Good afternoon from Southern Connecticut Weather.
It's time.
A major winter storm is already delivering snow, ice, and rain to the southern Plains and south. With extreme cold continuing to pour into the country, there are southern locations that are snowing in the teens and single digits!
This unusually cold and expansive air mass will heavily influence our potential snowfall, with the cold essentially enhancing the potential for a high impact storm with big snow totals across Connecticut.
So what is this that you're hearing about mixing?
Let's dive in.
It's time.
A major winter storm is already delivering snow, ice, and rain to the southern Plains and south. With extreme cold continuing to pour into the country, there are southern locations that are snowing in the teens and single digits!
This unusually cold and expansive air mass will heavily influence our potential snowfall, with the cold essentially enhancing the potential for a high impact storm with big snow totals across Connecticut.
So what is this that you're hearing about mixing?
Let's dive in.
Above: the final call forecast map. There were a lot of competing ideas that could have changed things, like the risk of mixing along the coast or the aggressive nature of some high resolution models. In the end, however, a broad 12-20" works. We did introduce special text for the NW and NE hills, which may have some areas with over 20" due to the long moisture train potentially maximizing accumulation there.
Overall Setup
Nothing has changed. I'll repeat it once more: extreme temperature regimes can trigger extreme atmospheric responses. Today we see this in action with the winter storm continuing to move through the south.
Overall Setup
Nothing has changed. I'll repeat it once more: extreme temperature regimes can trigger extreme atmospheric responses. Today we see this in action with the winter storm continuing to move through the south.
Above: national radar image of our winter storm spanning New Mexico to Virginia. The storm will continue to grow in geographic scale.
We have cold from the north, and we have moisture coming from the Gulf overrunning the Arctic dome. The scale of the cold allows for maximum moisture to be wrung out as the warmer air lifts over the cold, condenses into clouds, and falls as precipitation.
We have cold from the north, and we have moisture coming from the Gulf overrunning the Arctic dome. The scale of the cold allows for maximum moisture to be wrung out as the warmer air lifts over the cold, condenses into clouds, and falls as precipitation.
Above: a visible satellite image of the storm.
Because of the 500mb interaction between northern and southern lobes of energy, this storm will grow, spawn a coastal low, and ride up the coast. While the low overall will present like a nor'easter, the overrunning setup and displaced 850 and 700mb lows will make this more of a supercharged southwest flow event. This is critical to the question of mixing.
Because of the 500mb interaction between northern and southern lobes of energy, this storm will grow, spawn a coastal low, and ride up the coast. While the low overall will present like a nor'easter, the overrunning setup and displaced 850 and 700mb lows will make this more of a supercharged southwest flow event. This is critical to the question of mixing.
You can see this in the GFS depictions above. In the top image you see what happens at the surface. A low develops, slides off the coast, and stays to our south. However, if you look at the second image, which looks at 700mb, you will see that this section of the storm is a little further west. That looks slight, but it's significant, as it forces warmer air aloft from the southwest. This erodes the cold aloft, but not before an epic battle between warmth and cold which effectively wrings out even more moisture.
Regardless of whether sleet moves into the coast or not, the overall evolution is the following:
The storm rolls in as all snow because it is well below freezing below the entire column. The lift over the Arctic dome of cold will produce intense snowfall rates for a significant period of time. As the mix line gets closer to the coast, the more fluffy snow may turn heavier and wetter. Any mixing would be most likely as the intensity of the snow diminishes and the region may enter a pseudo dry slot as the 500mb evolution holds back the storm and likely wrings out more snow on Monday that is higher ratio before departing.
Regardless of whether sleet moves into the coast or not, the overall evolution is the following:
The storm rolls in as all snow because it is well below freezing below the entire column. The lift over the Arctic dome of cold will produce intense snowfall rates for a significant period of time. As the mix line gets closer to the coast, the more fluffy snow may turn heavier and wetter. Any mixing would be most likely as the intensity of the snow diminishes and the region may enter a pseudo dry slot as the 500mb evolution holds back the storm and likely wrings out more snow on Monday that is higher ratio before departing.
The Forecast
If you are a new follower, we grade our big forecasts for accountability and accuracy. We are graded on what the final forecast is, with snow accumulated weighted 2x to account for its importance.
Timing
There's still a little uncertainty over end time, but overall there is a much better handle on things now for a moderate confidence forecast.
Snow should begin from SW to NE between 7-11am. That means if you are in SW CT expect snow on the earlier side of this range and if you are in NE CT expect it during the latter side of this range. If you're in the middle of the state, be prepared for the middle of the range. While you may be able to get around for a short period after it begins snowing, you probably want to be at your location no more than an hour after the snow starts where you are. The combination of deep cold and fast onset of moderate to heavy snow means that road and visibility conditions will quickly deteriorate. Don't go driving unless you need to.
The afternoon is really where things start to get intense. There is high confidence in high snowfall rates. This system will be able to effectively produce snow due to an unusually large dendritic growth zone--basically the place where the atmosphere produces its snowflakes most efficiently. Sometimes you need to be on the razor's edge to get the best banding, and that is what may happen here as the mix line tries to move into coastal CT. High resolution models show an extended period of snowfall rates above an inch of snow per hour.
If you are a new follower, we grade our big forecasts for accountability and accuracy. We are graded on what the final forecast is, with snow accumulated weighted 2x to account for its importance.
Timing
There's still a little uncertainty over end time, but overall there is a much better handle on things now for a moderate confidence forecast.
Snow should begin from SW to NE between 7-11am. That means if you are in SW CT expect snow on the earlier side of this range and if you are in NE CT expect it during the latter side of this range. If you're in the middle of the state, be prepared for the middle of the range. While you may be able to get around for a short period after it begins snowing, you probably want to be at your location no more than an hour after the snow starts where you are. The combination of deep cold and fast onset of moderate to heavy snow means that road and visibility conditions will quickly deteriorate. Don't go driving unless you need to.
The afternoon is really where things start to get intense. There is high confidence in high snowfall rates. This system will be able to effectively produce snow due to an unusually large dendritic growth zone--basically the place where the atmosphere produces its snowflakes most efficiently. Sometimes you need to be on the razor's edge to get the best banding, and that is what may happen here as the mix line tries to move into coastal CT. High resolution models show an extended period of snowfall rates above an inch of snow per hour.
Above 12z HREF probabilities of 1" per hour rates tomorrow afternoon. That's as close to high confidence as you can get.
One of the big questions is whether or not we mix.
Yes. There is likely going to be some sleet.
Now lets put that into context. It's not a guarantee. Global models like the GFS and Euro have generally kept the mix line either offshore or just onshore. The NAM however, which is very good at identifying warm noses (warm air aloft) historically, tries to punch the mix line into CT. We give it some respect here.
We're not as concerned that this will significantly cut back on snow totals. Why? Because the initial burst of snow is extremely potent, even bringing a chance of thundersnow.
Here's the 12z high resolution NAM.
Yes. There is likely going to be some sleet.
Now lets put that into context. It's not a guarantee. Global models like the GFS and Euro have generally kept the mix line either offshore or just onshore. The NAM however, which is very good at identifying warm noses (warm air aloft) historically, tries to punch the mix line into CT. We give it some respect here.
We're not as concerned that this will significantly cut back on snow totals. Why? Because the initial burst of snow is extremely potent, even bringing a chance of thundersnow.
Here's the 12z high resolution NAM.
If you want all snow, that's the worst case scenario, as the warmth aloft punches the mix line all the way into northern CT.
Now look at the same model, six hours later.
Now look at the same model, six hours later.
The mix line still reaches CT, but it's more suppressed. That tells me that the model is having trouble resolving the extent of the warm nose.
In addition, look at the frames before mixing. That is a hellacious thump of snow that falls. While other models bring the mix line close to the state, none are as aggressive as that one run. As a result, we think that while sleet does occur late on Sunday, it happens in coastal CT, and maybe gets a little further north after the main batch of precipitation is done. This is critical, because it means that it would not significantly impact snowfall amounts. Southern CT is still likely to see a high end, double digit snowfall.
After the main batch pulls away around midnight Monday, we will watch for regeneration on Monday as the storm tries to pull away. That means that Monday is likely to be snowy with lighter, but higher ratio snow. Don't think the storm is over because things get light or stop late Sunday night and early Monday morning. Accumulating snow should be done by 5pm Monday.
In addition, look at the frames before mixing. That is a hellacious thump of snow that falls. While other models bring the mix line close to the state, none are as aggressive as that one run. As a result, we think that while sleet does occur late on Sunday, it happens in coastal CT, and maybe gets a little further north after the main batch of precipitation is done. This is critical, because it means that it would not significantly impact snowfall amounts. Southern CT is still likely to see a high end, double digit snowfall.
After the main batch pulls away around midnight Monday, we will watch for regeneration on Monday as the storm tries to pull away. That means that Monday is likely to be snowy with lighter, but higher ratio snow. Don't think the storm is over because things get light or stop late Sunday night and early Monday morning. Accumulating snow should be done by 5pm Monday.
Snow Accumulation
I've already talked about the depth of the cold, but just to visualize it one more time, here are soundings for Hartford (city) and Bridgeport during the peak of the system tomorrow afternoon. This strongly suggests very heavy snow. Note the sounding for Bridgeport with an ever so slight warm nose. Sometimes you have to get close to the mix line to get the best rates. These soundings could produce upwards of 2" per hour.
I've already talked about the depth of the cold, but just to visualize it one more time, here are soundings for Hartford (city) and Bridgeport during the peak of the system tomorrow afternoon. This strongly suggests very heavy snow. Note the sounding for Bridgeport with an ever so slight warm nose. Sometimes you have to get close to the mix line to get the best rates. These soundings could produce upwards of 2" per hour.
That is a cold powder look right there.
With this in mind, we kept the 12-20" zone for the state. Some may wonder why the zone is so large, but this is really to account for the variation in banding that we can see in high end storms. The likelihood that this is a general southwest flow event reduces the chances that we see extreme variation like we do in pure nor'easters but there will be some that get 12" and there will be someone a town or two over that gets 16". That's just how it goes.
Now, just because it says 20", that doesn't mean that everyone should be thinking 20" in their backyard. If you get 12" that's not a bust. I'd consider anything under 10" a bust in a location, and anything over 24" a "positive bust". Someone in the NW and NE hills may get close to 24" as the persistent easterly moisture train piles up against the hills, hence the wording, but everything in the world would need to break favorably for long duration snow for that to be widespread around CT.
For lower totals, which are most likely in coastal CT and especially SE CT, sleet and or dry slotting would need to arrive earlier than expected or last longer than expected. Again, not expecting that to happen here, but coastal areas know the deal--you're usually the "low" spot. The forecast is lower confidence here.
Wind & Power Outages
We still do not expect significant wind, though some guidance has turned a little more breezy. We probably don't see wind gusts higher than 20-35mph, which is no big deal with regard to power outages, but would impact visibility and the wind chill during this event.
What we will be watching for however is the potential for heavier wet snow along the coast should that mix line get closer to us late Sunday. Without strong wind heavy wet snow probably isn't too big a deal for power outages, but out of an abundance of caution, we will forecast a low chance of outages in that region. Nothing to be too concerned about, but just as folks should be during every big storm, be prepared, especially if you are in a place that loses power easily. There will be long duration cold after this storm.
Overall, power outages should be isolated.
Overall Impact
This is likely to be a high end event statewide. Nothing significant has changed from where our thoughts were during the first call. There will be heavy snow, high end accumulation, and cold temperatures and wind chills throughout the storm. The mix line getting close or into CT doesn't substantively change snow totals as we forecast at this time, but it would make shoveling a lot harder. Road conditions will be severely impacted from Sunday through Monday, with residual impacts possible into Tuesday. Everything is likely to be closed on Monday, with a chance of delays and cancellations on Tuesday.
It's not the biggest storm we've ever had but it's legitimately high end. Take it seriously and prepare yourself for the cold that is reinforced in its wake.
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
With this in mind, we kept the 12-20" zone for the state. Some may wonder why the zone is so large, but this is really to account for the variation in banding that we can see in high end storms. The likelihood that this is a general southwest flow event reduces the chances that we see extreme variation like we do in pure nor'easters but there will be some that get 12" and there will be someone a town or two over that gets 16". That's just how it goes.
Now, just because it says 20", that doesn't mean that everyone should be thinking 20" in their backyard. If you get 12" that's not a bust. I'd consider anything under 10" a bust in a location, and anything over 24" a "positive bust". Someone in the NW and NE hills may get close to 24" as the persistent easterly moisture train piles up against the hills, hence the wording, but everything in the world would need to break favorably for long duration snow for that to be widespread around CT.
For lower totals, which are most likely in coastal CT and especially SE CT, sleet and or dry slotting would need to arrive earlier than expected or last longer than expected. Again, not expecting that to happen here, but coastal areas know the deal--you're usually the "low" spot. The forecast is lower confidence here.
Wind & Power Outages
We still do not expect significant wind, though some guidance has turned a little more breezy. We probably don't see wind gusts higher than 20-35mph, which is no big deal with regard to power outages, but would impact visibility and the wind chill during this event.
What we will be watching for however is the potential for heavier wet snow along the coast should that mix line get closer to us late Sunday. Without strong wind heavy wet snow probably isn't too big a deal for power outages, but out of an abundance of caution, we will forecast a low chance of outages in that region. Nothing to be too concerned about, but just as folks should be during every big storm, be prepared, especially if you are in a place that loses power easily. There will be long duration cold after this storm.
Overall, power outages should be isolated.
Overall Impact
This is likely to be a high end event statewide. Nothing significant has changed from where our thoughts were during the first call. There will be heavy snow, high end accumulation, and cold temperatures and wind chills throughout the storm. The mix line getting close or into CT doesn't substantively change snow totals as we forecast at this time, but it would make shoveling a lot harder. Road conditions will be severely impacted from Sunday through Monday, with residual impacts possible into Tuesday. Everything is likely to be closed on Monday, with a chance of delays and cancellations on Tuesday.
It's not the biggest storm we've ever had but it's legitimately high end. Take it seriously and prepare yourself for the cold that is reinforced in its wake.
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
