There’s no doubt that the last snowstorm was a complex beast. In fact, many of our computer models had a hard time trying to pinpoint exactly where the storm would be situated, even 24 hours before the storm was set to hit the region.
As the storm started to make its pass, the National Weather Services (and some local news stations) actually INCREASED “Maximum Possible Snowfall” and “Most Likely Snowfall” estimates.
Why? Newer model data showed the storm’s “wrap-around” bands pushing further into portions of eastern and central Southern New England for a longer period of time than initially thought. Furthermore, temperatures did not seem to be as warm as initially anticipated over eastern MA locations at the beginning of the storm. This meant that both: 1. More precipitation will fall in the form of snow, rather than mix/rain.
2. Colder temperatures would cause the snowfall ratios to increase, meaning higher snowfall accumulation, even with similar forecasted QPF values.
The National Weather Service also upgraded portions of Southeastern MA (Bristol and Plymouth Counties) into the Winter Storm Warning as a result of the higher forecast totals.
By 4:30 PM Sunday, the Winter Storm Warning for coastal Plymouth County was dropped and replaced by a Winter Weather Advisory. By around 6:30 PM, the rest of Southeastern MA was also downgraded as well.
So what actually happened? Well…
As the precip shield pushed into our area through midday Sunday, banding features set up as expected through most of the area. Onshore flow eroded the cold air over southeastern/east-central MA as initially expected before the storm (but after the NWS ruled against this in their updated assessment early Sunday afternoon. Though, to be fair, they did mention the possibility…) However, the bombing surface Low formed slightly East than expected and moved out more quickly. This nudge allowed for most of the heavier bands to miss East-Central MA and even a large portion of Eastern MA (for the most part) and the precip. that DID fall in those areas was not as heavy as predicted. By midday Sunday, models trended away from the NAM’s more robust predicted totals and more towards the HRRR’s (ultimately better) values. Forecasters who placed more credence in the NAM’s solutions were proven wrong.
The result? Much lower snowfall totals than forecast. Here are some NWS estimated values 24 hours before the storm onset, compared to what verified. Note that these were the forecasted values BEFORE the NWS increased them even more early Sunday afternoon:
Saturday AM Forecasted Snowfall Totals From NWS vs. Reported:
Fitchburg/Leominster, MA -- Forecasted (as of 7:42 AM, 2/11): 13". Verified: 9.2" Worcester, MA -- Forecasted (as of 7:42 AM, 2/11): 11". Verified: 6.8" Taunton, MA -- Forecasted (as of 7:42 AM, 2/11): 4". Verified: 3" Boston, MA -- Forecasted (as of 7:42 AM, 2/11): 6". Verified: 4" Plymouth, MA -- Forecasted (as of 7:42 AM, 2/11): 5". Verified: 2" Amherst, MA -- Forecasted (as of 7:42 AM, 2/11): 10". Verified: 6.9" Provincetown, MA -- Forecasted (as of 7:42 AM, 2/11): 7". Verified: 2" Greenfield, MA -- Forecasted (as of 7:42 AM, 2/11): 11". Verified: 8"
To be fair, many forecast max wind gust values did verify. Every county in RI had a location with a max wind gust measuring > 50 mph. While NWS did not report any gusts over 60 mph, there were a few locations that gusted over 55 mph.
In conclusion, it’s easy to scorn over under/over-forecasting, but quite easy to forget when forecasts verify. Now we wait for the next storm…