A sortable table of historical data for the 2009/10 season can be found HERE
All data comes from 800m in the Ochikura area of Hakuba.
Notes to the data
The data collected here is a reflection of the standard weather observations used by the Canadian Avalanche Association (and taught in their Level 1 Ski Operations course). I have omitted a few data points, such as relative humidity, due to inaccuracy of available instruments in cold weather and also because of the redundancy of such data when recorded at valley floor (humidity is far more meaningful above tree line).
Data is used in assessing snowpack stability. It is best if the data is gathered from a site closest to the environment in which you will ski. For many ski operations this is mostly impractical as measurements must be recorded at 0700 or earlier each day, thus dependency on lift systems and helicopters is a problem. I am lucky to live in a non-suburban area of Hakuba with easy access to my weather station at 800m. Whilst it is not ideal, at a minimum the weather station should produce data that correlates with snow pack stability.
Comment on Snow Density
Density is measured as mass per unit volume. These data observations measure snow density as kg/m3. That is, a square block of snow 100cmx100cmx100cm would weigh so much, expressed in kg. For reference: ice has a density of 917 kg/m3. New snow is considered very light if it has a density of 30 kg/m3.
To determine the percentage of air in a new fall of snow: (1-density of new snow / density of ice) x 100.
Example: (1 - 30 / 917) x 100 = 97% air and only 3% ice. Thats very blower powder.