Untitled

- 8 -ground is not snow-covered . The winter climate is the governing factorfor many varieties of tree fruits, grapes and cane fruits . Beforeplanting, it should be ascertained if the variety to be grown can withstandthe winter lows likely to occur . As shown in Table 1, summertemperatures in the Chase-Tappen-Salmon Arm region are only slightlylower than those in the Kelowna-Penticton area of the Okanagan . Thisindicates that certain annual crops that do well in the middle Okanaganmay be tried for commercial production in the Thompson Valley section .The Frost-Free PeriodThe dates of the last spring and first fall frosts have a bearingon the type of agriculture that can be undertaken . The frequency offrosts and the places in which they occur depend mainly on latitude,altitude, air drainage, and cloud conditions . Because of the complexityof these factors and others, the frost-free period is irregular . Inany locality frost records over a period of years give an estimate ofthe frost-free season for use as a guide . The dates for stations havingfrost records are shown in Appendix Table 0 .PrecipitationThe precipitation pattern for the area is strongly influenced bythe onshore movement of air from the Pacific Coast . In winter theincoming low-pressure systems discharge most of their moisture as rainand snow on the western slopes of the Coast Mountains . East of thesemountains they cause considerable cloud-cover . In summer there is lesscloud and precipitation, and some variation occurs in different partsof the area, due to elevation and other influences .As the mapped area is approached upstream on the Thompson River,it is noticed that Monte Creek is one of the driest spots in BritishColumbia, with only about nine inches annual precipitation . Upstreamthere is a slight increase to Pritchard, and from there a more pronouncedeffect, changing the natural grassland to forest . At Chase theprecipitation has increased to 14,27 inches . There is a steadyincrease eastward to 21 inches at Salmon Arm, and there are highervalues farther east, In the Salmon River valley the increase is from13 .75 inches at Westwold to 17 .18 at Falkland, the latter probablybeing high owing to a limited period of record .Insofar as agriculture is concerned, effective rainfall isrequired during the important months for crop growth, regardless of theannual total . These are May, June, July, and August for the kinds ofcrops grown in the surveyed area . Since the rainfall is applied tosoils that have different moisture requirements, the lighter texturedones are marginal or submarginal if there is only sufficient moisturefor moderate crops on the heavy soils .It is therefore of interest to know how much rain falls during thefour important months, as this proves the need of supplemental moisture,Such information is given in Appendix Table P . This table indicates