BY JIM HOLCOMB & BOB ROBINSON

CLEARWEST, INC.

The early outbreak of cold air at the end of this October 2002 comes almost 11 years to the day after a similar destructive freeze in 1991. While the affects of cold temperatures on late harvested varieties such as Fujis may not be well known, it is evident that an extended cold period during harvest time reduces the quality of the fruit. This article looks at the frequency and intensity of past early cold outbreaks into Eastern Washington.

The consensus of local fieldmen is that the Fuji will be harvested in most years from about Oct. 10 to Nov. 10. The graph shows the first date in the fall of each year, from 1935 to 2002, that the mean temperature for the day (average of highest and lowest temperatures) dropped to 32 degrees or below at Wenatchee. It is likely that if the mean temperature for the day remains below freezing at this time of the year, especially for more than two consecutive days, this would cause freezing of apples. As the graph indicates, there have been a number of years since 1935 when the first day of mean temperature at or below 32 deg. have occurred before Nov. 10 and a few cases before Oct. 31. Not all of these early cold years would have been serious because in some cases the cold only lasted one day. However, most were associated with early Arctic outbreaks that lasted for several consecutive days.

This study was expanded to look at the situation throughout Central Washington and past records from Omak, Ephrata, Yakima and Kennewick were also examined. These showed that early outbreaks of cold air that could have been long enough and cold enough to have presented a problem with fruit quality, occurred on nine occasions. Before 2002, early cold outbreaks happened in 1935, 1936, 1940, 1945, 1951, 1971, 1973, 1984, and 1991. All of these outbreaks resulted in at least 3 consecutive days in which the mean temperature for the day was below freezing in at least one of the Central Washington fruit growing districts. As expected, the Okanogan district took the brunt of these cold outbreaks and usually recorded the lowest temperatures and longest duration of freezing. Omak had nearly twice as many days of sub-freezing mean temperatures as Kennewick during these cold outbreaks. However, the outbreaks were usually general and most of them reached the southern districts of the Yakima Valley for at least a few days during each episode.

The cold would always reach the Okanogan district first since it originated from Canada and would spread south to the Yakima area by the next day. The cold normally persisted a day or two longer in the Okanogan after the other districts to the south began to warm.

The most severe outbreak in terms of degree and duration of cold was in 1935. The cold air pushed into the state on Oct. 29, and lasted through the first week of November. On Nov. 1, minimums dropped to 5 above at Omak, 6 at Wenatchee, 8 at Ephrata and 9 above at Yakima and Kennewick. The mean temperatures stayed below freezing for a week in all districts. A less severe outbreak occurred the following year, in early November of 1936, with cold temperatures persisting for a week in the Okanogan.

In 1945, a cold outbreak beginning on Nov. 5 sent temperatures down to 9 above at Omak and 15 at Kennewick. The mean daily temperatures stayed below freezing for eight consecutive days in the Okanogan, Wenatchee and northern Basin areas and for four consecutive days in the Yakima Valley.

The 1971 outbreak came down on Oct. 28, very similar in duration to this year and to 1991, while the 1984 outbreak was limited to only three days.. The duration of cold this year was anywhere from 5 to 7 days, but the severity could be considered the greatest since the 1935 episode. In late October and early November of 2002, daily minimum temperature records were broken or tied on 6 days in both Wenatchee and Yakima. A minimum on Oct 31, 2002 of 13 at Wenatchee, and 4 above at Yakima were the coldest ever recorded in the month of October. Characteristic of the 2002 outbreak were dewpoints near or below zero deg. F. and a more uniform number of days duration across Central Washington.

As can be seen from this investigation, early (prior to Nov. 11) cold outbreaks are not particularly rare in this area. While there was no regular periodicity to them, one came along every 5 to 10 years (an average of 7.5 years) except for the 20-year period from 1951 to 1971. However, even in 1955 there was a severe Arctic outbreak, but that occurred on Nov. 11. The outbreaks normally lasted 4 to 8 days in which the mean temperature for the day remained near or below freezing. The Okanogan took the brunt of the outbreaks but all districts were affected by the cold in most episodes. Also it appears that if fruit is harvested before Oct. 25, there is little chance that cold damage will occur since all outbreaks in the past have occurred after this date.