Good evening from Southern Connecticut Weather.

There haven't been many changes to the winter storm watches today. The only addition has been a Winter Weather Advisory issued for Windham County and coastal Fairfield County. There's a reason for that.

​Although we are closer in time to the start of this winter storm, uncertainty for Connecticut has increased quite noticeably in the last 24 hours. Here is our latest update.

There are a couple of things to highlight here. The ranges have been maintained but shifted quite a bit.

2-4 Inch Zone
Our 2-4 inch zone has been expanded. In this zone, we are expecting most of the snow to fall during Part I, when the state receives a burst of snow and temperatures are most conducive for SE CT accumulation. This zone was expanded because the guidance is now unanimous in having some sort of dry slot aloft that would limit precipitation on Monday, particularly in the afternoon when we previously expected Part II to get going. 

4-8 Inch Zone
Our 4-8 inch zone has been expanded to cover much of the state, up into much of Tolland and Windham County. This zone could easily be reduced, but I do still believe that the guidance, which shows a massive dry slot in Connecticut, is overdone. As a result, most end up getting about what we originally thought, but there's a lower floor and lower ceiling with Part II. 

6-12 Inch Zone
Our 6-12 in zone has been reduced to the norther tier of Fairfield County, Central and northern Hartford County, and a smaller sliver of Tolland and Windham Counties. There is higher confidence that both Part I and Part II will produce as originally expected. 

8-14 Inch Zone
Our 8-14 inch zone was reduced slightly. There are no significant changes in our expectations for conditions here. 

Above: GFS trend for Monday evening since yesterday. Note how the dry slot was only introduced recently with a much more ragged precipitation shield appearance. I am not fully buying, but with the other guidance showing something similar at this time, it would be hard to discount. Let's take a look at Part I and Part II in more detail. 

Part I

Timing
The storm will start off as snow statewide. The timing remains more or less the same, though with the current dew points outside it is possible that onset is a bit slower with snow having trouble reaching the ground early. Snow should begin between 9am to 2pm from SW to NE. After a burst of snow that should drop a couple of inches, we will transition to sleet and freezing rain for most over the course of the afternoon. By evening, most should be mixing. Rain is likely for SE portions of the state during the overnight hours, and the mixing will likely continue and taper a bit into Monday morning. We should begin to see more influence from Part II begin in the afternoon. 

Impacts
As mentioned above, Part I should drop a few inches before icing via sleet and freezing rain begins. Roads should not be too bad at first, so those traveling in the morning will likely be ok. Once we get into the afternoon and evening road conditions will deteriorate. Given the uncertainty about how much mixing occurs, it is an open question as to whether schools and businesses are closed Monday. I think the further away from the coast you are, the more likely widespread cancellations are. There may be significant icing that occurs away from the coast. 

Above: HERF Ensemble view of accumulated freezing rain. This is a fairly robust signal for freezing rain for much of the state into Monday morning. 

Part II

Timing
Part II is likely to begin taking over late Monday morning into Monday afternoon, as a secondary low develops off the coast. Just like yesterday, this is expected to be a mostly snow event as temperatures drop. Part II will likely start off light because of the potential for dry slotting, but snow is likely to last in some fashion into Tuesday morning. 

Impacts
This is where a lot of the uncertainty lies as of this discussion. Usually, I would be more bullish given the conditions--a rapidly deepening low just underneath the state as temperatures crash--but with strong banding comes strong subsidence. The guidance has converged on dry slotting encompassing much of Connecticut, but I do not buy that fully yet.

Slight shifts would put us on the higher end of the projected totals, if not exceed them. The dry slot coming to fruition would likely put us on the lower end of totals. We'll have to watch closely. We're still nearly 48 hours from Part II beginning. That's a lot of time for more changes to occur. 

Widespread delays and cancellations are possible on Tuesday, but that will need to be reevaluated on Monday once we see how Part II produces. 

Above 12z European model depiction for Tuesday morning. Light snow may still be falling at that time as Part II is slow to depart. 

Bottom Line

• A major and long duration winter storm is still expected to impact Connecticut from Sunday morning/afternoon through Monday night/Tuesday morning. This is expected to be a moderate (SE and southern CT) to high impact (northern CT) winter weather event, especially if Part II is more robust. 
  
  
• Even with lower projected snowfall amounts in southern portions of the state, a period of icing is expected that will likely cause significant travel delays Sunday night. Monday is an open question depending on whether there is continued mixing at the shoreline.
  
  
• There is still significant uncertainty over how quickly the mixed precipitation line pushes north, how far it pushes north, and how long mixed precipitation lasts. This will have a significant impact on eventual snowfall totals, but not on the overall impact of the storm.  
  
  
• In addition, there is significant uncertainty over the intensity of Part II. Where the banding sets up is critical in overall snowfall totals and how widespread delays and/or cancellations there are on Tuesday. 
  
  

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.

Thank you for reading SCW. 

-DB​

Good evening from Southern Connecticut Weather. 

As the headline states, we are expecting a major and long duration winter storm to impact Connecticut beginning on Sunday. We expect a mixed bag of precipitation types, and both snow and icing are likely to cause significant travel delays and cancellations Sunday and Monday, with the possibility of delays or cancellations continuing into Tuesday.

Before diving into the details, here's our First Call map for the entire storm. I have moderate confidence in this forecast. Keep in mind that these are ranges. No one is guaranteed the maximum value. 

​Let's examine the first winter storm of the season.

The National Weather Service is beginning to issue Winter Storm Watches for much of Connecticut. More watches, and eventually, warnings, are likely to to be issued today and tomorrow. 

The storm that has brought significant weather across much of the western United States is the culprit for our upcoming winter weather event. It has been traversing the nation for days, and is expected to reach our region on Sunday. I view this system as having two parts:

Part I--Sunday into Early Monday
This part will feature overrunning precipitation. Essentially, as the storm approaches, warmer air will rise over the colder surface air and produce snow. Snowfall should begin between approximately 9am and 1pm from SW to NE. This part should produce accumulating snowfall during the afternoon, but as the warm air begins to erode the mid levels of the atmosphere, a change to mixed precipitation and even rain, in SE CT, is likely.

The critical questions here are how much snow falls before mixing begins, and how prolonged a period of icing (sleet and/or freezing rain) occurs. 

Above is the latest high resolution NAM, showing the onset of snow statewide on Sunday and the start of mixing. Snowfall may be heavy at times on Sunday before the mixing begins, causing travel delays. 

My current thinking is that for interior portions of the state, the northern four counties, this is a fully frozen precipitation storm. Temperatures there will drop below freezing. For southern portions, temperatures will hover near freezing or just below depending on proximity to the coast. 

Part I should produce accumulating snow for virtually everyone before the mixed precipitation line creeps northward. I think it's likely that most areas outside the NW hills will see mixed precipitation. Icing is possible as a result, and it may be a prolonged period of icing. 

I think the mixed precipitation is predominantly sleet, but there may be a period of freezing rain. That could cause significant problems later on Sunday and into early Monday. At this time, I expect widespread cancellations on Monday. 

Below is a quick primer on precipitation types during winter storms. I think the mixed precipitation, rather than snowfall, is the main story of Part I. 

Part II--Monday Afternoon into Tuesday Morning
Although all generally the same system, Part II is more of the snow element of the winter storm.

Overnight Sunday into Monday, a coastal low develops off the coast. As it does so, it intensifies rather quickly and as a boundary bringing colder air pushes through the state, the entire region changes over to snow. You can see it clearly via the high resolution NAM animations below, which cover approximately 1am Monday morning into 1am Tuesday morning. 

On the left, we are looking at a forecast of 850mb temperatures. These are temperatures in a layer above the surface. Notice how over most of CT at the start of the animation, temperatures are above freezing. That is a signal for mixed precipitation. As the animation continues you see those temperatures crash below freezing toward the coast. That's where we see the coastal wrap up and everything changes to snow via the depiction on the right. 

​Monday is snowy as a result, statewide. Note that on this NAM run, we see evidence of banding. The NAM is not my model of choice here--I am showing it because of how easily viewable it is. I expect stronger lift, which would result in a more robust precipitation shield/banding. I expect snow will be heavy at times.

This is the Euro depiction of precipitation early Monday afternoon. Even though we see parts of southern CT as rain and mixed precipitation, a look at the surface, 925mb, and 850mb tells the same story--most are likely to be snowing and possibly snowing heavily as the day progresses on Monday. Image courtesy of weathermodels.com

This part of the storm may also be the long duration piece. It is unanimous on the guidance that there is a mini "stall" of this low as it wraps up, which could prolong snowfall into early Tuesday. If that is the case, Tuesday could begin with significant delays, if not cancellations. 

Below is the very latest GFS model run. This is posted to to show a depiction of the event. I do not expect rain in northern CT, so do not take this depiction verbatim. 

Bottom Line

• A major and long duration winter storm is expected to impact Connecticut from Sunday morning/afternoon through Monday night/Tuesday morning. This is expected to be a moderate (SE CT) to high impact (rest of CT) winter weather event, especially on the roads. 
  
  
• Even with lower projected snowfall amounts in southern portions of the state, a period of icing is expected that will likely cause significant travel delays and possible isolated to scattered power outages as breezy conditions occur Sunday night into Monday.
  
  
• There is still significant uncertainty over how quickly the mixed precipitation line pushes north, how far it pushes north, and how long mixed precipitation lasts. This will have a significant impact on eventual snowfall totals, but not on the overall impact of the storm.  
  
  
• Everyone is expected to transition back to accumulating snow on Monday which is increasingly likely to last into Tuesday morning.

​
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.

Thank you for reading SCW. 

-DB​

First thing’s first; Happy Thanksgiving! We hope that you’re able to enjoy the day with your loved ones, and we’re thankful that you’ve made our SCW family a part of your day. For today we will have partly sunny skies with highs in the 40s, although temps will start to drop through the afternoon and into the evening. Winds will also diminish as well over the course of the day, and luckily they came down quickly enough that the balloons flew in New York today for anyone that went in to watch the parade.

Following sunny and seasonably cool weather tomorrow and Saturday, all eyes then shift to an approaching system for Sunday. Unlike the other coastal storms we’ve seen so far this winter, there doesn’t seem to be as much uncertainty with how this one is going to develop, likely because the system is already on shore (currently bringing snow to the mountain west) and has a fairly straightforward evolution; the system tries to run into the lakes to our west, but is then shunted to the east by a strong high pressure to our north. Pretty classic setup for a winter storm in the area, and one that models tend to be more reliable than a more complex system involving phasing. That said, there is still of course plenty of variability, both in the strength of the system and the positioning of the block. Those, along with the airmass, will determine the mix of precipitation types that we see, and will determine if we’re in for a snowstorm, an icy mix, rain, or nothing at all. Generally, the stronger the high pressure to the north, the further south the system tracks, and the colder the airmass becomes, making it more likely that we will see a wintry solution. Concurrently, a stronger system can be more dynamic, and allow for better transfer of cold throughout the column, eliminating the nasty warm layers that can sometimes be found in a weaker setup. Of course, get things too strong up north, and it's a snowstorm for the mid Atlantic while we’re cold and dry here in Connecticut. Conversely, a weaker, more strung out system would introduce the chance of some icing, or if the high pressure were to trend further north or weaker we could see a scenario where the low tracked over or north of us and we ended up as mostly plain rain.

Here's a look at the overall scenario on the GFS. Notice the low pressure going up into the Midwest and the strong high to our north limiting how far north the primary low can go before it moves east and transfers.

The trend over the last few model runs has clearly been to push the system south and therefore make it colder. Often, we see guidance do this in the short range as it recognizes the strength of the high pressure and the low-level cold that is in place, but as we’re still in the medium range here, it’s a rare medium range trend that does not correct back the other way at least to some extent. Whether that is from this point or an even colder set of runs in the next few cycles remains to be seen, but I don’t think we’ve seen the last of the warm solutions yet and it’ll take another day or so before we have some more confidence in this one.

As far as timing goes, this system looks to be relatively long duration. We’ll start off with overrunning precipitation from the parent low in the midwest on Sunday afternoon (the most recent GFS has snow just entering the state at 1 PM), with the parent low in the midwest transferring its energy to a new secondary low south of Long Island on Sunday evening and prolonging precipitation through Monday. Depending on how long the low stays stalled out, and where it ultimately tracks, there’s the potential for precipitation to continue right through Monday and into Monday night. Furthermore, as the low strengthens and moves east, we’ll see more cold air dump in from the NW behind it, so it’s certainly possible that we could see a flip back to snow later Monday or overnight into Tuesday for any areas that do change to rain from the primary.

Here's a look at temps on the GFS the last four runs of the GFS for 7 PM Sunday - you can clearly see the airmass ticking a bit colder on each run. I'd toss the thermal profiles on the GFS as it's notoriously bad for low-level cold, but the idea holds true across the other models.

Let’s take a look at the guidance and see the different solutions. 

The GFS has been the warmest model, flipping most of the state to rain after a quick burst of snow at the start. However, on the most recent run, we’ve seen the high to the north strengthen, pushing the whole system a little bit further south and allowing for a period of front-end snow. On this solution, however, most of the accumulations would come on the back side, as the low slowly strengthens and moves east, just cold enough air is able to work it’s way into the state to flip all areas back to snow Monday afternoon, with snow lingering through the night into Tuesday morning. On this scenario, we’d see noticeable accumulations in the hills, with lighter accumulations in the southern portion of the state. I would say that this scenario is the most likely, say 40-50%

Compare the GFS to the colder consensus (GGEM, Euro, NAM so far); on those models, the high is stronger and further south, allowing for better cold air to be in place and for more snow on the front-end. In fact, on last night's Canadian run, precipitation remained all frozen in the state, with all snow in the northern counties and snow to a mix to snow in the southern counties. While I think this scenario is overdone, it shows the bounds of what’s possible here if the system is able to stay on the colder side. Generally, the GFS keeps precipitation around longer than the rest of the model consensus, but all models agree that we’ll see continued precipitation into Monday at the earliest. Should a colder scenario like the GGEM verify, we could be looking at a significant snowfall for most of the state, especially away from the immediate shoreline. The Euro is a healthy compromise between the GFS and the GGEM, with a mostly snow scenario in the hills and snow-rain-snow for the rest of the state. This scenario is less likely than the first scenario, but becoming more realistic with each model that jumps onboard; I’d give it a 30-40% chance of occurring right now.

The third scenario, which the GFS was advertising until this morning’s run, is when the low passes to our north and puts us in the warm sector; a quick period of snow would flip to a cold rain for the state; an inch or two would be possible in the hills and no accumulation would be expected elsewhere. This is probably the least likely scenario given no guidance currently shows it, but I’d still give it a 20-30% chance of occurrence.

Here's an overview of the system on the most recent GFS and GGEM; I wouldn't pay too much attention to the actual outputs right now, but more get an idea of the track and evolution of the storm and the resulting impact to temps and precipitation type.

For QPF, the GGEM is the high outlier with 1-2” across the state, while the GFS is closer to 1-1.5” and the Euro is in the ½”-1” range. Of note, the Euro’s ensemble mean has QPF amounts just shy of 1” across the region, suggesting that the operational may be a bit underdone. At a 10:1 ratio, these numbers would imply the potential for double-digit snowfall in those areas that remain all snow. That said, we are still 3-4 days out from this system and it’s a very fine line between a whiff, a big snowstorm, and a lot of rain, so don’t go start preparing for a big hit yet because there’s a good chance you’ll be disappointed if you do. That said, the potential is real, and if you have travel plans for Sunday, I would keep a close eye on the forecast; the earlier you’re able to get on the road, the less painful your trip is likely to be. 

Here’s a view from the most recent Euro ensemble that shows the modeled probability of exceeding 6” of snow across the state. 

With odds ranging from 80% in the NW corner to 30% in the SE corner, there is certainly a realistic possibility that this could be our first warning snow of the season. However, I will caution that it’s likely that we will see further shifts in the temperature and track of the system as it continues to unfold, and personally I think these numbers are too aggressive given the amount of uncertainty we have (the product gives no credence to model shifts or timing; it’s just a straight average of the 51 members from that particular run). As this run is close to a best-case scenario for snow lovers, it’s not time to hang your hat on a big storm just yet, but should we see a similar presentation by tomorrow evening or so, we’ll grow more confident in the potential for warning level numbers.

The bottom line is that a significant coastal storm looks to impact the area from Sunday through Monday or Tuesday, and that the first significant snow accumulations of the season are possible. We’ll have more information and a first call map if needed tomorrow evening, until then, have a safe and enjoyable Thanksgiving!
​
-SA

 Disc: Other than a few light showers tomorrow afternoon and high wind gusts Thanksgiving afternoon, the week will be largely quiet until the weekend, when there are legitimate concerns for a winter storm, on one of the busiest travel weekends of the year.

Currently: Right now the only item of interest in our region is a cold front, currently located near Toledo, OH.  This front passes through tomorrow, with just a few rain showers and not much fanfare.

Tonight: On a night like tonight, there is no real reason to deviate from guidance.  We do not have cold air advection and it should be a mostly cloudy night.  Guidance is also tightly clustered.  There's always something that throws a monkey wrench into our temperature plans.  Whether it's a localized sea breeze or a valley that clears out and drops suddenly, it happens.  But there isn't really much you can do about that.  You just roll with the guidance on a night like tonight and if you verify for 90% of locales, that's great.  With that in mind, expect lows ranging from the mid 30s in the NW hills to the low 40s along the south coast.

Tomorrow: A warm day for this time of year, as we're pre-frontal during the day.  The NAM and GFS temperature guidance are world's apart, which is a bit disconcerning to see on day 2.  For now, I split the difference.  Temperatures tomorrow will largely depend on cloud cover and precipitation.  Although rainfall looks scattered and light, it occurs right around the middle of the day, so that could play a role in disrupting high temperatures.  Additionally, with it being late November, it is easier to stay cloudy this time of year, due to low sun angle.  Highs should generally be close to 50 degrees, but a few places in the CT Valley could make a run at 55.  As far as rain, the areas least favored to see much rain are areas in SW CT, while east of I 91 is favored to see heavier, longer-lasting rain.  In fact, across NE CT, rain coud linger into Thursday morning, when some sleet could mix in.  Rain begins mid afternoon in the far SW and then spreads slowly NE.

For Thanksgiving day, the GFS looks ridiculously warm.  It seems to not realize that there is cold air advection occurring.  So I have disregarded its thermal profiles completely an gone with the cooler NAM guidance.  The biggest concern for Thanksgiving day will be strong wind gusts.  Winds should gust to around 40 MPH, especially in the afternoon.  Otherwise, lots of sun and fairly comfortable temps.  Expect highs around 50 degrees.

Long Term (Thanksgiving shopping and travel weekend): For Black Friday, guidance looks fairly reasonable.  Highs should be in the mid 40s with plenty of sunshine, so not bad for shopping/traveling interests.

On Saturday, clouds should begin to increase ahead of the next system.  Because of this, temperatures may not follow a typical pattern, as clouds typically arrive last in NE CT.  Guidance temperatures look decent, showing highs generally around 40 degrees.  But a few places in NE CT, where the sun shines longer, may get into the lower 40s.

The Sunday to Monday timeframe is where things get very interesting.  A complex storm system ejects out of the High Plains states, then transfers off the east coast.  This scenario is generally a snowy one for the area.  In general, systems like this can produce a burst of snow, then a changeover to rain for most, followed by heavy snow, as the coastal low takes over.  However, we're still a way out at this point, so it isn't a very good idea to focus on any specifics or any specific "target areas".  Suffice it to say that a very messy travel period may be unfolding and those with plans may seriously consider adjusting them earlier or later.  A myriad of model solutions exist, ranging from the GFS, which is too far south to even affect northern CT very much at all, to the GGEM, which would favor interior areas, to the UKMET, which is basically a non-issue, to the ECMWF, which buries most of CT! So, as is usually the case at this lead time, it's a good idea to just follow the general trends in modeling and see which way they go,  Suffice it to say, there is a higher chance for most of CT to at least get some accumulating snow than not at this point, but there is a long way to go.  As far as temperatures for Sunday and Monday, I've chopped 3 to 5 degrees off guidance both these days, as Sunday will have clouds and precipitation falling and Monday will "likely" have at least some snowcover, and northerly winds gusting to 40 MPH, which is not a recipe for warm temperatures.  That said, expect high temperatures generally in the mid to upper 30s on Sunday and low to mid 30s on Monday.

Quick update: The new ECMWF has arrived, and looks pretty similar to the UKMET, but with heavier snow to start, before changing to rain.  Just goes to show that any solution is still on the table and if I wrote this discussion 12 hours earlier or later, the "modeling" part would look completely different.

Finally, going beyond that period one more day, I will continue to assume snowcover and chop 3 to 5 degrees off high temperatures for Tuesday, which yields highs once again in the mid to upper 30s.

A little heads-up to future shifts, the period Wednesday-Thursday of next week really needs to be watched.  There's an adequate cold air supply, and a system diving out of the Lakes region with redevelopment near or off the Mid-Atlantic coast.  Although not implicitly shown in today's guidance (other than as a weak system) that is usually a setup that can yield a winter storm in this area and needs t to be watched as our next potential threat.

Finally, I haven't really had all that much time to look into the long range, concentrating on a very active period coinciding with a very busy weekend.  However, after the mid-week threat, the pattern looks to moderate a bit for a while.  Now, having said that, I don't see any long, prolonged warm-ups on the horizon and we could be back to tracking winter storms very soon after.

Now, let's take a look at systems slated to affect the area in the upcoming week.  I'll post a map of tomorrow's frontal passage, and then the weekend storm.  You can see that rainfall amounts are generally light and that E CT, especially NE CT, gets favored.

​

Now, let's take a look at Sunday evening.  This is just one of many solutions available, and will likely change many times before the event.  This particular solution favors S CT the hardest, while something like the ECMWF (last night's version) would favor N Ct the hardest.  Just keep in mind, almost anything is still on the table.

​

Anyway, that's all for now! See you next week! Have a Happy Thanksgiving, stay safe, and stay tuned to here or other media outlets for updates regarding the Thanksgiving weekend storm!

​-GP!

Good evening from Southern Connecticut Weather

We will jump right into the forecast tonight. After a stormy Sunday which brought very minor snow to some of our hill towns, we warm up for an unsettled Thanksgiving week. 

Monday/Tuesday
The start of the week looks nice! We will see clear conditions and warmer temperatures as high pressure takes control. These will probably be the best days of the week weather wise. 

Wednesday
The day before Thanksgiving is looking wet, as a developing storm passes well to our west. The guidance is in good agreement on the timing and precipitation type: rain. I'm not sure the storm will be as wet as the one we just experienced, but I do think that with wet conditions during the day and evening we will see some travel disruptions. In the wake of the storm, wind will pick up and colder air will flow into the region.  

GFS depiction above of the storm on Wednesday. It does not look like the same washout as we saw today, but with so many traveling, disruptions look possible. 

Thanksgiving Day
Turkey day is looking good! As I mentioned above, colder air will flow in after the storm departs, but we are not expecting anything like last year--the coldest Thanksgiving on record. Conditions should be dry, maybe a bit breezy. We will need to watch the trends this week because wind may be an issue in the wake of the storm. 

Friday
The day after Thanksgiving is looking colder than normal, but nice as well. High pressure will likely dominate during this time period. 

Saturday-Sunday
There is a fair amount of uncertainty about the weekend. While Saturday is looking ok right now as high pressure remains in control, there looks to be another developing system by late in the day that will approach the area. We will see what kind of cold air is in place, but Sunday could bring a bout of wintry precipitation before a changeover to rain.

The Dailies
Monday: Mostly sunny and warmer. Highs in the low to mid 50s. 

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

Wednesday: Mostly cloudy with rain showers. Highs in the low to mid 50s. Chance of rain 50%. 

Thursday: Sunny, breezy, and seasonably cool. Highs low to mid 40s. 

Friday: Sunny and breezy. Highs in the upper 30s to low 40s. 

Saturday: Sunny early with increasing clouds late. Highs in the upper 30s to low 40s. 

Sunday: Mostly cloudy with a chance of rain and/or mixed precipitation. Highs in the upper 30s. Chance of precipitation 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.

Thank you for reading SCW. 

-DB​