Phew. We made it. It’s been a long week here at SCW, with the first major snowstorm of the season being one of the more difficult forecasts I can remember making during the almost three years that we’ve been doing this. We had our ups and downs for sure, with model guidance going from big hit to miss to small hit back to a big hit, but for only some of the state, within the span of a day or two. Rather difficult for a forecast team to process and communicate, and it most certainly made for some late nights and stressful model runs here at SCW. However, in the end, we came to a forecast that I thought verified, on the whole, exceptionally well, and I’m very happy with how we did during this system.
This discussion will be primarily a post-mortem of the system that we just had, where we take a quick walk back through the timeline leading up to it, break down our forecast, and grade ourselves on our performance (and you can grade us also!). We decided to introduce this discussion format because far too often in meteorology, forecasts die when the event takes place, and they are never analyzed and revisited, whether good or bad. We felt that it would be a good learning experience for us to go back and walk through our forecast (as well as hear from you all about how you think we did), and hopefully it will allow us to better serve you all in the future. We’ll have a quick forecast outline for the week ahead at the end of this discussion, with a detailed full forecasters discussion coming tomorrow evening.
But first, welcome!
We’ll go into more detail about the event and what we noticed from it(as well as grade our own forecast) in a minute, but first, I would like to welcome our new additions to the SCW family! We had quite the surge of traffic over the last few days, with over eighteen thousand people visiting the website for the first time and over a hundred and thirty thousand people viewing our posts on Facebook (In case you’re curious, that’s our third highest total of all time behind the lead up to the system on January 22nd, 2014 and the leadup to the Blizzard of 2015 on January 27th, 2015). To all our new readers, we’re glad that you found us, and we hope that you will continue to read and interact with SCW for many more storms to come. To our loyal regulars, thank you for spreading the word about us to your friends and for continuing to be unquestionably the best readership base of any website out there, meteorological or otherwise. We wouldn’t be where we are today without all of you.
A look back
Back to the storm. As you may remember, we were tracking this system from quite a ways out, with the system first making an appearance on guidance late last week. Originally, it was modeled as a large storm regionwide, and excellent model continuity on that front continued through all of last weekend and into last Monday. As such, we began to sound the alarms last Monday night, with Greg’s forecast discussion outlining the potential for a significant event to impact the state this weekend. However, within a few hours after hitting the post button on that discussion, model guidance began to shift rapidly, with an area of strong confluence introduced to our north and the development of an additional piece of vorticity that would interact with the low and pull it east appearing on the models. As such, the northern edge of the storm was quickly slashed, and the model consensus for the state very quickly went from a strong winter storm to almost nothing.
While we began hedging our wording in our discussions to account for the possibility of a miss, behind the scenes, the team was generally still confident in at least some snow for the state. The modeling continued to be bleak, however, with most guidance continuing to show a miss well south of us. In fact, Thursday morning, after issuing an initial snow map that showed a minor system for most of the state, accounting for what we believed would be a continued minor north trend that had begun the night before, the 12z guidance dropped even further south, with most of the state seeing nothing at all. We were about ready to pull the plug and cancel any idea of a significant impact from the storm when the 18z NAM rolled out, and the northern edge of the storm was hundreds of miles north of the previous consensus. A head scratcher for sure, especially since the NAM’s track record has been atrocious when it comes to winter storms, with the model being notoriously overamped and precipitation happy, extending precipitation shields far greater than reality on a consistent basis. Matters were only compounded when the 18z GFS, a far more reliable model than the NAM, made a definitive nod towards it and shifted a substantial amount north as well. We were now in a situation where the model consensus brought an inch or two of snow to the shoreline and little elsewhere, while the NAM would result in a blizzard for the entire state.
We hedged our bets, dropping totals across most of the state while increasing them along the shoreline to account for the possibility of the edge of the sharp band of heavier snow catching the shoreline. Turns out that we didn’t increase them enough, as the NAM proved to be more correct than not with the idea of a further north track, and while it’s northern edge was overdone as it usually is(Otherwise the whole state would have seen the totals we saw on the shoreline), it’s main idea of a much further north solution than the current consensus proved to be correct, as over the next 24 hours, we saw almost all of the global guidance continue to tick north, and with no signs of the trend stopping, we became confident in a significant snowstorm for the coastline with the meat of the heavier band of snow falling squarely on Southern Connecticut. As such, on the evening of the systems arrival, we upgraded the shoreline to warning level amounts, and advised preparations for a high-impact system, and we increased totals somewhat across the rest of the state as well.
As a reminder, here are the three forecast maps that we issued, from oldest to newest left to right, for this system.
So how did we do? Overall, I, and the rest of the team, think we verified pretty well. There were definitely some areas that we could have done better on, specifically, the western portions immediate shoreline and the northeast corner of the state, both of which received more snow than we forecast, but overall, I think we did pretty well. Many have asked why we did not upgrade our map to include higher amounts for the shoreline once it became clear early on in the storm that there would be some totals over a foot. The answer is twofold. First, our resources during a storm are limited, and we felt that they were better used answering reader questions, doing rapid-fire radar updates, and communicating with those who rely on us for forecasts rather than taking time away from what was going on right now to issue a new map(Each of our maps takes about an hour to make). In the grand scheme of things, the difference between 12” and 16” of snow is not all that large, as both are significant events that require preparation and planning. Since we had already forecast a significant event for that area, we felt that upgrading was not the best use of our resources since the eventual end impact would not be substantially different. We did mention several times in text and comments that we thought some snow totals would be higher on the shoreline than we had forecast once the storm was underway.
As far as the northeast corner of the state goes, that was our only true “bust” of the storm in my opinion. We as a forecast team were skeptical that the heavy band would make it that far north, and once it did and proved us wrong, it was too late to issue an updated map, as most of the snow came in a short period of time and it became a nowcast situation.
On the positive side, I’m happy about our performance in the northern portions of the state overall. Several models brought warning level snows all the way to the northwest corner of the state, and several forecast outlets, including the National Weather Service, jumped on those models and issued Winter Storm Warnings for the whole state. We remained relatively constant with our prediction as to where the cutoff of the heavier snow would be, and except for the northeast corner, verified that almost perfectly. Nailing such a sharp cutoff is not an easy thing to do, and I’m very happy with how close we were able to come to it.
Initial recognition: A SCW recognized this systems potential as far as a week out, and had a detailed discussion on it illustrating the potential for a major storm five days out. Those are very impressive lead times in meteorology.
Midrange: B I think we backed off the idea of a major storm a bit too much, but overall I think we did a good job illustrating the shifts in guidance and the fluctuating potential.
Preliminary forecasts: B-: Our initial maps, while getting the gradients reasonably correct, were too low on amounts for a large chunk of the state.
Final forecast: B+: Overall, I think our final call was pretty good, although we missed the higher amounts along the shoreline and the northeast corner of the state. I was very happy with our positioning of the cutoff of the heavier snows.
Rapid fire updates/communication B+: We recognized quickly that the storm would be a bit more intense than forecast for most of the state, and I think we did a good job communicating current conditions and uncertainties.
Overall Grade B+: A solid start to the season for us.
We want to hear what you think! Click here to be redirected to a quick survey about how you think we did with this last system. Your feedback is greatly appreciated and will help us to do better for you in the future!
Here’s an awesome visual satellite image from this morning. Look at the sharp gradient of snowfall in northwest Connecticut! If you're interested in the unofficial final snowfall reports that were sent to the National Weather Service, you can find them here(for the shoreline counties), here(for Litchfield county), and here(for Hartford, Tolland and Windham counties).
Generally calm and warmer weather appears in the cards for most of the week, with our next substantial snow chance coming on Friday from a late-developing Miller B system to our east. At this time, the UKMET, along with Euro and it’s ensembles, favor a solution that would bring some snow to the state on Friday, while the GFS and GGEM are further out to sea and as a result keep the precipitation shield off the coastline to our east. Temperatures are marginal, but most likely snow supporting for most away from the immediate coastline. At this point in time, I will simply add a chance of rain and snow to the forecast for Thursday night through Friday, and we will address this potential system in much more detail later in the week should it remain a possibility on model guidance. I have also included a slight chance of snow on Wednesday night from a frontal wave that develops along a cold front to our southeast, which most modeling keeps offshore. However, the Canadian model brings a light snowfall to our area from this wave, with an inch or two in the southeast corner of the state, and as such I will paint in a slight chance of snow to account for this possibility.
Otherwise, slightly above normal temperatures throughout the forecast period are expected.
Here are the dailies
Monday: Mostly sunny, with highs in the mid to upper 30s.
Tuesday: Mostly cloudy, with highs in the lower 40s.
Wednesday: A slight chance of snow, especially in SE sections of the state, otherwise, mostly cloudy, with highs in the mid to upper 30s. Chance of precipitation is 20%, except 35% southeast of a line from New Haven to Willimantic to the RI border.
Thursday: Mostly sunny, with highs in the mid 30s.
Friday: A chance of rain and snow, otherwise, mostly cloudy, with highs in the mid 30s. Chance of precipitation is 40%.
Saturday: Partly cloudy, with highs in the lower 40s.
Sunday: Partly cloudy, with highs in the lower 40s.
Much more on the forecast and a look at the long range is coming tomorrow evening, until then, have a great start to the week and thanks for reading SCW!