold front will set the state for a wild day of weather here in Connecticut on Monday. Periods of extremely heavy rainfall and even some thunderstorms will traverse the state. A strong pressure gradient combined with potential for thunderstorms will result in a windy day across the state. Due to the high winds and wet ground, the potential exists for scattered to widespread power outages and tree damage.

Forecast models show a sub-990mb low tracking through the Great Lakes by Monday morning with a strong area of high pressure across the western Atlantic setting up a strong pressure gradient across the eastern United States. The stronger the pressure gradient, the stronger the winds and with a strong gradient we'll some high winds Monday:

With such an intense weather system passing to or west and the strong high pressure to our east, winds only a few thousand feet above the ground Monday will become exceptionally strong. In fact, winds about 5,000 feet off the ground may approach or even exceed 100-110 knots...that is extremely impressive:

Thankfully, we will have what's called a temperature inversion in place. Typically, temperatures will decrease as you ascend through the atmosphere. However, due to strong southerly winds coming off the much colder waters of the Atlantic Ocean (south of Long Island) and Long Island Sound itself, this will keep temperatures in the lowest few thousand feet of the atmosphere "cool". What's happening is with the low pressure tracking so far to our west a warm front will approach. However, due to the colder air coming off the waters the push of warmer air in the lowest few thousand feet will come to a halt, however, as you ascent about several thousand feet into the atmosphere where the colder waters will have less of an influence, the push of warmer air will usher in much more quickly. This then forms the temperature inversion as temperatures here will warm faster then a few thousand feet below. This is extremely critical because if not for this temperature inversion, we would see widespread destructive wind damage. However, due to atmospheric mixing and potential for thunderstorms, some of these winds will mix down to the surface and this will create the potential for damaging winds. However, instead of 100-110+ knots (125-135 mph) down at the surface we may see wind gusts of 50-70 mph possible (with sustained winds 25-35 mph).

An example of what a temperature looks like visually is illustrated below. This is a bufkit forecast sounding for Windsor Locks, CT for noon EDT Monday. The green line is dewpoint temperature and the red line is air temperature from the surface (where we live and at the bottom of the sounding) rising through the atmosphere. When the lines slope to the left temperature/dewpoint is decreasing with height. When the lines slope to the right temperature/dewpoint is increasing with height. Looking at the lowest 5,000 feet of the atmosphere we see both dewpoint and temperature are increasing with height. This is our temperature inversion:

This warming of temperatures and an increase of moisture with height will also promote the atmosphere to be a bit unstable above the temperature inversion. Instability is one ingredient needed for thunderstorms. Not only will we see some extremely heavy rainfall on Monday, but there will be multiple opportunities for thunderstorms. 1) An embedded line of thunderstorms which moves through mid-morning through mid-afternoon and 2) A much smaller opportunity for discrete thunderstorms during the late afternoon sneaking into southwest CT:

Outside of any thunderstorms tomorrow, it will be quite windy with winds sustained 20-30 mph and gusting 50-60 mph at times. However, with thunderstorms the potential will exist for winds to gust 65-75 mph. Thunderstorms will increase the potential to mix some of those exceptionally strong winds a few thousand feet off the ground down to the surface. This would certainly lead to the potential for scattered to widespread power outages. We will closely have to monitor the potential for any discrete thunderstorms making their way into southwest CT late afternoon as these would pose an additional risk for severe weather.

So what can we expect Monday?

• Sustained winds 20-30 mph with gusts 50-60 mph
• Torrential rain at times with a line of thunderstorms moving through .
• As these thunderstorms move through localized wind gusts of 65-75 mph are possible. 
• Scattered to widespread power outages and tree damage 
• Pockets of flash flooding