A multi-day snowstorm affected much of Southern Ontario last week between Wednesday and Friday. As part of Instant Weather’s commitment to accountability and transparency, we collected reports from our community after each wave. Thank you to everyone who submitted their report to us!
We also utilized CoCoRaHS which contains an extensive database of reported snowfall totals from all over Southern Ontario. Between the two data sources, we were able to obtain snowfall reports from many locations across the region to compare to our custom forecast for each wave. In the case that we received multiple snowfall reports for a single location, these totals were averaged together to calculate an aggregate total for that location.
Starting with the first wave of the storm which includes snowfall received between Wednesday (Feb. 2) and Thursday (Feb. 3) morning. Our forecast (HERE) had widespread 15-25cm across much of Southwestern and Central Ontario with a localized zone of 20-30cm in Deep Southwestern Ontario.
Based on the data, it’s clear that the system underperformed compared to our forecast with only a handful of locations picking up over 20cm. This is particularly the case in Southwestern Ontario where locations such as Windsor, Chatham-Kent, Sarnia and London had to potential to pick up 20-30cm, but only received around 10-15cm from the first wave. This underperformance is also seen throughout the Golden Horseshoe where most locations in the GTA and Hamilton region reported around 5-10cm. Central Ontario was a bit better where most locations were within or very close to our forecast range, especially in the Muskoka and Kawartha Lakes region.
Why did this first round underperform? We had fairly good confidence based on the data, however, the major issue was the temperature which didn’t fall quite as fast as we expected. This meant that most locations in the south and around Lake Ontario saw a more prolonged period of rain or wet snow before transitioning over to regular accumulating snow. The snow that did fall ended up being wetter which has a harder time to accumulate so totals in the aforementioned regions were significantly cut down. Moving forward, we will be more careful of forecasting higher snowfall totals with the temperature near the freezing mark as the simulated totals don’t account for any melting.
When comparing the data to our forecast, we correctly forecasted around 20% of locations mostly in Central Ontario. This is not up to our standards and we will work towards tweaking our approach as mentioned. The slight underperformance in most areas is seen in the 42% of locations that were within 5cm of our forecast range. Around 25% of locations were off by more than 5cm which is mostly for those in Deep Southwestern Ontario that saw more mixing and a slower switch over. Overall, the error in our forecast was 4.6cm.
