Environmental Data

The city of Lethbride is located in the southerly portion of the province of Alberta within a climate area which may be classified as semi-arid, characterized by relatiavely low annual precipitation and hot dry winds in summertime.

A. Wind

Wind prevails from west-southwest (50% frequency). Wind velocity is greatest from these directions. Warm periods during winter occur as a result of westerly winds (chinooks). Cold winter winds are from the north and northeast.

B. Sun

Sun exposure is a serious consideration since the mean monthly and annual hours of bright sunshine are appreciable. The south-southwest exposure of the site, unprotected across the prairie, must be treated with special care.

C. Temperatures

Monthly mean temperatures do not indicate extreme conditions but there can be extreme and short-term variations particularly in winter. Monthly maxium and minimum range from -45 degrees F to 104 degrees F in summer.

D. Precipitation

A yearly average precipitation of 10.66 inches with maxium rainfall occuring in June of 3.15 inches clearly indicates regional dry climatic condititions. Maxium recorded 15-minute and 1-day rainfalls are 0.5 inches and 3.5 inches. Droughts in area are frequent and evaporation is fairly high.

Snowfalls, although recorded in all months, occur largely in the period from October to April. Maxium monthly snowfalls occur in Novembwr and February. Snowfalls are frequently followed by relatiavely rapid melting and runoff. Snow drifting is a common occurrence. Site observation suggests that slopes facing south will be covered with deep snow following storm periods, whereas orth exposures will have little snow cover. Driving of snow also occurs with chinooks.

E. Microclimate

No physical data has been collected for the river bottom or west site of Lethbridge. Observed exprerience on site indicates that appreciable wind protection is offered by coulee formations and existing caragana shrubs. Local wind and snow conditions should be investigated as design for individual projects proceeds.