Project Goals & Objectives

WARC is recording phenology of cider and heritage apples, pears and plums at several sites with the goal of classifying varieties as “early-, mid-, and late-” blooming and ripening.  Our findings will inform Montana fruit growers in selecting cultivars that will bloom late and ripen early given their local climatic conditions. Bloom data can also help with orchard planning for pollinators and timing for fire blight sprays. The Montana Climate Office will use our data in creating a “Frost Risk Resource” map for apples. We’ll also determine how frequently plum varieties may be susceptible to bloom-time frost damage. Project outcomes will be shared on this web page and in WARC workshops or presentations in the next several years. 

See relative apple fruit maturity for cultivars grown in orchards across Montana.

Preliminary frost risk mapping from the Montana Climate Office 

Prepared by Zach Hoylman

Here, we present a map showing the probability of observing minimum temperatures less than 25 F during critical time periods for apple development, defined here as growing degree days (GDD) between 350 and 500.  To produce this map, we followed a stepwise process. First, we calculated the cumulative GDD over each year and for each location in Montana using the single sine method for years between 1981 - 2010. Next, we located all areas/days (at a 4km resolution) that fell within the GDD range of interest (350 - 500). For each of these locations/days we extracted the associated minimum temperature for that location/day which allowed us to develop a pixel specific distribution of minimum temperatures that fall within the GDD range of interest. Using this minimum temperature dataset, a pixel specific empirical cumulative distribution function was used to estimate the probability that minimum temperatures will  be less than 25F during any day for the period of interest.  In general, frost risk is much higher in the south central portions of Montana, when compared to western and north eastern Montana.

MAP: Probability of Frost for Early Developing Apple Cultivars, Montana Climate Office

probability of frost for early developing apple cultivars map