I learned that in the 1993 Superstorm, was tracking 1.5-2"/hr on the deck and when it approached 10", I checked out the cul-de-sac and found ~6". Low 20s and late afternoon so no delay in accumulation.
(That storm was one of the more disappointing 10"+ events in memory, as essentially every other site in New England had more, and the forecast had been 1-3 feet. Warmth aloft caused heavy riming, such that my 1.70" LE only made 10.3".)
Moderate snow arrived about 4 PM, but without some inch-an-hour S+ we'll fall short of the 5-9" forecast.