Good evening from SCW!
Well, it’s quite the roller coaster of weather this week, as we move from record highs yesterday to a winter storm tomorrow. While the impacts will differ across the state depending on where you are, one thing is clear; tomorrow will be a nasty day (or at least morning) of weather, and we expect impacts to travel, schools, and businesses. Let’s dive in.
The Setup
Energy currently moving over the Midwest will eventually hit blocking high pressure to the north, forcing the surface low to move to the east and transfer to a secondary low, currently projected to form just south of Long Island. This will help lock in some low level cold air at the surface, however, as the primary low continues northeast into central New England, it will bring warm air further north in the mid-levels. This sets up a wintry mix scenario for areas that are far enough north for cold air to hold on while not far enough north to be free of the mid-level warmth. Unfortunately, that zone will encompass most of our state.
Well, it’s quite the roller coaster of weather this week, as we move from record highs yesterday to a winter storm tomorrow. While the impacts will differ across the state depending on where you are, one thing is clear; tomorrow will be a nasty day (or at least morning) of weather, and we expect impacts to travel, schools, and businesses. Let’s dive in.
The Setup
Energy currently moving over the Midwest will eventually hit blocking high pressure to the north, forcing the surface low to move to the east and transfer to a secondary low, currently projected to form just south of Long Island. This will help lock in some low level cold air at the surface, however, as the primary low continues northeast into central New England, it will bring warm air further north in the mid-levels. This sets up a wintry mix scenario for areas that are far enough north for cold air to hold on while not far enough north to be free of the mid-level warmth. Unfortunately, that zone will encompass most of our state.
Above is a loop of the 18z Regional Canadian model. You can see how most areas start out as a period of snow, but the warm air quickly works in aloft and changes most spots over to sleet by the early hours of the morning, and eventually brings some plain rain to the shoreline by mid-day. When that changeover happens, along with how far north the warm air can intrude, will be the primary contributor to our accumulations of snow vs. sleet/ice vs. plain rain. Let’s take a look at some of the modeled outcomes for gradients.
Above are snapshots from the GFS, NAM, RGEM, and high-res FV3 models for 7 AM tomorrow morning. You can see that the extent of the mixing varies fairly significantly across the guidance, with the RGEM (warmest solution) bringing the mix line nearly to the MA border (and shortly after crossing it). The colder FV3 and GFS are still mostly snow in the state, while the NAM is somewhere in the middle. By this time, we’ve seen about a half of an inch of liquid across the state; if it remains all snow, we would already have 5-6” of snow on the ground by sunrise, but those areas that see mixing will see those totals reduced.
At the end of the day, model consensus is fairly strong for about an inch of liquid, meaning double digit totals are likely for those who stay all snow. That said, those areas will likely be to our north, in northern MA and into VT/NH, and I do expect our state to completely mix with sleet/freezing rain, with the potential of plain rain along the shoreline.
So how much snow will we get? Depends on the solution you believe. The warmer solutions, like the RGEM, keep most significant snow to our north, and only bring a few inches to most of our state down to little to nothing on the shoreline. The colder solutions, like the Euro, bring a warning level snowfall to our northern zones, and a solid plowable snowfall for all. Those maps are shown below – keep in mind that these are algorithms, not forecasts, but should give you an idea of the differences between the solutions.
The Forecast
This is a tricky one, since as we just saw, the small differences in modeled temperature have a substantial difference in sensible impact. While we can’t know for sure if one is more correct than the other, we can use some logic to try to come to a conclusion. Here’s what we know:
-These sorts of systems, known as South West Flow Events (SWFE’s) are routinely underestimated by the models as far as the extent of lower level cold air.
-Similarly, they often under-do the extent of the warm tongue.
-The trend over the last few cycles has gradually been warmer, though by small amounts.
-We’re expecting a fairly heavy band of snowfall to kick off the storm, which will serve to put down some quick accumulations and cool the column. If heavy rates persist, this will help to temporarily hold off mid-level warming.
Given all of that, I think a blend of the models, biasing a bit towards a warmer mid-level and a colder surface, is the sensible approach. That yields something like the map below.
At the end of the day, model consensus is fairly strong for about an inch of liquid, meaning double digit totals are likely for those who stay all snow. That said, those areas will likely be to our north, in northern MA and into VT/NH, and I do expect our state to completely mix with sleet/freezing rain, with the potential of plain rain along the shoreline.
So how much snow will we get? Depends on the solution you believe. The warmer solutions, like the RGEM, keep most significant snow to our north, and only bring a few inches to most of our state down to little to nothing on the shoreline. The colder solutions, like the Euro, bring a warning level snowfall to our northern zones, and a solid plowable snowfall for all. Those maps are shown below – keep in mind that these are algorithms, not forecasts, but should give you an idea of the differences between the solutions.
The Forecast
This is a tricky one, since as we just saw, the small differences in modeled temperature have a substantial difference in sensible impact. While we can’t know for sure if one is more correct than the other, we can use some logic to try to come to a conclusion. Here’s what we know:
-These sorts of systems, known as South West Flow Events (SWFE’s) are routinely underestimated by the models as far as the extent of lower level cold air.
-Similarly, they often under-do the extent of the warm tongue.
-The trend over the last few cycles has gradually been warmer, though by small amounts.
-We’re expecting a fairly heavy band of snowfall to kick off the storm, which will serve to put down some quick accumulations and cool the column. If heavy rates persist, this will help to temporarily hold off mid-level warming.
Given all of that, I think a blend of the models, biasing a bit towards a warmer mid-level and a colder surface, is the sensible approach. That yields something like the map below.
Along the immediate shoreline, I’m expecting two to four inches of snow and sleet, with a glaze to perhaps a tenth of an inch of ice, and an eventual changeover to plain rain. I’d expect that by the morning commute, most folks here are seeing an icy mix, which will make for slow travel, even if it’s not snowing. The cold air on the shoreline will probably hold on longer than modeled, but I would suspect that by lunchtime or so, we will be over to a cold rain in this area.
Across the interior, however, it’s a different story. The extra latitude, combined with the lack of marine influence, should keep temps colder, and allow precipitation to be mostly if not completely frozen. The further north you go, the more snow and less ice you’ll get, but the idea is the same – it’s a mess. Splitting the difference between the model camps generally suggests a solid advisory snowfall across the state, with the chance for warning level (6”+) most likely north of Hartford.
As such, I’ve gone with a general three to six inches of snow for most, followed by sleet and a glaze of ice, and have added a five to ten inch zone for the far north where I think confidence of remaining mostly snow throughout the heavy precipitation is highest. I would generally expect most in that zone to stay in the 5-8” range, but I am leaving some wiggle room up to 10” in case of either an overperforming band or colder than expected temperatures.
Winter Storm Warnings are in effect from the NWS for our northern four counties, while Winter Weather Advisories are in effect for the southern counties.
Timing
We should see snow arrive late tonight, with the leading edge of precipitation reaching the state by midnight. I’d expect snow to come in quickly once it arrives, as mesoscale guidance is in good agreement that we’ll see a heavy band to kick this event off. Snow will continue through the overnight hours, and towards sunrise, we should start to see a shift from snow to sleet and ultimately to freezing rain begin across the south. The morning commute will be messy for all areas, with snowy and icy roads in the south giving way to heavier snow up north. As the morning progresses, the mix line will move north, and plain rain will eventually make its way to the south coast. Mesoscale guidance suggests that the precipitation exits most of the state by early afternoon, and it’ll be a race between the warm air and the back of the precipitation to see if far northern areas will hang onto all snow or flip to sleet/freezing rain at the end of the storm. The evening commute should be improved from the morning one, though with cold air streaming back in after the system, expect roads (especially secondary and tertiary) to be icy and slow going throughout the evening as any melt/liquid refreezes.
Impacts
I got a new computer and don’t have the fancy impact scale graphic right now, so we’ll have to do this the old fashioned way…
Snowfall Accumulation: Moderate. Most of the state should end up with a solidly plowable snowfall, but don’t think we’ll see anything too crazy here.
Snowfall Rate: High. We should see an inch an hour or more during the heaviest snow, which for many areas, will be during peak commuting hours.
Wind: Low. Luckily, we aren’t expecting any significant winds with this event.
Power Outages: Low. If we get more freezing rain than expected, we could see some isolated outages, but I’d expect those to be few and far between.
Timing: High. With the heaviest precipitation coming during the morning commute, I expect significant impacts to schools and businesses tomorrow AM.
Road Conditions: High (Moderate on the immediate shoreline). Ice is never a good thing for the roads, and when you add heavy snow, it makes a real mess.
Overall: Moderate/High. While the totals won’t be spectacular with this storm, and it’s over quickly, the conditions tomorrow morning won’t be pretty, and we’ll likely see larger impacts to commutes and travel than we’d otherwise expect with these totals.
Bust Potential/Confidence
Overall, this is an average confidence forecast. I think we understand the storm well, and the overall model consensus on liquid is excellent. No sharp cutoffs or screw zones here, for the most part. The challenge will be determining temperature gradients both at the mid-levels and at the surface, as that is always what will ultimately determine precipitation types and thus accumulations. These systems tend to be fairly predictable, so I think I’m confident with our forecast, but I can’t help but notice the swings in outcomes still shown on the models and the resulting changes to our outcomes. I think the areas of highest bust potential are on the immediate shoreline (in both directions – could see things tick warm and see little to no snow, or a tick colder would bring 3-6” right to the coast) and far northern CT (if we see the transition quicker than expected, we’ll be closer to the 3-6” range there vs. 5-10”). I feel pretty good about the middle portion of the state, but we’ll just have to wait and see what happens!
As always, please like, share, and ask questions – I’ll be keeping an eye on our FB comments for the next few hours, so drop your questions there and I’ll do my best to get back to you. Please also send us your observations tomorrow morning, as they’re critical in knowing where the mix line is setting up and how we’re tracking vs. models and the forecast.
Thank you for trusting SCW, and enjoy the snow!
-SA
Across the interior, however, it’s a different story. The extra latitude, combined with the lack of marine influence, should keep temps colder, and allow precipitation to be mostly if not completely frozen. The further north you go, the more snow and less ice you’ll get, but the idea is the same – it’s a mess. Splitting the difference between the model camps generally suggests a solid advisory snowfall across the state, with the chance for warning level (6”+) most likely north of Hartford.
As such, I’ve gone with a general three to six inches of snow for most, followed by sleet and a glaze of ice, and have added a five to ten inch zone for the far north where I think confidence of remaining mostly snow throughout the heavy precipitation is highest. I would generally expect most in that zone to stay in the 5-8” range, but I am leaving some wiggle room up to 10” in case of either an overperforming band or colder than expected temperatures.
Winter Storm Warnings are in effect from the NWS for our northern four counties, while Winter Weather Advisories are in effect for the southern counties.
Timing
We should see snow arrive late tonight, with the leading edge of precipitation reaching the state by midnight. I’d expect snow to come in quickly once it arrives, as mesoscale guidance is in good agreement that we’ll see a heavy band to kick this event off. Snow will continue through the overnight hours, and towards sunrise, we should start to see a shift from snow to sleet and ultimately to freezing rain begin across the south. The morning commute will be messy for all areas, with snowy and icy roads in the south giving way to heavier snow up north. As the morning progresses, the mix line will move north, and plain rain will eventually make its way to the south coast. Mesoscale guidance suggests that the precipitation exits most of the state by early afternoon, and it’ll be a race between the warm air and the back of the precipitation to see if far northern areas will hang onto all snow or flip to sleet/freezing rain at the end of the storm. The evening commute should be improved from the morning one, though with cold air streaming back in after the system, expect roads (especially secondary and tertiary) to be icy and slow going throughout the evening as any melt/liquid refreezes.
Impacts
I got a new computer and don’t have the fancy impact scale graphic right now, so we’ll have to do this the old fashioned way…
Snowfall Accumulation: Moderate. Most of the state should end up with a solidly plowable snowfall, but don’t think we’ll see anything too crazy here.
Snowfall Rate: High. We should see an inch an hour or more during the heaviest snow, which for many areas, will be during peak commuting hours.
Wind: Low. Luckily, we aren’t expecting any significant winds with this event.
Power Outages: Low. If we get more freezing rain than expected, we could see some isolated outages, but I’d expect those to be few and far between.
Timing: High. With the heaviest precipitation coming during the morning commute, I expect significant impacts to schools and businesses tomorrow AM.
Road Conditions: High (Moderate on the immediate shoreline). Ice is never a good thing for the roads, and when you add heavy snow, it makes a real mess.
Overall: Moderate/High. While the totals won’t be spectacular with this storm, and it’s over quickly, the conditions tomorrow morning won’t be pretty, and we’ll likely see larger impacts to commutes and travel than we’d otherwise expect with these totals.
Bust Potential/Confidence
Overall, this is an average confidence forecast. I think we understand the storm well, and the overall model consensus on liquid is excellent. No sharp cutoffs or screw zones here, for the most part. The challenge will be determining temperature gradients both at the mid-levels and at the surface, as that is always what will ultimately determine precipitation types and thus accumulations. These systems tend to be fairly predictable, so I think I’m confident with our forecast, but I can’t help but notice the swings in outcomes still shown on the models and the resulting changes to our outcomes. I think the areas of highest bust potential are on the immediate shoreline (in both directions – could see things tick warm and see little to no snow, or a tick colder would bring 3-6” right to the coast) and far northern CT (if we see the transition quicker than expected, we’ll be closer to the 3-6” range there vs. 5-10”). I feel pretty good about the middle portion of the state, but we’ll just have to wait and see what happens!
As always, please like, share, and ask questions – I’ll be keeping an eye on our FB comments for the next few hours, so drop your questions there and I’ll do my best to get back to you. Please also send us your observations tomorrow morning, as they’re critical in knowing where the mix line is setting up and how we’re tracking vs. models and the forecast.
Thank you for trusting SCW, and enjoy the snow!
-SA
