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. 

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 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.

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. 

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. 

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. 

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...

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. 
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A​s 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.
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Thank you for reading SCW.
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​-DB

Good evening from Southern Connecticut Weather! 

Back at it again! This most recent cold stretch is reflective of our overall seesawing of the Pacific pattern, which has led to colder than normal air oscillating between being blocked and being ushered into the region. This has taken the place of the persistent pattern that brought us warm and dry weather during much of the fall. The week ahead features this back and forth once again, with rain and wintry precipitation in the forecast, alongside warmer than normal and colder than normal temperatures. 

Above: the 12z EPS showing the 500mb evolution between Monday and Christmas Day. The key feature here is the Pacific pattern, and where/how amplified the ridging over the western U.S. is. When there is stronger ridging over the west, that opens the door for cold from Canada to flow into the east in the form of troughing. When the troughing is in the west, be prepared for warmer than normal conditions in the east. This is why the "seesaw" metaphor works. Our weather is generally tied to which side the ridge tips. 

Monday
The antecedent cold that has dominated our weather the last few days will open the door for wintry precipitation overnight tonight and into tomorrow morning. A weak system is moving toward the region, and as it does, it's getting ripped apart in the overall flow (an issue we've had with winter storms the last few years actually). That means that precipitation looks light, but with temperatures hovering around freezing for most inland spots, we have to watch for minor accumulations and light icing.

Above: the latest high resolution NAM showing snow and mixed precipitation in much of interior CT after midnight and into tomorrow morning, before temperatures warm above freezing and rain arrives later Monday and into Tuesday. I think the NAM has the right idea here, but I do think it could take a little longer to scour out the cold, particularly in the CT River Valley.  

For snow totals, not expecting much. Perhaps a coating for inland areas. The bigger issue is the risk of a glaze of ice with freezing rain. It may be minor overall, but folks have to be careful tomorrow morning when heading out and driving. Give yourself more time to travel, and be prepared for delays and possible cancellations. Winter weather advisories are up for most of the state. 

By afternoon, we should all be above freezing, and should see some lingering rain showers. 

Tuesday-Friday
The active weather continues, as a follow up boundary/system brings much warmer weather on Tuesday. We will have rain early in the day, with improving conditions by afternoon. Wednesday we cool off some, but remain above normal with quieter weather. That is until our next weather maker arrives late in the day to bring rain to the state. The storm passes to our north, putting us in the warm sector. The rain continues into early Thursday, and in the storm's wake the seesawing continues and we go back to cold filtering into the region. This sets us up for the weekend potential. 

Above: the 18z GFS depiction of midweek. Tuesday brings rain early. Wednesday brings another storm late but it is too far to the north to bring us wintry precipitation. The storm however brings the baroclinic zone further south, opening the door for a weekend winter storm...if a storm can develop close enough to our region...

​Saturday-Sunday
The weekend looks cold at least, but the question is whether we can get a storm. If you are looking for a White Christmas, this is your chance. As you will see in the 18z Euro 500mb vort depiction below, there is a clipper trying to dive down in the wake of our Wednesday/Thursday storm.

The pattern, with the ridge over the western U.S. amplifying, suggests that there will be cold air coming into the eastern part of the country, with a window for this clipper to redevelop at some point after reaching the coast. This gives us a chance at a Miller B type storm developing. However, what looks like a good pattern doesn't guarantee anything, because we have some relatively unfavorable conditions to our northeast (lack of blocking for a storm, and a flow that may be too fast) that could cause a storm to develop too far southeast, too late, or not at all. 

I do think some kind of storm develops, and for now I think that there's going to be a chance of snow showers at least given the cold air advecting in, but don't buy into talk that a big storm is definitely coming. There are a lot of hurdles to overcome at this time. 

The Pattern Around Christmas
Unlike prior years, where we had our blowtorch temperatures or "Grinch" storms before Christmas, it looks like we have a good shot at avoiding both this year. It looks as if our western pattern will be favorable enough for at least a colder period in the days right up to Christmas. However, the seesaw will tilt again, and we likely have mild conditions lurking right after the Christmas holiday. 

Below is the 12z EPS showing 5 day averaged temperature anomalies. Note how we get colder in the days leading to Christmas, followed by warmth returning for at least part of the time before the new year. If you want a snowy landscape, you have to hope for next weekend to produce, or some weak clipper in the flow that cannot be seen right now in the hours before Christmas. 

The Dailies
Monday: Snow and wintry mix inland with rain at the coast, turning to rain everywhere by early afternoon. Highs in the upper 30s to mid 40s. Chance of precipitation 70%. 

Tuesday: Rain early followed by improving but breezy conditions. Highs in the low to mid 50s. Chance of rain 70% early. 

Wednesday: Increasing clouds with rain late. Highs in the mid to upper 40s. Chance of rain 80%

Thursday: Rain early followed by improving but breezy conditions. Highs in the low to mid 40s. Temperatures may drop during the day. Chance of rain early 60%. 

Friday: Mostly sunny, breezy, and colder. Highs in the mid to upper 30s. 

Saturday: Partly cloudy and cold with a chance of snow. Highs in the low to mid 30s. Chance of snow 30%. 

Sunday: Mostly sunny and cold with a chance of snow. Highs in the low to mid 30s. Chance of snow 30%. 

​A​s 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.
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Thank you for reading SCW.
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​-DB

Good morning from SCW!

I couldn't get to this until early morning, but here's the forecast for your week ahead! The cold of last week recedes temporarily as a pattern shift allows for warmth to start the week and a significant storm by midweek. The midweek storm is likely to bring significant rainfall, but what I'm really watching is the wind potential. 

Above: the 18z EPS depicting the 500mb pattern progression from last week through the week ahead. Note how the ridging in the west at the start of the animation creates the ability for cold to flow into the east, but the pattern becomes less stable as we shift to ridging over the east leading to warmth, a storm, and then more cold back in the east. How this pattern cycles will be important as we get closer to the holidays. 

Monday-Tuesday
This is an active week, with multiple chances of rain. A weak system will approach the region, with rain overspreading the state during the afternoon. Expect a wet evening commute, but the temperature will be too warm for any frozen precipitation. This is a quick mover, so while showers may be around during the evening we should be clear Monday night. 

Tuesday looks quiet and warmer than normal as our next system approaches. 

Above: the 00z GFS depicting the weak system impacting CT later today. 

Wednesday-Thursday
I'm declaring Wednesday a SCW Period of Interest. In recent years, we've had powerful winter storms, but most of those storms were "screamers", i.e. storms that cut to our west, putting us in the warm and windy sector. It looks like the pattern continues with another storm this week. 

Rain is likely to start in the predawn hours of Wednesday, as low pressure rides up a slow moving boundary that will divide the warmth from the cold. As you will see below, we will be on the warm sector, and there's a strong signal for significant rain, on the order of 2-4 inches. As the storm moves up the boundary and rapidly deepens we will watch for a strong low level jet that could bring significant wind. The further west the storm trends, the more likely a significant wind event will be possible in CT.

As it stands, the biggest risk is in eastern CT and further east. Some guidance shows strong mixing of the wind aloft, and with winds possibly 60-70 knots above the surface, this is something to watch. For now, it's worth caution, and we will continue to follow trends. 

Above: the 00z GFS depicting the progression of the storm, which brings heavy rain over the state and cold air in the wake of the storm. 

Below: the 18z Euro depicting the progression of the storm, which very heavy rain and significant wind as the storm passes over the region. 

Thursday-Sunday
​We quiet down in the wake of this big storm, and the colder than normal temperatures return. As I mentioned at the start of this discussion, the pattern looks to cycle frequently, so this could be a fairly brief intrusion. By Sunday, we may be watching another coastal storm. 

The Dailies
Monday: Mostly cloudy with rain. Highs in the mid to upper 40s. Chance of rain 100%. 

Tuesday: Mostly cloudy. Highs in the upper 40s to low 50s. 

Wednesday: SCW Period of Interest. Rain and wind. Highs in the upper 50s to low 60s. Chance of rain 100%. 

Thursday: Decreasing clouds, breezy and cold. Highs in the mid to upper 30s. 

Friday: Mostly sunny. Highs in the upper 30s to low 40s. 

Saturday: Mostly sunny. Highs in the low to mid 40s.

Sunday: Partly cloudy. Highs in the low to mid 40s. Chance of precipitation 30%. 

Grading Last Week's Clipper
The first forecast for our first measurable snow event was ok, but left something to be desired. We had 1-3" with isolated 4" amounts in hill towns, and that was too conservative. While our C-2" zone worked for most of the state, there were some places that ended up higher.

I regret the Trace zone, as there were places in SE CT that saw snow accumulations and places in south central and SW CT that saw northing, which was odd. I'm thinking the radar returns weren't strong enough to deliver a cold enough column for measurable snow. The hill town accumulations hurt the grade significantly, Timing worked well with the storm starting and ending on time. Impact was higher than I thought, particularly because many ended up at the higher end of the forecast range, and for the hill towns, well over. Meh. 

Timing: A-
Accumulation: C (double weighed)
Impact: D

Overall Grade: C

​A​s 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.
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Thank you for reading SCW.
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​-DB

Good morning from Southern Connecticut Weather. 

We have our first map of the season for a minor snow event that's coming to the state. While some precipitation may start late Wednesday, the bulk of the event will occur on Thursday, possibly impacting the morning commute. The storm will be followed with a breezy and frigid (by early December standards) Friday. 

Above: Our SCW forecast map. This is a minor event. For most, a coating to an inch or two is likely. For our hill towns in NW and NE CT, 1-3" looks more likely, with some isolated areas getting 4" if everything breaks right for them. Along part of SE CT, it looks as if temperatures will be too warm for much if any accumulation, though snowflakes are still likely. 

Timing 
The timing looks pretty straightforward for this one. Our clipper is currently over central Canada and is moving east. Today looks like another colder than normal but quiet day, with increasing clouds later in the day as the clipper approaches the region. Precipitation may start as early as 8-10pm across the state and because of the track of the storm, it may start out as rain, particularly in coastal and eastern CT. The expectation is that overnight we see a gradual change over to snow for most, especially inland. Some of that snow could be moderate at times, especially in hill towns, leading to our accumulations. 

The Thursday morning commute does look to be impacted as bouts of precipitation continue into the morning hours on Thursday. By the afternoon, the storm will be mostly over, with some scattered rain or snow showers gradually ending. This will be a windy storm, with wind advisories up for each of the southern four counties. The wind should die down by Thursday night, with breezy conditions possible Friday. 

Above: the latest 12km NAM depicting the evolution of the storm. There are a number of factors that influence our snow forecast below. 

Snow Accumulation
As you see in the map above, this is a minor event. For winter weather lovers, that's probably frustrating, as usually we do not have precipitation type issues for a clipper. There are a few things that have me leaning more conservative. First and foremost, the track of the clipper puts us in a southerly and southwest flow. If this were the kind of clipper that tracked under the region, we'd be in much better shape for all snow statewide. However, the clipper will track to our north, giving us that relatively warm wind direction. As a result, temperatures at the surface look marginal. 

For places like the coastline and CT River Valley, you know what that means. Snow may fall because it's cold enough aloft, but it may struggle to accumulate because the surface is too warm. The timing with snow falling overnight helps, which is why I think a measurable coating is likely for most. The further inland you are, the more likely you end up with a higher total. 

The other significant factor is the nature of the system itself. It's not terribly dynamic, but may have enough "juice" to allow for minor but more meaningful accumulation in our hill towns, especially in eastern CT where the precipitation shield may be more likely to blossom and a southwest flow could enhance lift in the NE hills. If there's a place that could overperform some and top out with an isolated 4 or even 5" total, it's in this zone. That said, if this comes in weaker, accumulations will be lower in the forecast range. 

I would say that there's a 60% chance that we fall within our range on balance, with a 25% chance of a widespread bust (less snow than forecast), and 15% chance of a widespread boom (more snow than forecast).

It's important to remember that although we can get significant storms around this time of the month, climatology overall is still pretty hostile, especially at the coast. It's not until mid to late month that conditions for snow become much more prevalent historically. 

Above: the latest GFS depiction of the storm. The temperatures just look too marginal for most for a significant event, though even here much of the state does get measurable snow verbatim. Note that the GFS does keep some precipitation around Thursday afternoon, which is why I think rain/snow showers will still be around though less impactful. 

Impact
This looks like a minor event overall. For interior CT, especially the hill towns, the impact may be a touch higher given the timing of the snow. We also have to watch for isolated to scattered power outages due to wind. That said, because the leaves are down, widespread outages and tree damage looks unlikely, especially since we're not expecting major accumulation.

It's important to note that the majority of car collisions happen under these very conditions--with minor snowfalls. People overestimate their ability to drive in the snow. Give yourself plenty of time to travel on your Thursday morning commute, and during the evening commute as any water on the roads could refreeze. I do not expect major airline issues with delays or cancellations. 

In the wake of the storm, Friday looks very cold. Both the Euro and GFS has most of the state below freezing through the day. The Euro even toys with temperatures struggling to escape the low 20s for many inland. With breezy conditions possible, expect even colder wind chills. 

Above: GFS temperatures Friday afternoon. 

Below: Euro temperatures Friday afternoon. 

​A​s 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.
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Thank you for reading SCW.
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​-DB

Good evening and happy meteorological winter from Southern Connecticut Weather! 

December is here and for once it actually feels wintry outside. Many of us saw first flakes this week, and some of our highest elevations saw some minor measurable snow. The incredibly stable pattern that brought us the warmest November on record and driest fall (September-November) on record has radically changed, driven by a major flip in the Pacific that has dislodged cold into the continental US.

This pattern--featuring colder than normal temperatures (on balance) and continued precipitation chances--is likely to hold on until the middle of the month. For the first time in quite some time, the Climate Prediction Center believes a winter month has greater odds to finish below normal in our neck of the woods. It's important to remember that cold does not automatically mean snow, but this week it looks like the pattern is trying to bring back a seemingly near extinct weather system--a clipper. 

Above: the CPC temperature outlook for December. Note that these are probabilities, but even a few weeks ago the CPC had December warmer than normal.

Just as a reminder, for Hartford at the start of December the average high is 45, while the normal low is 29. At Bridgeport, the December 1st average high is 48, with a normal low of 34. We will be well below normal at times in the first half of this month. 

Monday-Tuesday
The start of the work week is cold and quiet. For inland areas, we will see highs in the mid to upper 30s, while the shoreline could be a little warmer, but not by much with highs in the upper 30s to around 40. With a fairly persistent northwest flow and the lake effect machine gradually slowing down, there could be some random flurries in NW CT. Nothing meaningful. 

Wednesday-Thursday
Wednesday should be a fine day for the most part, and I do not expect any travel issues. By the overnight period we should see our clipper move into the region. We have to watch to see if this becomes a little more amplified over the next few days on the guidance, but for now it looks like a weak system that will bring our first measurable snow to many in CT overnight Wednesday into Thursday. Despite the colder than normal pattern, a weak system and southerly flow ahead of the precipitation make temperatures look marginal, especially in southern CT. That would cut back on snow totals. 

For now, I expect a general coating to 2" of snow, with light coatings in southern CT and more measurable the further north and NW you are. If this requires a map, we'll issue one. The system clears Thursday, and we get a reinforcing shot of cold air in its wake. It's too soon to know if there will be widespread delays, but they could be possible in northern CT. 

Above: the latest GFS depicting the marginal nature of temperatures and precipitation on Thursday. 

Below: the latest NAM with a little more robust depiction of the clipper system. Note the more coherent precipitation shield, at least early on. This helps cool the column and bring snow further south. 

Friday-Sunday
The end of the week looks cold and quiet again, though there is a faint signal that another system could try to pop near the very end of the forecast period. IF it did, the airmass looks more favorable for snow, but a system is far from guaranteed or even likely at this time. Highs statewide look to be in the 30s, well below normal once again. 

Below are the 12z EPS temperature anomalies at the surface. For winter lovers, you need these kind of patterns to produce if you want to have a shot at a normal snowfall winter. 

The Dailies
Monday: Mostly sunny and cold. Highs in the upper 30s to low 40s. 

Tuesday: Mostly sunny and cold. Highs in the upper 30s to low 40s. 

Wednesday: Increasing clouds with snow likely late. Highs in the upper 30s to low 40s. Chance of snow 50%. 

Thursday: Mostly cloudy with rain and snow. Highs in the mid to upper 30s. Chance of precipitation 50%. 

Friday: Mostly sunny and cold with snow showers possible. Highs in the mid to upper 30s. Chance of snow 10%. 

Saturday: Mostly sunny and cold. Highs in the low to mid 30s. 

Sunday: Partly sunny with snow possible. Highs in the low to mid 30s. Chance of snow 20%. 

​A​s 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.
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Thank you for reading SCW.
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​-DB