Climate in Southeast Idaho

Pocatello is located at the mouth of the Portneuf Canyon along the southeastern edge of the Snake River Plain. The elevation of the city is approximately 4500 feet above mean sea level. Generally mountainous terrain borders the city on the east and south. The mountains rise abruptly to over 9000 feet elevation within 15 miles to the east, and to over 7500 feet elevation 10 miles south. The broad Snake River valley extends to the west and north with intensive agriculture practiced in the immediate area. A desert composed mostly of lava rock along with sagebrush and sand is located approximately 25 to 30 miles north and west of the city.

Pocatello's climate is characterized by variety. The area's semi-arid climate is the result of the Cascade and Sierra mountains to the west and the Bitterroot and Rocky Mountains to the north which effectively block Pacific moisture. Summer monsoonal moisture intrusions are infrequent and significantly modified by the arid Great Basin of Utah and Nevada. The Rocky and Bitterroot Mountains form the headwaters of the Snake River and receive copious amounts of winter snow. The success of local agriculture is dependent on irrigation, both from deep wells and a system of canals supplied by storage reservoirs on the Snake River.

During winter, brisk southwesterly winds often persist for days or weeks. These winds may moderate cold winter conditions, producing unusually mild temperatures compared to surrounding areas. There are usually a number of days each winter when temperatures remain below freezing. Sub-zero temperatures usually occur only a few days each winter. During especially cold outbreaks, snowfall may accumulate to a depth of a foot or more. Cloudy and unsettled weather is common during the winter with measurable precipitation occurring on about one-third of the days.

Spring months are normally wet and windy. Winds of 20 to 30 mph may persist for days at a time. Weather conditions fluctuate quickly during the spring. Afternoon temperatures in the 30s and 40s with precipitation in the form of rain or snow may occur after a period of sunny skies and afternoon temperatures in the 60s or 70s. Thunderstorms are not uncommon, and are usually accompanied by rain showers and occasional snow. Low elevations snow pack usually melts quickly during the spring, but high elevation snow pack can persist into late June.

Summer may begin suddenly with a rapid change to warm and dry weather. Home heating is usually not required after the first week in June, but chilly nights can persist into early July. Showers and/or thunderstorms are common from late spring through summer. These storms often produce very localized precipitation. Thunderstorms are seldom severe, and tornadoes occur infrequently in the area. Brief heavy rain, lightning, small hail, and gusty winds may cause very localized damage at times. Long periods of excessively hot weather in July and August are uncommon. Afternoon temperatures often rise into the 90s, however low humidity usually results in overnight temperatures in the 50s or even cooler. The average growing season in Pocatello is around 120 days, extending from late May to late September.

Autumn ushers in cooler weather with daytime highs generally in the 70s in early fall dipping into the mid 40s by mid November with generally dry conditions. Autumn storms are usually very fast moving, and seldom persist for more than a few days. Sunny, warm days with cool nights are delightful for outdoor activities. Continuous home heating is seldom needed until mid October. The first cold wave with highs below 20 and lows around 0 or lower may arrive anytime between late November and Christmas.