Good evening from Southern Connecticut Weather. 

In the last decade, the 2010s, we saw a string of historic winter storms and historic winter stretches. The decade brought the stretch of winter storms in western/SW CT in January 2011, the October 2011 Blizzard, the Great Blizzard of 2013, February 2014 snowy month, all-time historic cold and top three snow in February 2015, and the blizzards of 2016, 2017, and 2018. 

Since then however, winter has been all but absent, with an equally impressive period of historic warmth and low snow seasons. Unfortunately for those that like four seasons, winter 2023-24, while better than last "winter", will also end historically warm and almost certainly well below normal in snowfall, despite an exceptionally wet start to the season with big storms. 

Each year I write about the "March toward Spring" when the worst of winter is likely over. First, our days are quickly getting longer. Today the sun set at 5:35pm in Hartford. We are gaining nearly three minutes of daylight each day. By March 9th, just before we spring ahead on the clocks, the sun will set at 5:51--going to 6:52pm the very next day with the time change. With the increase in sun angle, we know that even cool days won't feel as bad as they do in January. 

That doesn't mean snow or cold can't happen--in fact snow may come this week and colder temperatures may reappear mid-March--but it means that the expectation is for more spring-like days than wintry days as the annual progression into what we usually think and see of as spring accelerates. 

The first stage of this march is usually the seesawing between a more spring-like pattern bringing sustained high temperatures in the 50s or greater and brief shots of colder than normal temperatures and perhaps even snow. Keep in mind that March has been more of a winter month than November (or December) in recent years so to begin the march toward Spring now is a big deal. 

​Let's talk about the week ahead. 

Above: an average temperature departure map from expert map maker and climatologist Dr. Brian Brettschneider covering the period from the start of meteorological winter through a few days ago. These departures will only increase with the week ahead. It has been historically warm and snowless again in much of the northern tier, and warmer than normal over the entire period of meteorological winter for just under 98% of the continental US. Where's winter? Nowhere to be found on balance. 

Monday-Tuesday
Ironically, while we're declaring the start of the march toward spring there is the potential for a tricky commute tomorrow because of snow/freezing rain. The signal has waned today, but with a weak front moving into the area during the early morning hours we could see light snow and/or freezing rain. It won't amount to much, if anything, but it does not take much to cause a lot of issues. With temperatures near to below freezing tomorrow morning just be cautious if you walk out the door and find precipitation falling. 

Tomorrow will feel like quintessential spring however, because after whatever happens in the morning we will clear out and warm up. Our pattern of colder than normal temperatures arrived two weeks ago with our one big storm of the season, but it will break without any other significant snowfall. Highs tomorrow should reach the low to mid 50s around the state. 

Tuesday looks dry, partly sunny, and seasonably warm with highs in the low to mid 50s. Keep in mind that average high temperatures this time of year are in the low 40s and rising. Tuesday is mostly dry, but we will see increasing clouds and shower chances late.  

Above: the 18z GFS depiction of late Tuesday through Thursday morning. The middle of the week is unsettled as we have a rainy period followed by a potential brief period of snow. 

Wednesday-Thursday
A more potent frontal passage comes late Wednesday into early Thursday. In advance of the front, we will see warmer temperatures and rain showers, along with breezy conditions that shouldn't cause too much trouble. Wednesday will be an umbrella day. 

Although the model above shows a quick change from rain to snow in the wake of the front, you should be cautioned that cold chasing precipitation doesn't usually work out around here. As such, while the rainfall is highly likely, I do not think we see any meaningful snowfall with this frontal passage this week. 

Thursday will be sunny, dry, and breezy and in the wake of the front it'll also be colder with temperatures closer to normal with highs in the low to mid 40s. 

Friday-Sunday
The end of the week and weekend look uncertain currently, but overall I think we will be fine. Friday looks nice but seasonable with the temperature regime brought in by the front still being in place, but by the weekend, we warm right back up and likely have nice conditions with high pressure taking over.

The potential fly in the ointment is a trough that could bring some clouds and rain showers, but for now I think that's a low probability. If I'm right, the coming weekend will be the first spring-like weekend we see in 2024. 

The Dailies
Monday: Light snow/freezing rain possible early, followed by clearing and warming temperatures. Highs in the low to mid 50s. Chance of precipitation 30%. 

Tuesday: Partly sunny with increasing clouds and showers late. Highs in the low to mid 50s. 

Wednesday: Mostly cloudy with rain showers and breezy conditions. Highs in the upper 50s. Chance of rain 80%. 

Thursday: Mostly sunny and breezy. Highs in the low 40s. Chance of snow early 20%. 

Friday: Mostly sunny. Highs in the low to mid 40s. 

Saturday: Partly sunny and warmer. Highs in the low to mid 50s. Chance of rain 20%. 

Sunday: Partly sunny. Highs in the mid to upper 50s. Chance of rain 20%. 

​A​s always, please like, share, and interact with us on our social media--on Facebook to share our discussions, and follow us on Twitter @southernctwx to retweet our posts. Hit the buttons below to join.
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Thank you for reading SCW.
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​-DB

Good evening from Southern Connecticut Weather. 

Whew. What a day!

When I woke up this morning, less than 24 hours before the start of our coming storm, I was prepared to make the argument for the SCW team to do an 8-16" snowfall map for all of CT. I thought that a forecast of 12-18" wouldn't have been unreasonable for parts of interior Connecticut. 

Then came the extraordinary shift south on the guidance this afternoon. 

While we still believe this will bring a significant snowfall to the state and be a high impact event, there is an incredible amount of uncertainty on the floor and ceiling of this storm. 

If you just want to know what we think will happen in your backyard, that's totally fine and we have our section at the bottom of the discussion. 

If you want to get a deep rundown of what the heck happened today and why we're placing our chips on the snowfall map below, get your favorite beverage and settle in because this is going to be quite a read. 

Above: our final call snowfall map. We think that Litchfield County has the greatest uncertainty as we closely follow the northwest edge of the coming precipitation shield, with a gradient from far NW CT down toward I-84 where a substantial snowfall is expected. For the rest of the state, we think a general 6-12" is most likely. Given the uncertainty, we should all be prepared for surprises.

​What Happened?
If you recall, at the beginning of this journey about a week ago, we wrote about the track uncertainty and how a further north track could allow for rain for many, especially at the coastline. A few days after that, the storm track on the guidance started shifting south, but it was still too close for comfort for our southern Connecticut friends. Then we saw the track stabilize. This brought the most dynamic conditions and greatest amount of precipitation over CT, which led us to start raising the interest level for a major winter storm. Even yesterday afternoon, there was strong consensus among our most reliable operational and ensemble guidance that a major storm was coming. 

Last night however, more models started gradually moving the storm south, before seemingly reversing this morning.

This afternoon's model runs however accelerated the trend in a dramatic way.

I loathe to do this, because we do not use or post model snow maps in our forecast, but I am making an exception here because it will be easiest for you to visualize. On the first model, the GFS, it is least pronounced. These are total snowfall algorithm outputs for each GFS operational model run between yesterday morning and this evening. There are two things I want you to notice. The first is the shift of heavier snow across southern CT. This is because the heaviest precipitation has trended further south. The second thing is Litchfield County. Notice how the amount of modeled snowfall collapses across much of New England before entering CT. It's not so much the specific numbers that are cause for high uncertainty. It's the trend.

On the once vaunted European model, the trend is even more extraordinary. Because of how often the model runs, I am showing a multi-day trend. The acceleration at the end, inside 24 hours of onset of a storm, is almost unbelievable. Adding to this are the ensemble shifts that cut precipitation by upwards of 50%. ​

Let's talk about the science of this. 

There are a few key reasons why we think we've seen so much change. 

First, the southern stream system has changed quite a bit in both its strength and orientation. It has become weaker due to the lack of convection generated in the south yesterday. The lack of convection also leads to lower heights ahead of the system, which feeds into a more southern track. Here's the Euro depiction of this happening the last few days. Notice how it's weaker with fewer closed isobars and further south than at the start of this gif. 

In addition, the tilt of the trough here is more positive than neutral trending negative. Negatively tilted troughs are what bring us our explosive storms. This has always been a thread the needle storm. Too early and this cuts so far north we rain. Too late and we run the risk of what the Euro is depicting. 

The other critical piece that you see above is the Great Lakes region vorticity trending stronger. While enough of this was good to allow for colder air to press in via a southern colder track, too much of it makes it difficult for the southern stream to turn north and get close enough for a partial phase, which would more efficiently trigger bombogenesis. 

​Let's fast forward to what the Euro shows for Tuesday afternoon. 

The northern stream is overpowering the southern stream and pushing it south, and it also helps create a gradient in precipitation that introduces the risk of a whiff, particularly in northern CT. 

In a vacuum, this would be a gigantic red flag to cut snowfall numbers across the board and prepare for a whiff. A more southern track from a weaker storm in a marginal temperature environment is the recipe for a bust. However, the guidance has been consistent on a vital element of the forecast even through the craziness of the last 12 hours: the upper level centers. Let's look specifically at 700mb. 

Here is the trend on the European model. Note how the 700mb center has shifted south, but it has also become stronger (closed isobars/red shading) and more consolidated. That indicates that a band of heavy snow is likely to be northwest of that center. It is even more pronounced on the GFS below, which again, has been more consistent thus far. 

These images tell us that there's a lot more going on here than the surface depiction, and when we look at the soundings, which are critical forecasts of every layer of the atmosphere we need for snowfall, we see signs that it wouldn't take much for accumulating snow and heavy snow would be on the for a period tomorrow if there are minor shifts in track northwest. 

These are GFS soundings for tomorrow at Hartford, BDL, and Bridgeport (BDR) each show heavy snow and very efficient snow growth tomorrow morning. 

By afternoon, intensity gets tricky which makes temperatures and intensity of snow tricky. Any further moves back north would squarely put the rest of CT in line for a major snowfall.

​Shifts south would create the risk of only a quick burst of heavy snow for interior CT, in particular NW CT. 

Here's the 3km NAM just to show what a glancing blow would look like. 

As a result, we have major mixed signals as the storm approaches tonight. It makes for an exceptionally difficult forecast. 

The Forecast
This is what we're getting graded on. Snowfall accumulation as is customary practice will be weighted twice. 

​Timing
This is a fast mover and with the southern track the timing has shifted. While there is some precipitation on the front end of this on radar, it looks like the start time will be from south to north between 2-5am. While the onset timing has changed a bit, the end time looks fairly consistent. The heaviest snow looks to be during the daylight hours, particularly in the morning, with a gradual tapering off early to mid afternoon between perhaps 2-5pm. This is highly impacted by track. A further north track would bring a longer duration (but still fast moving) snowstorm. 

Wind/Power Outages
Given the changes we've seen, it doesn't look as windy. This should help keep power outages isolated to scattered. Maximum gusts should be between 25-40mph with strongest gusts at the coast. With a further south track the snow does not look as pasty, but we will need to watch the track closely in case things bump northward tonight. 

Snow Accumulation
As the map above shows, our final call is 4-8" in part of central and NW CT, with lowest amounts in far NW CT. We see 6-12" in the rest of the state. I cannot emphasize enough how dependent this is on the track and intensity of the low. We will almost certainly see high snowfall rates tomorrow with very efficient snow growth tomorrow morning. The longer we hold onto that the higher the snowfall totals will be. While it's not out of the realm of possibility that NW CT sees less than 4" and other parts of the state see 12+", it looks unlikely at this time.  

Impact
While this may be a more moderate impact event in NW CT, this looks like a high impact event for most of the state. We already have closures, roads will deteriorate tomorrow during the heavier snow, and this will likely be a substantial snowfall for most. The latest European model run at 18z stopped its south trend, but that's not saying much. We should all be prepared for a period of hazardous driving conditions tomorrow, low visibility because of gusty winds, and potential minor to moderate coastal flooding. 

It's time to let the chips fall and watch the hour by hour trend. 
​
A​s always, please like, share, and interact with us on our social media--on Facebook to share our discussions, and follow us on Twitter @southernctwx to retweet our posts. Hit the buttons below to join.
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Thank you for reading SCW.
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​-DB

Good afternoon from Southern Connecticut Weather. 

Winter storm warnings are being issued as consensus continues to build on a high impact winter storm that threads the needle to bring much of Connecticut its biggest storm in at least 2-3 years. Despite the broader trend, as of this first call forecast we still have some concerns for part of southern CT due to remaining track uncertainty.

​Even if the maximum potential isn't realized, we anticipate a high impact snowfall statewide. 

Above: The SCW first call snowfall map. We have a general 3-6" for part of southern CT with 6-12" for the rest of the state. At this time, it looks like the warmer solution possibilities are diminishing, and if that holds our numbers may change with our final call tomorrow. 

​Overall Setup
The setup remains the same. We have been tracking a system in the Midwest that is moving east. Early Tuesday it slides off the East Coast and begins to explosively develop. As it does so, it runs into a marginal airmass over New England, but the rapid intensification and dynamic nation of the storm is likely to overcome marginal temperatures and bring significant snowfall statewide. 

In the absence of a classic block to our north and lack of full phasing with the northern stream of the Jet Stream, this looks like an impressive system but fast mover. This should put a ceiling on snowfall potential. 

While the GFS and Euro remain consistent in depicting a major snowstorm, some of the other guidance (which is being discounted at this time) are only now starting to align themselves with the GFS and Euro. What is particularly impressive is the ensemble support for a major storm even to the coast on the GFS and Euro. At this juncture in forecasting, ensembles aren't used much, but here I think they provide some value in illustrating the higher potential with this system. 

What is unanimous among reliable guidance is how explosively this system develops once it reaches the coast. Here are the 500mb depictions of the storm aloft on today's Euro and GFS. It's quite impressive. With a full early phase this likely would have been much further north, and with a weaker system we'd be battling temperatures and barely accumulating in much of the state. We're really threading the needle to receive a major storm.  

What's not depicted here is the 700mb low track, which is critical for analyzing how much warmth moves into CT. Yesterday there was significant concern for the coast that we'd see continued northward ticks of both the surface and 700mb low, but the opposite has happened since late last night. The adjustments south have been slight, but make a huge difference for coastal CT. 

Now is the time when we start to get into the details of banding, timing, wind, and impact. This looks like another high precipitation event, and with such a dynamic system we can have surprises in either direction. To illustrate this, let's look at two different versions of the hot-off-the-presses NAM model. 

The first one below is the 12km NAM. It shows one end of the spectrum where we see strong banding that leads to subsidence (read: dry slotting) across much of CT. Snow totals suffer as a result. As an outlier, this is discounted but we watch for trends. While the general solution is discounted, tote that even with weaker precipitation it's virtually all snow even at the coast. This does lend greater confidence that this is a snowstorm for the whole state. 

The second depiction however, the 3k and more high resolution NAM, shows the opposite. It goes nuclear, as the NAM tends to do at times, with the banding as the storm rapidly intensifies to our south. The result is a truly high end storm with double digit totals across most of the state, even down to the coastline. This is also discounted, but I will note that another high resolution model, the RGEM, is also looking similar. That's interesting, but we're not locked onto that kind of solution...yet...

Anything close to this would be very high impact.

So what are we actually expecting? Let's take a look below. 

Timing
This is a fast mover. We expect snow to begin from SW to NE very early Tuesday morning, shortly after midnight. It may start off as brief mixing or rain at the coast but that should quickly change over to snow. The worst of the storm is through the daylight hours--that's both morning and afternoon, and we see the snow end from west to east between 6-8pm. 

Wind/Power Outages
It looks like this will be a windy storm, but not overwhelmingly so. Maximum gusts look to be between 30-45mph statewide with highest gusts at the coast as usual. As a result, it'll have an impact, but it doesn't look too bad. That said, we are closely watching how pasty the snow ends up in southern CT. The combination of heavy snow and gusty winds will not only create low visibilities, but the possibility of heavy wet snow in southern CT could create isolated to scattered power outages.

Snow Accumulation
As the map above shows, our first call is 3-6" in part of southern CT and 6-12" in the rest of the state. We have a low floor for the state because of the continuing uncertainty over track and banding. You have to take that seriously. As it stands however, most would probably see 4-6" in the southern CT zone and 8-12" in the northern zone.

Folks, these numbers could change substantially between now and tomorrow. Warmer solutions look less likely now, but as we get into the high resolution guidance wheelhouse, if they continue to show exceptional banding across CT watch out--for both dry slotting and bigger snow amounts. 

Impact
This is a high impact event statewide. School closures statewide are about as close to a lock as I remember forecasting in recent years. Even if you end up with heavier wet snow at the coast which reduces overall snow totals, the heavier paste with wind gusts of 30-45mph will cause issues. Inland, as long as we don't end up with a track too far south or subsidence (read: dry slotting) a big snow is likely. Further inland the snow should be drier which lessens the risk of power issues, but increases ratios which should allow for higher snow totals. This is looking like a major storm around the state. 

Stay tuned for our final call discussion and snowfall map tomorrow afternoon. 

A​s always, please like, share, and interact with us on our social media--on Facebook to share our discussions, and follow us on Twitter @southernctwx to retweet our posts. Hit the buttons below to join.
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Thank you for reading SCW.
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​-DB

Good evening from Southern Connecticut Weather. 

It's crunch time. If we're going to get close to normal seasonal snowfall it's time to turn the model depictions of pattern change into production at the surface. So far, it has been much wetter than normal, warmer than normal, and below normal snowfall, especially at the shoreline.

As I said earlier in my update--if this were five years ago we'd be locking in a major snow storm all the way to the coast as we were in the midst of a historic period of big winter events. The tide turned in a dramatic way however over the last half decade, which on balance has allowed us to snatch defeat from the jaws of victory--if you are inclined to like winter. 

This is one of those storms that looks good on paper, but has enough red flags that there's still a fair amount of uncertainty. 

Before talking about the storm, let's recap where we are. 

Hartford (BDL) Normals
February Snowfall: 14.8"/ Snowfall to date: 0" (0% of monthly normal)
February Precipitation: 3.13"/ Precipitation to date: 0.01" (0.3% of monthly normal)

Normal To Date snowfall: 41.2"/ Snowfall to date: 15.5" (37.62% of normal)
Normal December-February precipitation: 14.45"/Precipitation to date: 16.42" (113.63% of normal)

Bridgeport (BDR) Normals
February Snowfall: 10.7"/ Snowfall to date: 0" (0% of monthly normal)
February Precipitation: 3.12"/ Precipitation to date: 0.04" (1.28% of monthly normal) 

Normal To Date snowfall: 25.7"/ Snowfall to date: 5.5" (21.40% of normal)
Normal December-February precipitation: 10.28"/Precipitation to date: 14.45" (140.56% of normal) 

We have some work to do in the snowfall department, but we always expected a backloaded winter. The next four weeks are critical.  

Let's dive in. 

Above: the current winter headlines issued by the NWS. Winter storm watches are up for all of CT, with the exception of the shoreline. Why? There is higher confidence of a 6"+ snowfall away from the coast than there is at the coast currently. As we get closer and the uncertainty diminishes, the coast will either see a winter storm watch/warning or winter weather advisory. 

Overall Setup
You haven't seen us write much because there hasn't been much to talk about! The overall pattern evolution since late January has turned out as expected. After a series of big storms in early to mid January, the pattern, which has turned over quite frequently and rapidly this winter, quieted down through early February. 

The overall evolution of El Nino suggested that we would have another period for winter between mid-February and perhaps into mid-March. The pattern is changing, and we have a system right at the front end of it. 

That has implications for the state. First, the wintry pattern you'll feel later next week isn't going to be ripe by Tuesday. The storm is coming into a marginal airmass, which introduces the risk of a warmer solution at the shoreline. 

Second, and related to this, the lack of true cold at least initially is due to the lack of a classic block to the north. This can (and likely will) be overcome, but it introduces the risk of northern shifts of the storm track which, you guessed it, put the coast and maybe even southern CT at risk of more rain before a change to snow. 

This is a thread the needle type storm. This is one that more than five years ago would have brought snow to the coast with the luck we had, but would almost certainly fail to produce a major winter storm with in the last five years with the luck we have. Yes, sometimes these marginal events come down to fortune. 

But let's get back to the science. There is quite a bit of discrepancy among the global and high resolution models, but among our two best, the European and GFS, there is strong consensus among the operational models and ensembles. This gives me confidence that at least for now I can focus on these two while just watching trends among the multitude of other guidance. 

First, let's look at the GFS, which has been further south overall and colder as a result. 

Above: 18z GFS surface look courtesy of Tropical Tidbits.

Looking at this surface, even without a classic block in place we get a rapidly developing system that is far enough south that it's almost all snow even down to the coastline. Specific snowfall amounts would vary based on banding, but verbatim that's probably a nice statewide 6-12" snowfall with some areas higher. The numbers don't matter here as much as the evolution. The surface track is south. The storm is strong. This allows for heavy banding that overcomes marginal temperatures particularly in southern CT. 

Importantly, while the 700mb low--a critical element of any winter forecast--is close to the state, it's good enough for strong frontogenesis (read: banding) to deliver significant accumulating in a fast moving storm. 

Above: the GFS depiction of the 700mb low Tuesday afternoon. I like seeing that it is strong, which allows for some wiggle room if the track is less than ideal for snow (further south). 

Below is the 700mb frontogenesis. Just a slight tick southeast with the 700mb low would keep the state colder aloft to allow for greater snowfall statewide, but this would bring a period of heavy snow into CT though the best would probably be to our northwest. 

The European model has been mostly aligned with the GFS, but shows what can happen if the low is further north. 

Above: the 12z European model. The 18z is even further north. 

This depiction shows why a significant snow is likely for northern CT, even with a further north track. With a closer surface (and 700mb low) track we introduce warmth into southern CT. That'd mean rain changing to snow on Tuesday.

However, the storm intensifies rapidly offshore, which allows the rain/snow line to crash back to the coast and verbatim, brings a plowable snow for coastal CT and widespread 12"+ amounts to the rest of the state.

The latest 18z Euro which I referenced above cuts back significantly (showing why we don't care about numbers yet) but still brings a significant to major storm to the state. 

Current Expectation
We are not putting out any numbers until our first call tomorrow. Given the uncertainty, we want to see if high resolution guidance begins to join the general consensus of the Euro/GFS. However, we don't need numbers to say the following. 

• A high impact event is increasingly likely, even at the shoreline, as we expect periods of moderate to heavy snow on Tuesday causing widespread cancellations. 
  
  
• While snowfall totals are still TBD, we are looking at a significant to major snow event inland with more uncertainty along the shoreline (areas without a winter storm watch currently). Even there, a plowable snowfall is likely. 
  
  
• It is a little too soon to have details on snowfall ratios and wind, but we are closely watching if a heavier wet snow in southern CT this could cause power issues. Wind does not look terribly strong, but it doesn't need to be if there's a lot of paste-like snow. 
  
  
• This is a fast mover. Rain/snow likely starts in the pre-dawn hours Tuesday and is out of the area by approximately 7pm Tuesday night. 

Stay tuned for our first call discussion and snowfall map tomorrow afternoon. 

A​s always, please like, share, and interact with us on our social media--on Facebook to share our discussions, and follow us on Twitter @southernctwx to retweet our posts. Hit the buttons below to join.
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Thank you for reading SCW.
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​-DB