Forecast for Weekend Snows Too Aggressive
Dry Air Mitigating Factor
Clearly the forecast for this weekend's snows was not one of the better efforts from Eastern Mass Weather, as the 6-10" and 5-8" forecast ranges ended up verifying as 5-8" and 3-6".
The short answer as to why this was the case is that the encroachment of the drier air from the south, as discussed in the Final Call, was both faster and more aggressive than expected.
This acted to essentially put an end to accumulating snowfall by around dawn on Sunday, as opposed to lingering throughout much of the morning. There were some subtle warning signs amongst guidance that snowfall could be a slightly less prolific than forecast as a direct result of less proficient snow growth.
Lift and Moisture Less Than Ideally placed Within Snow Growth Region
Here is data derived from the NAM forecast sounding for Lawrence, MA during yesterday's
storm.
Note how the maximum area of lift and moisture was not colocated with the -12 to -18c snow growth region, which is the ideal thermal range within the atmosphere for moisture and lift to combine for the optimal production of snow flakes, which of course accumulate the most efficiently. While this data was considered, it was obviously not weighted heavily enough into the forecast. The reason forecasting is so difficult is because not only is it incumbent on the forecaster to complete an exhaustive review of the data, but its also crucial to determine how heavily two weight each piece of data and when to disregard.
Final Grade: C+