Good afternoon from Southern Connecticut Weather!
That was quite a storm! For the first time in a while, we had a widespread and significant all snow event for the entire state. This was a high stakes forecast, with post-Christmas travel impacted and a very aggressive last minute trend that made me grapple with whether to change our forecast numbers, which were on the aggressive side when they were issued a day before the start of the storm. We held firm and that decision paid off.
For those new to SCW, we grade the forecasts of significant winter storms for two reasons. First, in our effort to "show our work" we want to show what the result of the forecast was to hold ourselves accountable to you. This becomes even more important in our fast paced world because we believe it helps build a record of accuracy and trust. Second, and just as important, grading our forecasts allows us to see what went right and what went wrong, so we can be better in the future.
We weigh the key components of our final call forecast, and because snowfall accuracy is king to the public, we count snow accumulation double in our grading to ensure that it gets the proper weight in the final grade.
Our verification map takes the overwhelming majority of National Weather Service reports and although not placed to scale we do our best to place the reported snowfall number in the right spot in a given town. It's an approximation, which doesn't mean your backyard got more or less, we're just using the official numbers to be as objective as possible.
Now, let's get to the grade.
That was quite a storm! For the first time in a while, we had a widespread and significant all snow event for the entire state. This was a high stakes forecast, with post-Christmas travel impacted and a very aggressive last minute trend that made me grapple with whether to change our forecast numbers, which were on the aggressive side when they were issued a day before the start of the storm. We held firm and that decision paid off.
For those new to SCW, we grade the forecasts of significant winter storms for two reasons. First, in our effort to "show our work" we want to show what the result of the forecast was to hold ourselves accountable to you. This becomes even more important in our fast paced world because we believe it helps build a record of accuracy and trust. Second, and just as important, grading our forecasts allows us to see what went right and what went wrong, so we can be better in the future.
We weigh the key components of our final call forecast, and because snowfall accuracy is king to the public, we count snow accumulation double in our grading to ensure that it gets the proper weight in the final grade.
Our verification map takes the overwhelming majority of National Weather Service reports and although not placed to scale we do our best to place the reported snowfall number in the right spot in a given town. It's an approximation, which doesn't mean your backyard got more or less, we're just using the official numbers to be as objective as possible.
Now, let's get to the grade.
Above: The storm verification map. It's like opening up a Christmas present when you place accurate numbers in your snowfall zone!
Timing
This is where I am most disappointed. In these kind of warm air advection scenarios, the snow usually rolls in faster, and exits faster, than on the guidance. I tried to beat that by forecasting that conditions would deteriorate between 6-10pm from CT from west to east, and while that was right for most, it was too late in western CT which saw flakes start flying just after 5pm. Now, you might say it's just an hour, but in a storm where we went from light snow to near whiteout conditions in under 20 minutes, that's not great. The saving grace here is that we identified the earlier start time and put out a warning 2.5 hours before flakes started flying.
Other than that, the forecast was great. We called the quick change from light to heavy snow, and accurately called the snow being gone before 9am, though that too was a little on the earlier side. We accurately called that the worst was essentially from onset through the early morning hours. That piece of information was vital.
So great overall, but that missed hour really bugs me.
Grade: A-
Snow & Ice Accumulation
Folks, I am incredibly excited that we held to our map. Not only did it seem like we were one of the first out there with a more aggressive call on Thursday, but when the models were aggressive even hours before the storm started yesterday we didn't fully buy widespread double digits that would have made us up the numbers to a 6-10 or 6-12. Not that it matters to be first, but the best is being first and right, and I feel like we were there.
Now, the result isn't perfect. It wasn't further southwest that did the best in this storm as the banding ended up further north (as we suspected it might), and in our 2-5" zone New London County did very well, with a few spots above but within an inch of our 5" ceiling and one spot with a surprise (and believable) 8", but we still did an excellent job here.
That was about as good as you can get, and I'm proud of that.
Grade: A
Wind & Power Outages
This was always going to be an easy call. The storm wasn't windy (40+ mph winds) and we didn't have power issues. Aside from one report, we didn't hear anything contradicting that we saw a drier type of snow versus paste.
Grade: A
Overall Impact
Once again, excellent work here. We accurately called that despite the weekend timing and timing later in the evening that this would be a moderate to high impact event. In NE CT it was more moderate, but for much of the state last night was high impact with very high snowfall rates and substantial snowfall. We stated that the banding signal suggested heavy snow that would make travel hazardous, and that was spot on.
Grade: A
Final Grade
It is truly wonderful to know that when the stakes are highest, we do our best work, and for winter you'd be hard pressed to find a higher stakes forecast than one around Christmas. I know there was a fair amount of skepticism at taking the numbers up so aggressively Thursday, and maybe a little at not taking them up even more on Friday, but this was about as good as you can get for a forecast.
I am incredibly proud of this one.
Final Grade: A
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 and trusting SCW.
-DB
Timing
This is where I am most disappointed. In these kind of warm air advection scenarios, the snow usually rolls in faster, and exits faster, than on the guidance. I tried to beat that by forecasting that conditions would deteriorate between 6-10pm from CT from west to east, and while that was right for most, it was too late in western CT which saw flakes start flying just after 5pm. Now, you might say it's just an hour, but in a storm where we went from light snow to near whiteout conditions in under 20 minutes, that's not great. The saving grace here is that we identified the earlier start time and put out a warning 2.5 hours before flakes started flying.
Other than that, the forecast was great. We called the quick change from light to heavy snow, and accurately called the snow being gone before 9am, though that too was a little on the earlier side. We accurately called that the worst was essentially from onset through the early morning hours. That piece of information was vital.
So great overall, but that missed hour really bugs me.
Grade: A-
Snow & Ice Accumulation
Folks, I am incredibly excited that we held to our map. Not only did it seem like we were one of the first out there with a more aggressive call on Thursday, but when the models were aggressive even hours before the storm started yesterday we didn't fully buy widespread double digits that would have made us up the numbers to a 6-10 or 6-12. Not that it matters to be first, but the best is being first and right, and I feel like we were there.
Now, the result isn't perfect. It wasn't further southwest that did the best in this storm as the banding ended up further north (as we suspected it might), and in our 2-5" zone New London County did very well, with a few spots above but within an inch of our 5" ceiling and one spot with a surprise (and believable) 8", but we still did an excellent job here.
That was about as good as you can get, and I'm proud of that.
Grade: A
Wind & Power Outages
This was always going to be an easy call. The storm wasn't windy (40+ mph winds) and we didn't have power issues. Aside from one report, we didn't hear anything contradicting that we saw a drier type of snow versus paste.
Grade: A
Overall Impact
Once again, excellent work here. We accurately called that despite the weekend timing and timing later in the evening that this would be a moderate to high impact event. In NE CT it was more moderate, but for much of the state last night was high impact with very high snowfall rates and substantial snowfall. We stated that the banding signal suggested heavy snow that would make travel hazardous, and that was spot on.
Grade: A
Final Grade
It is truly wonderful to know that when the stakes are highest, we do our best work, and for winter you'd be hard pressed to find a higher stakes forecast than one around Christmas. I know there was a fair amount of skepticism at taking the numbers up so aggressively Thursday, and maybe a little at not taking them up even more on Friday, but this was about as good as you can get for a forecast.
I am incredibly proud of this one.
Final Grade: A
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 and trusting SCW.
-DB
