Good evening from Southern Connecticut Weather.
It's a cold night across Connecticut, and we're about 24 hours before the start of our first significant winter storm in quite some time. That means it's time for a final call forecast and as it has been in recent years, this one is tricky. Let's dive in.
It's a cold night across Connecticut, and we're about 24 hours before the start of our first significant winter storm in quite some time. That means it's time for a final call forecast and as it has been in recent years, this one is tricky. Let's dive in.
Above: our final call snow map. We considered taking the numbers down in the shoreline zone because of the risk of warming, but decided to hold with our forecast. The only changes are a slight expansion of the 4-8" zone northward, and explicitly calling for a gradient distribution in the coastal zone. Areas right on the water run the risk of being at the lowest range of the snowfall, and perhaps even a little lower, while inland areas will be closer to 6-8" inches. Again, literally a few miles in a town can make the difference between 3-4" and 7-8" of snow.
Overall Setup
Just a brief recap here. We have a storm in the south that is quickly moving east that will begin turning up the eastern US in the next 24 hours. While earlier in the week there were questions about track, that is settled now. It will slide under the coast, south of New England. That puts us in the game for snow.
It gets complicated because there are essentially two parts of the system. The first is effectively the lead wave we see over the southern US. That will cross New England tomorrow and early Sunday and bring our initial burst of snow. If that were the only piece, we'd see a lower end event because the lead wave is weak and moving fast.
However, there is another piece of vorticity that will try to catch up and phase with this lead wave on Sunday. That allows for the intensification and slowing of the overall storm. The faster that interaction happens, the longer accumulating snow falls and the colder the system is. That's critical to higher end snowfall potential.
While yesterday the trend was toward a weaker and warmer system, today's trend has been toward a faster interaction of the two pieces and a colder system. This is extremely close.
Overall Setup
Just a brief recap here. We have a storm in the south that is quickly moving east that will begin turning up the eastern US in the next 24 hours. While earlier in the week there were questions about track, that is settled now. It will slide under the coast, south of New England. That puts us in the game for snow.
It gets complicated because there are essentially two parts of the system. The first is effectively the lead wave we see over the southern US. That will cross New England tomorrow and early Sunday and bring our initial burst of snow. If that were the only piece, we'd see a lower end event because the lead wave is weak and moving fast.
However, there is another piece of vorticity that will try to catch up and phase with this lead wave on Sunday. That allows for the intensification and slowing of the overall storm. The faster that interaction happens, the longer accumulating snow falls and the colder the system is. That's critical to higher end snowfall potential.
While yesterday the trend was toward a weaker and warmer system, today's trend has been toward a faster interaction of the two pieces and a colder system. This is extremely close.
Above is the latest GFS and you are looking at the 500mb vort forecast from basically now through early Monday morning. You can pretty easily see the first wave move over (at the surface it's south) the region late Saturday and early Sunday, and then another big piece of vorticity move under the region on Sunday. You can see how it spins up a relatively strong system east of New England quickly. The faster that happens, the colder and snowier the storm is Sunday after the initial wave brings a quick but intense burst of snow later Saturday and early Sunday.
Below is what this ends up looking like at the surface, zoomed into our area. Since earlier the timing has tried slowing down a little, but we know that these systems tend to start earlier and leave later. You see an intense burst of snow late tomorrow into early Sunday, with snow slacking until the second vort starts to really get the low going. That in between period is where it will be warmest. The shorter the time, the more impactful the storm at the coast.
Below is what this ends up looking like at the surface, zoomed into our area. Since earlier the timing has tried slowing down a little, but we know that these systems tend to start earlier and leave later. You see an intense burst of snow late tomorrow into early Sunday, with snow slacking until the second vort starts to really get the low going. That in between period is where it will be warmest. The shorter the time, the more impactful the storm at the coast.
Final Forecast
Those that have followed us for years know that we grade ourselves when it comes to these forecasts based on the factors we forecast.
Timing
Timing has been more tricky today after looking rock solid for the last few days. Most of Saturday still looks fine in Connecticut. We expect snow to begin from SW to NE between 4pm and 8pm. It should start out light but fairly quickly become heavy during the nighttime and early morning hours. In fact, the worst of the storm is now expected to take place between about 10pm and 4am. This is the critical part for the accumulation forecast for the shoreline which I'll get into later.
By around sunrise, we should be staring down something like a lull. This is where if there's real mixing at the immediate shoreline it takes place. With lighter rates, the column at the coast would warm. However, by late morning the second vort is likely already interacting with the first, and we get a significant drain of cold into the state even to the shoreline. Through the day we would get progressively colder with snow all the way to the coast. Once again, if the system is weaker, the warmth remains at the coast.
Snow ends Sunday evening from west to east.
Wind/Power Outages
We haven't talked much about this, but it's a pretty windy storm. With the gradient between a developing coastal low and cold high pressure to the north, there will be wind that will gust between 25-40 mph. The windiest conditions will obviously be at the shoreline. With the potential for heavy wet snow, that increases the chance for outages. Overall however, the wind isn't anything novel to us, so scattered outages are the greatest likelihood.
Snowfall Accumulation
For years we have rolled snake eyes for a big storm. This one is right on the cusp of a major snow event. The trend today has been toward a colder and more snowy system, right in the snowfall range we posted last night. As a result, we feel a little more confident in our snowfall ranges and zones.
For inland CT, we haven't talked much about you. This one seems locked. A good bit of the snow accumulation comes from the initial wave tomorrow into early Sunday, and you are cold enough for all snow to continue into the warmest part of the day Sunday morning and of course as temperatures crash Sunday afternoon and evening. With the second vort, your chances of higher end snow also increase the faster that takes over.
Just looking at the latest Euro and NAM guidance, the trend has been toward a faster interaction throwing back cold conveyor belt snows (strong banding) into part of the state Sunday afternoon. The best chance of this happening is in NE CT, closest to the low, but we know the drill with NW CT having elevation enhanced snowfall as well. If anyone ends up close to a foot, it's most likely in those hill towns. This is a widespread 6-12" of snow, and the ceiling is a touch higher if the low continues trending stronger earlier.
The shoreline zone is very tough, but here's the thing: even in the shoreline zone we're really only talking about places within about 5-10 miles of the coast, and if we're being really honest, it's an even smaller zone. We've said it before and will say it again. You may very well be on Woodward Avenue in South Norwalk with 3-4 inches of glop while just a few miles inland at Norwalk hospital folks are frolicking in a half foot of snow.
The key time period is the initial burst of snow Saturday night into early Sunday. If that produces, our map will verify nicely. If that initial burst fails to cool the column near the shoreline it's going to be hard (but not impossible) to meet the 4" minimum we put out. The thing that gives us a little more confidence in more than an inch of slush is the timing. This burst will be falling during the nighttime hours.
The mixing is most likely later Sunday morning as we stare down a relative lull. Temps probably warm and that's where I know folks will try to cancel the storm. However, the cold push looks real on the guidance and makes synoptic sense late morning into afternoon and evening. By Sunday evening even the shoreline should be below freezing and in the 20s.
The trend has been colder. Let's take a look at the last few runs of some guidance.
The first is the Euro which is almost certainly way too warm but worth posting because even this gets plowable snow south. This is Sunday morning around 7am before temperatures crash.
Those that have followed us for years know that we grade ourselves when it comes to these forecasts based on the factors we forecast.
Timing
Timing has been more tricky today after looking rock solid for the last few days. Most of Saturday still looks fine in Connecticut. We expect snow to begin from SW to NE between 4pm and 8pm. It should start out light but fairly quickly become heavy during the nighttime and early morning hours. In fact, the worst of the storm is now expected to take place between about 10pm and 4am. This is the critical part for the accumulation forecast for the shoreline which I'll get into later.
By around sunrise, we should be staring down something like a lull. This is where if there's real mixing at the immediate shoreline it takes place. With lighter rates, the column at the coast would warm. However, by late morning the second vort is likely already interacting with the first, and we get a significant drain of cold into the state even to the shoreline. Through the day we would get progressively colder with snow all the way to the coast. Once again, if the system is weaker, the warmth remains at the coast.
Snow ends Sunday evening from west to east.
Wind/Power Outages
We haven't talked much about this, but it's a pretty windy storm. With the gradient between a developing coastal low and cold high pressure to the north, there will be wind that will gust between 25-40 mph. The windiest conditions will obviously be at the shoreline. With the potential for heavy wet snow, that increases the chance for outages. Overall however, the wind isn't anything novel to us, so scattered outages are the greatest likelihood.
Snowfall Accumulation
For years we have rolled snake eyes for a big storm. This one is right on the cusp of a major snow event. The trend today has been toward a colder and more snowy system, right in the snowfall range we posted last night. As a result, we feel a little more confident in our snowfall ranges and zones.
For inland CT, we haven't talked much about you. This one seems locked. A good bit of the snow accumulation comes from the initial wave tomorrow into early Sunday, and you are cold enough for all snow to continue into the warmest part of the day Sunday morning and of course as temperatures crash Sunday afternoon and evening. With the second vort, your chances of higher end snow also increase the faster that takes over.
Just looking at the latest Euro and NAM guidance, the trend has been toward a faster interaction throwing back cold conveyor belt snows (strong banding) into part of the state Sunday afternoon. The best chance of this happening is in NE CT, closest to the low, but we know the drill with NW CT having elevation enhanced snowfall as well. If anyone ends up close to a foot, it's most likely in those hill towns. This is a widespread 6-12" of snow, and the ceiling is a touch higher if the low continues trending stronger earlier.
The shoreline zone is very tough, but here's the thing: even in the shoreline zone we're really only talking about places within about 5-10 miles of the coast, and if we're being really honest, it's an even smaller zone. We've said it before and will say it again. You may very well be on Woodward Avenue in South Norwalk with 3-4 inches of glop while just a few miles inland at Norwalk hospital folks are frolicking in a half foot of snow.
The key time period is the initial burst of snow Saturday night into early Sunday. If that produces, our map will verify nicely. If that initial burst fails to cool the column near the shoreline it's going to be hard (but not impossible) to meet the 4" minimum we put out. The thing that gives us a little more confidence in more than an inch of slush is the timing. This burst will be falling during the nighttime hours.
The mixing is most likely later Sunday morning as we stare down a relative lull. Temps probably warm and that's where I know folks will try to cancel the storm. However, the cold push looks real on the guidance and makes synoptic sense late morning into afternoon and evening. By Sunday evening even the shoreline should be below freezing and in the 20s.
The trend has been colder. Let's take a look at the last few runs of some guidance.
The first is the Euro which is almost certainly way too warm but worth posting because even this gets plowable snow south. This is Sunday morning around 7am before temperatures crash.
By itself folks would be tempted to cancel the storm, but let's look at the trend. It has been colder and stronger.
This is the last three high resolution NAM runs today during the heavy initial burst. It has trended colder and stronger.
This is the last three high resolution NAM runs today during the heavy initial burst. It has trended colder and stronger.
Now for the GFS. The GFS was once the warmest and weakest model, but while the trend is subtle, it's likely a colder look early Sunday which is important because the GFS often has a warm surface bias.
Your eyes may be glazing over at this point, but it's important to lay this all out so you understand what we're following and the meteorology of why we think this isn't a complete bust for the shoreline zone.
Overall Impact
A weekend storm automatically reduces impact as most aren't on the roads for work or school. We expect the worst of the storm to take place overnight Saturday into Sunday. Schools should be fine Monday as we expect the snow to be done by Sunday evening.
We expect a moderate to high impact storm however. With heavy wet snow and wind, outages should be scattered. High snowfall totals inland should give us our biggest storm in a few years. At the shoreline, while the overall snowfall totals are still in question, we think it will be plowable and even a few miles from the immediate coastline, this is a significant snowfall. Driving conditions will not be great much of the weekend, and we should watch for the potential of a flash freeze later Sunday afternoon.
Our first significant winter storm in quite some time is expected tomorrow and Sunday. No matter how it turns out, it's a sign of things to come...
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
A weekend storm automatically reduces impact as most aren't on the roads for work or school. We expect the worst of the storm to take place overnight Saturday into Sunday. Schools should be fine Monday as we expect the snow to be done by Sunday evening.
We expect a moderate to high impact storm however. With heavy wet snow and wind, outages should be scattered. High snowfall totals inland should give us our biggest storm in a few years. At the shoreline, while the overall snowfall totals are still in question, we think it will be plowable and even a few miles from the immediate coastline, this is a significant snowfall. Driving conditions will not be great much of the weekend, and we should watch for the potential of a flash freeze later Sunday afternoon.
Our first significant winter storm in quite some time is expected tomorrow and Sunday. No matter how it turns out, it's a sign of things to come...
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
