HPC's winter weather forecasts are available in ESRI shapefile format from this ftp site.

The guidance is broken down by forecast day, and as you'll note, there are three directories, one
for each day.  In each directory is a .tar file containing the 4 files that are necessary to 
display the shapefiles properly.  Either the "tar" command or standard zip/unzip programs should be 
able to extract the files.  

There are 4 forecasts created per cycle (00Z and 12Z) and they are all valid for a 24-hour period.  
They are:
  - probability of snowfall > 4 inches
  - probability of snowfall > 8 inches
  - probability of snowfall > 12 inches
  - probability of freezing rain > .25 inch

The latest forecasts will always be available in the files with the word "latest" in the filename.
There are also usually several days worth of previous forecasts available; the date and time of 
those forecasts can be identified in the filename.  For example:

The file day1_psnow_gt_04_2010090800.tar is the Day 1 probability of snow greater than 4 inches and 
was issued on September 8, 2010 for the 00Z cycle.  The filenames take the form

day1_psnow_gt_04_yyyymmddcc.tar where:
 - yyyy - 4-digit year
 - mm     2-digit month
 - dd     2-digit day
 - cc     2-digit hour (or cycle). This will either be 00 or 12.

Please note that if no areas are forecast for a particular product, the file size will be 0 bytes.