WINTER FREEZES OF FRUIT-TREES IN THE OKANAGAN VALLEY, BRITISH-COLUMBIA - RELATIONSHIP WITH THE PACIFIC NORTH-AMERICA TELECONNECTION AND THEEL-NINO-SOUTHERN-OSCILLATION

Every 5-7 years there are severe winter freezes in the Okanagan Valley which lower yields or kill apple trees. Our goal was to determine whe ther winter freezes (December, January and February) could be related to the Pacific North America teleconnection (PNA) and the El Nine/Sout hern Oscillation (ENSO). Fall and spring freezes were also discussed. A list of ENSO warm event, cold event and neutral years was available from 1947 to 1986 as well as monthly temperature and precipitation rec ords. Months were classified as having a PNA, reverse PNA (r-PNA) or n eutral pattern. There was a tendency for the r-PNA pattern to occur mo re and the PNA pattern less frequently in cold event winters than in w arm event winters. The average temperature was lower when the r-PNA pr edominated but ENSO events had no additional effect. No relationship w as detected with precipitation. Fall and winter freezes occurred when there was an r-PNA pattern combined with either a neutral or a cold ev ent ENSO. These results suggest that the risk of winter freezes will b e low during ENSO warm events and high when the r-PNA pattern predomin ates.