Usage within USA
When used within the continental USA, SASHA figures out the default date range for averaging sunlight as follows:
- SASHA finds the weather stations nearest your current GPS coordinates
- SASHA retrieves the last spring frost date from that weather station
- SASHA retrieves the first fall frost date from that weather station
- SASHA uses these two dates as the default “From” date and “To” date over which to average daily hours of direct sunlight.
- The user can set any other date range from 2 days to 365 days in the options menu.
These frost dates are computed by NOAA and described in “NOAA’s 1981-2010 Climate Normals: Supplemental Normals” (https://www.ncdc.noaa.gov/data-access/land-based-station-data/land-based-datasets/climate-normals/1981-2010-normals-data). SASHA sets the “From:” date from the earliest spring date after which there is less than a 10% probability of frost, and sets the “To:” date to the latest fall date before which there is less than a 10% probability of frost.
These data are compressed and stored inside SASHA; SASHA does not need access to the internet to obtain these values.
Usage outside the USA
If SASHA is used in a location which is more than 50km away from one of NOAA’s weather stations, a warning will be presented to the user, and the default “From:” and “To:” dates will be inaccurate. This will be the case in virtually all locations outside the USA.
The user should click on the options menu and choose the “set custom date range” option.