Here is the official description of the service:
“This app searches Twitter for real-time snow reports and displays them on the map.
Tweet the hashtag #uksnow, your location(postcode, town name or geotag your tweet), and rate the snow that is falling out of ten (0/10 for nothing – 10/10 for a blizzard).
You can also include the depth of snow (cm or inches), attach a photo and add a description to your tweet.”
Here is an example: #uksnow N4 7/10 80cm – Can’t open the door
Got to http://uksnowmap.com/ to see the result