Gusty Thunderstorms with Small Hail Possible Tuesday, April 21, 2020.

A vigorous shortwave trough is expected to amplify (strengthen) as it digs through southeast Canada Tuesday:

Associated with the shortwave trough will be a pool of very cold temperatures between about 10,000 feet and 20,000 feet above the ground with temperatures up around 18,000 feet around -25C (-30 diving through southeast Canada!). This will provide steep mid-level lapse rates (temperatures decreasing rapidly with height):

With such a vigorous shortwave we will also see some rather impressive dynamics aloft characterized by the nose of a mid-level jet streak of 80+ knots punching into the region with a low-level jet exceeding 40-50 knots:

Mid-level jet:

Low-level jet:

With temperatures climbing into the 50's with dewpoints into the 40's combined with the steep mid-level lapse rates this will yield a marginally unstable airmass. Combination of a marginally unstable airmass, strong dynamics, and strong forcing from the cold front and shortwave energy will likely be enough to spark off scattered showers and thunderstorms Tuesday afternoon. Some of these will be capable of producing gusty winds and/or small hail. The greatest overall risk looks to be across NY, northern PA, and VT, however, depending on overall timing some of these may sneak into parts of MA and CT before fizzling due to loss of daytime heating. These will be scattered so not everyone sees any thunderstorms or even rain. 

Friday, April 17, 2020 into Saturday, April 18, 2020 Snow Event

Well...welcome to winter I guess. Computer forecast models for the past few days have been rather consistent in a fast moving weather system producing a narrow swath of moderate snow across parts of New England. There have been uncertainties, however, regarding where this band of snow traverses, but computer forecast models seem to be converging on a more likely solution.

A vigorous piece of shortwave energy is expected to amplify (strengthen) as it moves through the Northeast. This will help promote the strengthening of a surface low pressure as it passes just south of southern New England. Forecast models indicate a swath of rather impressive upward vertical motion will traverse southern New England overnight Friday into Saturday morning. This will result in moderate (perhaps even heavy) precipitation...which will likely be snow:

Friday morning's bufkit run of the NAM forecast model at Windsor Locks, CT shows a period Friday night of moderate lift extending into the dendritc snow growth zone with plenty of available moisture (not shown). This indicates there will be a period of moderate-to-heavy snow across the northern part of the state overnight Friday into Saturday morning:

Both the NAM and European computer forecast models indicate a thermal profile across northern CT which will be just supportive of snow. Looking at a forecast sounding for Windsor Locks, CT on the NAM notice the green line (dewpoint) and red line (temperature) are hugging the 32 line. This constant temperature through the lowest 5,000 feet of the atmosphere will result in what's called to an isothermal snow bomb...a several hour period of moderate-to-heavy snow which will be wet and heavy:

What to expect:

• Snow may start out as some rain but will quickly change to snow (away from the shoreline) with precipitation beginning between 7:00 PM and 10:00 PM EDT. 
• Heaviest rates between 12:00 AM and 5:00 AM EDT Saturday morning with snowfall rates 1'' to 1.5'' per hour.
• Snow will be heavy and wet. Due to weakened state of trees, tree limbs, and power poles from the wind storm this may result in isolated-to-scattered power outages. 
• Snow ends by 8:00 AM Saturday morning with some residual snow showers through mid-morning.
• Melting happens also immediately as temperatures warm into the 40's. 

Below, is my snow map:

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