Good evening to you from Southern Connecticut Weather!
Over the last few model cycles, some of the model guidance has tried to bring an anafrontal wave, previously modeled to slip harmlessly southeast of the area, further north and west into the state. The result, should that guidance verify, would be an accumulating snow event on Friday morning for the majority of the state. On the other hand, two models, the GFS and NAM, continue to keep the system out to sea, and would result in absolutely nothing for the forecast area. This discussion will break down the three camps of model guidance, evaluate their likelihood, and present our first call snowmap and forecast timing for this system.
The Models
Group 1: Miss
Originally, as early as 36 hours ago, this camp was the dominant solution, with all of the model guidance in good agreement on a miss to the southeast and little to no impact to the state. While the majority of guidance has trended further northwest, two models, the GFS and NAM, continue to keep the impulse that powers the wave much weaker, and as a result, the precipitation slides harmlessly out to sea. With this solution, all we’d see is some cirrus and maybe a flurry or two in the far southeast corner of the state. Pretty boring.
However, as of now, I don’t think that this solution is likely, for a couple of reasons. Firstly, the GFS and NAM are relatively poor models, with both ranking towards the bottom as far as verification scores go. Secondly, the trend with these anafrontal waves is frequently to move northwest in the final cycles leading up to the event. Thirdly, the seasonal trend this winter has been to pull events further north and west as we approach verification. And finally, they are essentially outliers. When combining these factors, I am fairly comfortable with discounting this guidance, and thus, I weight it as a twenty percent likelihood of occurring.
Here’s a look at the 18z GFS for 7 AM Friday morning. Notice how all the precipitation is confined well to the south and east of the state.
Over the last few model cycles, some of the model guidance has tried to bring an anafrontal wave, previously modeled to slip harmlessly southeast of the area, further north and west into the state. The result, should that guidance verify, would be an accumulating snow event on Friday morning for the majority of the state. On the other hand, two models, the GFS and NAM, continue to keep the system out to sea, and would result in absolutely nothing for the forecast area. This discussion will break down the three camps of model guidance, evaluate their likelihood, and present our first call snowmap and forecast timing for this system.
The Models
Group 1: Miss
Originally, as early as 36 hours ago, this camp was the dominant solution, with all of the model guidance in good agreement on a miss to the southeast and little to no impact to the state. While the majority of guidance has trended further northwest, two models, the GFS and NAM, continue to keep the impulse that powers the wave much weaker, and as a result, the precipitation slides harmlessly out to sea. With this solution, all we’d see is some cirrus and maybe a flurry or two in the far southeast corner of the state. Pretty boring.
However, as of now, I don’t think that this solution is likely, for a couple of reasons. Firstly, the GFS and NAM are relatively poor models, with both ranking towards the bottom as far as verification scores go. Secondly, the trend with these anafrontal waves is frequently to move northwest in the final cycles leading up to the event. Thirdly, the seasonal trend this winter has been to pull events further north and west as we approach verification. And finally, they are essentially outliers. When combining these factors, I am fairly comfortable with discounting this guidance, and thus, I weight it as a twenty percent likelihood of occurring.
Here’s a look at the 18z GFS for 7 AM Friday morning. Notice how all the precipitation is confined well to the south and east of the state.
Group 2: Brush
This next group represents the middle ground of the guidance. Like the first group, it keeps the system as an anafrontal wave, but brings it a little further northwest, allowing some light snow to brush eastern portions of the state. With this scenario, we’d see light snow break out across southeast portions of the state Friday morning, with a quick period of moderate snow centered around the morning commute possible. Further northwest, some light flurries or snow showers are possible, but I don’t think any accumulations would result as a result of this scenario there. Snow should wrap up by around noon under this setup, with total accumulations of a couple of inches in far SE areas, and perhaps an inch or so back to central portions of the state.
This scenario is represented by the majority of the models, including the NAVGEM, GGEM, RGEM, 4km NAM, SREFS, and JMA. Generally, in meteorology, one should trust a consensus over outliers(on either direction), and in this setup, this group of models represents the consensus. I also would generally lean towards a slightly further NW solution for the inverse of the reasons described to disprove the NAM/GFS combo, and as a result, I’m leaning heavily towards this solution, and will weight it sixty percent in the final forecast.
Here’s a look at the 18z RGEM for 7 AM Friday morning. Notice the heavier precipitation in the eastern portions of the state, with lighter snows making it back into NWCT.
This next group represents the middle ground of the guidance. Like the first group, it keeps the system as an anafrontal wave, but brings it a little further northwest, allowing some light snow to brush eastern portions of the state. With this scenario, we’d see light snow break out across southeast portions of the state Friday morning, with a quick period of moderate snow centered around the morning commute possible. Further northwest, some light flurries or snow showers are possible, but I don’t think any accumulations would result as a result of this scenario there. Snow should wrap up by around noon under this setup, with total accumulations of a couple of inches in far SE areas, and perhaps an inch or so back to central portions of the state.
This scenario is represented by the majority of the models, including the NAVGEM, GGEM, RGEM, 4km NAM, SREFS, and JMA. Generally, in meteorology, one should trust a consensus over outliers(on either direction), and in this setup, this group of models represents the consensus. I also would generally lean towards a slightly further NW solution for the inverse of the reasons described to disprove the NAM/GFS combo, and as a result, I’m leaning heavily towards this solution, and will weight it sixty percent in the final forecast.
Here’s a look at the 18z RGEM for 7 AM Friday morning. Notice the heavier precipitation in the eastern portions of the state, with lighter snows making it back into NWCT.
Group 3: Direct Hit
While the majority of models leave the system as an anafrontal wave, two, the UKMET and EURO, tilt the trough negative enough to allow the system to re-form into a full on coastal storm as the impulse that causes the anafrontal wave to move further north catches the trough and spawns a new system. The system would move much further inland under this camp than the middle camp, and would result in warning level(6”+) snows for eastern portions of the state, with accumulating snows reaching all the way across the state. Under this scenario, we’d see snow break out overnight Thursday, and we’d be seeing moderate to heavy snow across most of the state, especially in eastern areas, throughout the morning commute and into the early afternoon, where it would taper off.
While I don’t think this scenario is impossible, and in fact it would be the closest match to how this system was initially modeled last week when it appeared on the models, the fact that only two pieces of guidance support it(Although, they are the #1 and #2 models by verification scores), I don’t think it’s likely, as it’s too radical a shift at such a short range and it would represent a fundamental overhaul of the synoptics of the system. However, the fact that the Euro and UKMET, our two highest scoring models, show this outcome, is enough to make me raise an eyebrow. As such, we weighted it twenty percent in the forecast, essentially, canceling out the twenty percent weight of the miss.
Here’s the 12z UKMET for 7 am Friday morning. Look how far NW precipitation makes it!
While the majority of models leave the system as an anafrontal wave, two, the UKMET and EURO, tilt the trough negative enough to allow the system to re-form into a full on coastal storm as the impulse that causes the anafrontal wave to move further north catches the trough and spawns a new system. The system would move much further inland under this camp than the middle camp, and would result in warning level(6”+) snows for eastern portions of the state, with accumulating snows reaching all the way across the state. Under this scenario, we’d see snow break out overnight Thursday, and we’d be seeing moderate to heavy snow across most of the state, especially in eastern areas, throughout the morning commute and into the early afternoon, where it would taper off.
While I don’t think this scenario is impossible, and in fact it would be the closest match to how this system was initially modeled last week when it appeared on the models, the fact that only two pieces of guidance support it(Although, they are the #1 and #2 models by verification scores), I don’t think it’s likely, as it’s too radical a shift at such a short range and it would represent a fundamental overhaul of the synoptics of the system. However, the fact that the Euro and UKMET, our two highest scoring models, show this outcome, is enough to make me raise an eyebrow. As such, we weighted it twenty percent in the forecast, essentially, canceling out the twenty percent weight of the miss.
Here’s the 12z UKMET for 7 am Friday morning. Look how far NW precipitation makes it!
The Forecast
Here’s our forecast snowmap for this event.
Here’s our forecast snowmap for this event.
Across most of the state, we’re expecting a relatively minor event, with some flurries and snow showers on Friday morning resulting in up to an inch of snow. While the accumulation will generally be light, the timing will be impactful, as snow will fall right in the middle of the morning rush hour, causing some travel delays and potential school delays.
As you move east, the snow amounts begin to increase. In the eastern third of the state or so, we’re expecting a steadier period of light to moderate snow to break out Friday morning, and the end result will be one to three inches of snow across this zone. Precipitation could start as rain, especially along the coastline, but rain should change over to snow in time for the morning commute. Travel impacts are likely in this zone for the morning commute, and I expect to see some school delays and possibly a cancellation or two. In far eastern portions of the state, I have included a zone of 2-4” of snow to account for the probability of a heavier band moving into this area, but it’s also just as much a CYA in case we do see a shift towards scenario 3 above.
Timing
3-5 AM Friday: Snow breaks out from SE to NW, potentially starting as rain in southern and eastern portions of the state before changing to snow.
5-9 AM: Snow persists in the eastern portions of the state, while in western areas, flurries and snow showers are the general theme of the morning. Some impacts to the morning commute are likely.
9 AM – 12 PM: Snow begins to taper off from west to east, with snow showers lingering into early afternoon in eastern areas.
Impacts
We’ll keep watching the models and hopefully, by tomorrow morning, we’ll be able to provide an update on which camp we’re trending towards on our Twitter and Facebook. We’ll have a final snowmap and forecast discussion tomorrow evening, and rapid fire coverage on Friday morning if needed. Considering the short lead time and the fact that this system “appeared out of nowhere”, please share this discussion with family and friends to spread awareness about the upcoming system!
Thanks for reading SCW and have a great night!
-SA
As you move east, the snow amounts begin to increase. In the eastern third of the state or so, we’re expecting a steadier period of light to moderate snow to break out Friday morning, and the end result will be one to three inches of snow across this zone. Precipitation could start as rain, especially along the coastline, but rain should change over to snow in time for the morning commute. Travel impacts are likely in this zone for the morning commute, and I expect to see some school delays and possibly a cancellation or two. In far eastern portions of the state, I have included a zone of 2-4” of snow to account for the probability of a heavier band moving into this area, but it’s also just as much a CYA in case we do see a shift towards scenario 3 above.
Timing
3-5 AM Friday: Snow breaks out from SE to NW, potentially starting as rain in southern and eastern portions of the state before changing to snow.
5-9 AM: Snow persists in the eastern portions of the state, while in western areas, flurries and snow showers are the general theme of the morning. Some impacts to the morning commute are likely.
9 AM – 12 PM: Snow begins to taper off from west to east, with snow showers lingering into early afternoon in eastern areas.
Impacts
- A light to moderate snowfall across most of the state, with plowable amounts possible in eastern areas.
- A tricky morning commute on Friday, especially along I395 and eastern parts of I95 where steadier snow will fall.
- Some school delays and maybe a cancelation or two are possible.
- Should the system become more significant(Scenario 3), some downed trees and power outages would be possible due to the fact that this will be a heavy wet snow.
We’ll keep watching the models and hopefully, by tomorrow morning, we’ll be able to provide an update on which camp we’re trending towards on our Twitter and Facebook. We’ll have a final snowmap and forecast discussion tomorrow evening, and rapid fire coverage on Friday morning if needed. Considering the short lead time and the fact that this system “appeared out of nowhere”, please share this discussion with family and friends to spread awareness about the upcoming system!
Thanks for reading SCW and have a great night!
-SA
