Over the weekend, modeling continued to vary, but the general trend was west, bringing a more significant impact to the state in the form of rain and snow. The stronger system also allowed this to trend into more of a snow event, with dynamic cooling bringing a heavy wet snow event for all. We reached the peak of the west trend at yesterdays 12z runs, where most modeling was so far west that most of the state saw mostly rain, but the 0z and todays 12z suite has slowly shifted back east to near a benchmark track, which shifts the heaviest precipitation a little east, and at the same time, works colder air into our region as we are further west of the storm, bringing higher snow amounts back to the region.
Modeling is now in relative agreement on a storm passing on top of or just west of the 40/70 benchmark, starting most of the state as rain except for far interior areas, and then, as the low bombs out and brings in cold air, flipping all areas to snow from NW to SE. The warm ocean will have an influence here, but given that modeling usually overestimates coastal impacts, I don’t think it’ll have much impact on totals outside from right on the beaches to maybe a mile inland or so. Otherwise, a general NW to SE gradient looks to be in effect here, relating to when the event changes over to snow. Models all in good agreement on this gradient.
What models are not in agreement over is the exact track and temperatures, as well as to a lesser extent, the amount of QPF that we have to work with. Let’s look at the latest guidance one by one and break down what solution it would have for our area, and then we’ll talk about what we’re weighting and why.
To start us off, here’s a gallery of the NAM, GGEM, GFS, and UKMET’s MSLP positions, all for 7 PM Wednesday night. We can’t include the EURO here due to copyright restrictions, but it’s similar to the GFS, perhaps a hair west of it.
Modeling is now in relative agreement on a storm passing on top of or just west of the 40/70 benchmark, starting most of the state as rain except for far interior areas, and then, as the low bombs out and brings in cold air, flipping all areas to snow from NW to SE. The warm ocean will have an influence here, but given that modeling usually overestimates coastal impacts, I don’t think it’ll have much impact on totals outside from right on the beaches to maybe a mile inland or so. Otherwise, a general NW to SE gradient looks to be in effect here, relating to when the event changes over to snow. Models all in good agreement on this gradient.
What models are not in agreement over is the exact track and temperatures, as well as to a lesser extent, the amount of QPF that we have to work with. Let’s look at the latest guidance one by one and break down what solution it would have for our area, and then we’ll talk about what we’re weighting and why.
To start us off, here’s a gallery of the NAM, GGEM, GFS, and UKMET’s MSLP positions, all for 7 PM Wednesday night. We can’t include the EURO here due to copyright restrictions, but it’s similar to the GFS, perhaps a hair west of it.
ACCUMULATING SNOW EXPECTED FOR THE ENTIRE STATE ON WEDNESDAY, LEADING TO MAJOR IMPACTS ON THANKSGIVING TRAVEL.
Good evening to you from Southern Connecticut Weather!
As we’ve been talking about for almost a week now, a coastal storm is expected to develop in the gulf tomorrow and come up the coastline, passing near the 40/70 benchmark on Wednesday and bringing significant QPF to the state, with quite a bit of that being in the form of snow due to strong dynamics and a fresh source of cold air from a front coming in from the west. This event will produce accumulating snow for the entire state, and in the process, thoroughly mess up thanksgiving travel.
This discussion is broken into two parts: The first breaks down the models and provides technical discussion; the second is the actual forecast and impacts. If you’re interested in the science, read on, otherwise, skip down towards the end of the discussion for the map, forecast, timing, and impacts. We’ve bolded where you should join us again, look for it right below the snowmap.
In terms of models for this event, we’ve had an interesting progression over the last several days. Modeling was previously in relatively good agreement in having this event pass well to our east, bringing no impact to the region. However, a few days ago, we began to see the EURO model bringing the event west, introducing some interaction between the northern and southern streams and as a result bringing the storm further west as well as making it stronger. The EURO continued as the western outlier for several runs before the rest of the guidance began to catch on Thursday and Friday, bringing the event closer to the coast and introducing precipitation into the forecast. Here’s the GFS for 0z Friday and 0z Saturday for this event, showing the shift west(Notice it's not even on the map on Friday it's so far east!)
Good evening to you from Southern Connecticut Weather!
As we’ve been talking about for almost a week now, a coastal storm is expected to develop in the gulf tomorrow and come up the coastline, passing near the 40/70 benchmark on Wednesday and bringing significant QPF to the state, with quite a bit of that being in the form of snow due to strong dynamics and a fresh source of cold air from a front coming in from the west. This event will produce accumulating snow for the entire state, and in the process, thoroughly mess up thanksgiving travel.
This discussion is broken into two parts: The first breaks down the models and provides technical discussion; the second is the actual forecast and impacts. If you’re interested in the science, read on, otherwise, skip down towards the end of the discussion for the map, forecast, timing, and impacts. We’ve bolded where you should join us again, look for it right below the snowmap.
In terms of models for this event, we’ve had an interesting progression over the last several days. Modeling was previously in relatively good agreement in having this event pass well to our east, bringing no impact to the region. However, a few days ago, we began to see the EURO model bringing the event west, introducing some interaction between the northern and southern streams and as a result bringing the storm further west as well as making it stronger. The EURO continued as the western outlier for several runs before the rest of the guidance began to catch on Thursday and Friday, bringing the event closer to the coast and introducing precipitation into the forecast. Here’s the GFS for 0z Friday and 0z Saturday for this event, showing the shift west(Notice it's not even on the map on Friday it's so far east!)
First, the 12z NAM. The NAM has consistently been the eastern outlier on this event, being weak and unorganized as a result of missing the phase between the northern and southern streams and as a result having a strung out system with little QPF to work with. The run is quite cold though as a result of being further east and bringing less of the warm sector into the state, and as a result, it is the snowiest solution for those areas that would have temp issues on other models, that being SECT. The NAM begins as snow in all areas except for possibly beginning as a little light rain on the coastline, and stays as snow throughout the entire event. Light precip would break out over the course of Wednesday morning, with the heaviest rates being during the afternoon into evening hours. By 1 AM Thursday morning, precip has exited the state mostly because of the weaker event leading to less wraparound precipitation. Total QPF is .5”-1.25” from NW to SE, all of which falls as snow except for a start as rain in coastal sections. Verbatim, the NAM is a 6-8” snowstorm for NW areas, increasing to 8-12” in SE areas. Here are images of the NAM’s estimated precipitation types (We don’t use these when forecasting because they can be somewhat inaccurate, but for a simple visual representation, they are a good display tool) at 7 AM, 1 PM, 7 PM, and 1 AM Thursday, along with a total QPF map.
Next, the 12z GFS. The GFS is the closest to the consensus right now with a track right over the benchmark, and has been relatively consistent for this event for the past several runs. The model has much stronger phasing than the NAM, but does not bring the system as far west as some of the earlier EURO runs due to a faster southern stream acting as a kicker and ejecting out the low to the east. It’s warmer though, as the storm comes closer to the coast, and as a result, most areas start off as some rain aside from interior hills before a changeover occurs NW to SE over the afternoon, and by 1 PM Wednesday, most of the state is heavy snow. Snow also lasts longer into the night because of more mature wraparound. Total QPF is .75-1.25” almost due west to east, and total snowfall is in the 6-10” range statewide, with a little less right on the coastline. Here are the same 5 images from the NAM, but for the GFS. The 12z GEFS mean agrees with the GFS, and is perhaps a hair SE of it.
Continuing our move west, we next come to the 12z GGEM. The 12z GGEM carries a track similar to the 12z GFS, perhaps a hair west, but is much warmer in the midlevels and at the surface as a result of tracking the mid level low centers further north and therefore introducing mixed precipitation and rain into much of the state, especially in southern areas. While the model does have a warm bias and therefore we are inclined to discount its temperatures, we are taking notice of it as a possible solution that can occur. Verbatim, the GGEM would start pretty much everyone as rain before a quick changeover Northern areas and a much more drawn out one in southern areas. It would have a general 6-8” snowfall in the northern areas, and much less towards the coastline, with probably less than 2” at the beaches, especially SE areas. It’s a marginal solution, and we aren’t giving it a lot of weight as a result, but it’s a way that this system can bust on the warmer side and therefore it’s worth pointing out. It’s also got a good amount of wraparound snow, which is where the more marginal areas would get their limited accumulations. Again, here are our 5 images from the GGEM.
Next up is the 12z EURO. We legally can’t post images of the EURO because it’s a paid service, but we can tell you what it’s got, so let’s do that J. The 12z EURO, after being a western outlier the last several runs, has shifted east towards the consensus, and now tracks a little west of the benchmark, but with a very strong storm, bringing quite a bit of QPF to the region. The EURO is cooler than its 0z runs, but warmer than the GFS, so southern areas would start as rain before flipping to snow in the afternoon as the day goes on. The EURO has quite a bit of QPF associated with it, meaning that the areas which stay all snow would see over 10” verbatim, mainly the NW hills. Coastal areas would start as rain before flipping to dynamically impacted heavy snow later in the day, and while not ringing up the blockbuster totals, would still result in several inches of snow for all. The EURO also introduces the possibility of mixed precipitation in eastern areas that see mid level warmth infused, primarily in the form of sleet east of around I91 or so. This is certainly a possibility and something to keep an eye on, but the possibility of sleet is relatively low considering right now the EURO is one of the only models bringing it in. Not including it in the forecast, but we’ll keep an eye on it. EURO also is aggressive with back end precipitation, allowing snow to persist for most of the overnight. EURO Ensembles are similar to the operational, although a bit cooler, which would mean a little more snow in those coastal areas.
Finally, we have the 12z UKMET. The UKMET is an outlier in having a strong tucked in low close to the coast, flooding the midlevel’s with warm air and producing a ton of rain/sleet across the region with little to no snow except for far NW areas. As of right now, it’s a significant outlier, and considering the general east trend, we are tossing it for the purpose of the forecast, although we’ll mention it here just to cover all the bases. It’s the biggest way that this storm could melt down and result in mostly rain for us, but as of right now, it’s a low probability scenario. Here’s a map of 850 mb temps from the UKMET, showing the vast intrusion of mid level warmth and rain as a result.
Finally, we have the 12z UKMET. The UKMET is an outlier in having a strong tucked in low close to the coast, flooding the midlevel’s with warm air and producing a ton of rain/sleet across the region with little to no snow except for far NW areas. As of right now, it’s a significant outlier, and considering the general east trend, we are tossing it for the purpose of the forecast, although we’ll mention it here just to cover all the bases. It’s the biggest way that this storm could melt down and result in mostly rain for us, but as of right now, it’s a low probability scenario. Here’s a map of 850 mb temps from the UKMET, showing the vast intrusion of mid level warmth and rain as a result.
As far as the other guidance goes, SREFS are clustered in two camps, one that is a warmer and weaker solution, the other an all out snow bomb with 10”+ for all. Mean is on the BM. RGEM looks like the NAM, but it’s at the very end of it’s range and as a result will not be heavily weighted. JMA similar to those as well. We are not weighting any of this guidance due to notorious unreliability at these ranges.
So, what guidance are we weighting in this forecast? The EURO and GFS are the two middle ground solutions here, and as a result, we will give both fairly high weight, with a 50% weight to the EURO/EUROens and 30% to the GFS/GEFS. We will assign 10% weight to the GGEM and NAM as outliers, and will discount the UKMET entirely. When we put it all together, we get this map.
So, what guidance are we weighting in this forecast? The EURO and GFS are the two middle ground solutions here, and as a result, we will give both fairly high weight, with a 50% weight to the EURO/EUROens and 30% to the GFS/GEFS. We will assign 10% weight to the GGEM and NAM as outliers, and will discount the UKMET entirely. When we put it all together, we get this map.
If you’re scrolling down from the top looking for impacts, join us again here.
We’re forecasting one to three inches of snowfall in the SE corner of the state, two to five inches for the majority of the coastline, four to eight inches for most of the interior, and six to ten inches in the NW hills. In general, we went towards the more conservative side of the forecast, considering we’re still 2 days out and there’s several ways this can trend into a lesser event, either too far to the east and limiting QPF or too far to the west and bringing in warmth. If modeling holds or becomes more optimistic on amounts tomorrow, we will likely issue an updated map tomorrow evening raising totals, and likewise, if it becomes less aggressive, we will lower totals or hold with this map for a final map. This map is slightly lower than the model consensus, so if the models remain exactly the same, we’ll probably nudge up slightly tomorrow afternoon. As always, exact totals will end up being determined by mesoscale banding and timing differences, and some areas will bust high and some low, but for the most part, this is a good starting point.
Timing: Most modeling is in relatively good agreement as far as timing goes; although there are some minor differences, which could influence start and end times. For the most part, the mornings commute looks to be OK, with skies likely dry or perhaps some light rain or snow falling. Do not make the mistake though that it is OK to head to work or school, because precipitation arrives with a vengeance from SW to NE throughout the course of the morning on Wednesday, and by noon or so, most areas are seeing moderate to heavy precipitation. Northern interior areas should start as snow from the start, while southern areas likely start as a mix or rain, before changeover takes place from northwest to southeast over the course of the early afternoon. By the time the afternoon commute rolls around; pretty much everywhere should be seeing snow, with heavy snow quite possible in many areas. The afternoon commute will be nothing less than a disaster, with heavy snow and exceptionally heavy traffic due to the thanksgiving travel rush. Conditions will not begin to improve until after midnight, and it may be until Thursday morning before all of the roads are back to semi-normal conditions.
We highly recommend travelling tomorrow to your thanksgiving plans if at all possible, but if you must travel on Wednesday, try to leave as early in the day as possible and expect major delays, poor conditions, and dangerous driving conditions. Have an emergency kit in your car with warm clothes, food and water, and a fully charged cell phone, and be prepared to deal with accidents and spinouts if they come up. Stick to major roads, which will be better plowed if possible, and don’t be above pulling over if conditions get too dangerous for you to handle. Better to be late for thanksgiving than not make it at all because of an accident that could have been avoided by waiting.
Air travel is also likely to be impacted. In general, the earlier in the day your flight is on Wednesday, the better chance you’ve got to get out OK, but it’s possible that airlines will make pre-emptive cancellations and flights earlier in the day will be impacted as well. Thursday should be OK for the most part, although residual delays and cancellations can be expected.
Many schools are closed for Wednesday, but those that are open certainly could be impacted either in the terms of a closure or early dismissal, depending on timing shifts over the next few runs and the whims of each individual district.
Bust potential: For the interior, bust potential is low with this event, as all guidance is in good agreement. For the coastline, bust potential is moderate, and it comes down to how models are estimating temperatures and track vs. reality. A little warmer than forecast, and we see mainly rain at the coastline, a little cooler, an all snow event. The current forecast takes a middle ground. A solution like the UKMET, bringing all rain for all, or like the JMA, which fringes NW areas and lowers accumulations for all due to less QPF, is possible, and would result in a more spectacular bust of the forecast to the low side, but the odds of that are low, likely less than 10%. Similarly, we could see something like the ARW and SREF members have which is a full out snow bomb with a western track and cold temps and be looking at widespread 12”+ amounts, but this is also comparatively low, likely less than 10%. Overall, forecasters confidence is moderate with this event.
To summarize: Precipitation moves in Wednesday morning, mainly as snow north and rain south, before changing over to all snow throughout the afternoon. Major travel impacts for the Thanksgiving period, with possibly treacherous conditions on roads, especially later in the evening. Storm moves out Wednesday night, with total accumulations of 4-8” interior, 3-6” coastline, and 2-5” SECT.
We are in storm mode here at SCW, with a forecaster on duty around the clock watching the models and updating as needed. We will have a small update tomorrow morning, with our final call package and map tomorrow at around the same time as tonight’s update. We will be updating rapid fire during the event on Wednesday on Facebook and Twitter, and will post significant updates to the site as well. Don’t forget to follow us @SouthernCTWX if you haven’t already and like us on Facebook at www.facebook.com/southernconnecticutweather for the most up to the minute info.
In closing, enjoy the snow, and remember, when deciding to travel or postpone, that your safety is more important than whatever plans you may have. If you’ve got specific questions, comments, or want advice on travel etc. leave us a comment here or on Facebook (quicker response likely), and we’ll get back to you as soon as we can, although if the response is load is overwhelming, we can’t promise a response, although we’ll do our absolute best.
As always, thank you for reading Southern Connecticut Weather! We’ll have another update tomorrow morning.
-SA (Map by TW).
We’re forecasting one to three inches of snowfall in the SE corner of the state, two to five inches for the majority of the coastline, four to eight inches for most of the interior, and six to ten inches in the NW hills. In general, we went towards the more conservative side of the forecast, considering we’re still 2 days out and there’s several ways this can trend into a lesser event, either too far to the east and limiting QPF or too far to the west and bringing in warmth. If modeling holds or becomes more optimistic on amounts tomorrow, we will likely issue an updated map tomorrow evening raising totals, and likewise, if it becomes less aggressive, we will lower totals or hold with this map for a final map. This map is slightly lower than the model consensus, so if the models remain exactly the same, we’ll probably nudge up slightly tomorrow afternoon. As always, exact totals will end up being determined by mesoscale banding and timing differences, and some areas will bust high and some low, but for the most part, this is a good starting point.
Timing: Most modeling is in relatively good agreement as far as timing goes; although there are some minor differences, which could influence start and end times. For the most part, the mornings commute looks to be OK, with skies likely dry or perhaps some light rain or snow falling. Do not make the mistake though that it is OK to head to work or school, because precipitation arrives with a vengeance from SW to NE throughout the course of the morning on Wednesday, and by noon or so, most areas are seeing moderate to heavy precipitation. Northern interior areas should start as snow from the start, while southern areas likely start as a mix or rain, before changeover takes place from northwest to southeast over the course of the early afternoon. By the time the afternoon commute rolls around; pretty much everywhere should be seeing snow, with heavy snow quite possible in many areas. The afternoon commute will be nothing less than a disaster, with heavy snow and exceptionally heavy traffic due to the thanksgiving travel rush. Conditions will not begin to improve until after midnight, and it may be until Thursday morning before all of the roads are back to semi-normal conditions.
We highly recommend travelling tomorrow to your thanksgiving plans if at all possible, but if you must travel on Wednesday, try to leave as early in the day as possible and expect major delays, poor conditions, and dangerous driving conditions. Have an emergency kit in your car with warm clothes, food and water, and a fully charged cell phone, and be prepared to deal with accidents and spinouts if they come up. Stick to major roads, which will be better plowed if possible, and don’t be above pulling over if conditions get too dangerous for you to handle. Better to be late for thanksgiving than not make it at all because of an accident that could have been avoided by waiting.
Air travel is also likely to be impacted. In general, the earlier in the day your flight is on Wednesday, the better chance you’ve got to get out OK, but it’s possible that airlines will make pre-emptive cancellations and flights earlier in the day will be impacted as well. Thursday should be OK for the most part, although residual delays and cancellations can be expected.
Many schools are closed for Wednesday, but those that are open certainly could be impacted either in the terms of a closure or early dismissal, depending on timing shifts over the next few runs and the whims of each individual district.
Bust potential: For the interior, bust potential is low with this event, as all guidance is in good agreement. For the coastline, bust potential is moderate, and it comes down to how models are estimating temperatures and track vs. reality. A little warmer than forecast, and we see mainly rain at the coastline, a little cooler, an all snow event. The current forecast takes a middle ground. A solution like the UKMET, bringing all rain for all, or like the JMA, which fringes NW areas and lowers accumulations for all due to less QPF, is possible, and would result in a more spectacular bust of the forecast to the low side, but the odds of that are low, likely less than 10%. Similarly, we could see something like the ARW and SREF members have which is a full out snow bomb with a western track and cold temps and be looking at widespread 12”+ amounts, but this is also comparatively low, likely less than 10%. Overall, forecasters confidence is moderate with this event.
To summarize: Precipitation moves in Wednesday morning, mainly as snow north and rain south, before changing over to all snow throughout the afternoon. Major travel impacts for the Thanksgiving period, with possibly treacherous conditions on roads, especially later in the evening. Storm moves out Wednesday night, with total accumulations of 4-8” interior, 3-6” coastline, and 2-5” SECT.
We are in storm mode here at SCW, with a forecaster on duty around the clock watching the models and updating as needed. We will have a small update tomorrow morning, with our final call package and map tomorrow at around the same time as tonight’s update. We will be updating rapid fire during the event on Wednesday on Facebook and Twitter, and will post significant updates to the site as well. Don’t forget to follow us @SouthernCTWX if you haven’t already and like us on Facebook at www.facebook.com/southernconnecticutweather for the most up to the minute info.
In closing, enjoy the snow, and remember, when deciding to travel or postpone, that your safety is more important than whatever plans you may have. If you’ve got specific questions, comments, or want advice on travel etc. leave us a comment here or on Facebook (quicker response likely), and we’ll get back to you as soon as we can, although if the response is load is overwhelming, we can’t promise a response, although we’ll do our absolute best.
As always, thank you for reading Southern Connecticut Weather! We’ll have another update tomorrow morning.
-SA (Map by TW).
