Good evening from SCW. 

December has been off to a fast start. The state is running below normal in overall temperature, and above normal on snowfall. This is about as wintry as Connecticut can get during early December. The second half of December looks to continue the trend, with a significant winter storm looking increasingly likely and an Arctic blast afterward that will bring the coldest air of the season so far.

This forecast looks at the week ahead, with a focus on Tuesday's storm. I am doing this to give everyone a heads up on this week's forecast. Tomorrow we will have a dedicated forecast and final call for the storm. 

Let's jump in. 

Winter Weather Advisories have been issued by the National Weather Service for the southern four counties of Connecticut, with the exception of the shoreline. I expect advisories to cover the state over the next 24 hours. 

Monday
The warmer weekend that we experienced will be a distant memory tomorrow, as we see colder air filter in tonight and give us a chilly start tomorrow. Overall, tomorrow isn't a bad day, as we see increasing clouds and chilly conditions in advance of the storm. It is possible that parts of southern CT see some flakes begin to fly very late tomorrow, but the consensus is that snow begins in earnest very early on Tuesday. 

Tuesday
This is the stormy day. As a weak area of low pressure develops over the eastern US and tracks toward the coast, an area of high pressure will have established itself over the region. This will create a clash that will bring a mixed bag of precipitation to the state. Here are our thoughts right now:

• A moderate to high impact winter storm is increasingly likely to impact the state on Tuesday. Widespread delays are likely, and widespread cancellations are possible.  
  
  
• Currently, I expect 1-3 inches of snow and sleet along the shoreline. The icing looks to be relatively low here, but at this time we need to closely watch temperature trends in case this changes. I think a colder trend is more likely than a warmer one. 
  
  
• For inland areas, I expect 2-4 inches of snow and sleet and at least a glaze of freezing rain. I am intentionally hedging conservative here. The icing risk here is moderate. Again, we need to watch closely for temperature trends. 
  
  
• Snow is likely to overspread the state in the pre-dawn hours of Tuesday. Along the shoreline, snow will quickly change to sleet, freezing rain, and eventually rain. Even with this change, accumulating snow and some icing is possible. 
  
  
• For inland areas, the snow will hang on longer, but it is also likely that much of interior Connecticut will change over to sleet and freezing rain. With cold air damming (CAD) taking place, there may not be a changeover to rain, which increases icing chances through freezing rain. 
  
  
• Mixed precipitation and rain is expected to end Tuesday night. 

There are still a number of things that need to be resolved, but even with a relatively small snowfall there is higher confidence in a significant winter weather event for most of Connecticut due to the icing potential. 

Above is the latest high resolution NAM depicting the storm. Note how quickly the mixed line rises through the state, but how it holds over much of central and southern CT. This would be an all day mess for the state, even if precipitation wanes during the afternoon hours. 

Above is an average sounding for the western part of the shoreline during the storm early Tuesday afternoon. There are a couple of things to note here. First the temperature. At the surface, the temperature is 33F, or above freezing. Note the line just above however. There is a shallow layer of below freezing air, which means that even close to the shoreline, cold air will be hard to erode. This is something to watch in areas like New Haven.

​Stay tuned for updates tomorrow. 

Wednesday-Thursday
The storm departs late on Tuesday, but we're not done with feeling the winter hammer. On Wednesday, an Arctic front will cross the state, bringing the chance of snow showers, snow squalls that could drop a quick coating, and gusty conditions. The front is expected to pass during the evening hours so we have to watch out for the latter part of the evening commute.

Although it'll be cold on Wednesday, Thursday and Friday are looking frigid, with the brunt of the cold occurring on Thursday and early Friday. Temperatures will struggle to reach the 20s on Thursday, with nighttime lows in the single digits to teens and wind chills below zero. This is big cold for this time of year. 

Above you can see the 850mb temperature depiction from the European Model. With those temperatures, Thursday and Friday look downright frigid. 

Saturday-Sunday
You may have heard some rumblings on social media about a big storm, but for now, I'm not biting. This will be a period for us to casually watch during the week, as I do see a signal for continued stormy conditions, but there is nothing worth wasting writing space over yet. 

The Dailies
Monday: Increasing clouds and colder. Highs in the mid to upper 30s. 

Tuesday: Snow starting early, changing to mixed precipitation inland and rain at the shoreline. Highs in the low to mid 30s. Chance of precipitation 90%. 

Wednesday: Partly cloudy with a chance of snow. Breezy. Highs in the mid 30s. Chance of snow 30%. 

Thursday: Cold and breezy. Lows in the single digits to teens with highs in the upper teens to low 20s. 

Friday: Cold. Lows in the single digits to teens with highs in the mid to upper 20s. 
 
Saturday: Mostly cloudy with a chance of rain or snow. Highs in the mid to upper 30s. Chance of precipitation 20%. 

Sunday: Mostly cloudy. Highs in the mid to upper 30s. 

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​ 

A pattern that becomes increasingly supportive of winter weather seems to be unfolding.  But first, let's get through the short term details.

Currently: Strong (1042) high pressure was located right about over Dulles Airport.  This is keeping fair weather in place across our area.

For tonight, this is a good radiative night, and as such, temperatures will not be uniform.  With nearly no wind, expect big differences between the urban corridor and outlying areas.  We won't radiate to full maximum potential, because high clouds will increase toward morning.  However, still expect a big range in temperatures, from the upper teens to the upper 20s.  Some places along the SE coast may not get below 30.

Tomorrow: Precipitation arrives in the mid to late afternoon hours, from W to E.  With warmer air rapidly filling in and daytime arrival of precipitation, this should be just light plain rain everywhere.  However, it will be a chilly rain.  With low dew points to start, I'll go a few degrees below all temperature guidance and call for highs in the low 40s.

Tomorrow Night/Sat: Most of the steadiest and heaviest rain should end by dawn on Saturday.  However, it will largely be a cloudy day and a brief rain shower is possible at any time, with a better chance for a quick round of showers later in the afternoon.  Although it will not be cold, I'll go a couple degrees cooler than all guidance due to clouds and precipitation.  Even so, temperatures should rise to near 50 degrees.

Long Term (Sunday through most of next week); The main focus of the long term period revolves around a storm system slated for later Monday into part of Tuesday.  This storm should bring wintry weather to all of the state, with an emphasis on NW areas.

First, for Sunday, The GFS, as it has done recently in events like this, refuses to believe there is strong cold air advection occurring, despite it showing NW winds gusting to 35 MPH.  Therefore, I'll undercut its max temperatures by 3 to 5 degrees.  This results in high temperatures in the mid 40s.

For Monday, clouds will increase, but the day should be dry.  Any precipitation from the next system should hold off until nighttime.  Guidance temperatures do not look too bad.  Highs should be in the mid to upper 30s.

Now, for the next storm threat.... models are coming into a bit better agreement with this system, but still have their differences.  The GFS is playing into its usual bias of kicking the cold air out too quickly.  After reviewing all available data, the best forecast I can come up with at this time would be for a burst of snow to develop everywhere Monday night.  That snow will then quickly change to rain along the south coast, but sleet and freezing rain elsewhere.  Significant accumulations of ice are possible from Route 84 northward, with accumulations of lesser impact down to about the Merritt Parkway.  Stay tuned, as updates could be forthcoming to refine this thiking.  Precipitation then tapers off during the day on Tuesday.  In far NE CT, a band of snow showers or squalls is possible later in the day, possibly with coatings.  With the GFS tendency to scour out the surface cold too fast, I'll undercut its guidance by a few degrees.  This results in high temperatures in the mid 40s on Tuesday.

For Wednesday, very cold air will move in around the back side of the low.  With  a breeze, high temperatures will only be around 30 and feel even colder! More of the same is expected Thursday next week, with highs only in the upper 20s.  I undercut temperature guidance a few degrees both days, as temperature guidance does not do well with strong cold air advection that far out.

Looking into the longer range, the pattern continues to look very wintry, with storm threats just before and just after Christmas.  The storm just before Christmas happens to look extremely potent.  Of course, we're a long way out and things can (and will) change, but the pattern definitely seems to offer plenty of winter weather chances in the long range, as of this writing!

Now, let's take a look at some of the weather systems slated to affect our area in the upcoming week.  We'll start with tomorrow evening's system, since that is first up.  This map, valid Friday night at midnight, already shows light rain falling across the state, with heavier rain getting ready to move in from the south.

​

Now, let's take a look at Monday night, also valid around midnight.   On this frame, temperatures from I 84 on north, could still be at or below freezing.  The heavier precipitation in northern New Jersey is headed ENE toward the state.  This could make for very icy conditions in that part of the state, if this plays out as advertised.

​

Good evening from SCW. 

Snowflakes are starting to fly in northwest Connecticut as our snow event begins to take shape. Currently, we are seeing temperatures drop in advance of a period of snow that is likely during the overnight hours into tomorrow morning.

​Here's the latest.

You will notice that the snow map has not changed. We are still expecting a broad 1-3 inches of snow, but there are some towns that could pull a spot 4 inch accumulation. 

Impacts
Although this is a relatively minimal snowfall accumulation for Connecticut, the timing will likely create an out-sized impact for the state. As I mentioned at the top, snow is already beginning to fall in NW CT, and over the next few hours we should see a transition from rain to snow across the state, after a brief period of mixing. The snow will arrive faster than the temperatures will drop below freezing, so some of this snowfall will be lost to warm surfaces. 

We do expect accumulation, however, and there are likely going to be widespread delays in the morning. That said, things should clear between 7-10am, so cancellations are unlikely. 

Overnight, we'll see where banding sets up. There will likely be a brief period of moderate to heavy snow, tapering off to light snow as the morning progresses. Overall, this looks like a moderate impact event due to timing. 

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 SCW,
 
It’s hard to believe that we’re going to see snow in just over a day given that it’s 55 degrees in Hartford right now, but snow is indeed in the forecast just in time to mess up Wednesday’s commute.
 
Models & Analysis
 
As the system that brought rain to the state today gets pushed out tomorrow evening by a cold front (after more rain tomorrow), that cold front will stall out just south of us, and at the same time, another wave moves up along the front and bring snow on the northern side of the front. These anafrontal events can occasionally be prolific snow producers, but have a well-earned reputation as one of the “fraud five” in weather forecasting; things that are often modeled and rarely occur. That said, as we’re getting close to go time on this one and all signs still point to some snow, it’s time to look at the details.
 
Here’s a look at the setup on the GFS. You can see the main system moving out to the northeast, but there’s still trailing energy left to our southwest that extends out along the frontal boundary and brings precipitation with it. As we’re on the cold side of the front, it would be mostly snow here. 

​If you’re a snow lover, this depiction is pretty much the best-case scenario for the event. You’ve got ample precipitation, good timing (most of the snow falls at night), and the cold front in the perfect place to allow for temps to drop enough for snow while not being too far offshore which would keep precipitation to the southeast of us. There’s also a strong band of lift oriented along the axis of the front, which will provide the best chance of a period of higher rates. The model consensus right now is that band is positioned right over us, which supports some of the higher totals that guidance is suggesting.
 
That said, there’s a lot that can go wrong here. If we see the front shift in position slightly, we could see a solution where most precipitation is offshore (should it shift SE) or we don’t cool off in time and just see more rain (should it shift NW). Even as modeled, temps are borderline; we’ll be close to 60 degrees tomorrow and so we’ll need to cool off quickly if we want to see accumulating snow tomorrow night. Heavier rates will help cool the column, but in order to get those heavier rates, we’ll need strong atmospheric lift; if that fails to materialize as forecast or sets up differently than modeled, we’d just see light snow that wouldn’t amount to much of anything. This is shown well here on the GFS – the area of highest lift (the center of the purple contours) is in SECT away from the short, and the simulated radar shows the heaviest precipitation focused right there.

Finally, here’s a look at the 18z 3km NAM, which is closer to the “worst-case” scenario; just about everything that I explained that could go wrong does and the result is just a coating to an inch in eastern areas and nothing elsewhere. Notably, the 0z run of this model corrected back somewhat towards the GFS, so I think this is an outlier solution and am not considering it very much in the forecast, but I wanted to show it as an example of the negative bust potential here.

​Forecast & Timing
 
Here’s our forecast snowmap for this event.

​If everything were to work out perfectly with this event, models suggest a third to a half of an inch of QPF is about the upper ceiling with this event, which would suggest a 3-5” forecast. However, I think that’s overdone for several reasons. It’s likely that some of the QPF that the models predict to be snow will be lost to “white rain” while the column is cooled, especially if we see lower rates. I also think that we will still see some shifts with the frontal position in the final hours leading up to the event, either way you shift the front, it’s likely that we’d lose some snow accumulation, whether it’s from lack of QPF, minimized forcing, or warmer temps. And finally, there’s the old saying “Fool me once, shame on you. Fool me twice, shame on me”. Past performance is no indicator of future results, but we’ve been burned by these anafrontal events before and they have a nasty history of negative busts.
 
All in all, by mid-morning Wednesday, we’re expecting one to three inches of snow across the state. We had discussed adding a 2-4” band in interior southern areas up into the NE hills where we think the highest likelihood of good rates is, but we decided to play it conservatively for now and upgrade totals a bit tomorrow if needed once we get a better understanding of where we may see that band of heavier forcing and therefore higher totals set up.
 
As far as timing goes, rain should change to snow overnight tomorrow from NW to SE, and by daybreak it should be snowing across most of the state. Snow will taper off from NW to SE through mid-morning, but snow is likely for at least the start of the commute in all areas and through it in some.
 
Impacts
 
I expect widespread school delays and possibly some cancellations depending on how quickly the storm moves out and how districts choose to handle the event. Roads will be passable but expect slow going across most of the state for the morning rush, so if you can work from home Wednesday, it might not be a bad idea to do so. I don’t expect any power or other infrastructure impacts from this system. Overall, I would say that this is a moderate impact event; totals are relatively low, but snowfall rates could approach 1” per hour in some areas for a short time during the morning commute, which will cause slow going and the potential for school delays. Bring this event in six hours earlier and I would call it low impact, but timing is everything in operational meteorology.
 
We’ll be back tomorrow with a final call map, until then we’ll be on our social platforms for questions and comments; use the buttons below to join us. Thank you for reading SCW!
-SA

Good evening from SCW. 

It has been a cold and wintry start to December, with this weekend continuing the theme of colder than normal conditions. In fact, at BDL, we've seen temperatures come in at 4.6 degrees below normal! With the cold has come the snow, even for parts of the shoreline. Both BDL and BDR (Bridgeport) are above normal in snowfall so far. 

In recent years, December hasn't passed without a warm up, and that's coming early in the week. It looks short lived, however, with another chance of accumulating snow looking possible for Wednesday. Let's jump in. 

Snowfall totals so far. With continuing apologies to snow lovers in SW CT, the rest of the state is above normal for snowfall so far this season. 

Monday-Tuesday
As I mentioned, the start of the week will also be our period for the warm up. It will be brief and come at a cost. Tomorrow we will see warmer temperatures, but only into the upper 40s to low 50s. Rain will move into the region associated with a strong low well to our west. The combination of warmer temperatures, moderate to heavy rain, and higher dew points will cause significant melting of the snow and ice on the ground. 

Showers will begin on Monday and the rain will get heavier during the afternoon and evening. The evening commute looks very wet. Tuesday looks relatively warm, with highs in the upper 50s to low 60s in the warmest spots. Rain will continue into Tuesday, but should be a bit more spotty in intensity and coverage until later into the afternoon and evening hours, when a strong cold front approaches and brings the focal point for potential wintry weather on Wednesday. For NW CT, we may see a transition from rain to snow in some of the highest hill towns as early as late Tuesday evening. 

Latest high resolution NAM depicting the onset of rain showers and heavier rain through Tuesday. As you can see, coverage may be spotty at times, but both Monday and Tuesday are certainly umbrella days. 

Wednesday
Here is our latest SCW Period of Interest. As you can see from the NAM depiction above, as the storm departs we will see colder air pushing toward the region. Along the front that will bring the colder air, it is increasingly likely that the state sees a period of snow, as the column cools and a potential weak mid level low develops along the front, maximizing lift to produce snow.

There is still a fair amount of uncertainty here. We're still more than 48 hours out, and these setups are notorious for failing to produce as we see less robust moisture, warmer than expected temperatures, or poor timing that minimizes snowfall accumulations. Right now, it is looking like a period of snow will develop statewide during the early morning hours of Wednesday. The snow may continue during the morning commute and into the early afternoon in eastern portions of the state, and as temperatures continue to fall, widespread delays and cancellations are possible, even as we're not expecting major snowfall accumulations.

We are not putting out numbers now, but stay tuned as these details will be sharpened as we get closer.  

Above is the GFS depiction of the potential event on Wednesday. It shows the potential for snowfall on the surface, but a deeper look shows a possible red flag. Below is the sounding for the Hartford area (Wednesday morning) shows a layer of dry air (the spike in the green line) that could minimize the impact. Note that the other guidance has less of a flag here. 

Thursday-Friday
At any rate, this front means business in terms of cold. We will see temperatures hover near to below freezing on Wednesday, and temperatures should be below freezing statewide on Thursday. Although conditions will improve with moderating temperatures by Friday, the end of the week will feel like winter in terms of temperature. 

Saturday-Sunday
The weekend is not looking good at this time. The guidance has been consistent for quite some time that a major storm will develop and cut to our west. That means rain, especially on Saturday. Conditions look to slowly improve by Sunday, as colder air begins to flow in once again. 

The Dailies
Monday: Mostly cloudy with rain. Rain will be heavy at times, especially during the afternoon and evening. Highs in the upper 40s to low 50s. Chance of rain 100%. 

Tuesday: Mostly cloudy with rain showers. Highs in the upper 50s to low 60s. Chance of rain 50%.  

Wednesday: SCW Period of Interest. Snow likely. Daytime highs in the upper 20s to low 30s. Chance of snow 60%. 

Thursday: Mostly sunny, cold, and breezy. Highs in the upper 20s to low 30s. 

Friday: Mostly sunny and cold. Highs in the low to mid 30s. 

Saturday: Mostly cloudy with rain. Rain may be heavy at times. Highs in the mid to upper 40s. Chance of rain 60%. 

Sunday: Mostly cloudy with a chance of showers. Highs in the mid 40s. Chance of rain 30% 

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​