Good evening from Southern Connecticut Weather.
The trickiest storm of the season thus far is approaching, with a modestly high ceiling and very low floor. Looking at all the data, here's our forecast, which is fairly low confidence. We expect a minor impact event with a rain and snow system that starts tomorrow end ends on Monday.
The trickiest storm of the season thus far is approaching, with a modestly high ceiling and very low floor. Looking at all the data, here's our forecast, which is fairly low confidence. We expect a minor impact event with a rain and snow system that starts tomorrow end ends on Monday.
Above: our snowfall accumulation map. For virtually all of the southern four counties this is a low impact mostly rain event. Don't expect much if any accumulation, even if you are away from the coast.
For lower elevation northern CT, we have a 1-3" zone with most, especially in the CT River Valley, struggling to accumulate as well. Slightly cooler temperatures should allow for a minor measurable accumulation.
Our highest zone is in the NW and NE hills where 3-6" of snow is possible. Here too, we think most are on the lower end but have greater respect for the possibility that in a marginal temperature environment these areas can verify colder than current guidance suggests.
For lower elevation northern CT, we have a 1-3" zone with most, especially in the CT River Valley, struggling to accumulate as well. Slightly cooler temperatures should allow for a minor measurable accumulation.
Our highest zone is in the NW and NE hills where 3-6" of snow is possible. Here too, we think most are on the lower end but have greater respect for the possibility that in a marginal temperature environment these areas can verify colder than current guidance suggests.
Overall Setup
The general evolution of this one is reflective of the season thus far: another missed opportunity if you are a winter weather lover. We have a system to our west that will transfer energy from the Ohio Valley to off the coast tomorrow. This by itself prevents an all rain event for interior CT. However, instead of a classic nor'easter that brings snow throughout the state, the low at both the surface and aloft is unable quickly organize and intensify.
In addition to that, we have a marginal airmass at best in place, meaning that for any meaningful snow we are heavily reliant on accumulation that comes from the initial wave of precipitation that occurs tomorrow morning and early afternoon to both accumulate and cool the column/surface. That's a massive red flag and the primary reason we are more bearish on this system overall.
I'm going to do something a little different than usual forecasts and really go under the hood.
If you're one of those folks that is just looking at how much falls in your backyard or what time it starts and ends haha it's ok to skip ahead to the timing and impact section now.
Technical Discussion
If you're looking purely at the snow maps certain websites generate, you're probably wondering why we're bearish while the maps show 6+ inches for large parts of the state. Let's take a closer look at the meteorology.
Here's the latest version of the GFS, which is actually one of the more favorable solutions for a real winter storm. All the animated images below are from 1am Sunday through 1pm Monday. All images are courtesy of Tropical Tidbits.
The general evolution of this one is reflective of the season thus far: another missed opportunity if you are a winter weather lover. We have a system to our west that will transfer energy from the Ohio Valley to off the coast tomorrow. This by itself prevents an all rain event for interior CT. However, instead of a classic nor'easter that brings snow throughout the state, the low at both the surface and aloft is unable quickly organize and intensify.
In addition to that, we have a marginal airmass at best in place, meaning that for any meaningful snow we are heavily reliant on accumulation that comes from the initial wave of precipitation that occurs tomorrow morning and early afternoon to both accumulate and cool the column/surface. That's a massive red flag and the primary reason we are more bearish on this system overall.
I'm going to do something a little different than usual forecasts and really go under the hood.
If you're one of those folks that is just looking at how much falls in your backyard or what time it starts and ends haha it's ok to skip ahead to the timing and impact section now.
Technical Discussion
If you're looking purely at the snow maps certain websites generate, you're probably wondering why we're bearish while the maps show 6+ inches for large parts of the state. Let's take a closer look at the meteorology.
Here's the latest version of the GFS, which is actually one of the more favorable solutions for a real winter storm. All the animated images below are from 1am Sunday through 1pm Monday. All images are courtesy of Tropical Tidbits.
I've slowed this animated image down to make it easier to follow. The GFS has us starting out as mostly snow tomorrow morning before 7am. Even this is in dispute on the guidance. As the coastal low takes shape off the coast, you can see the warmth engulf southern CT while northern CT has a period of moderate to heavy snow. That's the key period on the guidance as that's where most of the accumulation would be likely to happen. As the storm pulls away we get colder air coming in and overnight Sunday into early Monday morning brings a little more snow.
If you look at that by itself you probably say while southern CT is cooked northern CT probably does ok. On the snow map, which uses a standard 10:1 ratio (ten inches of snow for every one inch of rain), you'd be correct.
If you look at that by itself you probably say while southern CT is cooked northern CT probably does ok. On the snow map, which uses a standard 10:1 ratio (ten inches of snow for every one inch of rain), you'd be correct.
Looking simply at the map above, you'd probably say wow, this is 6+ for most and even 8+ in the hill towns. Even Bridgeport is sporting a 4" total from this one. This is exactly the time to dig deeper.
A lot of what the GFS is selling is falling quickly in a less than dynamic storm. Let's look at a key piece of this that is often left out of discussion, the 700mb low. Again this depiction is from 1am Sunday through 1pm Monday. We are looking at the vorticity or energy at 700mb.
A lot of what the GFS is selling is falling quickly in a less than dynamic storm. Let's look at a key piece of this that is often left out of discussion, the 700mb low. Again this depiction is from 1am Sunday through 1pm Monday. We are looking at the vorticity or energy at 700mb.
What does this show? You see a fairly dynamic 700mb low with closed contours the Ohio Valley just become strung out as it crosses into the Atlantic and very close to New England. If this were developing quickly (and we had a cold high to the north), you'd get colder air advecting in aloft to allow for a colder temperature profile, and you'd also get better frontogenesis to bring heavier and more efficient snowfall. We do not have that here outside of the initial burst.
This all feeds back into temperatures, which are marginal at best. If we had a little more cooling this would be more impactful, but we're on the edge in northern CT. Again using the same time period.
As you can see, outside of NW CT temperatures are marginal to say the least. Now, exact surface temperatures are not something we tend to embrace on any given model because they all have their biases. The GFS for instance tends to be a little warmer than reality.
However, this is where soundings are critical to a forecast. They allow us to look at every layer of the atmosphere and understand not just temperature but things like moisture and lift profiles. Let's quickly look at New Haven, Hartford (City), and Bradley Airport tomorrow afternoon at 1pm.
Here is the surface depiction from the model at 1pm tomorrow. Heavy rain in much of southern CT with moderate to heavy snow in much of northern CT.
However, this is where soundings are critical to a forecast. They allow us to look at every layer of the atmosphere and understand not just temperature but things like moisture and lift profiles. Let's quickly look at New Haven, Hartford (City), and Bradley Airport tomorrow afternoon at 1pm.
Here is the surface depiction from the model at 1pm tomorrow. Heavy rain in much of southern CT with moderate to heavy snow in much of northern CT.
Let's look at New Haven first. You'll see that each of the three soundings below have some significant issues.
New Haven's issue is easy. It's too warm. It's a rain sounding throughout the column, which I've circled in red. This gives high confidence that it's plain rain in much of southern CT tomorrow, especially in coastal CT, after a possible initial burst of snow in the morning.
New Haven's issue is easy. It's too warm. It's a rain sounding throughout the column, which I've circled in red. This gives high confidence that it's plain rain in much of southern CT tomorrow, especially in coastal CT, after a possible initial burst of snow in the morning.
Hartford has a different issue. While the GFS surface depiction shows moderate to heavy snow, there is very poor lift present. While lift is better in the preceding frame (not shown here) it makes me question how long the accumulating snow window actually is for central CT. I circled lift on the left side of the image, and you will see it's weak in the DGZ, which is the prime area for efficient snowfall. You want lift to be very strong and the DGZ to be much larger than the sounding shows. I added a red line on the central image to show that it is snowing aloft and even at the surface according to this model depiction.
Weaker precipitation rates in northern CT even part of southern CT means a warmer solution.
Weaker precipitation rates in northern CT even part of southern CT means a warmer solution.
Furthest north, looking at BDL, we have the same issues. Temperatures are less of a concern here (note how it's slightly colder aloft), which means we can infer they are less of a concern in hilly sections of NW and NE CT. Usually if the CT/MA line is torching, that means warmth is reaching our higher NW and NE elevations as well, even if it's a bit more muted.
We repeat this analysis throughout the duration of the system other global models like the Euro, and at close range (inside 48 hours) we do it on the high resolution models like the HRRR and NAM too.
For this storm we come to the same conclusion: the surface depiction looks more impactful than it's likely to be because the situation is marginal. The combination of temperatures and a less dynamic storm means snow changing to rain and then back to snow for most. If either of these are slightly off it could mean more/less accumulation across much of northern CT tomorrow while much of southern CT is out of the game for anything significant regardless of what happens.
For this storm we come to the same conclusion: the surface depiction looks more impactful than it's likely to be because the situation is marginal. The combination of temperatures and a less dynamic storm means snow changing to rain and then back to snow for most. If either of these are slightly off it could mean more/less accumulation across much of northern CT tomorrow while much of southern CT is out of the game for anything significant regardless of what happens.
Timing & Overall Impact
Timing looks straightforward. Precipitation will begin between 2-6am from south to north. It may start out as some snow in southern CT but should quickly change to rain, while northern CT sees snow. Snow in northern CT changes to rain late morning into the afternoon, with the chance of things changing back to snow tomorrow night even down toward the coastline. That may be the chance to pick up accumulation there. While some guidance has snow lingering later into Monday afternoon, I think snow winds down Monday morning.
With temperatures above freezing for most during this event, roads could become slick especially under heavier snow, but I don't anticipate the same kind of road issues we saw during much colder storms earlier this month.
We don't expect wind issues or significant power outage/flooding issues. The snow is likely to be heavy wet snow, so if we end up with more accumulation there could be slightly more impact. Overall this looks minor for most, with no major issues expected Monday in southern CT and scattered delays or cancellations possible in northern CT, especially hill towns.
We will be closely watching temperatures and how quickly this organizes. We'll know if the forecast is on track pretty quickly tomorrow as we watch temperatures and observation.
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
Timing looks straightforward. Precipitation will begin between 2-6am from south to north. It may start out as some snow in southern CT but should quickly change to rain, while northern CT sees snow. Snow in northern CT changes to rain late morning into the afternoon, with the chance of things changing back to snow tomorrow night even down toward the coastline. That may be the chance to pick up accumulation there. While some guidance has snow lingering later into Monday afternoon, I think snow winds down Monday morning.
With temperatures above freezing for most during this event, roads could become slick especially under heavier snow, but I don't anticipate the same kind of road issues we saw during much colder storms earlier this month.
We don't expect wind issues or significant power outage/flooding issues. The snow is likely to be heavy wet snow, so if we end up with more accumulation there could be slightly more impact. Overall this looks minor for most, with no major issues expected Monday in southern CT and scattered delays or cancellations possible in northern CT, especially hill towns.
We will be closely watching temperatures and how quickly this organizes. We'll know if the forecast is on track pretty quickly tomorrow as we watch temperatures and observation.
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
