Good evening from Southern Connecticut Weather.
I started writing this Sunday night, but a combination of family duties and the time needed to really deep dive into the upcoming pattern required me to move this to tonight.
Since the warm and dry pattern broke in November, I've been writing a lot about our "oscillating" or "seesaw" pattern. In this pattern, we've seen relatively fast flips between warmer than normal and colder than normal temperatures, along with a lot more low pressure systems bringing rain and snow. The pattern has generally leaned toward colder and more snow (though still below normal for many). The timing of the pattern left many of us with snow for the Christmas holiday, and will leave us with rain on New Year's Day.
This rain storm however will usher in the start of the next pattern shift, and there is cross guidance agreement that this flip will mean business and possibly be of longer duration during January. This week will give some of us whiplash. Let's dive in.
I started writing this Sunday night, but a combination of family duties and the time needed to really deep dive into the upcoming pattern required me to move this to tonight.
Since the warm and dry pattern broke in November, I've been writing a lot about our "oscillating" or "seesaw" pattern. In this pattern, we've seen relatively fast flips between warmer than normal and colder than normal temperatures, along with a lot more low pressure systems bringing rain and snow. The pattern has generally leaned toward colder and more snow (though still below normal for many). The timing of the pattern left many of us with snow for the Christmas holiday, and will leave us with rain on New Year's Day.
This rain storm however will usher in the start of the next pattern shift, and there is cross guidance agreement that this flip will mean business and possibly be of longer duration during January. This week will give some of us whiplash. Let's dive in.
Above: the 12z European Ensembles, looking at the 5 day averaged temperature anomaly through about mid January. Our warm period currently ends shortly after the start of the new year as Arctic air floods the central and eastern part of the country. Note how the coldest anomalies are west of us. That is critical to our snow chances down the road.
The Pattern
Before looking at the daily details for the week ahead, let's talk about this coming pattern change and why it's garnering so much attention. To date, the Pacific pattern has been critical to our cold(ish) December. It has been an oscillating pattern, where the Pacific upper level pattern has essentially acted as a valve that periodically allows for cold to dive into the eastern U.S. before closing, forcing us to warm up. This Pacific pattern has also been favorable for fast moving low pressure systems to cross the nation.
While we talk about the EPO a lot, the PNA is a massively impactful teleconnection during the winter for the eastern part of the nation. In recent years, we've seen troughing buried in the west, cutting off cold from the east and in combination with the positive phase of the EPO flooding the east with warmth. The PNA has been critical for our seesawing so far, and will play a prominent role in the Arctic intrusions coming in January.
The Pattern
Before looking at the daily details for the week ahead, let's talk about this coming pattern change and why it's garnering so much attention. To date, the Pacific pattern has been critical to our cold(ish) December. It has been an oscillating pattern, where the Pacific upper level pattern has essentially acted as a valve that periodically allows for cold to dive into the eastern U.S. before closing, forcing us to warm up. This Pacific pattern has also been favorable for fast moving low pressure systems to cross the nation.
While we talk about the EPO a lot, the PNA is a massively impactful teleconnection during the winter for the eastern part of the nation. In recent years, we've seen troughing buried in the west, cutting off cold from the east and in combination with the positive phase of the EPO flooding the east with warmth. The PNA has been critical for our seesawing so far, and will play a prominent role in the Arctic intrusions coming in January.
The Pacific only accounts for part of our overall pattern, however. The fast flow we've seen is partially because the lack of Atlantic "blocking", another regional pattern this time to our northeast that acts to 1) slow down low pressure systems that move off the coast and allow them to intensify, and 2) lock in the cold air necessary to allow for wintry precipitation systems.
The combination of a favorable Atlantic and Pacific pattern has been virtually impossible to align in recent years, but every indication is that it's coming starting this week.
The combination of a favorable Atlantic and Pacific pattern has been virtually impossible to align in recent years, but every indication is that it's coming starting this week.
Before folks go wild, however, a word of caution.
Above is the 12z EPS running from start to finish at 500mb. This is an almost textbook progression of a deeply rooted cold pattern for the central and eastern U.S., but whether storms hit our backyards are left to details that cannot be resolved at this range.
With ensemble guidance, we're just looking at windows for activity. Although this pattern looks different than the ones we've seen in recent years because of how favorable the Pacific looks, there are ways to fail.
That said, one of the key things here is something I mentioned above, the biggest cold anomalies are to our west. If you want an active storm pattern, you usually can't be in the deepest part of the trough. You want to be east of the dip in the Jet Stream so that storms track your way. For our friends in the Midwest and south, big cold is coming. For us, we will get cold for sure, but it's unlikely that the Arctic blast is so directly thrown at our region that it's merely cold and dry. If we cannot produce snow, other factors will likely be at play than trough positioning.
With ensemble guidance, we're just looking at windows for activity. Although this pattern looks different than the ones we've seen in recent years because of how favorable the Pacific looks, there are ways to fail.
That said, one of the key things here is something I mentioned above, the biggest cold anomalies are to our west. If you want an active storm pattern, you usually can't be in the deepest part of the trough. You want to be east of the dip in the Jet Stream so that storms track your way. For our friends in the Midwest and south, big cold is coming. For us, we will get cold for sure, but it's unlikely that the Arctic blast is so directly thrown at our region that it's merely cold and dry. If we cannot produce snow, other factors will likely be at play than trough positioning.
The image above is also of the Euro, but you could pick any model and see the same thing. This is where the biggest risk lies. Too much of a good thing if you like winter, in this case, Atlantic blocking. A shortwave dives out of the west at the beginning of the animation and is becoming a strong storm by the time it gets to the Midwest. If you just paused things right there you would expect a big storm coming to New England with the block in place to the northeast of New England.
However, the latter half of the animation shows what happens when you have too much blocking and too much interference via confluence. The low is shunted pretty well south but even worse for the low is that it gets sheared as it reaches the coast. The result is a much weaker system on the guidance.
Here is the surface depiction at the same time range. Sheared apart and much weaker. With less confluence this is a possible big dog snowstorm for New England between January 6-8. This is our first real window for a winter storm after the New Year's Day storm that ushers in the cold in its wake.
However, the latter half of the animation shows what happens when you have too much blocking and too much interference via confluence. The low is shunted pretty well south but even worse for the low is that it gets sheared as it reaches the coast. The result is a much weaker system on the guidance.
Here is the surface depiction at the same time range. Sheared apart and much weaker. With less confluence this is a possible big dog snowstorm for New England between January 6-8. This is our first real window for a winter storm after the New Year's Day storm that ushers in the cold in its wake.
I mentioned earlier that we have multiple windows. The discussion above references the first, but there is another even bigger signal for a storm between January 8-11. If we're looking for a normal snowfall winter, one of these two windows likely needs to produce. These kind of patterns do not come around often, particularly since our period of futility began in winter 2018-19.
The Week Ahead
New Year's Eve (Tuesday) & New Year's Day (Wednesday)
Back to our regularly scheduled programming. The year is coming to an end! We're finishing December on the warm side of the oscillating pattern, and the last day of 2024 looks warmer than normal and decent. We will have partly sunny skies to start, which should allow us to reach the 50s again, but increasing clouds will signal our coming storm.
Unfortunately, the timing for our storm has sped up some, meaning that we are likely to have rain showers, some heavy, moving in from SW to NE before the ball drop. If you have outdoor activities planned, plan accordingly as rain could start between 8-11pm. Hopefully, this slows down some so everyone can enjoy celebrations without rain.
New Year's Eve (Tuesday) & New Year's Day (Wednesday)
Back to our regularly scheduled programming. The year is coming to an end! We're finishing December on the warm side of the oscillating pattern, and the last day of 2024 looks warmer than normal and decent. We will have partly sunny skies to start, which should allow us to reach the 50s again, but increasing clouds will signal our coming storm.
Unfortunately, the timing for our storm has sped up some, meaning that we are likely to have rain showers, some heavy, moving in from SW to NE before the ball drop. If you have outdoor activities planned, plan accordingly as rain could start between 8-11pm. Hopefully, this slows down some so everyone can enjoy celebrations without rain.
Above: the latest 3km NAM depicting the strong storm that arrives in time for the new year.
The first day of 2025 looks wet, particularly in the morning. Right now it doesn't look like a total washout, but it won't be pleasant. Temperatures look warm at the start of the day, but as the storm departs later in the day temperatures will drop significantly, and some of the hill towns could finish with snow showers. Not expecting any accumulation there.
Thursday-Sunday
It will be a shock to the system when the initial batch of cold arrives Thursday. Cold air will be advecting in strongly, and we actually have some concerns about wind on Thursday in the wake of the storm. We could see peak wind gusts of 45-55mph, and as a result, some isolate to scattered power outages are possible. Highs will struggle out of the 30s, and with strong winds, it's going to feel like winter no matter where you are despite the sun. Winds die down Friday, but it will still be breezy and cold. Each day to end the week gets colder.
With this kind of cold advecting in, we could easily see some isolated to scattered flurries or snow showers from lake effect streamers. The main story is the cold though. By Saturday, it we may be getting back into the freezer with highs below 32, especially inland. We will also be watching our first window...
The first day of 2025 looks wet, particularly in the morning. Right now it doesn't look like a total washout, but it won't be pleasant. Temperatures look warm at the start of the day, but as the storm departs later in the day temperatures will drop significantly, and some of the hill towns could finish with snow showers. Not expecting any accumulation there.
Thursday-Sunday
It will be a shock to the system when the initial batch of cold arrives Thursday. Cold air will be advecting in strongly, and we actually have some concerns about wind on Thursday in the wake of the storm. We could see peak wind gusts of 45-55mph, and as a result, some isolate to scattered power outages are possible. Highs will struggle out of the 30s, and with strong winds, it's going to feel like winter no matter where you are despite the sun. Winds die down Friday, but it will still be breezy and cold. Each day to end the week gets colder.
With this kind of cold advecting in, we could easily see some isolated to scattered flurries or snow showers from lake effect streamers. The main story is the cold though. By Saturday, it we may be getting back into the freezer with highs below 32, especially inland. We will also be watching our first window...
Above: the GFS depiction of temperatures as we move through the rest of the week. Get ready for deep winter cold. That is a lock.
Monday
For now, let's just call next Monday cold with increasing clouds with snow possible. We will be closely watching what happens with that possible shortwave diving into the Midwest. There's a lot of potential in this pattern...
The Dailies
Tuesday: Partly sunny early with increasing clouds. Rain showers late. Highs in the low 50s. Chance of rain 80%
Wednesday: Mostly cloudy with rain early, some heavy at times. Showers later in the day before clearing. Highs in the low 50s. Chance of rain 100%. Chance of snow showers in hills 20%.
Thursday: Decreasing clouds, colder, and windy. Highs in the upper 30s to low 40s.
Friday: Seasonably cold, mostly sunny, and breezy. Highs in the mid to upper 30s.
Saturday: Mostly sunny. HIghs in the upper 20s to mid 30s (shoreline).
Sunday: Mostly sunny. Highs in the mid to upper 20s.
Monday: Increasing clouds with snow possible. Highs in the mid to upper 20s. Chance of snow 40%.
If you've made it this far, just know that I do plan to get to reader questions! Eventually haha.
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
Monday
For now, let's just call next Monday cold with increasing clouds with snow possible. We will be closely watching what happens with that possible shortwave diving into the Midwest. There's a lot of potential in this pattern...
The Dailies
Tuesday: Partly sunny early with increasing clouds. Rain showers late. Highs in the low 50s. Chance of rain 80%
Wednesday: Mostly cloudy with rain early, some heavy at times. Showers later in the day before clearing. Highs in the low 50s. Chance of rain 100%. Chance of snow showers in hills 20%.
Thursday: Decreasing clouds, colder, and windy. Highs in the upper 30s to low 40s.
Friday: Seasonably cold, mostly sunny, and breezy. Highs in the mid to upper 30s.
Saturday: Mostly sunny. HIghs in the upper 20s to mid 30s (shoreline).
Sunday: Mostly sunny. Highs in the mid to upper 20s.
Monday: Increasing clouds with snow possible. Highs in the mid to upper 20s. Chance of snow 40%.
If you've made it this far, just know that I do plan to get to reader questions! Eventually haha.
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
