mask swe with current day fsca

[dschneiderch]

need to mask swe with fsca upon output (maybe in calc_swe.pro?). not sure how to do it.

[dschneiderch]

actually, swe is always more constrained that fsca because swe can't increase while fsca is allowed to vary based on the satellite observations. so maybe you want to mask fsca with swe extent for consistency.