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Warm nights contribute to low chill hours

I got a phone call today from a peach producer here in Georgia who was wondering why the chill hours this year are so low compared to previous years.  For example, near my office in Watkinsville GA we have only received 28 chill hours from October 1 through yesterday compared to 79 in 2014, 62 in 2013, and 46 in 2012 (based on the chill hour calculator from www.georgiaweather.net).

I think the culprit has a lot to do with the rainy weather and especially the warm nights we have been experiencing lately.  If you look at the rankings of minimum temperature on the Southeast Regional Climate Center’s Perspectives maps for the last few days, many stations are flirting with record high minimum temperatures if not breaking the records outright.  The map for November 5 shows that most of the stations in Florida set record high minimums, while many stations in Georgia, Alabama and the Carolinas were in the top two or three.

I don’t think the lack of chill hours is anything to worry about yet.  We are still early in the chilling season and there should be plenty of time for us to accumulate the needed cold hours the plants need to set fruit.  However, since El Niño winters tend to have more cloudy conditions and hence warmer nights, the total number of chill hours this year is likely to be lower than in some previous years.  The chill calculator for Oconee County from AgroClimate.org (http://agroclimate.org/tools/Chill-Hours-Calculator/#) shows that last year (blue line) got off to an early start but settled down to near the middle of the curve by the end of February.  The pink envelope shows the range of values possible, with the lowest value at a little over 1100 chill hours.  There is little variation between El Niño, La Niña, and neutral years.

high min temp 11-5-2015 ranking  oconee projected chill accum 11-6-2015