SNODAS
SNODAS provides modeled snow data daily at 1 km resolution grid cells from 2003 to present, combining satellite observations, ground-based measurements, and numerical weather models. DEVISE provides the following SNODAS variables.
Cumulative Snow Depth (snowdepth-cum)
This is a derived variable from SNODAS snow depth (snowdepth) and represents the cumulative amount of snow gain.
- Daily data does not exist for this variable.
- Monthly data are the summation of each day’s snow depth within the month
\[\text{Monthly snowdepth-cum} = \sum_{i=1}^{d} \text{daily snowdepth-cum}_i \]
\(d\): # of days in the month | \(i\): Current day (iterator)
- Annual data are the cumulative sum of each day’s snow depth within the water year (Oct 1 - Sep 30 of the given year, e.g. 10/01/2003 - 09/30/2004 would be labeled as 01/01/2004).
\[\text{Annual snowdepth-cum} = \sum_{i=1}^{d} \text{daily snowdepth-cum}_i \]
\(d\): # of days in the water year | \(i\): Current day (iterator)
% of Days Snow Depth > 1.5 in (38mm, snowcover)
This is a derived variable from SNODAS snow days (snowdays) and represents the percentage of days snow depth was greater than 38 mm (1.5 inches).
- Daily data is unavailable for this variable.
- Monthly data is the percentage of days with snow within the month
\[\text{Monthly snowcover %} = \frac{\text{Days with snowcover}}{d} \times 100\] \(d\): # of days in the month
- Annual data are the percentage of days within the water year (Oct 1 - Sep 30 of the given year, e.g. 10/01/2003 - 09/30/2004 would be labeled as 01/01/2004).
\[\text{Annual snowcover %} = \frac{\text{Days with snowcover}}{d} \times 100\]
\(d\): # of days in the water year
# of Days Snow Depth > 1.5 in (38mm, snowdays)
This is a derived variable from SNODAS snow depth (snowdepth) and represents a portion of Winter Severity. It is the count of the number of days the snow depth was greater than 38 mm (1.5 inches), calculated on a cell by cell basis on three temporal scales (daily, monthly, and annually).
- Daily data represent a binary response of 1 (true) or 0 (false)
\(\text{snowdepth daily} >\) 1.5 \(inches\): 1 snowday
\(\text{snowdepth daily} <\) 1.5 \(inches\): 0 snowday
- Monthly data are the summation of each day’s value within the month
\[\text{Monthly snowdays} = \sum_{i=1}^{d} \text{daily snowday}_i \] \(d\): # of days in the month | \(i\): Current day (iterator)
- Annual data are the summation of each day’s value within the water year (Oct 1 - Sep 30 of the given year, e.g. 10/01/2003 - 09/30/2004 would be labeled as 01/01/2004).
\[\text{Annual snowdays} = \sum_{i=1}^{d} \text{daily snowday}_i \]
\(d\): # of days in the water year | \(i\): Current day (iterator)
Snow Depth (snowdepth)
Daily snapshots of Snow Depth calculated on a cell by cell basis on three temporal scales (daily, monthly, and annually).
- Daily data represent the raw value from SNODAS
\[\text{Daily snowdepth spatial layer unit} = \frac{\sum_{j=0}^{n} ({snowdepth}_j)}{n}\]
\[\text{Daily snowdepth cell} = \text{snowdepth}_{j}\]
\(j\): current cell | \(n\): # of cells in the spatial layer unit
- Monthly data are the average of each day’s value within the month
\[\text{Monthly snowdepth} = \frac{\sum_{i=1}^{d} \text{daily snowdepth}_i}{d} \]
\(d\): # of days in the month | \(i\): Current day (iterator)
- Annual data are the average of each day’s value within the water year (Oct 1 - Sep 30 of the given year, e.g. 10/01/2003 - 09/30/2004 would be labeled as 01/01/2004).
\[\text{Annual snowdepth} = \frac{\sum_{i=1}^{d} \text{daily snowdepth}_i}{d} \]
\(d\): # of days in the water year | \(i\): Current day (iterator)
Snow Depth Accumulation (snowdepth-accum)
This is a derived variable from SNODAS snow depth (snowdepth) and represents the amount of snow gain compared to the previous day.
- Daily data represent the change in snow depth from the previous day. If the value is negative, it is changed to 0.
\[\text{Daily snowdepth-accum} = \text{snowdepth-accum}_{today} - \text{snowdepth-accum}_{yesterday}\] \(\text{Daily snowdepth-accum} <0\): 0
- Monthly data are the summation of each day’s gain within the month
\[\text{Monthly snowdepth-accum} = \sum_{i=1}^{d} \text{Daily snow depth-accum}_i \]
\(d\): # of days in the month | \(i\): Current day (iterator)
- Annual data are the summation of each day’s gain within the water year (Oct 1 - Sep 30 of the given year, e.g. 10/01/2003 - 09/30/2004 would be labeled as 01/01/2004).
\[\text{Annual snowdepth-accu} = \sum_{i=1}^{d} \text{Daily snowdepth-accum}_i \]
\(d\): # of days in the water year | \(i\): Current day (iterator)
Snowmelt (snowmelt)
This is a derived variable from SNODAS snow depth (snowdepth) and represents the amount of snow loss compared to the previous day.
- Daily data represent the change in snow depth from the previous day. If the value is negative, it is changed to 0.
\[\text{Daily snowmelt} = snowmelt_{yesterday} - snowmelt_{today}\] \(\text{Daily snowmelt} < 0\): 0
- Monthly data are the summation of each day’s loss within the month
\[\text{Monthly snowmelt} = \sum_{i=1}^{d} \text{(Daily snowmelt)}_i \]
\(d\): # of days in the month | \(i\): Current day (iterator)
- Annual data are the summation of each day’s loss within the water year (Oct 1 - Sep 30 of the given year, e.g. 10/01/2003 - 09/30/2004 would be labeled as 01/01/2004).
\[\text{Annual snowmelt} = \sum_{i=1}^{d} \text{(Daily snowmelt)}_i \]
\(d\): # of days in the water year | \(i\): Current day (iterator)
Start Day of Winter (snowstart)
This is a derived variable from SNODAS snow depth (snowdepth) and represents the Day of Year snow began to accumulate and winter begins (7 consecutive days of at least 2.54 mm (0.1 inch) of snow).
- Daily & monthly data are unavailable for this this variable.
- Annual data describe the Day of Year snow accumulated and winter begins for the water year (Oct 1 - Sep 30 of the given year, e.g. 10/01/2003 - 09/30/2004 would be labeled as 01/01/2004).
Snow Water Equivalent (swe)
Daily SWE (Snow Water Equivalent, amount of water in the snowpack) calculated on a cell by cell basis on three temporal scales (daily, monthly, and annually).
- Daily data represent the raw value from SNODAS
\[\text{Daily swe area} = \frac{\sum_{j=0}^{n} ({swe}_j)}{n}\] \[\text{Daily swe cell} = \text{swe}_{j}\]
\(j\): current cell | \(n\): total cells in spatial layer unit
- Monthly data are the average of each day’s value within the month
\[\text{Monthly swe} = \frac{\sum_{i=1}^{d} \text{daily swe}_i}{d} \]
\(d\): # of days in the month | \(i\): Current day (iterator)
- Annual data are the average of each day’s value within the water year (Oct 1 - Sep 30 of the given year, e.g. 10/01/2003 - 09/30/2004 would be labeled as 01/01/2004).
\[\text{Annual swe} = \frac{\sum_{i=1}^{d} \text{daily swe}_i}{d} \] \(d\): # of days in the water year | \(i\): Current day (iterator)