Garden with Insight v1.0 Help: Weather next day functions: generate today's precipitation (if any)

This function generates the amount of rainfall or snowfall today. If the mean air temperature for the day is below freezing, all of the generated precipitation is regarded as snow; otherwise all of the precipitation is rain. Often in these explanations we will refer to "rain" instead of precipitation -- this always includes both rain and snow.

If the "simulated" option for precipitation is chosen: First the simulation decides if today is a "wet day" by choosing a random number from a uniform distribution from zero to one. If it rained yesterday, the random number is checked against the probability of having a wet day after a wet day. If it didn't rain yesterday, the random number is checked against the probability of having a wet day after a dry day. If the random number is below the probability chosen, it is a wet day. Now, if today has been determined to be a wet day, the simulation generates the amount of rainfall today by choosing it randomly from a distribution of amounts of rainfall. This distribution is called the "skewed normal" distribution, and it takes its mean, standard deviation, and skew coefficient from parameters. Rainfall patterns tend to fall into a skewed normal pattern because a larger number of days have less rain than a non-skewed normal distibution would predict.

If the "always 0.0" option for precipitation is chosen: There is no precipitation today. If the "smoothed" option for precipitation is chosen: A smoothed value is calculated from the long-term monthly values for daily rainfall and that value is used for today's rainfall (instead of randomly choosing an amount from a distribution). If the "unchanging" option for precipitation is chosen: It rains as much as it did yesterday.

EPIC Precipitation
Model contents