How chill is counted
Chill hours: every hour with a mean temperature from 32 to 45 °F counts as one hour, day or night. Cold hours need not be consecutive, so cold nights count even after a warm afternoon. Approximate needs: Payne 630, Serr 830, Chandler, Hartley and Howard about 1,000.
Chill portions (Dynamic Model) are more realistic: the low 50s still contribute, and warm spells can undo chill that is still building, but a completed portion is never lost. UC's 2024 walnut guidance puts Chandler at about 60 to 65 portions. Portions are model units, not days.
Counting starts Nov 1. The hatched "pledged" segment is what the Weather Tools forecast adds over the next 10 days.
Sources: Counting winter chill · Winter chill and walnut management, 2023-24 · UC Davis: chill hours, units and portions
