Arisia always seems to coincide with the coldest weekend of the winter. As a prelude to the 2009 edition, halfway down this
AccuWeather article, see the long-range GFS temperature
forecast map for New England on Friday morning (1/16). See how Boston is shown at approximately -10F. The long-range forecast should not be taken too literally, especially when the model results are this extreme, but be prepared.
Brrrrr.
PS - post corrected for degrees C/F confusion. Also NOAA's
Boston Forecast (not strictly GFS-based) shows temperatures around zero, wind chill -11F. Still cold.