Thursday, January 20, 2022 Light Morning Snow

 A strong Arctic cold front is set to cross the state late Wednesday evening. Ahead of the Arctic front, temperatures will be several-plus degrees above-freezing, thus precipitation at the onset will be in the form of rain. However, much colder air rapidly filters in on the backside of the front. Typically with these Arctic cold front, there is a race between the ending of the precipitation and the advection of drier air vs. the advection of colder air (cold enough for precipitation to transition from rain to snow). In this instance, however, forecast models are advertising an abundance of moisture on the backside of the front (coined an anafront). 

As a result of a very tight pressure gradient between the airmass ahead of the Arctic front and the Arctic air behind the front, there will be a very narrow corridor of enhanced low-level convergence and forcing which forecast models are in great agreement on this narrow corridor traversing southern Connecticut. This indicates at least a few hour period of light-to-moderate snow (perhaps even briefly on the heavier side) traversing portions of southern Connecticut:

Temperatures along the immediate shoreline will take a bit longer to drop below-freezing as the Arctic front may actually slow down just before clearing the state. This will keep precipitation falling as rain a bit longer along the immediate shoreline, however, even here rain should end as a bit of snow. 

This mini event could have implications on a potential storm this weekend, however, there is very little consistency or agreement within the forecast models at this time, however, the potential certainly exists for a storm to work up the coast bringing the potential for snow and/or a wintry mix. More on that later in the week :)

What to expect:

• Showers begin working into the state anywhere between 1:00 AM - 4:00 AM EST Thursday.
• Showers will quickly transition to light snow statewide (exception being right along the immediate shoreline) with some more moderate snow across southern Connecticut just away from the immediate shoreline. 
• Snow begins to taper off between 9:00 AM -11:00 AM Thursday morning.
• Expect a slow Thursday morning commute and anticipate icy conditions due to snow and temperatures falling below-freezing. 

Monday, January 17, 2022 Connecticut "Snowfall" Forecast

 Computer forecast models have been incredible agreement the past several days on a significant low pressure system blossoming within the Tennessee Valley and Southeast and then turning up the mid-Atlantic. The question was whether we would be looking at a significant winter storm or not here in Connecticut. If you're a snow lover, unfortunately the news is not very good. Disclaimer: Just because I am posting images from a particular forecast model below does not mean I am siding with that model or solely using that model in the deriving of my forecast. It is just being used for illustrative purposes.

A piece of shortwave energy currently diving southeast through the central Plains rapidly strengthens and amplifies as it moves into the Southeast. This system will have already reached maturity within this region early Sunday. This is evident by a tighly closed 500mb low and jet streak already having rounded the base of the trough:

To begin the day Sunday, high pressure will initially be present over New England with the strengthening low pressure system across the Southeast. High pressure over New England is expected to depart off to the northeast moving into Monday while the low pressure turns up the mid-Atlantic:

With the system strengthening so rapidly and so far to our southwest this will result in a very strong onshore flow developing within the lower-levels of the atmosphere. This combined with the retreating high pressure is going to allow for much warmer air to rapidly advect into Connecticut. This will ultimately result in snow quickly changing over to some sleet, freezing rain, and then heavy rain:

Despite a lackluster storm in the snowfall department, this will be a fairly impactful storm. Heavy rain with a frozen ground could result in runoff and localized flash flooding potential. Strong winds are expected across the state with gusts 50-60 mph along the shoreline and gusts 35-50 mph inland resulting in scattered power outages. Very strong onshore winds combined with astronomical high tides may bring about major coastal flooding as well. 

What to Expect:

• Precipitation likely begins as snow across the entire state between 11:00 PM Sunday - 2:00 AM EST Monday. The only exception may be right along the immediate shoreline where precipitation may be a bit of a sleet/freezing rain mix (if not plain rain).
• Snow overspread inland areas during the overnight with snow coming down moderate at times (even heavy in the northwest and northeast hills). 
• Warmer air rapidly moves into the state causing snow to briefly change over to sleet and freezing rain and then heavy rain. The northwest hills will be the last to change over. 
• Winds will begin to ramp up as well with gusts 35-50 mph inland and 50-60 mph along the shoreline. Scattered power outages are likely. 
• Strong onshore flow and astronomical high tides may yield major coastal flooding. 
• Rain tapers off during the morning and may actually end with some scattered snow showers across the state.
• Below is my current thoughts for snow accumulations:

Friday, January 7, 2022 Connecticut Snowfall Forecast Update

 It is time to bring 'em up! After assessing forecast model data from overnight Wednesday through Thursday afternoon, there have been trends towards more snow across Connecticut. Why is this? Forecast models are becoming in stronger agreement that the storm will intensify more quickly with this occurring closer to the coast. The end result in a greater abundance of precipitation over Connecticut, hence, higher snowfall totals. This will be a fast-moving storm which will limit totals to a degree.

Given the earlier development, forecast models are in general agreement low pressure at 850mb (roughly 5,000 feet above the ground) will become better defined as it is passing southeast of Connecticut. This is a historically favorable track for moderate-to-heavy snow to overspread Connecticut:

As the low is tracking northeast just south of Connecticut, a band of very strong frontogenesis will traverse the state. This is indicative of heavy snow and this should occur for the majority of the state:

12z NAM Bufkit for Windsor Locks, CT (BDL) indicates upwards of 20 units of omega (the negative-valued red contour indicate upward vertical motion) just touch the top of the dendritic snow growth zone (purple/yellow contours). This further indicates a period of heavy snow will occur:

So this what can ex expect:

• Snow begins between midnight - 3:00 AM across the state. 
• Snow quickly becomes moderate-to-heavy across the state with peak snow intensities occurring between 5:00 AM - 9:00 AM EST. 
• During this time snowfall rates could approach 1.5'' per hour. 
• Snow ratios approaching 13:1 to 14:1 so snow will be rather light and fluffy.
• Snow rapidly begins to subside moving into the late morning and is out of the state by early afternoon outside of some residual flurries. The sun may even make an appearance by mid-afternoon. 
• Winds will be light during the storm, however, increase as the storm pulls away with gusts 20-30 during the afternoon. Wind chills Friday evening and overnight into the single digits and teens. 

Friday, January 7, 2022 Connecticut Snowfall Forecast

For snow lovers, unfortunately, this storm will just get going a bit too late and a bit too far southeast to deliver a big hit to Connecticut. While computer forecast models have struggled (and continue to do so a bit) with the exact evolution of the storm, there is a consensus things just won't transpire in time for a bigger hit. 

Forecast models do brush some decent lift across Connecticut as the low pressure passes well to the south and east. Given the strong upper-level jet dynamics and favorable jet placement, the state will be under the presence of upper-lever divergence which will help enhance the development of snow as the low passes by. This will bring a several hour period of light-to-moderate snow through the state.

What to Expect:

• Snow starts: Midnight - 3:00 AM EST Friday 
• Snow ends: By noon 
• Heaviest snow: 4:00 - 7:00 AM EST (rates up to 0.50'' per hour). 
• Expect delays to the morning commute. Plan for delays.

Friday, January 7, 2022 Connecticut Snowstorm Potential

 For snow lovers, the start of the 2021-2022 winter season has been nothing but subpar. While the weather pattern has been on the active side, we just haven't been able to muster up a good, solid snow event. There is a chance that could change as we move towards the end of the week. 

As of Tuesday evening, a low pressure system was rapidly strengthening across the northern Plains with a strong Arctic cold front plunging through the northern-tier of the country. This Arctic cold front is then slated to move across the Northeast Thursday and that will usher in Arctic air into the state, planting the more than sufficient cold air needed for snow:

There are two things we will be watching over the next few days:

1) Wednesday night and early Thursday morning, an area of low pressure develops across northern Texas and moves east across the Southeast Thursday bringing wintry precipitation across that region. This low pressure continues to emerge east-northeast into the mid-Atlantic states, towards the coast. 

2) A sharp longwave upper-level trough amplifying as it moves across the Ohio Valley into the Northeast:

As the upper-level trough catches and phases with the surface low pressure, this, combined with strong upper-level divergence thanks to the jet stream structure, should result in rapid cyclogenesis of the low pressure system. The BIGGEST key here is how quickly does this process happen? While all the cards are there for a significant snow event, this is far from certainty. 

As it stands right now, the timing of these key features may be a bit off. This would result in storm intensification happening just a bit too far offshore to bring significant snows, BUT we would likely still see at least snow with the chance for minor accumulations. 

Given this is tied into phasing that aspect is very tough to pindown and nail even getting past a few days out. This is because the likelihood of phasing and subsequently, a storm is all tied into the timing of the key pieces involved. 

We should get a much clearer idea on this picture moving into Wednesday afternoon!

Saturday, December 18, 2021 Wintry Mix

 A fast moving low pressure will bring a wintry mix to much of Connecticut Saturday with the exception being near the shoreline where predominately rain is expected (though some mixing is certainly possible at times). 

While snow is possible at the onset of precipitation, this is looking like predominately a sleet or a light freezing rain event. This will not be a significant storm by any means, however, roads will become slick through the day Saturday, especially untreated surfaces. 

Low pressure moving northeast across the Ohio Valley begins to get shunted south as it moves into the Northeast. This is largely due to an area of high pressure across southeast Canada which will act as a "wall":

The flow around the high pressure system (clockwise flow) will help to feed some colder air from Canada into our region within the lowest 5,000 feet of the atmosphere, keeping temperatures through this portion of the atmosphere very close to freezing at the surface and just a few ticks below freezing as you begin ascending through the lower atmosphere. However, with the low pressure system ultimately tracking just to our north and west, this will promote a more west-southwesterly flow above 5,000 feet. This will bring about very strong warm-air advection. This push of warmer (and higher moisture content air) into colder (and drier air) results in a thump of heavy precipitation blossoming over the region:

So for precipitation type, why are we more likely to see a mixture of sleet and freezing rain as opposed to snow? In order to get dendrite (snowflake production) you need the following:

1. Cold enough temperatures (Colder than -4C) within the cloud for the formation of ice crystals and ice nucleation to occur.

2.  Sufficient upward vertical motion and moisture into the snow growth zone (with snow growth maximized between temperatures of -12C and -18C). 

In the case of Saturday, we are actually looking at relatively warm temperatures within the clouds. In fact, temperatures may be a bit too warm for the formation of sufficient ice crystals (first image below). In addition, the depth of the warmer air in the mid-levels of the atmosphere will also result in a relatively high snow growth zone (second image below). Initially, upward vertical motion may be strong enough to produce some snow (as evident by the green/light blue shadings inside of the black outline box in the second image below, however, as that strong upward vertical motion subsides the chances for snow vastly decreases and we are looking at sleet/freezing rain:

What to Expect:

• Precipitation begins to break out mid-to-late Saturday morning. There will be an initial burst of snow away from the shoreline, but this should quickly transition to some sleet and freezing due to the processes described above...very quickly. 
• The heaviest precipitation rates occur with the initial burst with rates more light when sleet and freezing rain is falling. This continues well into the evening. 
• Overnight, a second burst of heavier precipitation traverses the state, however, this will be predominately rain as warmer air has pushed in. 

Below are my thoughts:

Wednesday, December 8, 2021 Connecticut Snowfall Forecast

 Forecast models have been in general agreement for several days in the potential for accumulating snow Wednesday. While there continues to be uncertainties regarding overall strength and track there is a growing consensus and several signals which indicate an area of low pressure will not only track far enough north to overspread the state with snow, but for the low pressure to strength enough and in time to result in a band of moderate-to-heavy snow traversing at least a part of the state. 

A strong upper-level jet places the region in a very favorable position for enhanced upper-level divergence. This will work to strengthen the low pressure system and support large scale upward vertical motion (favorable for the generation of precipitation):

One of the key players here is the interaction between shortwave energy and the amplification (strengthening) of an upper-level trough as it moves across the Ohio Valley. Should this shortwave trough amplify (as the NAM continues to suggest ) earlier this would increase the degree of large-scale lift across the region along with aid in the faster development of the low pressure. This is a signal which appears to be strengthening:

Forecast models are also in general agreement an 850mb closed low pressure circulation will pop just south of Long Island. This indicates system strengthening and would also place a good portion of Connecticut, Rhode Island, and eastern Massachusetts in a potential path for a band of moderate-to-heavy snow to traverse. This is also highlighted by strong 850mb vertical velocities:

There is still plenty of room for this to trend in a direction which favors less snow, however, the signals are pointing towards we may end up in the direction of accumulating snow. In fact, it is very possible snowfall totals (map below) may have to be adjusted upwards by an inch or two. 

What can we expect Wednesday?

• Snow starts off around daybreak Wednesday (maybe a bit later) across much of the state with snow very light. 
• Snow intensity gradually begins to increase through the morning. 
• The heaviest snow rates occur under where the band of snow traverses and the timing of this is between about 11:00 AM - 3:00 PM Wednesday. Snowfall rates could approach 1'' per hour during this window.
• Snow begins to wind down moving into the late afternoon with some flurries and light snow continuing into the evening. 
• Travel will be slick so give yourself extra time traveling. Travel impacts should not be severe but plan accordingly. 
• Below is my first call snow map, however, keep in mind adjustments are likely Tuesday afternoon.