Good afternoon to you from SCW!

Since we last wrote yesterday, we have unfortunately seen the warmer set of solutions for tomorrows storm system become dominant in the guidance, and so have lowered snow totals a bit from our initial forecast yesterday. You can see our newly revised map below.

The biggest change to the forecast is that we expanded the zone of little to no snowfall to cover all of southern Connecticut and a large portion of eastern Connecticut as well. With the warm push in the low levels becoming more prominent, areas closer to the storm will see the most warm intrusion, and so it's going to be hard to get more than a quick coating on the front end and a chance at a quick accumulation from any back end snows that develop. Some of the guidance, in particular the 3km NAM(shown below) and the RGEM show a potent backlash band that would bring a period of heavy snow to almost all of the state, but I've seen these scenarios modeled many times and it's not often that they actually work out. Perhaps this one will and so I've left an area of up to 2" in the forecast for this zone to account for the possibility, but I think a coating to an inch at best is the more likely scenario. Otherwise, the forecast remains similar to yesterday - we trimmed the edges of the 3-6" zone slightly but I still think the same general area of the Litchfield hills and possibly northern CT river valley is the best area to remain all snow. It's possible that we'll see a solution where heavier precipitation at the start and end of the event gets some of northeast CT past the 3" mark, but I'm not confident enough in that solution compared to the warmer look to revise the map accordingly and so we'll leave it where it is for now.

Here's the 3km NAM I referenced above - should this scenario verify, there will be a brief period of very heavy snow for all tomorrow morning as the strong dynamics in the band would be enough to flush out any warmth at the surface.

While we can't rule out the possibility of a death band forming like the NAM shows, the more likely scenario remains similar to what we've been seeing; snow moves in very early tomorrow morning, quickly changes to rain from south to north in all areas except the Litchfield hills, and then rain possibly changes back to snow as the low moves east and colder air comes in. We should have all precipitation out of the state by the mid-morning hours at the latest and so travel within the state should be fine by the afternoon hours. However, if you're heading north, interior MA as well as VT, NH, ME and upstate NY are expected to see a much more significant snow event, so check local forecasts for your route before heading out tomorrow. One positive side effect of the storm becoming wetter here is that it will increase snow totals in ski country; between the storm yesterday and tomorrows snow, northeast ski areas are set up for a great Christmas week!

​The other thing that's worth pointing out about this event is the wind potential. Strong cold air advection on the backside of the system will allow for some gusty winds to develop later in the day; wind gusts in the 40-50 MPH range are likely with an outside shot at 50+. A Wind Advisory has been issued for the entire state by the NWS to cover this risk.

Here's a look at the forecast winds from the GFS and at the SCW impact scale for this event - only change from yesterday was to upgrade the impacts from wind from moderate to high as some strong gusts could cause minor tree damage and perhaps a couple of very scattered power outages.

Finally, while this system may not bring the White Christmas for all that we were hoping for, we still wish you a wonderfully merry Christmas with your loved ones! We certainly hope that you enjoy the time with friends and family tomorrow and that good fun is had by all. We will be on a reduced posting schedule from now through the end of the year as we will be partaking in the festivities as well, but rest assured that if an event pops up on the guidance we'll be talking about it and keeping you informed.

Until then, Merry Christmas, Happy Holidays, and thank you for reading SCW!
​-SA

Good morning to you from SCW!

When this Christmas storm first appeared on the models a few days ago, I was hopeful that it would finally snap our five year streak of Grinch storms on or near Christmas, and until last night, it looked like that would be the case. However, meteorology loves to throw curveballs at us, and quite a bit of the overnight guidance came further west with our low pressure system for Monday, making the net result a rain storm for a lot of the state.  Whether this trend is real or not remains to be seen, and there are still two days for it to go back the other way, but if you're a snow lover hoping for a White Christmas, the trend is not your friend in this case. Nonetheless, we will still see some snow across at least part of the state, and so a snowmap and discussion is in order.

Models and Trends

Since yesterday, we've clearly seen a trend towards later development of the secondary coastal low, which means that there is less time for cold air to get wrapped up in the system and the boundary layers warm above freezing as a result. This is shown well by looking at the last couple of NAM runs - you can see the center of the system jump quite a bit NW and the net result go from primarily a snowstorm to primarily a rainstorm.

The other issue we're seeing is in the midlevels - the midlevel low pressures have both weakened and shifted NW - that means that we'll see less favorable dynamics and snow growth, so any snow that does fall will more likely be of the lower ratio variety and less likely be of the fluffy dendrite variety. Something to keep in mind when considering snow totals.

While most of the guidance follows the NW trend shown here on the NAM, the Euro is the exception and actually ticked a hair colder last night, which would allow for a mostly snow event across the region. Because of it's earlier development of the coastal, it allows the northeastern portion of our forecast area to get into the band of inverted trough snows that are otherwise forecast to be to our north and actually jackpots that area with 6"+. Unfortunately, that solution is currently an outlier and I am hesitant to give it too much weight considering the trends, but the Euro is a good model with thermal profiles as well as being one of the most reliable pieces of guidance in general, so I feel like I have to give it at least some weight in the forecast. Therefore, will go with a 70/30 blend of the consensus model forecast excluding the Euro at 70% and the Euro at 30%. That blend gives us the snowmap below.

Forecast & Timing

Here is our snow forecast for this event.

As we discussed last night, the state is split up into three zones for this event, but we moved the zone boundaries a bit NW from what I outlined in that discussion. In the NW portion of the state, mainly Litchfield county and some of the higher terrain in Fairfield and Hartford counties, this should be a mostly snow event. We could see some brief mixing during the height of the system, but a solid 3-6" of snow seems to be a good bet here. In the southeastern corner of the state, I unfortunately am now expecting a mainly rain event. The potential saving grace for a White Christmas there may be a final backside band that comes in as the storm departs - some of the hires models show this band as being strong enough dynamically to flip any rain over to snow and drop a quick coating to an inch or so of accumulation. Will leave a C-2" in the forecast for this zone as a result of that possibility, but wouldn't be surprised to see all rain there.

The rest of the state makes up the battleground zone where this is a tricky forecast. On the Euro, we see mostly if not all snow here, whereas on the rest of the guidance it is a messy rain/snow mix for most of the event or just plain rain, and snow accumulations would likely be minimal at best. I do think that we might see things go a bit colder as we do have some high pressure in play to our north that is often under modeled, and so have gone with a 1-3" forecast here, but that will probably be a messy 1-3". The next couple of model cycles will tell us a lot about the fate of this zone - should we see the warm trend continue, we can probably get rid of this zone and lump this area in with the rain to the southeast, but I'm not ready to go there quite yet. We'll see where the guidance is at tomorrow and if needed we can update then.

As far as timing goes, looks like precipitation comes in after midnight Monday and should be out of the state by 10 AM or so at the latest, even earlier in western areas.

Impacts

​Here is the SCW Impact Scale for this event.

The timing of this event isn't great for those of you heading out for Christmas travel - that final band could sweep in right as folks are getting on the roads. If you're traveling Christmas morning, make sure to keep an eye on the radar and try to leave after 10 AM or so if possible as conditions will be much improved then. Otherwise, looks like a fairly run of the mill event, nothing we haven't seen before or can't handle.

We'll be back tomorrow afternoon with a final update on this system, until then, stay safe out there today with the freezing rain and thank you for reading SCW!
-SA

Good evening to you from Southern Connecticut Weather!

We're currently dealing with a real mess of a system - freezing rain and drizzle is falling across most of the state and it's leading to some slick spots on the roads. If you have to head out tonight or tomorrow morning, please take it very slow on the roads and use caution when walking around on untreated surfaces as they could be very slippery!

Tonight-Tomorrow

For the rest of tonight, we'll see rain and freezing rain showers across the state, becoming more widespread in coverage as we approach tomorrow morning. As the morning goes on tomorrow we will see warmer air attempt to work into the boundary layer and turn any freezing rain over to plain rain, but with a drain of low level cold to the north this is a situation where it will be difficult to warm the surface enough to get temps over the freezing mark, especially in the valleys. This is shown well on the hourly HRRR below - note the areas of freezing rain remaining into mid-day in the Connecticut River valley and up in the quiet corner of Windham County.

Given the rain of both the liquid and freezing types that we're expecting tomorrow, it won't be a great travel day across the state, but given that it's one of the last shopping days of the season I'm sure many of you will need to be out tomorrow. If you can hold off on your travel until later in the day, you'll have a better chance of avoiding any freezing rain, but if you do need to go out in the morning keep a close eye on the car thermometer and leave plenty of space around you in the event that you lose traction. 

Sunday

Clear and cold for Sunday as high pressure briefly crosses the area before our next system. Should see highs in the mid to upper 30s and sunny skies - a great day for your last minute Christmas shopping or holiday travel!

Monday

As the title of this discussion suggests, I'm certainly dreaming of a White Christmas, and if you believe the guidance it looks like we could see one across at least part of the state for the first time since 2009. A shortwave enters the area from the west Sunday evening and interacts with low pressure off the coastline, strengthening the coastal system and eventually causing it to become the primary. While this won't be a major event, it looks like we'll see somewhere between a quarter and a half of an inch of liquid across most of the state, enough for a few inches of snow in places where it remains all snow, which will likely not be everywhere due to warm boundary layer temps.

The challenge of this forecast then is predicting where the rain/snow line will develop and how quickly it will move south and east. A couple of things influence the ultimate placement. First off, the guidance has been varying a bit on the position of the low pressure system. The Euro amplifies the system more than the GFS and so correspondingly the system is a bit further northwest; that results in warmer air being drawn into the boundary layer and so temps are a hair warmer as a result. Here's a look at surface temperature on the Euro and GFS for 4 AM Christmas morning.

The other thing we need to consider is the strength of the cold air source to our north. We have a strong high to our north that will allow us to advect cold air in at the lower levels as the storm strengthens and therefore see a "flash" from rain to snow as the rain/snow line moves southeast. We'll need to keep an eye on that high in future model runs, as if it continues to trend stronger we could see a colder solution prevail(and of course the inverse is true as well). Finally, the timing of the system is important. If we see a trend towards earlier development, that will allow for stronger cyclogenesis before it reaches our area and therefore a colder airmass - a side effect of that solution would also be higher snow totals due to a strong storm. So far, we haven't seen a defined trend in that direction, but still something to keep an eye on.

So you're probably thinking "SA, that's cool, but is it going to snow in my backyard for Christmas?" The answer depends on where in the state you are. While I do think that everyone will at least see some flakes on the back end of the system as it pulls out, accumulations will likely vary on a NW/SE gradient. If you're north and west of I84, you should be in good shape for a mostly if not all snow event, and are probably looking at an advisory level snowfall. In the area between I84 and the immediate shoreline as well as the western shoreline, you're probably looking at some rain to start, but things should flash over to snow as the storm strengthens and colder air comes in and that should be in time for at least an inch or two of snow to accumulate - a small shift colder in the guidance and you're looking at an advisory level snow as well. For the eastern shoreline and southern New London county, there will definitely be a period of rain that could use up a good portion of the QPF, but the good news is that you are going to be the last ones to have precipitation exit and thus have the longest time to take advantage of colder air moving in. As such, I think you'll at least see some flakes on your Christmas morning and if we get a good band on the backside of the system(which the models have been hinting at) it shouldn't be too hard to pick up a light accumulation. Assuming no drastic changes overnight, we'll have an official snow map out tomorrow morning.

Snow should be out of the state by 10 AM or so, leading to a mostly cloudy afternoon with seasonably cool temps in the low to mid 30s - great weather for snowball fights, igloo building, sledding, or Christmas feasting!

Tuesday-Thursday

Quiet and COLD weather for the middle of the week as arctic air advects into the state. Per the GFS and Euro, we'll see highs ~10 degrees below normal on Tuesday and Wednesday and 15 degrees below normal on Thursday, and the lows are even further below average! Here's a look at low temperature anomalies and actual readings for early Friday morning from the Euro.

We'll see if these numbers moderate somewhat as we get closer in time, but for right now it certainly looks possible that we could see our first below zero readings of the season next week. Bundle up!

Friday-Saturday

Our next system of interest is way out at the end of the forecast period. Both the Euro and GFS along with their ensembles have been steadfast in phasing the northern and southern streams in this period and creating a classic Miller A coastal storm, which are known to be some of our most prolific snowmakers. While it's far too early to talk details and specifics on dates/timing/amounts/etc because the guidance is all over the map, the possibility certainly exists for a significant system to close out next week. We will continue to keep an eye on the models and keep you informed as things start to come together with some degree of confidence. Until then, here's a peek at the GFS for this system - if you don't like what it shows, don't worry, it'll probably change in a few minutes when the 0z run comes out :)

The Dailies

Here are the dailies:

Saturday: Rain and freezing rain likely. Highs in the mid 30s(sheltered valleys) to mid 40s. Chance of precipitation is 90%. Light ice accretion possible.

Sunday: Partly sunny, with highs in the mid to upper 30s.

Christmas Day: Rain and snow likely in the morning, then mostly cloudy. Highs in the low to mid 30s. Chance of precipitation is 80%. Moderate snow accumulation possible.

Tuesday: Partly sunny, with highs in the low to mid 20s.

Wednesday: Partly sunny, with highs in the low to mid 20s.

Thursday: Partly sunny, with highs in the mid to upper 10s.

Friday: A chance of snow, otherwise, mostly cloudy, with highs in the low to mid 20s. Chance of precipitation is 50%.

Saturday: A chance of snow, otherwise, mostly cloudy, with highs in the low to mid 20s. Chance of precipitation is 50%.

More to come tomorrow morning on our Christmas snow event, until then, stay safe out on the roads tomorrow and thank you for reading SCW!
-SA

Good morning from Southern Connecticut Weather!
 
The first half of December has been wintry. As we turn toward the last two weeks of the year it is time to start thinking about the holiday season, a white Christmas, and what the pattern looks like as we sprint toward the new year! Let’s get started.
 
Grading my last outlook
The first outlook of the 2017-18 winter season was likely my best ever! Not only were the temperature predictions in line with what happened, we got plenty of winter weather events too during the second week, keeping inland areas on track to finish the month above average in snowfall. Along the shore, Bridgeport has already exceeded normal snowfall for December. If there is a place I can get dinged, it would be overall precipitation. Despite a number of events, we’re actually running about a half inch below normal so far this month. That said, we only care about snow around here, so let me have this forecasting victory. Overall, I give my outlook an A.
 
Week one—Friday December 1 to Thursday December 7
Temperatures—above average (moderate confidence) Check
Precipitation—average (moderate confidence) Check
Wintry Precipitation—below average (moderate confidence) Check
 
Week two—Friday December 8 to Thursday December 14
Temperatures—below average (high confidence) Check
Precipitation—average (low confidence) Just off
Wintry Precipitation—above average (moderate confidence) ​Check
 
Two Week Outlook Summary

 * Note—high confidence (70% “sure”), moderate confidence (45-69%), low confidence (0-44%); nothing significant (less than 1” snowfall and .25” ice)
 
Week one—Sunday December 17 to Saturday December 23
Temperatures—above average (moderate confidence)
Precipitation—below average (moderate confidence)
Wintry Precipitation—below average (moderate confidence)
 
Unfortunately for winter lovers, it looks like there is growing consensus that we see the pattern begin to relax as we head into the week before Christmas. Things look a touch warmer than normal at the beginning and end of this forecast period, with no real winter weather threats in sight.
 
Week two—Sunday December 24 to Sunday December 31
Temperatures—above average (low confidence)
Precipitation—below average (low confidence)
Wintry Precipitation—average (low confidence) ​
 
If you’ve been counting, we’ve had an awful run recently around the Christmas holiday. The Grinch has shown up the last few years, bringing well above normal temperatures or some sort of rain event. We could be heading for another Grinch Christmas.
 
​Technical Discussion
Week One 
 
The pattern is relaxing. The trough that dominated our weather during the first half of December is retreating, and in its wake we’re going to see a movement toward warmer than normal conditions. There should be a chance of snow tomorrow but it’s nothing significant. After that, we warm up until midweek when we get a brief cold shot that will put us toward more normal temperatures. That will lead us into the weekend when I expect the development of the dreaded southeast ridge, which will modify storm tracks to an unfavorable position for us and bring warmer weather. It very well may be time to pay up for our fast(ish) start to winter. 

In terms of precipitation, I think we continue the drier than normal look that we’ve seen during the first half of the month. In fact, I think that we stay dry until the very end of this forecast period, as a storm cuts to our west and brings potential rain on Saturday.
 
​We’re dry. 

Week Two
This is the week everyone probably cares about. Winter lovers everywhere are hoping for a white Christmas. Right now, it doesn’t look good. This forecast period is lower confidence than normal, but what we do see is the building of a southeast ridge, which could throw a serious wrench in hopes for snow around Christmas. 

EPS images above courtesy of weather.us.

​Folks, that ain’t a pretty look for cold and snow. It’s still doable though. The guidance has a boundary near the region next weekend that could allow a wave of low pressure to develop and ride it northeast. However, we could very well end up on the wrong side of that boundary and see rain around or on Christmas.
 
After the period, I think we go back to dry conditions, and signals are mixed about what happens between Christmas and January 1. My current guess is that we trend colder as the trough in the west moves toward the region, but there are no guarantees for any meaningful snow events. It’ll just have to be a period we watch closely. 

Above you see a more winter like pattern, with a trough moving into the region. That could give us a couple cold days depending on how long it sticks. 
​
Overall, if you love winter weather around Christmas, it may be hard to come by again this year. All hope is not lost, as we have to watch what the trends are over the next week with the upper level pattern and where the boundary between warm and cold sets up, but at this moment in time, I think warmer than normal and drier than normal will be the theme until at least Christmas, where we could see a tick back toward colder conditions. A storm looks more likely around Christmas at this time, but it could be warm. 

As 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 afternoon to you from Southern Connecticut Weather!

It’s a chilly December day across the state as we’re seeing daytime highs only topping out in the 20s today and with the brisk wind it feels like it’s in the low to mid teens across most of the forecast area. Should see this general pattern continue through the end of the week before we warm up to more seasonal levels throughout the weekend and into early next week.

Tonight & Thursday

We’re expecting a bit of light snow later tonight into tomorrow morning. Here’s our forecast snowmap.

Best chance for precipitation in the forecast period comes tonight into tomorrow morning as an Alberta Clipper system moves in from our west. This is a pretty standard clipper system that unfortunately(or fortunately, depending on if you’re a snow lover or not) will hit an area of confluence left behind by the system that exited yesterday, preventing the classic coastal amplification and redevelopment that you often see in these sorts of systems. Had we not seen yesterday's system, we’d be looking at a much more significant snow event on deck, but instead we’ll be skirted by the northern edge of some light precipitation and then see the shortwave shredded by the fast flow and dry air in place. Here’s a look at the system on the RGEM - you can see how the system comes in relatively strong and then is weakened as it crosses through Pennsylvania and New York on its way to us so by the time it reaches our longitude it is relatively weak.

Both latitude and longitude will play a role here - the storm is passing to our south so those closest to the coastline will have the best chance of getting into any banding that develops, while those further west should catch the storm while it’s a bit stronger and so could see a bit more QPF. As far as snow totals go, not expecting very much as QPF generally looks light across the state - .05” or so in most areas with .1” ish in coastal areas and further west. However, there is a decent area of lift and the column looks great for high-ratio snow, and so I’m going to be a bit more optimistic on snow totals than I normally would be in this sort of setup. As such, expecting a general coating to an inch or two across most of the state, and will highlight the south coast and especially southern Fairfield county for a localized 3” possibility given the modeled desire to favor that area and the combination of favorable latitude and longitude there.

As far as timing goes, should see light snow break out across the state in the 2-4 AM range from SW to NE, and should see snow exit by the tail end of the morning commute. Could see some slowdowns tomorrow morning on the roads, especially on the south coast, and I wouldn’t be surprised to see a school delay or two, south coast again being the favored area.

Once snow moves out, expect a similar day to today for the rest of your Thursday with clearing skies and cold temps - highs only ranging through the 20s!

Here’s the SCW impact scale for this event. Thank you all for your feedback so far - keep it coming!

Friday-Sunday
Quiet weather for the weekend and a gradual warming trend each day - highs in the 20s again on Friday but then into the low 30s on Saturday and the mid 30s on Sunday. Should see mostly sunny skies, but there is the possibility of some snow showers Friday night from a weak shortwave passing to our north and then again on Saturday if any rouge lake effect bands make their way into our area. Will add low chance pops to the forecast to cover that risk.

Monday-Wednesday

Our next possible system approaches for early next week and looks to follow a somewhat similar pattern to yesterdays system although it may be displaced a bit further north. The GFS model is fairly warm and would be a mostly if not entirely rain event, while the European model is further south and would bring more of a chance for mixed precipitation in the northern portion of the state. Timing on the solutions differs as well - the Euro makes it a Tuesday event while the GFS waits until Wednesday to pass through our area. Will add chance pops for rain and snow into the forecast and wait for the details to become clearer on this system before we speculate any further. Otherwise, near-normal temperatures expected, although the ultimate result will depend heavily on what if any storm develops.

Here’s a look at the system on both the Euro and the GFS.

The Dailies

Thursday: Snow likely early, then clearing, with highs in the mid to upper 20s. Chance of snow is 70%. Snow accumulation possible - see snowmap for details.
Friday: Mostly sunny and cold, with highs in the mid to upper 20s.
Saturday: A chance of snow showers, otherwise, partly sunny, with highs in the low to mid 30s. Chance of precipitaiton is 30%.
Sunday: Mostly sunny, with highs in the mid 30s.
Monday: Partly sunny, with highs in the low 40s.
Tuesday: A chance of rain and snow, otherwise, mostly cloudy, with highs in the low 40s. Chance of precipitation is 30%.
Wednesday: A chance of rain and snow, otherwise, mostly cloudy, with highs in the upper 30s to low 40s. Chance of precipitation is 30%.

Have a great rest of your week and thank you for reading SCW!
-SA