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.

First Accumulating Snowfall Event of the 2021-2022 Season 11.28-2021 - 11.29.2021?

 Confidence is growing that many across New England (especially interior New England) may see the first accumulating snowfall event of the cool season Sunday, November 28 into Monday, November 29. This is something which has been appearing within computer forecast model ensembles for several days and is gaining traction within the operational guidance. (Note: I will be using GFS forecast model outputs for illustrative purposes. This does not mean I am favoring the GFS model). 

As we move through the Thanksgiving holiday and the upcoming weekend, a pattern change is set to occur across the country and this is hinted at by both the North Atlantic Oscillation (NAO) and the Pacific-North American (PNA). Both oscillations will be going through a phase change with the NAO becoming more negative through the weekend and then more positive and the PNA becoming more positive then becoming less positive. Not only do these changes indicate pattern change, but these changes are typically associated with storminess somewhere across the East Coast:

As a ride pumps up across the West a trough digs and amplifies across the Northeast. A potent piece of shortwave energy associated with the amplifying trough dives southeast across New England...perhaps as far south as Long Island. Due to the strong baroclinicity which exists between the still warmer waters off the coast and much colder air over land in the fall/winter/spring this can favor the rapid development and strengthening of a low pressure (cyclogenesis):

The warm sector of the system may be characterized by temperatures about 5,000 feet above the ground as warm as +2C to +5C while temperatures on the cold side of the storm as cold as -4C to -9C. This would result in a strong baroclinic environment across the region favoring rapid strengthening and very strong lift (upward vertical motion):

Given this is still several days away it is way too early to get into any specifics or details as many questions need to be resolved. Some of these questions include;

1) Where does cyclogenesis occur? 

2) Where does the low pressure track? 

3) How quickly does a low pressure develop and materialize? 

4) Do any mid-level low pressure circulations form, and if so, where do they track?

These questions would determine who sees snow, how much snow may occur, and where the heaviest/highest snow totals occur. Obviously, given the time of year the most favorable areas for plowable snow (>3-4'') would be across the interior (moving away from the coastline). 

This signal has been growing stronger over the past few days and now we work to resolve these (and additional questions) over the next few days. 

Hurricane Henri - What to Expect here in Connecticut

As we move through the remainder of this Saturday, all eyes are on Henri and just how much Henri strengthens as it now moves into a more favorable environment for strengthening. For the past few days Henri has been impacted by very strong wind shear to the north. Henri, however, is moving away from this stronger wind shear and is moving over the very warm waters of the Gulf Stream. As of this writing, Henri was not looking particularly great, but it is slowly trying to strengthen. 

Below, is the latest forecast track with cone of uncertainty from the National Hurricane Center (NHC):

The NHC is forecasting Henri to make landfall across the eastern tip of Long Island as either a strong tropical storm or a low-end category 1 hurricane with the center then passing over Madison, CT with maximum sustained winds of 70-mph with gusts upwards of 85-mph and tropical storm-force winds (my estimation of gusts 40-60 mph) across the majority of the state. However, notice there is still a quite a bit of spread in potential landfall with the cone as far west as western Long Island and as far east as eastern Rhode Island. This is due to the questions regarding exactly how strong Henri gets today and interactions with an upper-level low to our west:

My anticipation is that Henri will make landfall across central or eastern Long Island (more likely eastern Long Island) and then swing northwest into the Connecticut shoreline. I am unsure of strength but if it is as strong as what the NHC is suggesting...we will see big problems statewide. Below are my thoughts on each storm phenomena:

Wind: The latest GFS computer forecast model, with it's forecast track of Henri, forecast winds anywhere from 50-70+ knots about 2,500 feet above the ground east of the Connecticut River as Henri moves into southeast Connecticut. 

It is my estimation this would result in widespread wind gusts of 40-60+ mph across much of the state for a solid 3-5 hours. Wind gusts along the shoreline just east of the center could approach 80-90 mph. 

Power Outages: These winds would cause extremely widespread wind damage, some structural damage, and power outages along the shoreline just east of the track with widespread power outages and tree damage across a large portion of the state. Hardest hit areas should prepare to be without power for upwards of several days.

Storm surge/Coastal Flooding: Forecasts are for 3-5 feet of storm surge along the Connecticut shoreline and this would bring about significant-to-devastating coastal flooding. 

Rainfall/Freshwater Flooding: The heaviest rain and highest totals would occur just west of the track and that places the highest rainfall totals along and west of the Connecticut River. Rainfall of 4-8'' with a narrow swath of 8-12'' is likely. This would promote widespread significant flooding. 

Tornadoes: Isolated tornadoes are possible with embedded thunderstorms, especially just to the east and northeast of the storm track. This would likely be northeast Connecticut into Rhode Island and into southeast Massachusetts. 

Timing: It is very possible we see some bands of torrential downpours and embedded thunderstorms move into the state later tonight (which would carry a isolated tornado risk). Weather conditions begin to rapidly deteriorate moving through late Sunday morning. The worst of the winds happen late morning through late afternoon but the rain/flooding threat should persist well into the evening.  

Let's be very thankful this is not a much stronger storm or that it is not approaching us at a faster speed.

Wednesday, April 21, 2021 Low Topped Squall Line Potential

 A cold front is set to sweep across southern New England early Wednesday evening. Combination of marginal instability and rather strong dynamics and forcing from the front will promote the development of a low-topped squall line ahead of the cold front. While the greatest overall potential for damaging winds and even hail exists across New York and Pennsylvania, localized embedded damaging wind gusts and hail will be possible across southern New England (particularly western and central sections). 

Instability is not the driver here with temperatures predominately in the 60's with dewpoints into the 40's and lower 50's, however, steep mid-level lapse rates (~7 C/KM) will aid in the development of marginal instability characterized by about 500-750 J/KG of mixed-layer CAPE. 

The driver is going to be the strong forcing associated with the cold front and very strong jet stream dynamics which are characterized by 50-60+ knots at 500mb (~18,000 feet above our heads) and 35-40+ knots at 850mb (~5,000 feet above our heads). These shear values are more than enough to support the development of organized convection. 

The line initially develops across western New York and central Pennsylvania and rapidly progresses east through the afternoon and evening. Combination of dry low-level air and strong low-level winds will support the potential for damaging wind gusts on the leading edge of the squall line. Wind damage may be more scattered across New York and Pennsylvania but then become more isolated across New England. Given cold mid-level temperatures characterized by -20C at 500mb (~18,000 feet) some of the more robust convection within the line could even produce some small hail. The line is likely to move across Connecticut between 5:00 PM and 8:00 PM Wednesday evening likely causing some localized damaging wind gusts on the leading edge and even potential for some small hail:

Vigorous Upper-level Low Pressure to Bring Accumulating Snow to Parts of Connecticut Overnight 04/15/21 to 04/16/2021

 A vigorous upper-level low pressure system across New England prompts the developments and strengthening of a surface low pressure right in the vicinity of Connecticut moving through Thursday night. If the processes involved with this system occurred say another 50-75 miles farther south and east..at least the northern part of the state would be looking at a pretty significant winter storm, however, looks like the most significant snows occur across parts of western Massachusetts, southern Vermont, and perhaps around the Worcester Hills in east-central Massachusetts. 

As of Thursday afternoon moderate-to-heavy rain has overspread much of Connecticut. As we move into the overnight and the low pressure system really gets its act together, anomalous cold will transpires within the lowest levels of the atmosphere. In fact, surface temperatures look to even dip as low as the mid-30's and even colder across the hills. As this occurs rain begins to transition to snow across the hills and even parts of northern Connecticut. In fact, the majority of the state could even some some snow mix in with the rain. 

This is a highly complex setup due to the features and processes involved, however, forecast models have been zeroing in on a solution which features a band of heavy snow which becomes established across southern Vermont through the Berkshires of western Massachusetts even extending into extreme northwestern Connecticut. This would result in a several-hour period of moderate-to-heavy snow overnight. Snowfall rates could approach 2'' per hour so despite the warm ground, these rates, combined with it being overnight would result in snow accumulating, though taking a bit longer on paved surfaces. Another band of moderate-to-heavy snow looks to originate across the Worcester Hills of east-central Massachusetts with this band pivoting and clipping parts of northeast Connecticut Friday. 

Given this snow will be wet in nature and very heavy, the potential exists for downed tree limbs and power lines. In fact, scattered-to-numerous power outages could be expected in areas which receive greater than 4'' of snow...power outages could even be on the widespread side. 

This is a very dynamic storm and add in the time of year and you get a very challenging forecast which is ultimately going to come down to nowcasting...meaning we won't really know how the situation unfolds until the processes involved get going. 

What to Expect:

• Moderate-to-heavy rain persists through the overnight
• Around midnight, rain begins to mix with and change over to snow across the northwest and northeast hills with snow becoming moderate-to-heavy through the overnight. 
• The heaviest of the snow across the northwest hills winds down between 6:00 - 8:00 AM Friday morning, however, moderate-to-heavy snow may persist through much of the morning across parts of northeast Connecticut. 
• The majority of the state may see some snow mix in, however, most people will probably be counting cows when this happens. 
• Gusty and cold Friday with temperatures only into the lower 40's with a stiff northwest wind gusting 20-25 mph.

Below is what I am currently expecting in terms of snowfall accumulations:

Burst of Moderate-to-Heavy Snow Thursday Night (March 18, 2021)

 A strong Arctic cold front arriving from the northwest moves across Connecticut early Thursday evening. Meanwhile a low pressure system (responsible for the ongoing tornado outbreak across the deep South) approaches from the southwest Thursday morning. As the low pressure approaches, heavy rain pushes into the state early Thursday afternoon. The combination of the approaching cold front and strong Arctic high pressure behind the front helps to push the approaching surface low south of the state Thursday evening.

By early Thursday evening, the Arctic cold front rapidly pushes through the state resulting in much colder temperatures quickly overspreading the state. Despite the cold front moving through the state, lift will remain rather strong (thanks to the surface low passing south of the state) and ample moisture will be thrown into the colder airmass. This results in rain changing over to a period of moderate-to-heavy snow by late evening Thursday before exiting during the late overnight or early pre-dawn hours Friday. 

Forecast models indicate some pretty strong lift across the state during the early overnight hours Thursday night with forecast soundings showing a thermal profile favorable for snow:

Breakdown of what to expect:

• Heavy rain moves into the state early Thursday afternoon.
• Temperatures get into the lower 40's, but during the evening begin to drop rather quickly with increasing winds as the cold front moves through. Wind gusts of 30-40 mph are possible overnight Thursday 
• Snow begins to transition to rain during the mid-to-late evening Thursday with the changeover occurring more quickly across the northwest hills. 
• Snow end during the late overnight or early pre-dawn hours Friday morning. Some parts of the hills could see as much as 4-5' of snow.
• Majority of the snowfall accumulations occurs on the grassy/colder surfaces, however, roads will become slick, especially as temperatures drop below-freezing. Give yourself extra time for the Friday morning commute.
• Sun comes out through Friday morning, but a cold/breezy day with temperatures only into the 30's.
• Snowfall Forecast:

Thursday, February 18, 2021 Winter Storm

 The active February continues as yet another winter storm approaches Connecticut. Like this past storm, this one has been rather challenging in the forecast department (though I must admit, I have not done much detail look into this due to other pressing weather issues around the country) as even now within 48-hours there continue to be inconsistencies within the forecast models regarding strength, overall track, and storm structure. All of these will play a crucial role into the evolution of the storm across Connecticut. 

Typically, I go into the science first then follow with my snowfall forecast, however, this go around I am going to start with my snowfall forecast and then explain the reasoning below it. Why am I doing this? No reason other than I feel its appropriate. So what is my snowfall forecast?

When looking at this, you're probably noticing...that is one helluva difference (gradient) between the northern part of the state and the southern part of the state. You also may be saying, "wait, since when does southern Connecticut do better in the snowfall department than the northern part of the state?". Well, this is why I've elected to do my snowfall forecast first. There is a reason why I believe we will see such a gradient across the state and why southern Connecticut will do better. 

First off, I have concerns about dry air which may eat away at the precipitation shield and these concerns increase as you move north across the state. Thursday morning starts with a fairly stout area of high pressure stretched from southeastern Canada through New England. This high pressure does slide to the north and east as the day progresses paving the path for the storm to continue its northward journey towards the state. I drew an arrow showing the counterclockwise flow around the high pressure (very important here):

Referring to the above image, at the surface, the winds are coming from a northerly direction. This is usually associated with drier air from Canada advecting into our area. Thursday morning, forecast dew points are only in the teens in Connecticut with 20's south of Connecticut and single digits and below-zero north of us. As long as the surface winds remain north, drier will will continue to drain into the state:

 But...before we call this dry air we need to reference this with surface temperatures. After all, if surface temperatures are going to be close to these dew point values, well the air isn't so dry anymore. Wednesday night, temperatures drop back into the teens after temperatures climb into the 20's to around 30 Wednesday afternoon. One thing to consider regarding temperatures Wednesday night, is increase in cloud cover. This could prevent temperatures from falling much back into the teens. Anyways, moving through Thursday morning temperatures should quickly rise into and through the 20's. Note: I am not a major fan of model output 2M temperatures. I often find them kind of low. So this does present a bit of a different (dew point depression) between dew point and temperature. Basically, the farther apart the two are, the drier the air is and the closer together the two are, the more moist the air is.

We can also visualize this by assessing a forecast sounding. Below, is a forecast sounding for Windsor Locks, CT Thursday morning. The green line indicates dewpoint temperature as you ascend through the troposphere (with the lower portion the surface) with the red line indicating temperature as you ascend through the troposphere. Notice how far apart the two lines are. That indicates dry air. Now, as you progress through the morning the column does moisten up a bit. This is due to the high pressure continuing to depart north and east and winds start to shift more easterly which slows down or shuts off the dry air drain from the north:

Anyways, without getting much more into this, I do believe dry air will be a bit of a concern across the northern part of the state and this results in less snow there. 

Towards the southern part of the state, there are decent signals for a band of pretty heavy snow (which may be on the wet side) which is enhanced from warm air advection as warmer air progresses northward. Note: Due to forecast storm track, the warmer air should not fully get into the state keeping the majority of the precipitation snow, however, there will likely be some sleet and freezing involved, especially during Thursday evening and overnight when precipitation intensity is more light. Forecast models indicate a strong push of warm air advection (just check out the scale at the bottom of the image...nearly maxed out!) racing north towards southern Connecticut as the afternoon progresses:

This will be associated with very intense frontogenesis with what will be a very heavy band of snow just north of it...and that would be right across southern Connecticut. The signals for getting this much farther into Connecticut are not very strong:

What to Expect:

• This will actually be a pretty long duration storm, however, the most intense part of the storm will not be that long-duration. Perhaps a 3-5 hour window of the most intense snow. Outside of this window precipitation is pretty light. 
• Starr time: Snow begins to move into the state between 7:00 AM and 9:00 AM Thursday across southern Connecticut and between 9:00 AM and noon across northern Connecticut. 
• Heaviest snow: Between 1:00 PM and 6:00 PM Thursday 
• This is where the long duration part comes in as there will be on and off precipitation which consists of light snow, freezing drizzle, or sleet Thursday evening through much of Friday. 
• Expect the Thursday afternoon and evening commute to be significantly impacted and this could continue through the Friday morning commute. Please allow extra time if traveling. 

Tuesday, February 16, 2021 Sleet/Freezing Rain Potential

 Saying the upcoming storm is going to be a mess doesn't do it justice. The storms we have dealt with this winter have been predominately easy in the precipitation-type department. This time, however, is not going to be the case. Despite Connecticut being such a small state, the differences in weather may vary significantly within the state. This adds immense challenges to the forecasting process and to the communication aspect of this storm. 

Before we get into our weather in Connecticut, let's take a moment to appreciate (meteorologically) what is transpiring across the majority of the country. Record-breaking Arctic cold (and prolonged cold) plunges well into the deep South with multiple winter storms impacting areas which aren't accustomed to winter weather. Why is this happening? We'll take a brief look below (well if you read my posts, you know I'm usually never brief with these things).

For the better part of the past few weeks a piece of the polar vortex has been displaced south and has become positioned in the vicinity of the United States/Canadian border. With the polar vortex being displaced from the Polar region, strong ridging has built into the Arctic and polar regions. Meanwhile, ridging has become established across the North Pacific. This is the perfect recipe for Arctic air outbreaks to sag south into the United States:

Flash forwarding to Monday morning (February 15) the jet stream will be digging extremely far south...pretty much into Mexico! With the jet stream displaced this far south combined with the configuration shown above, this is prime for Arctic air all the way into southern Texas:

At the surface, a very strong and robust high pressure (with central pressure greater than 1040mb!) is positioned across the upper-Midwest associated with the polar vortex lube. This is just funneling low-level Arctic cold into the majority of the country:

What does all of this have to do with our potential weather here in Connecticut? Well, quite a bit actually. There is something else I would like to illustrate and I am going to use forecast temperatures at 850mb (roughly 5,000 feet above the ground) for Monday morning. Off the Southeast coast of the United States is a large ridge (known as the Southeast ridge). The colors here can be correlated to warmer temperatures and colder temperatures. The brighter colors represent warmer temperatures while the darker colors represent colder temperatures. I've outlined in red the "battle" ground between Arctic cold and more tropical warmth with an orange arrow directed towards Connecticut. We are going to be in this "battle" ground between Arctic air and more tropical air. This is what is going to result in a slew of precipitation types across the state Tuesday:

By Monday evening, low pressure moves northeast up along the Eastern Seaboard and approaches Connecticut. Initially, temperatures at the surface will be below-freezing as winds out of the northeast (or east-north east) will funnel in low-level cold thanks to that extensive high pressure which stretches through eastern Canada:

 However, as the low pressure system continues to organize, we'll see temperatures between 3,000 feet and 7,000 feet above the ground actually warm above-freezing. This is due to low pressure up around 5,000 feet developing well to our west:

What can we expect? Well what we won't see much of is snow. In fact, outside of maybe the Northwest hills I don't think anyone sees any snow so this can be ruled out. The bigger challenges arise with sleet and freezing rain potential. In terms of sleet and freezing rain potential this will be determined by;

1. EXACT track of the surface low pressure. The closer to Connecticut this tracks and the earlier this strengthens, the greater the likelihood for warmer air to move in at the surface. This scenario would present more of a mix to rain for a greater portion of the state. Should this track not so close to Connecticut, there is greater potential to keep colder air locked in at the surface, resulting in higher likelihood for sleet and freezing rain. 

2. The configuration of the thermal profile (how temperatures are changing as you ascend through the atmosphere). This will be easier to explain with a visual, but the structure of the thermals will be a determent in sleet versus freezing rain. 

At this juncture, the potential exists for a quite a bit of sleet and freezing rain across the state (away from the immediate shoreline) with even the potential for significant icing (> 0.50'' icing) which would bring about power outages. All of these details are extremely complex and there is a quite a bit to resolve moving through Sunday. Below, is what we could be facing:

 

Super Bowl Sunday Snowfall Forecast

 The second significant snowstorm within a week impacts Connecticut Super Bowl Sunday as a potent coastal storm looks to track close enough to the coast to bring a band of moderate-to-heavy snowfall across the state Sunday. This will be a fast moving storm which will preclude the potential for even higher amounts. 

Forecast models are showing an intense band of heavy snow traversing the state from late Sunday morning through late afternoon. Snowfall rates once again could approach 2 to 3 inches per hour during this window:

There is pretty strong agreement in the 850mb low to track just south and east of Connecticut with very strong 60+ knots of inflow feeding moisture into the storm. This track is perfect for heavy snow across the state. Should also be noted the 700mb low tracks just south and east of Connecticut as well:

What to Expect:

• Snow starts 4:00 - 7:00 AM Sunday morning and quickly becomes moderate-to-heavy through mid-to-late morning.
• Heaviest of the snow falls in a window between 11:00 AM - 3:00 PM EST. Snowfall rates of 2 to 3'' per hour at times in this window. 
• Wind gusts 25 to 35 mph along the coast
• Snow rapidly tapers off by late afternoon and is out by evening. 
• Lowest confidence: Northwestern Connecticut

Super Bowl Sunday Snowstorm? Active February Ahead?

 We may be starting what could be quite an active month in terms of storm chances of Arctic cold shots. After getting our second major snowstorm of the season to start the week, there is potential for yet another significant snowstorm for Super Bowl Sunday. Below, are some of the piece to watch over the next few days.

The polar vortex across the southern Arctic is going to be heavily disrupted over the next couple of days when a piece (or multiple pieces) breaking off and becoming displaced across southeastern Canada:

There will also be confluence to the north of our region. This area of confluence could be a major determinant in whether the storm tracks close enough to the coast to give us snow or it stays out to sea and is fun for the fish:

 The key piece of energy which looks to be responsible for the potential storm quickly accelerates through the jet stream and is expected to move into the Pacific-Northwest region Thursday night:

There is very strong agreement within forecast model ensembles that the pattern (at least through mid-month) will be extremely favorable for Arctic cold shots and plenty of storm chances. Forecast models indicate in the Pacific-North American pattern (PNA) becoming increasingly positive as a large ridge builds across the eastern Pacific into the Gulf of Alaska. The Arctic Oscillation (AO) is expected to become extremely negative and favoring polar vortex (PV) displacement to southern Canada. Meanwhile the ridge off the Southeast coast holds strong:

This pattern screams Arctic cold blasts across much of the eastern-third of the country with numerous storm threats. In fact, the upcoming week features THREE different storm chances;

1) Super Bowl Sunday

2) Tuesday/Wednesday

3) End of week/next weekend

February is certainly no stranger to active weather and cold and it looks like February 2021 may deliver in both categories. Rejoice snow lovers, your time may be coming.

Significant Winter Storm Update

 I have been very impressed with the potential for heavy banding to materialize across Connecticut all along and we we get closer to the event I've become way more impressed. There are signals for a hellacious band of extremely heavy snow to impact southwestern Connecticut and northeastern Connecticut. It is a bit more challenging in the Connecticut River Valley (Windsor Locks, Hartford, this corridor) as subsidence could lead to totals on the lower end of the range. 

Forecast models are indicating extreme frontogenesis traversing the state by Monday afternoon into the early evening. Now, usually when forecasting higher end totals (getting above 15-18'') you would like to see the signal for banding stall and pivot. While this isn't necessarily happening here, very high snowfall ratios (perhaps 15:1 - 18:1) combined with hefty QPF totals tell me that it will dump 2-3'' per hour for several hours:

Below is looking at White Plains, NY. While not Connecticut, this is just over the border and not far from Greenwich. The two isotherms (-12C and -18C) highlight the dendritic snow growth layer (DGZ). This is the layer in which snow growth is maximized. At this location, this is showing the most extreme lift just below the DGZ, however, in southwest Connecticut, we may maximize this lift into the layer. This is a very strong signal for extremely heavy snow:

Let's break all this down:

• Snow begins likely during the pre-dawn hours Monday morning (especially across southern Connecticut) with snow spreading north through the early morning. 
• Snow rates quickly increase by late morning and early afternoon. 
• The absolute heaviest of the snow falls between 12:00 PM - 8:00 PM EST. This is when snowfall rates could approach 2-3 inches per hour (potentially even 4).
• Some thunder is possible
• Winds increase out of the northeast to 15-25 mph (25-35 along the shoreline) with gusts 40-50 mph (upwards of 55 along the shoreline). This will bring about blizzard conditions with extremely poor visibility, drifting snow, and isolated power outages.
• Afternoon and evening commute may be near impossible and extremely dangerous due to rapidly accumulating snow, very poor visibility, and high winds. 
• Light snow continues well into Tuesday morning.
• There will likely be some sleet and freezing rain involved along the shoreline and even extending well inland, especially during the overnight as precipitation intensities wind down and the storm takes a wonky track. 

Below, is my update:

Significant Snowstorm to Impact Connecticut to Start February

 There continue to be signals for a significant and long-duration winter storm to impact Connecticut as we begin the month of February. While all the pieces are there, a lot has to play out correctly for this to happen. I am on the aggressive side with this forecast, however, I feel quite confident these pieces will evolve in such a way that a band of very heavy snow traverses the state. Should this system materialize just a bit quicker, more of the state could get into even heavier snows. Why am I so aggressive? I'll explain below. Note: Just because I'm using graphics from a particular forecast model does not mean I am basing my forecast off that model. I am just using the graphics for illustrative purposes. 

Baroclinic Zone:

I am very impressed with the temperature gradient in the lower-levels of the atmosphere which will be in place across New England. Choosing the 850mb level (~5,000 feet above the ground) too illustrate, temperatures in the warm sector may as as warm as +7C. Meanwhile, temperatures at the same level across interior New England may be as cold as -6C to -7C. Also note the very strong easterly winds in the warm sector (the flags indicate 50+ knots of wind feeding into the storm). This will provide sufficient moisture into the storm. This is all even more impressive if we were to look down around 2,500 feet (925mb). This favors very strong lift (upward vertical motion) across the region.

Forecast models indicate the 700mb low closing off south of Connecticut with the low tracking to our south and east. There are uncertainties regarding the exact evolution of this feature which poses some challenges to the overall forecast. As modeled, this might be a bit farther south than I would like for heavy snow into Connecticut, however, given this low does not become very tightly compacted (the more "rings" or circles" the more compacted and tightly closed it is) and is more elongated indicates to me that the band of heaviest snow would actually be displaced farther northwest than usual. That would place this band over Connecticut:

In terms of how much liquid will fall (this can be a huge assistance when forecasting snow totals), forecast models generally are not very impressive here in Connecticut as they keep the heaviest south and east of the state. I feel very strongly that this is underdone based on analysis of the setup. I feel based on the degree of warm inflow into the very cold air mass that will be in place combined with the strong baroclinic zone and favorable region-wide large-scale lift, we will certainly see a band of heavy snow traverse the state.

Here is a breakdown of my thoughts:

• Snow begins during the overnight Sunday into Monday morning. 
• Snow intensities begin to increase rapidly thorough Monday morning (especially the southern part of the state) with conditions deteriorating rapidly. 
• Winds begin to increase out of the northeast or north-northeast and may gusts between 40-50 mph during the height of the storm. This may lead to blizzard-like conditions at times along with potential for drifting snow and isolated power outages. 
• The heaviest of the snow falls from late Monday afternoon through early overnight Monday. Light snow may even stick around through the first half of Tuesday. 
• Snowfall rates during the peak range between 1 to 2 inches per hour. 
• Monday late afternoon and evening commute will be extremely difficult due to heavy snow and snow covered roads. Given how cold it is the snow will stick rapidly and easily. 
• There are some wildcards to consider, including the potential for dry air to filter in the lower-levels from the north. This could put a major wrench in totals.
• Below is my initial forecast:

Significant Storm Potential Around February 1, 2021

 There are signals for a rather significant winter storm to begin the month of February. In a winter which has been well...non-existent in terms of the snow department and chances few and far between, it makes monitoring this that much more fun. For us here in Connecticut, there are a wide range of possibilities from a small hit, very large hit, or no hit at all as the storm could miss out out to sea or well off to the south. How the overall pattern progresses through the weekend will determine what type of solution we have.

Since our massive snowstorm back around mid-December two things have been constant;

1) A negative North Atlantic Oscillation (NAO)

2) A positive Pacific-North American (PNA) (however, the PNA has become more negative recently)

Now...typically when you see this sort of combination there are two things you can expect;

1) Colder temperatures

2) Snow...and lots of it

Well neither of these have happened...but we won't get into that here. 

Moving towards the first of February we start to see some changes occur. The NAO trends more positive while the PNA, which has become more negative recently, is expected to become more positive:

When both the NAO and PNA are in this transitory process, this can be a signal for a major East Coast storm. 

The 12z GFS ensemble mean for 500 hPa height anomalies come Monday morning features a very exciting look for snow fans;

1) A ridge across the Inter-mountain West and Great Plains region

2) Trough amplifying across the East with a trough axis into the Southeast

3) A large area of anomalous above-average height anomalies over much of Canada. This will create a "block" and when combined with the look of #1 and #2 sharply increases the likelihood for a storm to develop and either sort of ride up the coast or if it comes from the Ohio Valley, the block should keep the storm farther south and also supply us with cold air. 

One thing we've been lacking all winter is a baroclonic zone off the East Coast. Baroclinicity is a huge driver in cyclogenesis and that has been lacking. 12z GFS forecast temperatures at 850mb indicate there could be a pretty decent barloclinic zone across our area with temperatures about 5,000 feet above the ground to our south as high as +6C with across northern New England they could be as cold as -10 to -12C. This type of steep temperature gradient favors strong upward motion and favorable conditions for low pressure development and strengthening (cyclogenesis):

Forecast models are indicating the potential for energy riding around the crest of the ridge out west digging and amplifying as it moves into the eastern trough. This will be a focal point for the development of low pressure which could rapidly intensify. 

Being nearly a week out, it's way too early to get into details or specifics, however, the signals are there for a pretty significant winter storm which could impact Connecticut around February 1. Details should become clearer moving through the week.