Hello,
I struggle a bit to understand the exact definition of the variables accessible through the products of HRRR. I am using Herbie to retrieve the HRRR data, which is very convenient to retrieve all HRRR data since 2014, and fits the requirements of this challenge using the setting priority='azure'.
HRRR variables are listed here, and as it has been already noticed, it already contains a SWE variable (variable 068, WEASD). I compared this variable with the provided SNOTEL data and obtained the following correlations:
We can notice a high correlation (around 0.80) with HRRRv2 released in 2016. The correlation is good in the first months (~december to february) but decreases in the melting season. The corresponding RMSE cumulates all these errors and thus increase over time before decreasing when the SWE levels go to zero. I guess this observation motivates the challenge overall 
Back to my variable question, the documentation is very sparse for newcomers. For instance, how should I retrieve the total snowfall (ASNOW) or total precipitation (APCP) between 2 dates ?
So far if I want the accumulated snowfall from 12:00 to 13:00 on the 1st of january, I download the file at 12:00 and look at the forecast for 1h. Using Herbie: Herbie('2022-01-01 12:00', product='sfc', fxx=1).xarray('ASNOW'). Is it the good way to proceed ?
If you know any documentation on HRRR data it would be very welcome,
Simon