The source of this snow data is SNODAS (Snow Data Assimilation System) product from NSIDC (National Snow and Ice Data Center).
The snow data coverage is continental USA only.
The snow values are updated once a day with a one day lag. All sites within the continental USA, will have snow data starting 2012-03-01 onwards. When a new site is added, or its address changed, all the historical snow data will be available for that site starting the following day onwards. There will be a delay of up to 24 hours.
Ex: After 2016-12-18 0730 US/Pacific (this is when the images are made available to us via SNODAS) we will have snow data for the day of 2016-12-17.
Locus does not have control in terms of when these snow images are made available to, and it's possible for snow data to take 2 days to show up in the data API, if the delay is from SNODAS.
Snow data is only available if the user making the API call has VI enabled. Please contact your account manager to discuss VI further.