An illustrated step-by-step guide for calculating Chill Portions (CP) using weather data and the Dynamic Model. Available here: The guide, a PowerPoint presentation: Dynamic Model & Chill Accumulation Guide Glozer (pdf) and The Dynamic Model, an Excel file: Dynamic Model (xls)

• California often provides too little chilling for optimum dormancy and rest-breaking for some chill-requiring crops. Research to overcome lack of chilling includes developing methods to measure chill accumulation under California’s conditions.  

• Chill accumulation can be calculated using various mathematical models. UC Davis researchers, with the cooperation of many growers, have tested the Dynamic Model as a way of calculating chill accumulation. The model calculates chilling accumulation as ‘chill portions’ using a range of temperatures from ~35-55°F, and accounts for chill cancellation due to fluctuating warm temperatures.

Hourly data is needed for the Dynamic Model. Information and calculation instructions for those who collect temperature data every 10 minutes is provided. (added 12/14/09)