is_snow_day#

hydrometlib.meteorology.is_snow_day(albedo_expr, albedo_min_threshold, albedo_max_threshold)[source]#

Calculate if a given day is a snow day. True is snow, False if not.

\[\begin{split}\text{snow}_t = \begin{cases} \alpha_t \ge \tau_{max} & \text{if } \alpha_{t-1} \text{ is null} \\ \alpha_t \ge \tau_{min} & \text{if } \alpha_{t-1} \ge \tau_{max} \\ \alpha_t \ge \tau_{max} & \text{otherwise} \end{cases}\end{split}\]

where \(\alpha_t\) is today’s albedo, \(\alpha_{t-1}\) yesterday’s, \(\tau_{min}\) the lower threshold and \(\tau_{max}\) the upper. Below the corresponding threshold the result is False; if it falls between the two it is null.

Simple rules:

  • If today’s albedo is None, then is_snow_day is None

  • albedo >= albedo_max_threshold is a proxy for is_snow_day = True

  • albedo < albedo_min_threshold is a proxy for is_snow_day = False

Normally: albedo_min_threshold = 0.5, albedo_max_threshold = 0.35, see: https://doi.org/10.1002/hyp.14048

Complex rules:

  • It is more likely that today is (not) a snow day if yesterday was (not).

  • If there was snow the previous day, i.e. the previous day’s albedo >= 0.5, then

    the current day is a snow day if the albedo > 0.35.

  • If there was no snow the previous day, i.e. the previous day’s albedo < 0.5, then

    the current day is a snow day if the albedo >= 0.5.

Parameters:

  • albedo_expr (Expr) – Albedo - measure of reflection with values between 0 and 1 [unitless fraction]

  • albedo_min_threshold (Expr) – Site attribute - albedo threshold below which there is no snow [unitless fraction, 0-1]

  • albedo_max_threshold (Expr) – Site attribute - albedo threshold above which there is snow [unitless fraction, 0-1]

Return type:

Expr

Returns:

Expression or Series with boolean values.

Note

Order-dependent: rows must be sorted by time (one row per day), as the calculation compares each day with the previous one.