A development index is a physical trait that can be expressed numerically as a relative value. The model is an accumulation over time, of growing-degree units calculated from an asymmetric response curve. The graph below is specific to Sweetheart and can be used to assess the progression of development. Weather station data from 34 sites contribute to these models (Columbia Gorge Fruit Growers Weather Network).
How to read the graph:
Information is listed from the start of winter Solstice until the current day (4/6/2019).
The left axis lists the current date, and pertains to the different colored lines, referring to Gorge locations: Dufur, HR Upper Valley, The Dalles, HR Mid Valley, Mosier Dallesport, HR Lower Valley.
The right axis lists relative water content (rwc). The model (blue line) uses rwc as a measure of bud/flower development. This axis will change as development progresses, to show bloom, diameter, fresh weight and redness of fruit.
The two sets of lines both relate to the lower axis – hours from Winter Solstice.
The intersection of the dropdown lines (Dufur, HR Upper Valley, The Dalles, HR Mid Valley, Mosier Dallesport, HR Lower Valley) with the model (blue line) is the predicted bud/flower development value (right axis).
Using the model (blue line), first swelling is predicted to begin at 0.56 rwc (30 VFB hours).
The fastest development at the moment is in the HR Lower Valley, having the warmest ambient air temperature at 25 VFB hours.
Currently, for all gorge locations sampled, none are out of dormancy.