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About Apple Frost Risk Maps

The maps and animations are for Red Delicious, Empire, and McIntosh apples. The Accumulated Chill map shows number of chill units acquired by the plant. The North Carolina Chill model (Shaultout and Unrath, 1983) is used. Growing Degree Days are a measure of heat accumulation and hence bud development. Base 43°F GDD accumulate only after the tree’s winter chill requirement (1000-1200 depending on variety) has been met. The Phenological Stages map shows the current estimated stage of bud development. The Kill Probability map compares the hardiness temperature at each phenological stage to the observed daily air temperature. Crop damage occurs when the observed temperature falls below the hardiness value. These maps are produced from mid-September through the end of June and are updated three times a day around 11am, 1pm, and 3pm.

Shaultout, D. and Unrath, R. (1983). Rest completion prediction model for Starkrimson Delicious apples. Journal of American Society of Horticultural Sciences 108: 957–961.

About Apple Seasonal Kill Risk Maps

These maps show the historical (1979-2015) probability of experiencing a minimum temperature that is capable killing a bud on any day from the present date through June 30. The set of three maps reflect temperatures capable of killing 10%, 50% and 90% of the buds. Since lethal temperatures increase as bud development progresses, separate sets of maps are given for each phenological stage. Users should consult those maps that reflect the current development stage of trees in their orchard.

The colors on the maps reflect the kill-producing temperature probabilities. Red indicates that more than 90% of the historical years saw a temperature between today and June 30 that would result in bud kill. In orange areas between 50 and 90% of the historical years saw a temperature between today and June 30 that would have resulted in bud kill; in yellow areas between 10 and 50% would have resulted in bud kill. Green areas indicate where less than 10% of historical years saw temperatures that would have caused a kill event.

The maps are updated daily around 5:00 a.m