A very active pattern, basically a pattern that has been active all year, has now coincided with cold air and will start to deliver winter threats to the region, beginning with a little appetizer event tomorrow night into Friday morning and a much bigger/more important event over the weekend.
Currently: A cold front is about to move into the Susq Valley. This front will pass through the area around midnight or so tonight with little fanfare. There really isn't much of an impetus to produce precipitation with this front. However, there could be a brief wind gust to 30 MPH with the frontal passage.
Tonight: Because of the timing of the cold frontal passage, we may have "late" overnight lows that don't occur until around 8 AM or so. Because all the guidance is in good agreement, a blend seems prudent for low temperatures tonight, with lows ranging from 10 to 15 in the NW Hills, to near 20 along the south coast.
Tomorrow: Chilly, as cold air advection behind the cold front builds in. With the cold air advection, and given the trends of the past week, I'll go about a degree or two cooler than the bulk of the guidance, with highs In the mid to upper 20s.
Tomorrow Night/Friday: An Alberta Clipper storm system will move toward the area. There has been a trend in recent guidance to move that clipper further south and weaken it as it crosses the mountains. However, this trend has seemed to have halted, and the 18Z NAM is in fact a bit more aggressive. Therefore, I feel pretty confident that the state will get up to 2" of snow. Accumulations should not vary much, since it's a quick moving clipper, precipitation is all snow, and because snow to water ratios will be higher in the north, yet there will probably be less total precipitation, or negating factors. Generally, the snow should fall from about 3 AM to 11 AM, so it could impact the morning commute. However, since the snow will be so light, total impacts should be quite minor. As far as temperatures, guidance is pretty tightly clustered, showing highs in the low 40s. Morning temperatures will be in the 20s, with some teens up north, so snow will have no trouble sticking. But a warm surge occurs during the afternoon before the cold front pushes through.
Currently: A cold front is about to move into the Susq Valley. This front will pass through the area around midnight or so tonight with little fanfare. There really isn't much of an impetus to produce precipitation with this front. However, there could be a brief wind gust to 30 MPH with the frontal passage.
Tonight: Because of the timing of the cold frontal passage, we may have "late" overnight lows that don't occur until around 8 AM or so. Because all the guidance is in good agreement, a blend seems prudent for low temperatures tonight, with lows ranging from 10 to 15 in the NW Hills, to near 20 along the south coast.
Tomorrow: Chilly, as cold air advection behind the cold front builds in. With the cold air advection, and given the trends of the past week, I'll go about a degree or two cooler than the bulk of the guidance, with highs In the mid to upper 20s.
Tomorrow Night/Friday: An Alberta Clipper storm system will move toward the area. There has been a trend in recent guidance to move that clipper further south and weaken it as it crosses the mountains. However, this trend has seemed to have halted, and the 18Z NAM is in fact a bit more aggressive. Therefore, I feel pretty confident that the state will get up to 2" of snow. Accumulations should not vary much, since it's a quick moving clipper, precipitation is all snow, and because snow to water ratios will be higher in the north, yet there will probably be less total precipitation, or negating factors. Generally, the snow should fall from about 3 AM to 11 AM, so it could impact the morning commute. However, since the snow will be so light, total impacts should be quite minor. As far as temperatures, guidance is pretty tightly clustered, showing highs in the low 40s. Morning temperatures will be in the 20s, with some teens up north, so snow will have no trouble sticking. But a warm surge occurs during the afternoon before the cold front pushes through.
Long Term: The long term section will be devoted to our weekend storm system and subsequent Arctic outbreak, for the most part, although I will briefly write about what happens beyond there.
Model(s) of choice: Going with a blend of about 70% UKMET, 20% ECMWF, and 10% ICON model. For those of you who do not know, the ICON model is a new German model. It has been handling this situation pretty well and has been pretty consistent this week. The pattern DOES NOT support a warm storm. There are a few reasons why this is the case. FIrst off, there is average cold air In place to start the storm (and averages are at their coldest part of the year). Secondly, there is Arctic air coming in along the back side of the storm. Finally, the mechanism is all wrong to get warm air here. If there was no high pressure to the north, and the low slid through the difference between pressure systems to our west, and the area warmed, that would make sense. However, the last remaining holdout model that really warms the area, the GFS (which is not getting any use in this forecast), warms the area up by phasing our coastal low into the polar vortex. The polar vortex VERY VERY rarely phases into storm systems.
All this having said, from Saturday evening until at least early Sunday afternoon should be very wintry in our area. Snow will break out Saturday evening and probably come down heavy at times. The snow could then change to something other than snow, especially near the coast. Down in New London and SE Middlesex Counties, a change to plain rain will likely occur. In far northern Connecticut, precipitation will probably remain as all or at least mostly snow. In between, a period of icy precipitation is likely- most likely freezing rain. The warm layer aloft is steep and probably supports freezing rain over sleet. As colder air builds in later in the day, all areas should flip over to snow, with minor additional accumulations, before ending.
Now, there is also a second possibility, and that is of a second wave of low pressure riding up the front and producing another round of snow, with at least moderate additional accumulations, later Sunday. The ECMWF model has this, the UKMET to a much lesser extent, as does the ICON model. The new 18Z NAM was also trending that way. Models were more bullish on this idea a few days ago, but now to see them start to try to trend back that way is interesting. Right now, I would say the chance of this actually happening is low, but not zero.
It should also be noted that the ICON model, and to a lesser, but still notable extent, the ECMWF and UKMET Models are spitting out areas with VERY large amounts of total precipitation, in the area of 2 to 4 inches total liquid equivalent precipitation! This could be plausible, given that there is an intense thermal gradient setting up, with very large temperature differences over a relatively small area. Extratropical cyclones feed off that, so there is a mechanism for that to happen.
The bottom line is, there is a large event headed for the region, with the potential for a lot of snow, ice, and high winds! Behind the storm, temperatures will plummet. It should be noted that the GFS has trended warmer with Monday morning's lows. However, the GFS does not think there will be snow on the ground, and this could very well be why it trended warmer. Stay tuned to SCW for updates on this weekend, as we get closer. As of this point, it is way too early to pinpoint exact amounts, precipitation type, or duration. Winds should gust to 45-50 MPH around the back side of the storm and throughout the day on Monday.
I did not really have any time to look at the longer range. There is another winter storm slated to affect the area around Wednesday. Of course, the exact effects of this storm will not be known for quite a while, but with such a strong antecedent cold air mass in place, I can't imagine how it wouldn't at least be wintry to start.
Going even further down the road most of the long range guidance continues the theme of an overall stormy pattern with frequent visits from the Arctic. This should continue the active days of a meteorologist's life, as we'll have multiple storms to track over the coming weeks!
Now, let's take a look at some graphics for Sunday's storm... First - let's take a look at an animation of the system from the CMC model. This shows the system well, but keep in mind that the model is likely overestimating the warming at the surface - most of what it's showing as rain I would expect to be
Model(s) of choice: Going with a blend of about 70% UKMET, 20% ECMWF, and 10% ICON model. For those of you who do not know, the ICON model is a new German model. It has been handling this situation pretty well and has been pretty consistent this week. The pattern DOES NOT support a warm storm. There are a few reasons why this is the case. FIrst off, there is average cold air In place to start the storm (and averages are at their coldest part of the year). Secondly, there is Arctic air coming in along the back side of the storm. Finally, the mechanism is all wrong to get warm air here. If there was no high pressure to the north, and the low slid through the difference between pressure systems to our west, and the area warmed, that would make sense. However, the last remaining holdout model that really warms the area, the GFS (which is not getting any use in this forecast), warms the area up by phasing our coastal low into the polar vortex. The polar vortex VERY VERY rarely phases into storm systems.
All this having said, from Saturday evening until at least early Sunday afternoon should be very wintry in our area. Snow will break out Saturday evening and probably come down heavy at times. The snow could then change to something other than snow, especially near the coast. Down in New London and SE Middlesex Counties, a change to plain rain will likely occur. In far northern Connecticut, precipitation will probably remain as all or at least mostly snow. In between, a period of icy precipitation is likely- most likely freezing rain. The warm layer aloft is steep and probably supports freezing rain over sleet. As colder air builds in later in the day, all areas should flip over to snow, with minor additional accumulations, before ending.
Now, there is also a second possibility, and that is of a second wave of low pressure riding up the front and producing another round of snow, with at least moderate additional accumulations, later Sunday. The ECMWF model has this, the UKMET to a much lesser extent, as does the ICON model. The new 18Z NAM was also trending that way. Models were more bullish on this idea a few days ago, but now to see them start to try to trend back that way is interesting. Right now, I would say the chance of this actually happening is low, but not zero.
It should also be noted that the ICON model, and to a lesser, but still notable extent, the ECMWF and UKMET Models are spitting out areas with VERY large amounts of total precipitation, in the area of 2 to 4 inches total liquid equivalent precipitation! This could be plausible, given that there is an intense thermal gradient setting up, with very large temperature differences over a relatively small area. Extratropical cyclones feed off that, so there is a mechanism for that to happen.
The bottom line is, there is a large event headed for the region, with the potential for a lot of snow, ice, and high winds! Behind the storm, temperatures will plummet. It should be noted that the GFS has trended warmer with Monday morning's lows. However, the GFS does not think there will be snow on the ground, and this could very well be why it trended warmer. Stay tuned to SCW for updates on this weekend, as we get closer. As of this point, it is way too early to pinpoint exact amounts, precipitation type, or duration. Winds should gust to 45-50 MPH around the back side of the storm and throughout the day on Monday.
I did not really have any time to look at the longer range. There is another winter storm slated to affect the area around Wednesday. Of course, the exact effects of this storm will not be known for quite a while, but with such a strong antecedent cold air mass in place, I can't imagine how it wouldn't at least be wintry to start.
Going even further down the road most of the long range guidance continues the theme of an overall stormy pattern with frequent visits from the Arctic. This should continue the active days of a meteorologist's life, as we'll have multiple storms to track over the coming weeks!
Now, let's take a look at some graphics for Sunday's storm... First - let's take a look at an animation of the system from the CMC model. This shows the system well, but keep in mind that the model is likely overestimating the warming at the surface - most of what it's showing as rain I would expect to be
This next map is the 12Z ECMWF (European) model. The low pressure center over interior Southern Virginia is probably a touch west of where you would like it for all snow, at least for the southern two-thirds of Connecticut. However, with strong high pressure enveloping much of Southern Canada, much of the state of Connecticut would be getting an icy mix should this map verify.
You can see the same general evolution on the German (ICON) model. The low pressure center is actually further northwest, but at the same time, high pressure is stronger. This combination is even more of an ice setup, whereas the ECMWF would probably favor more snow. Anyway, here is the German model.
Anyway, that's all for now! Enjoy the rest of your week!
-GP!
-GP!
