There are several
things that influence the climate of any area:
1. latitude - the farther from the equator a place is, the cooler the
average temperature will be.
2. altitude (or how high an area is above sea level) - the top
of a mountain is always cooler than the bottom of the mountain.
3. distance from the ocean - areas far away from an ocean have
greater changes in temperature than areas close to the ocean.
4. wind - direction and speed of air currents of wind that reach
an area. Idaho has extremely varied topography.
Our highest mountain, Mount Borah, rises to 12,662 feet above sea level. Our lowest valley is only 770 feet above sea level (Snake River at Lewiston). The higher altitudes have mild summer days and are extremely cold in the winter months. The lower valleys and plains seldom drop below zero degrees even in the winter. The ocean does not affect our temperature too greatly in Idaho. What it does affect is the amount of precipitation we receive. North Idaho receives large amounts of rain and snow from storms blown in from the Pacific Coast. There are no high mountain ranges to keep the clouds from that area, so precipitation may be more than four times as much as that received in the southern part of the state. Southern Idaho is protected on all sides by mountains. For that reason, much of the area receives very little rain or snow and is usually called a desert.Although t he climate varies greatly in different areas of the state, in general the climate of Idaho is temperate. Temperate means an area has four seasons with great changes in the average temperatures between summer and winter.
All areas of Idaho undergo the transition through the four seasons, but the seasons manifest differently according to geographic location. Idaho has three main geographic provinces: mountains, valleys, and plains. There is little difference in climate between the mountains and the valleys, except that the mountains shelter valleys resulting in a moderated climate compared to the mountains. Scientists call this the orographic effect; in which: wind encounters a mountain, rises and cools, loses it’s moisture, and warms while descending into the valley. The plains are semiarid flatlands that have nearly equal amounts of precipitation and evaporation. Annual highs and lows, or seasonal extremum, also vary greatly resulting in bone-chilling winters and blistering summers.
January is the coldest month of the year in Idaho; usually having average temperatures below freezing. Some areas have temperatures well below zero through much of the winter. The record low in Idaho is minus 60 degrees Fahrenheit, recorded at the Island Park Dam in 1943. Temperatures routinely drop to 20 degrees below zero in mountainous northern and eastern Idaho. Snowfall is often heavy in these areas and the annual precipitation from snow and rain is between 20 and 35 inches, respectively. However, the average annual precipitation for Idaho is 12.44 inches, a result of the very dry conditions existing on the plains.
July is the hottest month of the year in Idaho. Temperatures are highest on the plains that occupy regional lowlands: the Snake River Plain, and on the lower reaches of the Clearwater, and Snake rivers, especially from Bliss to Lewiston. The all-time record high for Idaho is 118 Fahrenheit, recorded at Orofino on July 28, 1934. Temperatures greater than 100 degrees occur each year at many locations in southwestern Idaho. For example, on July 26, 1987 the temperature at Mountain Home was 108 degrees; 104 degrees at Boise; and 102 degrees at Twin Falls. You can access archive data from Climate Stations on Idaho climate in the Atlas, click here. Additional information on climate can be obtained from our web links page, Climate Web Links.