​Good evening to you from SCW!
 
First of all, an apology for the lack of updates this week; GP is in bed with the flu and DB is taking care of sick family so we’ve dropped the ball on coverage. Luckily it was a quiet week, and the upcoming forecast looks relatively uneventful as well, so this should be a pretty quick update.
 
Friday
 
Warm and mostly cloudy tomorrow as a cold front crosses the state throughout the day, bringing some scattered showers for the morning hours. Could see some sunshine developing towards the end of the day, but otherwise expect mostly cloudy skies to hold. Highs generally in the mid to upper 50s
 
Saturday-Monday
 
Few more scattered showers possible late Friday or early Saturday, otherwise, looks dry for the weekend aside from some more widely scattered showers overnight Saturday from a weak system passing to our north. It should be a fantastic spring weekend with temperatures generally in the low to mid 50s and nearly full sunshine both days, and if you want to make it a long weekend Monday looks almost as good, with highs in the upper 40s and full sunshine once again.

Here are highs from the GFS for Saturday/Sunday/Monday – with sunshine and spring wavelengths in place I’d take the over on all of those maps.

​Tuesday-Wednesday
 
Another warm system on tap for this time frame with most models two rounds of relatively light precipitation. The first round comes on Tuesday in the form of overrunning rain while the low is still in the Midwest, while the second comes on Wednesday as the parent low finally passes to our north. While colder air moves in behind the system, I don’t think it will be in time for us to see any snow out of this storm, although it wouldn’t shock me to see a brief flurry to end it in the northwest hills.  Although I expect rain on both Tuesday and Wednesday, I don’t think either day will be a total washout, so expect mostly cloudy skies otherwise with highs in the 40s on Tuesday and then well into the 50s on Wednesday as we warm-sector ahead of the cold front.
 
Here’s both parts of the storm as shown on the GFS.

Thursday
 
Cool and quiet weather behind the storm with high pressure in control. Temps in the upper 30s to lower 40s.
 
The Dailies
 
Friday: Showers likely, otherwise, mostly cloudy, with highs in the mid to upper 50s. Chance of precipitation is 70%.
Saturday: Mostly sunny, with highs in the mid 50s.
Sunday: Mostly sunny, with highs in the low to mid 50s.
Monday: Mostly sunny, with highs in the upper 40s to lower 50s.
Tuesday: A chance of rain, otherwise, mostly cloudy, with highs in the mid 40s. Chance of precipitation is 40%.
Wednesday: A chance of rain, otherwise, mostly cloudy, with highs in the mid to upper 50s. Chance of precipitation is 50%.
Thursday: Mostly sunny, with highs in the upper 30s to lower 40s.
 
Have a great weekend and thank you for reading SCW!
-SA

​Good evening to you from SCW!
 
It’s no secret; we had a big forecast bust last week. Our forecast for a warning-level snowfall for most of the state ended up as a couple of inches of snow (if that – some folks got nothing at all) for almost everyone aside from some lucky towns on the shoreline. We took a lot of heat for that bust, and rightfully so; you depend on us to get the forecast right, and in that event, we got it wrong. In this discussion, I want to show you why we got it wrong and what was going through our minds when we made the call that we did, with hopes that you’ll not only understand what happened with this storm but what goes into making a storm forecast.
 
6 days out – The Signal
 
This storm was on the models in some form from fairly far out in time. We first mentioned it in GP’s disco on 3/15(6 days out) where he outlined the model solutions and explained that they showed everything from suppression to a snowstorm to a rainstorm – the models agreed that there would be a storm in the region, but didn’t agree on much else regarding the track. Things change rapidly at that time so there’s no point in getting into details, but we had pretty good model consensus for a hit of some sort.
 
4-5 days out – The Fakeout
 
Of course, as soon as GP mentioned the storm, it disappeared, which seems to happen every time you stick your neck out on a long range threat. Models kept the system safely out to sea, with little to no impact to the state. While we never let our guard down, it started to look like this would be a non-event.
 
2-3 days out – The Return
 
Just when we were ready to write this system off, it did what just about every other system this winter has done and jumped northwest around the 72 hour mark. Over the course of the day on that Sunday and into Monday, we saw a shift of several hundred miles in the model guidance; with a direct hit now being shown on several models. That trend continued right up through forecast time on Monday, and when we sat down to make the first call map, the models looked something like this.

As you can see, there was unanimous consensus for at least 6” of snow in almost all of the state, with only the Euro being a bit lower in the NW corner. In fact, some of the models were so strong with the storm that the SE corner ended up flipping to rain and/or dryslotting, keeping totals down there. Combine that with the fact that the models had been continuously ticking northwest for 4-5 cycles now, and Don and I were comfortable going big with our first call map, which featured 6-12” for most with the heaviest snow falling during the PM commute. We recognized concerns around warm temps and sun angle, but believed that heavy rates would offset those factors and we would still see significant accumulations.

1 day out – The Uncertainty
 
Forecasts are supposed to converge as you approach go time, but in this case, the exact opposite happened. We woke up Tuesday morning to find that the overnight Euro had cut totals fairly substantially, the NAM reduced its totals slightly, and the GFS increased its forecast for the state. At that point, a consensus blend of the three models still verified the low to middle end of our forecast, and so we decided to hold off on making any changes until after the midday guidance rolled in and allowed us to assess all of the data available to us.

Below are the Euro(left) and the GFS(right) from early Tuesday morning. 

​As the midday models started rolling in, everything looked on track. The NAM came in first with a big area of foot plus totals for most of the state, reverting its earlier cut from overnight. Next was the GFS, which backed off a bit from its bullish overnight run but was still in line with our forecast for most areas, followed by the GGEM and UKMET which were perfect matches for our thinking and both increases from their overnight runs. The forecast became clear; 4-8” in NW areas to account for the slight shift south, with 6-12” everywhere else, most in the 6-9” range with some lucky spots with banding seeing up to 12”. We started to sketch out the template for a map as the Euro rolled in, waiting for it to confirm that the trend that we’d been seeing on all of the other guidance was real. Instead, we ended up with a solution that looked like this.

(Sorry for the terrible image – I snapped this on my phone from my computer to send to the rest of the team and it’s the only saved image I have of this run, but I think it’s important to include as it clearly shows the contrast between the Euro and the other guidance).
 
Oof. While all of the other guidance had a large area of 6”+ across the state, the Euro argued that we would see essentially nothing in the north with a couple of inches in the south. Given the light rates, that solution would likely verify as little to nothing on the ground at the end of the event save the south coast and whoever else was able to get into some banding. It's worth pointing out that for our area, this solution was probably the closest to verifying out of every run I saw for this storm, with the heavy accumulations on Long Island tapering to near nothing in Connecticut being correctly modeled.
 
While we had the best guidance in the world showing a non-event, it was literally the only model showing a scenario like that, and the Euro isn’t so much better than every other model that I would take it over the consensus of the rest of the guidance. Clearly, we couldn’t stick with the original plan, but how far down to revise totals was the question. We ended up going with roughly a 50/50 blend of the Euro and everything else, hedging our bets that we’d see the camps converge towards a consensus. That’s a common bet that forecasters make, and it turns out that they’re right more often than not, but the difference is that we’re usually making that bet in the 3-6 day timeframe, not 12 hours before an event. I’m not sure I remember another time in my five years of forecasting that we had this much model spread this close to an event.
 
Gameday
When I woke up Wednesday morning, looked at the GFS, and saw a hit, I felt really good about our forecast, figuring that there was no way that the models could possibly be that far apart at literally zero hours before an event. Nope. The Euro still had little to nothing for most of the state. You may recall my update from that morning essentially saying that we had no idea what was going to happen, and I well and truly meant it when I said we had no idea what was going to happen. Tracking the storm throughout the day, it became clear that we were not seeing heavy banding move north, and by the mid afternoon we largely knew that the storm was a bust, but some snow would finally move in after dinner. With that in mind, we were able to release a new map with expected amounts for the overnight hours, and we got those numbers largely correct. A small consolation prize for the massive forecast bust from the main event.
 
What happened to keep the main event south of us? Primarily, the culprit was a very dry airmass over us and to our north. The heavy bands of snow were there, and actually briefly made it into the state for a time in the afternoon(especially aloft), but because it was so difficult to saturate the column, the leading edge of the precipitation kept evaporating away as it tried to push north and eventually the storm was beat back out of the state. The more aggressive solutions assumed that we would saturate the column much more quickly than we did, and when that failed to materialize, it became evident that we had a bust on our hands. Furthermore, because precipitation ended up being much lighter, the March sun angle was able to keep that snow from accumulating on roads and other hard surfaces. If we’d seen this event in January, we probably would have still managed a couple of inches in most areas during the daytime, but light snow doesn’t cut it during the daytime in late March. It’s no surprise that we started seeing steadier accumulations after dark.
 
Conclusion
 
All in all, the forecast was a bust. That said, I’m not unhappy with how we handled the event. We clearly conveyed the uncertainty, showed the different scenarios, and chose the one that we thought was most likely. To me, the most important lesson from this storm is to not hide anything from the readers. I know that many of you appreciated the fact that we were willing to admit when we didn’t know entirely what was going to happen instead of bluffing and hoping we were right, and it reinforces our long-standing belief that people want to know all of the possible outcomes when looking at an event. With that said, we’d love your feedback on what we can do to provide a better and more informative forecast for you. Drop me a line at spencer@southernconnecticutweather.com or connect with us on our social media channels.
 
With that said, we’ll have a full forecast update tomorrow (don’t worry – there’s no snow in the forecast!), until then, thank you for reading SCW!
-SA

Good evening from Southern Connecticut Weather!
 
As you have all seen the last few days, this winter storm has been very difficult to forecast in terms of its path and evolution. However, The models have begun to converge on a somewhat similar track. The storm looks a bit more delayed, with my expectation being that light snow begins a few hours later Wednesday morning, and snow ending by early Thursday morning. Statewide winter storm warnings have been issued by the NWS, winter doesn’t want to let go yet. In this discussion we will cover the track of the storm and how much snowfall you can expect to see in your area tomorrow. 

Track
With this system, the models had difficulty pinning down the exact track. All the models agree that the center of the low will pass south of the 40/70 benchmark. This would tend to keep most of the heavy precip bands to the southern portion of the state. Now comes the model disagreement…

​The NAM takes the system a few ticks more south, and therefore the result is banding that affects mostly the coastal areas of the state, though as you can see above, northern Connecticut does get some decent banding tomorrow if this verifies. 

​The GFS on the other hand takes the storm a bit further north, and this would therefore take the heavier snowfall further inland.

And the Euro track, which really opened eyes this afternoon when it barely brought precipitation into northern Connecticut. With this in mind, we're weighing this relatively strongly and have honed in on our snow totals, cutting in certain spots. 
 
What we know
Snow will start to fall in earnest across the coast late Wednesday morning, and will increase northward by noon. There is a chance for an initial wintry mix then changeover to snow for SE Connecticut. By mid-afternoon most of the state should see snowfall. The real heavy banding will look to slam the southernmost areas of the state, especially the southwest corner by late Wednesday evening. Snowfall rates of 1.0-1.5” per hour are to be expected within the bands, and by early Thursday morning the snow will move out of the state, as high pressure builds in behind. We expect widespread cancelations tomorrow. 
 
What we don’t know
Models support widespread snowfall for Connecticut, but exact totals in a particular location depend on the placement of the heaviest snow bands, and the eventual track of the storm. Latest models show very strong frontogenesis forming over SW Connecticut, which would indicate a very intense band of snow forming over the state late Wednesday evening. With strong frontogenesis also comes strong subsidence, which could make for a “hit or miss” in terms of snowfall totals. The setup and positioning of the snow banding is definitely a factor that will affect local snowfall totals.

The track of the storm is another uncertainty that will potentially affect snowfall amounts. The trend of the models over the past two days has been tending to move the low further south. With this in mind, it could suggest that the storm is favoring a more southerly track than what is expected, but we don’t know for sure.
 
And last but not least, it’s March! Storms this late in the season do not behave the same as mid-season storms. Warmer surface temperatures and variable upper air dynamics will all play a role in this system. Because of all these variables, we decided to go with 6-12” along the SW and southern coast of the state, with the chance of locally higher amounts depending on the setup of the snow bands. 4-8” along the rest of the state, all depending on how far north the bands travel. And for the northernmost part, 3-6”. These numbers agree with QPF output, suggesting 1-1.25” across extreme southern Connecticut, and for the rest of the state 0.25-0.75”.  

For this system, timing will be an issue because snow will occur during the day, meaning your commute home will probably be messy. We are confident this will be a moderate to high impact event. 

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 following SCW! - LD 

Good evening from Southern Connecticut Weather...

Winter will end eventually, but right now we're in the midst of one epic last stand. Our fourth significant winter storm in just a few weeks is looking more likely this evening, and we are making a relatively bullish first call. Winter storm watches cover the entire state, and will likely be converted to warnings late tonight or at some point tomorrow. 

We expect this event to be a fast moving system that is a moderate impact event for most and high impact event for those with the best banding over them. 

Overall Setup
A series of lows will develop in the south and Mid-Atlantic over the next 24-48 hours. The first low, as mentioned yesterday, will pass to our south. The one we're focused on is wave two, which will develop off the Mid-Atlantic coast, deepen rapidly, and begin moving northeast towards our region.

Over the last few days, some of the guidance kept this low further south, but a strong trend has brought it closer and closer to our region. In fact, today's runs have brought it near the famous benchmark track, which is often a classic location for a significant snowfall in Connecticut. 

As a result of this trend, the National Weather Service has enough confidence to issue statewide watches. 

Impacts

Snowfall Accumulation & Snowfall Rate
We expect a moderate to high impact snow accumulation event. On the graphic, we have it listed as moderate because I do not currently expect most of the state to reach the upper end of our snowfall forecast.

First, we have to consider banding, which will determine who gets the most. I think the place most likely to see banding is Litchfield County. Second, I think we will see a warm nose in the column for a while in SE CT. That will cause mixing with sleet and could cut down on accumulations slightly. 

That can be adjusted if necessary tomorrow if we see guidance tick colder or 700/800mb features trend in another direction with regard to the best banding.

As for snowfall rates, I think it's a fine call right now to say that we could see some rates reaching 1" an hour, which will be difficult for road crews to keep up with. 

Latest GFS run showing a depiction of the two wave development over the next two days. Note that this is not a forecast, but rather one simulation that hones in on timing generally. Below is an image of the UKMET model, showing a near benchmark track and heavier precipitation over the state. 

Wind & Power Outages
Although we should see some gusty conditions, I do not expect particularly high winds in Connecticut during the storm. As such, I lowered the predicted impact of wind. However, I left the impact of power outages at moderate, as we could see some heavier wet snow, especially during the onset of the event, which could cause problems. Overall I expect isolated to scattered power outages. ​

Timing & Road Conditions
Timing looks to be high impact. Tomorrow should be fine throughout the day, but we should see increasing clouds as we head into the evening. Light snow is expected to break out from southwest to northeast during the overnight hours with the more significant snow beginning by mid-morning.

​Now, I think we all remember a recent storm where things did not pick up until later in the afternoon. Here, I think we're also looking at the afternoon being the time for the most significant snow. We're going to watch this closely, but right now I think we see statewide cancelations rather than delays on Wednesday and some delays possible on Thursday. 

As for road conditions, I think I'm torn. This late in the season I tend to believe that the higher sun angle could assist our road crews a bit. However, that is heavily rate dependent. That is not to say road conditions will not be bad. Give the road crews time to do their work. 

RGEM depiction of timing and banding. Note the snow begins by sunrise and we see banding (darker blues) of snow hitting the state during the day and into the evening. 

In closing, this is a significant winter storm that will impact the state during Wednesday. I expect snow to begin early on Wednesday, with the worst conditions during the afternoon and early evening of Wednesday. Snow should taper off by early Thursday. Expect widespread cancelations, difficult road conditions, and isolated to scattered power outages. 

Winter just doesn't want to let go. 

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

​Good evening to you from Southern Connecticut Weather!
 
The calendar says that astronomical Spring starts on Tuesday, but the current weather seems to be saying otherwise. Despite the sunshine today, we are only seeing temps in the mid to upper 30s across the state, those highs are similar to what we’d expect at the end of January compared to the middle of March. Furthermore, we’ve got another chance at some snow in the forecast; while it’s not a sure thing by any means, the trends today have been towards at least getting some snow into the state and given our seasonal trend this winter to bring storms northwest in the short range, this system bears watching.
 
Monday – Tuesday
 
Calm and cool weather to start off your workweek as a leading wave of energy passes to our south and out to sea. Daytime highs will once again be only in the mid to upper 30s across the state, which is approximately 5-8 degrees below normal. Should see mostly sunny skies for Monday, but expect clouds to move in for Tuesday as the previously mentioned system passes to our south and out to sea. Could see some flurries make their way onto the immediate south coast, but no accumulation is expected.
 
Wednesday-Thursday
 
Interesting setup with a “bowling ball” storm moving west to east across the country and then breaking up into two distinct systems when the storm reaches the east coast. While the first system scoots harmlessly out to sea (after bringing a major snowstorm to the mid Atlantic), there are some signs that the trailing wave will try to develop into its own coastal storm and bring snow up the coast into New York and New England. Over the last couple of days, the model guidance has generally agreed that the system will pass to our southeast and spare us from its precipitation shield, but various pieces of guidance have occasionally bucked the trend and brought a more significant event to the area. We’ve seen that accelerate a bit today, with all three of the major ensemble suites now suggesting at least some impact from the storm.
 
Let’s take a look at the two extremes on the guidance. Here’s a look at the 12z GFS for the period in question.

​And here’s a look at the 18z NAM.

​Quite the difference. The GFS is a mostly cloudy day with perhaps a flurry or two, while the NAM is a blockbuster blizzard.
 
What’s causing the difference? One of the main variables in this system is the first system. If it remains weak, there is enough space for the followup wave to amplify and become the main event, keeping the low closer to the coast and resulting in a snowstorm for us. If the first event is stronger, it keeps the second event weaker, and so by the time it is finally able to intensify it is too far east to bring precipitation back to our area.
 
Here’s a look at the ensemble spread on the GEPS (Canadian ensembles). You can see that the biggest cluster of the ensemble members is to the west of the mean, suggesting that the mean may continue to move west in future cycles. This trend repeats itself on the other two ensembles as well.

​So, while it’s still too early to make any sort of definitive statement as to what will happen from Wednesday into Thursday, I think it’s safe to say that the chances of at least some impact are increasing. At the same time, don’t get too excited about a major storm yet. As of right now, the consensus track on most of the model guidance is for a close miss, and we’ll need to see the NW trend continue if we want to get into the heavier snows.
 
Finally, some interesting statistics from todays Euro ensemble, which is the farthest northwest of the three ensembles. At Bridgeport Airport, 28/51(55%) of the members have at least 2” of snow, with 18/51(35%) having at least 6” of snow. At BDL, those numbers are 21/51(41%) and 12/51(23%) respectively, which makes sense given that this storm will likely favor coastal areas. To me, that suggests that while the chance of significant snow is present, it’s far from a lock by any means, and we need to keep an eye on future runs to see where this system ends up tracking. Stay tuned!
 
Friday-Saturday
 
High pressure once again takes control for the end of the week into the upcoming weekend, leading to clear skies and seasonably cool temps. Expect highs in the mid 40s.
 
The Dailies
 
Monday: Mostly sunny, with highs in the mid to upper 30s.
 
Tuesday: A slight chance of snow showers, otherwise, mostly cloudy, with highs in the mid to upper 30s. Chance of precipitation is 20%.
 
Wednesday: A chance of snow, otherwise, mostly cloudy, with highs in the mid 30s. Chance of precipitation is 50%.
 
Thursday: A chance of snow, otherwise, mostly cloudy, with highs in the mid 30s. Chance of precipitation is 50%.
 
Friday: Mostly sunny, with highs in the mid 40s.

Saturday: Mostly sunny, with highs in the mid 40s.
 
Have a great week and thank you for reading SCW!
-SA