Additional Climate Variables

**Yearly Variables**
### Cold:
- [ ] Number of days with killing frosts (killing @ -4C)= pGSKF by month.
- [ ] Daymet includes snow water equivalent, which we can use to more directly estimate monthly precipitation as snow.
- [ ] Annual Growing Season Start Date (GSSD) (soil temperature >5C)
- [ ] Annual Growing Season Start Date delay (based on sum of low winter temps with no snow cover)
### Heat
- [ ] Monthly sum of days with tmax exceeding temps in 5C intervals from 30-50C
### Drought
- [ ] Annual Winter precip deficit adjusted soil water (SMI) or CMD.total (adds lack of nonGS soil recharge to GS CMD)

**Normal Period Variables (extremes) **
- [ ] Monthly/Seasonal Normal period number of years with a killing frost event by month (values are 0-20 years)
- [ ] Annual Drought period: multiyear drought (highest 3-year moving sum of accumulated CMD.total over the normal period)
- [ ] Palmer Drought Severity Index
- [ ] Monthly/Seasonal Excess Heat Days. Mean and max number of excess days by month over 20 years. (for 30, 35, 40, 45, 50+)

The issue lists additional yearly and normal-period climate variables but names no files, tests, or entry points. Start by mapping the package's existing climate-variable calculation workflow and clarifying which variables and definitions are in scope. Done means the agreed variables are implemented with verification for their stated periods and thresholds.

Written by the indexing model from the issue text.