Happy New Year’s Eve from Southern Connecticut Weather​!

I am working feverishly on completing my next two week outlook, which I plan releasing tomorrow. Snow and cold lovers...it will be a must read.  

​In the meantime, here is a brief update on the week ahead. After a very active period with numerous precipitation events, the next 7 days look to be quiet, as high pressure takes control for the majority of the period.

The latest GEFS run showing a below normal period of precipitation for the next 7 days. 

In terms of temperatures, the mega torch that prevailed during part of November and all of December is over for the foreseeable future. A pattern change is afoot. Connecticut will see temperatures near normal temperatures this weekend, and it will feel far more seasonable. A shot of arctic air is looking more likely for Monday and Tuesday of next week. It will finally feel like winter. In fact, the latest run of the European model shows most of Connecticut with a period of temperatures below 10 degrees on Tuesday morning. We'll continue to watch and see if that happens. The story of the week will be the arctic blast, bringing the coldest weather of the season so far.

Above you can see the arctic chill coming through GFS projections of temperatures at 1pm on New Year's Day and Tuesday January 5th. The real cold will be short lived, but will herald the arrival of a regime change. Images courtesy of Weatherbell Analytics. 

The dailies:
New Year’s Eve: Partly cloudy day and seasonable. Partly to mostly cloudy evening as you countdown to 2016. Lows in the upper 20s to low 30s. 

New Year’s Day: Mostly sunny early with increasing clouds and a chance of snow showers or snow squalls in the evening. Snow squalls could produce a quick coating. Snow showers are most likely to be confined to northern CT. Highs in the mid 30s to near 40 in the cities. Lows in the mid 20s to low 30s. Chance of snow 20%. 

Saturday: Snow showers possible, mainly areas north. Otherwise, mostly sunny, with highs in the mid to upper 30s. Lows in the mid 20s to low 30s. Chance of snow 10%. 

Sunday: Mostly sunny. Highs in the mid 30s to near 40 in the cities. Lows in the low to mid 20s.  

Monday: Partly sunny and much colder, with snow showers and squalls possible. Highs in the low to mid 20s. Breezy conditions making it feel like the upper teens during the day. Nighttime lows in the teens. There could be some single digits in colder spots late Monday night into early Tuesday morning. Chance of snow 20%

Tuesday: Mostly sunny. Highs in the mid to upper 20s. Lows in the low to mid 20s.  

Wednesday: Sunny with moderating temperatures. Highs in the upper 30s to low 40s. Lows in the mid to upper 20s. 

Thank you for reading. Please do not forget to like this post, like us on Facebook and follow us on Twitter @SouthernCTWX. Thanks!

An image of all the traffic hazards earlier this morning, courtesy of WFSB.​

While the bulk of the precipitation may have ended, we are still seeing plain rain moving and developing from the south and west. Temperatures south of the parkway and 95 are above freezing, along with a number of locations in central Connecticut, but there seems to be residual sleet still covering the ground, so beware of slick conditions.

Precipitation should be cleared out by the PM commute. 

A quick glance backward
All of the reports have not yet come in, but this looked like a run of the mill SWFE that was minor in the scheme of things but had a higher impact for those on the roads this morning due to the timing of the storm. The accumulations that have come in so far seem to be within our forecast range.

When thinking of the models that performed well, you have to give a nod to the NAM, HRRR, and European model, which were all warmer and showed a more accurate onset of precipitation. The NAM and HRRR are higher resolution short range models, and the Euro is our bulwark global model. The loser was clearly the GFS, which was the coldest model and wrong on how warm the system would be. Looking at this kind of data helps us make better forecasts in the future. 

Snowfall/sleet totals reported to the National Weather Service (note that southern CT totals have not been updated yet):

...LITCHFIELD COUNTY...
   3 SSE ROXBURY          1.0   724 AM 12/29  FACEBOOK


...HARTFORD COUNTY...
   3 E SOUTHINGTON        2.0   700 AM 12/29  COCORAHS
   1 NW COLLINSVILLE      1.4   700 AM 12/29  COCORAHS
   EAST FARMINGTON HEIG   1.3   708 AM 12/29  TRAINED SPOTTER
   3 SSE WEST HARTFORD    1.1   700 AM 12/29  COCORAHS
   2 SE ENFIELD           1.0   700 AM 12/29  COCORAHS
   1 ENE NORTH GRANBY     1.0   745 AM 12/29  COCORAHS
   3 SW CENTRAL MANCHES   1.0   700 AM 12/29  COCORAHS


...TOLLAND COUNTY...
   SOMERS                 1.1   939 AM 12/29  NONE
   TOLLAND                1.0   821 AM 12/29  NONE
   NNW STAFFORDVILLE      1.0   500 AM 12/29  COCORAHS


...WINDHAM COUNTY...
   1 SW EAST KILLINGLY    0.9   700 AM 12/29  COCORAHS
   2 NE MOOSUP            0.5   600 AM 12/29  COCORAHS

Looking forward
Expect a soggy day that gradually improves as the precipitation clears out. Take it easy on the roads and sidewalks, though temperatures will continue to rise into the upper 30s to mid 40s by the afternoon. Expect foggy spots later this evening, and a cloudy day tomorrow with temperatures in the low to mid 40s. 

We will resume our regular forecaster discussions showing you the week ahead soon. 

Thank you!
Finally, although I have forecasted many weather events in the past, this is my first time doing it on this scale. It was truly an honor being the source of information that reached tens of thousands of people the last few days, and being relied upon for updates. It is something we all take seriously at SCW, and we do our very best to provide you with the information needed to make an informed decision without hype. It was a pleasure to do our “live chat” where I was around to answer your burning questions and discuss weather generally before the event began, all the way until 5am! I hope to do many more of those in the future. 

Thanks for reading, sharing, and following us the last few days! All of our success is because of you! We cannot continue to grow without your support. If you haven’t done so already, please like us on Facebook and follow us on Twitter @SouthernCTWX. I will be contacting folks that entered our photo contest by tonight. 

This tired forecaster is signing off to get some sleep. Take care.  

-DB (with additions from TW)

Our first winter storm of the season will affect Connecticut beginning later tonight.  It will not be a major winter storm, but for some, especially those living away from the coast, it might be a good idea to refresh those winter driving skills, especially for those traveling late at night or early in the morning.  This discussion will focus mainly on the winter storm and not as much on the long term, but I do want to cover a few points as we head into the long term, and cover those with New Year's travel plans.

First off, for tonight's storm: Precipitation will overspread the state before midnight.  The feeling is that precipitation should begin as snow everywhere, since the dew points are low and the column is cold (minus the surface, but that should be overcome by evaporative cooling).  The changeover to rain will probably progress more west to east than south to north.  The reasoning for this is that we have high pressure to the North, which will probably keep winds Easterly or Northeasterly, and not incorporate much of a fetch off Long Island Sound.  Warm air may travel more south to north in the upper levels.  As the surface low passes well to the west of the area, southwesterly or southerly winds will be established aloft.  Based on the above, here is the general thinking (no drastic changes from before):

Along the south coast, although a burst of snow could develop tonight, temperatures at the surface will be above freezing and will not fall to freezing.  Warmer air moving in aloft will quickly change precipitation over to rain before any accumulations.

In Central Connecticut, snow will develop tonight and could accumulate, mixed with sleet at times, up to an inch or two.  After that, a brief period of freezing rain is possible with a tenth of an inch of ice or less.​

Northern Connecticut will be split into two groups, with I 91 being the dividing line.  In Northwestern Connecticut, snow and sleet could accumulate an inch or two, before changing to freezing rain.  A tenth or two of an inch (0.1-0.2") of ice is then possible before changing over to rain.  For Northeast Connecticut, the snow and sleet will hold on longer, and could accumulate 2-4".  This area should see a changeover directly from snow and sleet to freezing rain, with little or no ice accumulation.  (The surface may actually warm before the upper levels in this region, due to their distance from the low).

By mid-morning, the entire state should have changed over to rain.  Rain should be heavy or even briefly very heavy at times during the morning hours.  Rain winds down from Southwest to Northeast between noon and 4 PM.

New Years outlook.. For those with plans heading into New Years, here is a general outlook of what to expect. A frontal system will bring a shot of rain mostly late Wednesday night into very early Thursday morning.  A secondary cold front may touch off a few showers later in the day on Thursday, especially to the Northeast.  These showers will likely fall as snow or a snow/sleet mix, but will be very light and inconsequential.  High temperatures on Thursday will range from the mid 40s to the low 50s.
For New Year's Day, much cooler air gets ushered into the region on Northwest breezes.  Highs will range from the mid 30s to low 40s.  A rogue snow flurry is also possible in the Northwest hills, from some blowoff from Lake Effect streamers.

Long Range Discussion: The pattern continues to be in a state of change, and is rapidly changing into a pattern more favorable for winter-like temperatures, and eventually, significant winter storms.  The first week of January should feature chilly temperatures, with perhaps a bit of a moderation in the 2nd week of January, then we could plunge into the freezer after that! Initially, the trough orientation favors most of the cyclogenesis to be out to sea, east of the area.  However, as we head deeper into January, by the 2nd or 3rd week of the month, this changes, and there could be more of a pattern supporting East Coast cyclogenesis... stay tuned!

-GP and thanks to TW for the map!

Good evening to you from Southern Connecticut Weather!

Yesterday, Spencer explained the general setup could put Connecticut in a place to receive snow, sleet, freezing rain, and rain early next week. Another day has passed, and we are closer to Connecticut’s first significant winter weather event of the season. How significant remains to be seen. 

This update will provide a brief update on where computer guidance stands, and, more importantly, what we think is the most likely scenario over the next 72 hours. We will put out our first call map, showing our thoughts on snow and ice accumulations across the state, tomorrow afternoon. 

Recap
For those that are just beginning to pay attention to this winter weather threat, the system that is coming is the result of two important things working in tandem to provide wintry precipitation. First, a strong surface low forming in Texas, and second, a strong Canadian high-pressure system that passes to our north.

Image courtesy of Weatherbell Analytics 

​On this latest run of the GFS, you can see the high pressure to our north and low pressure system to our west. This will serve to hold in the cold air, at least initially, as precipitation and warm air aloft from the southwest arrives in association with an area of low pressure that passes to our west. Guidance has shown a secondary area of low pressure forming off the coastline, which could also assist in driving precipitation and colder air into the region.

The Guidance
At the start of this event, guidance continues to show the potential for a period of snow throughout the state, when temperatures both at the surface and throughout the column of air aloft are below freezing. 

As was said yesterday, the strength and placement of the high to our north, the push of warm air over the surface and upper levels, and the onset time of precipitation will be critical to determining who gets what. The guidance has begun settling down on large scale changes to the time period, such as whether a storm will actually form, but small scale changes are the ones to watch. Location and timing will have a substantial impact on what we experience. 

Let’s look at the GFS model quickly and the changes we still see between two runs. On the first run, you will see that the midday run (12z) has a slower onset of precipitation which results in less snow before the air aloft warms to bring sleet that transitions to a period of freezing rain or drizzle. In the latest run, onset occurs sooner, resulting in a significant thump of snow before a change to sleet and freezing rain/drizzle before the precipitation ends. This looks like a situation where, as usual, areas along the coast change over the fastest and are most likely to change to rain.

12z (midday) GFS run for 1am on Tuesday (left) and 7am Tuesday (right)

Latest run of the GFS (18z) for the same time period. Note how the precipitation overtakes the state earlier, and the heavier snow in northern sections of Connecticut at 7am on Tuesday. This is only one run of one model, but this continues the idea of a snow to mixed precipitation to rain scenario. 

The GFS is one of the colder models showing this evolution, earlier the European model came in a bit colder than its prior overnight run, but showed more sleet than snow before a change to plain rain for much of the state. 
​
The Forecast – Latest Thoughts

There remains a significant amount of uncertainty in the forecast—especially with regard to final accumulations. I believe that there will be a storm, but timing and location are critical and we want to see more consistency in guidance before being able to make a deterministic forecast. 
Today, the models have trended a bit colder, and when factoring in the tendency for SWFE (Southwest Flow Events) to warm quickly in the midlevels, faster precipitation onset, and surface temperatures staying colder than projected generally, especially in interior Connecticut, we believe a winter weather event is likely, and that this will not be a system consisting of mostly rain. 
Precipitation is expected at this time to begin very late Monday evening and lasting into early Tuesday afternoon. The Tuesday AM commute is likely to be impacted. 

Takeaways

• Connecticut’s first legitimate winter weather event is becoming more likely on Monday evening into Tuesday
• Small changes in high pressure strength, location, and secondary low development that substantially impact on our final forecast remain possible
• Sleet remains the most significant winter weather threat, but with the models trending slightly colder today there could be a period of accumulating snow at the start. How significant this period is remains unknown
• Interior locations are most favored to receive a significant event, though everyone in the state could begin with frozen precipitation
  ​
  

As mentioned at the start of this post, we will release our first call accumulations map by tomorrow afternoon, with another update tomorrow evening with a more detailed look at what we expect.

Thank you for reading. Please like, share, and follow us on Facebook and Twitter @SouthernCTWX as we provide continuing updates on this winter weather threat. 

Until tomorrow, thanks for reading SCW!
-DB 

​A very good Christmas evening to you from Southern Connecticut Weather!

We have been experiencing what will almost certainly be the warmest December in recorded history, and given the record highs of the past several days, wintry weather seems to be the furthest thing from possible reality at the moment. However, lurking for several days on the model guidance, and now moving into the crosshairs of this forecaster, lays a complex system that will approach early next week and bring a wide variety of precipitation types to the area. In this first Storm Speculation of the season, we will break down the setup and the various model forecasts, and offer some first thoughts on possible outcomes, but due to with regard to the evolution of complex features, we will hold off on a definitive forecast map and timeline until Sunday morning, consistent with the ~48 hour timeline that we have used in the past.
 
The Setup
 
This system comes together as a result of two parts; a strong surface low forming in Texas, as well as a strong Canadian high-pressure system that passes to our north. The timing of these two features works out so that as the low is moving northward and advecting both precipitation and warm air into our region, the high is moving eastward and funneling colder air down into the Northeast. Here’s a look at the surface temperature departures from normal on the GFS on Monday evening, where you can see clearly the impacts of the high pressure on our corner of the country, as we are near normal while areas to our south-west are well above normal.

​This high acts as a psuedoblock for the system, forcing it out under the high and eventually forming a secondary area of low pressure off the coastline, which turns into a coastal system. The strength and placement of the high as the low approaches will determine at what point the low has weakened enough that warm air will no longer continue to push north and secondary development will begin. This will have a substantial effect on our sensible weather, as it will determine both surface temperatures and temperatures aloft, which will determine whether we see snow, sleet/freezing rain, or just a cold rain.
 
Here’s a look at the initial setup aloft on the GFS at hour 60, or 1 AM Monday morning. Notice the low-pressure system moving north out of eastern Texas, and notice the high pressure system arcing over the Great Lakes. 

The timing differences between the various model guidance with the ejection of the shortwave from the south and the placement of the Canadian high will be crucial in determining the overall setup. A faster ejection of the low should result in the low approaching the high while it is still anchored in a further westerly position, and as a result, will allow for colder air to persist and the system to be shoved out to our east before it approaches our latitude. This will keep our forecast area on the cold side of the system, and will result in a solution where most of the precipitation is frozen. A slower ejection, however, will result in the high beginning to slide to the east before the storm can reach it, allowing the storm to continue as a stronger primary low pressure system into the Great Lakes and flood the upper levels with warmer air, the end result being a brief period of snow before a flip to sleet, freezing rain, and rain. Models have not yet been able to nail down consistency on this evolution, and this kind of setup can be unusually difficult to project from this far out.
 
To show this, here are two sets of images from the day’s four GFS runs. The first set shows the placement of the low pressure system and the high pressure system at 7 PM Monday evening, and the second set shows precipitation type at 7 AM Tuesday morning. Notice the correlation between low placement/high position and the precipitation type!

And here are the corresponding surface reflections.

Quite the difference! On the mid-day run(12z), the GFS has rain all the way up to the northern border of the state, while on the overnight run(0z), the GFS has the entire state in moderate to heavy snow! This difference can be traced back to the images above. On the 0z run, you can see that the high pressure is stronger and further southwest, squashing the storm and it’s associated warm air further south and a secondary is beginning to form(which can be seen in the precipitation type image), while on the 12z run, you can see that the high pressure is much weaker and further to the northeast, allowing the storm a slot to cut to the west of us and flood our area with warmth, since the high is no longer in a position to fight it with cold air. The 6z and 18z runs fall somewhere in the middle between those two extremes as is typical with the models.
 
In what is a somewhat rare occurrence in meteorology, all three major global models, along with their ensemble sets, have been in relative consensus with the overall synoptic, or large scale, concept of this system for several days now. However, what they have been waffling around on is the timing of the system and the placement of the high, and as you can see from the images above, even minor changes can make a big impact. As such, this remains a low-confidence forecast until we begin to see some more consensus on the guidance.
 
The Forecast – First Thoughts

Here’s a graphic that breaks down our first thoughts with how we see the system playing out. For a somewhat more detailed explanation of possible outcomes, read on, otherwise, this graphic gives you a good idea of where we stand at the moment.

​There’s quite a bit of uncertainty with the forecast, most of which relates to the timing differences shown through the model images above. We had been seeing a trend towards an earlier ejection and thus a colder solution, but the mid-day runs reversed that trend in a rather dramatic fashion, although the evening GFS did cool back down somewhat. While it’s too early to get into specifics, I’m leaning slightly towards the warmer solutions at this time, taking into account the trends, the antecedent airmass being extremely warm, and the general tendencies of these SWFE’s(Southwest Flow Events) to always be a bit warmer in the mid-levels than expected and thus the sleet line is closer than you think. I’m also leaning towards a slightly faster scenario, given that SWFE’s often come in faster than modeled and that the general trend over the last couple of days has been to speed up the system. Finally, I’m thinking that we will see low-level cold hang on for longer than expected, considering that models frequently under-estimate the power of surface level cold, especially in the interior. As such, I think a period of sleet and freezing rain is likely, especially away from the immediate coastline.
 
Precipitation will begin to move in from the southwest on Monday evening. I expect all areas of the state to begin as snow, but areas along the coastline should quickly switch over to a combination of sleet and/or freezing rain as warm air moves in aloft. Further north, I expect this changeover to be more gradual, and thus we could see some light to moderate snow accumulations, especially in the northwest and northeast hills, before the warm air works in aloft and the interior also flips over to sleet. By daybreak, I think enough warm air will have worked in for the coastline and southern areas to change over to rain, but it’s likely that interior areas will still remain below freezing and some icing is definitely possible. Regardless, I think that Tuesday morning’s commute will be rather tricky, especially away from the immediate shoreline. Precipitation will move out Tuesday morning as all rain, and roads should be markedly improved by the evening commute as warmer air finally moves in at the surface and temps can move into the mid to upper 30s, melting any ice that has accreted on roads.
 
At this time, we’re holding off on releasing a snow/ice map due to the uncertainties that lie in both the arrival of the system and the changeover to sleet and then rain. Considering that precipitation rates will be on the order of .1” liquid per hour around the time of the changeover, that means that even a delay of two hours, which is nothing in the weather world, would be a 2” difference in the forecast. Considering the spread on model guidance and the fact that we are still 3 days out from the start of the event, we will hold off on releasing a first call map until most likely Sunday, with an outside shot at a map tomorrow evening if we find consensus on guidance within the next couple of model cycles. Either way, we will have another update tomorrow evening with more info and a look at the latest models and trends for you all.
 
Finally, on behalf of the SCW forecasting team, I’d like to wish all of our readers a very Merry Christmas! We hope you enjoyed this beautiful day with loved ones and were able to celebrate as you wished ;)
 
Until tomorrow, thanks for reading SCW!
-SA