Idaho has diverse climate types, with a predominantly continental flavor in the central and eastern regions (Köppen climate classification Dsa, Dsb). The western portion has a maritime influence (Köppen Cfb, Csb) from the Pacific Ocean. Idaho lies in the Pacific Northwest region of the United States. The state borders with Montana and Wyoming in the east, Utah, and Nevada in the south, Oregon and Washington in the west, and the Canadian province of British Columbia in the north. The variation in topography, altitude, geography, and proximity to the Pacific Ocean influences the climate.
Idaho, the Gem State, is home to rugged mountain ranges, grassy valleys, arid plains, and fertile lowlands. The average elevation is 1520 meters above sea level, with the highest point at 3859 meters at Borah Peak. The landscape is rugged, and the state has one of the largest natural areas in the United States. The Sawtooth Range is prominent, while others such as the Bitterroot Range, White Cloud Mountains, Clearwater Mountains, and stretches of the Rocky Mountains constitute the chiefly mountainous regions. The principal rivers are Snake, Clearwater, and Salmon, while the Snake River Plain in the south has fertile agricultural land. The panhandle and areas north of the Salmon River follow the Pacific Time Zone, while the south lies in the Mountain Time Zone.
The Pacific Ocean exerts a maritime influence in the north and west of Idaho, which results in cloudy, humid, and wet winters. The eastern part is free of the oceanic influence and exhibits the reverse pattern of wet summers and dry winters. Temperatures above 100°F (37.8°C) are rare in the summer. Summers have the highest difference between day and night temperatures that sees cooler nights even when days are hot. Winters are cold, but temperatures below 0°F (-17.8°C) are rare for extended periods. Fog is a regular feature in the cold season. Spring and autumn have comfortable temperatures in the majority of the state.
The average annual precipitation ranges from 10" (254mm) in the arid southwest regions, much of the Snake River and Central Plains to 50" (1270mm) at higher elevations and Clearwater, Payette, and Boise river basins. The north and west see the wettest period during the winter, while the east receives the majority of rainfall in the summer. Snowfall is abundant in the high mountains, with the annual total in Shoshone County at 500" (12700mm). Mullan Pass, which recorded the greatest snow depth of 182" (4622.8mm) on February 20, 1954, has a long-term seasonal average of 182" (4622.8mm) of snowfall in the winter. The average annual sunshine lasts for 2700 hours in Idaho.
Orofino recorded the highest temperature of 118°F (47.8°C) on July 28, 1934, in Idaho, while Island Park Dam recorded the lowest temperature of -60°F (-51.1°C) on January 18, 1943.
The best time to visit Idaho
The best time to visit Idaho is from mid-April to late October during the spring, summer, and fall seasons. Early spring is cold and often sees snow and ice in the highlands. The melting of snow begins by April and is the period of watching migratory birds on the lakes and rivers. Summer is warm to hot, with many sunny days, even during the period of high precipitation. Summers tend to be cool in the high mountain ranges and witness a large number of visitors. Early autumn has one of the best conditions with sunny days, a colorful landscape, and breezy evenings.
The worst time to visit Idaho
The worst time to visit Idaho, if any, is from December to February when the highlands are under cover of snow and ice. Cold fronts occasionally occur but rarely last more than a week, and temperatures below 0°F (-17.8°C) are rare. Fog is one of the challenges during the winter when the visibility limits to less than one-fourth of a mile. Mountain trails face closures during heavy snowfall, while roads become slippery in icy conditions. Many areas register between 20" (508mm) to 60" (1524mm) of snowfall in the winter season. Contrary to expectations, winter sees a fair number of tourists in Idaho.
Idaho is prone to thunderstorms and flooding in late spring and early summer. Strong winds accompany thunderstorms, which often bring heavy rain and cause lightning strikes. Windstorms are common during the summer and cause damage to trees and communication lines. Hot conditions during the peak summer and lightning during thunderstorms create the danger of wildfires in the forested areas. Snowstorms frequently hound the high mountain slopes in the winter and deposit vast amounts of snow. Hailstorms occasionally damage crops during spring as well as summer, but the size of hail rarely extends half an inch in diameter.
Weather in January
January is the coldest month of the year in Idaho, with temperatures in the frigid zone. The average low temperatures are in the icy -2°F (-18.9°C) to 22°F (-5.6°C) range, while the average high temperatures are in the cold zone of 26°F (-3.3°C) to 43°F (6.1°C). Boise, the capital in the southwest region, registers temperatures in the 25°F (-3.9°C) to mild 38°F (3.3°C) range, but Stanley in the central part is chilly between -2°F (-18.9°C) to 26°F (-3.3°C). The 3" (76.2mm) to 4" (101.6mm) of precipitation keeps the northern region wetter than the south. The snowiest month of January brings plenty of snow, with up to 37" (939.8mm) in McCall, and even the central region registers healthy numbers in the 20" (508mm) to 30" (762mm) range. Expect the snowpack to be deep in the mountains with hardly 4 hours of sunshine amid cloudy and dark skies. Snowshoe through the country landscape to reach the hot springs that offer a unique way to keep warm in the cold season. Campgrounds close in the cold weather as the roads become icy in January in Idaho.
Weather in February
February is icy in the winter of Idaho, with cloudy skies, and wetter north and west regions. The average temperatures range from 33°F (0.6°C) to 50°F (10°C) in the day and -1°F (-18.3°C) to 30°F (-1.1°C) during the night. Island Park in the east registers mostly below freezing between 8°F (-13.3°C) to 33°F (0.6°C). Snowfall between 10" (254mm) to 20" (508mm) is common in the majority of the state, including the south. Idaho has a long, mushing history similar to Alaska or Canada. Cross country skiing is for adventure lovers, while dog sledding is a thrill through the mountainous landscapes such as those of the Targhee National Forest. Enjoy the horse-drawn sleigh rides on the snowy terrain of the winter wonderland. Ice fishing is widespread, with plenty of trout and whitefish in the company of hot chocolate or a drink in hand. Watch out for snowstorms that deposit vast amounts of snow and stall everyday life. Expect the sunshine to be weak during the majority of daylight hours in February in Idaho.
Weather in March
March is cold at the beginning of the spring season in Idaho, with the average low temperatures in the freezing 10°F (-12.2°C) to 37°F (2.8°C) range. The days are in the mild zone of 41°F (5°C) to 60°F (15.6°C) across the state with a moderate amount of precipitation. Snowfall of 5" (127mm) to 10" (254mm) occurs in the northern highlands as the skiing season continues in the rising temperatures. Porthill in the north registers between 28°F (-2.2°C) to 49°F (9.4°C), while Idaho City in the range of 22°F (-5.6°C) to 48°F (8.9°C). The heavy rainfall during the winter ceases to a moderate level in spring in the north and west. Although the sunshine lasts for 7 hours a day, it is still cold to abandon winter coats entirely. Budget travelers find early bird discounts in early spring as the tourist season is yet to begin. Do not be surprised to experience a blast of cold air on a spring evening, especially in the northern region. Wildflowers begin to bloom and color the countryside by mid-March in Idaho.
Weather in April
April welcomes bright days to Idaho, with a significant decrease in rain and snow. The precipitation ranges from 1" (25.4mm) to 3" (76.2mm), and the snow season is over in the south. The icy cold gives way to bearable temperatures that average between 19°F (-7.2°C) to 43°F (6.1°C) during the nights. Days are warm and average in the 51°F (10.6°C) to 68°F (20°C) range, with 7 to 8 hours of beautiful sunshine. The white landscape of winter gradually gives way to a tinge of green everywhere, including the mountains. The melting of snow brings fresh water to lakes, rivers, and streams. Waterfalls roar with a renewed intensity, and the fresh air charges the atmosphere. Fishing enthusiasts are in search of the mountain trout, bass, and salmon that migrate with the change of season. The hibernating animals forage for food, and hunters have plenty of choices from deer, elk, goats, and bears. A jacket is handy to withstand the temperature drop in the evenings. April is the beginning of the tourist season in Idaho.
Weather in May
May is a beautiful time to visit Idaho with comfortable temperatures and plenty of sunshine. The spring blossoms with green contours all over the state. Pocatello in the east has comfortable temperatures in the 40°F (4.4°C) to 67°F (19.4°C) range, while salmon registers between 41°F (5°C) to 67°F (19.4°C). The average high temperatures register between 61°F (16.1°C) to 77°F (25°C), while the average low temperatures are between 27°F (-2.8°C) to 50°F (10°C) statewide. May is moderately wet, with 2" (50.8mm) of rainfall in the east and up to 3" (76.2mm) in the north. Snow is absent except for the high mountain ranges. Floods occur during late spring due to the melting of snow. The Kootenai River valley floods regularly in spring due to snowmelt and rain. Watch out for hail, which is common during spring storms. Thunderstorms and lightning strikes are highest in late spring, especially in the mountains. May has beautiful conditions in Idaho, but book accommodations in advance to avoid high rates during the tourist season.
Weather in June
June has the longest days of the year in Idaho as the state basks in glorious sunshine. The average high temperatures are in the warm 69°F (20.6°C) to 86°F (30°C) range, while the average low temperatures are in the mild zone of 42°F (5.6°C) to 57°F (13.9°C). Bruneau in the southwest witnesses temperatures in the 54°F (12.2°C) to 86°F (30°C) range, while Twin Falls in the central region is slightly cooler between 48°F (8.9°C) to 77°F (25°C). The eastern region receives little precipitation, and the north also sees less than 3" (76.2mm) of rain. Tourist activity is at a high during the early part of summer, and there are many candidates for horseback riding and whitewater rafting. Shooting is a popular sport in the bright early morning skies of June. Start early for outdoor excursions to counter the hot afternoons and humidity. Summer days are the time for sweatshirts, t-shirts, and shorts, while long pants are better during the evening. Keep an eye on the weather for thunderstorms during June in Idaho.
Weather in July
July is the hottest month of the year in Idaho, with average high temperatures in the warm zone of 79°F (26.1°C) to 95°F (35°C). Nights are comfortable in the range of 36°F (2.2°C) to 60°F (15.6°C), with a decrease in humidity compared to the day. Malad City in the east is considerably warmer between 51°F (10.6°C) to 89°F (31.7°C) than Grouse in the central region, which registers in the 45°F (7.2°C) to 81°F (27.2°C) range. Sunny days are back in Idaho as the bright sunshine lasts for a daily 10 hours. The eastern portion of the state is wetter than the north and west, which receive negligible rainfall. Lakes, streams, and rivers, along with navigable waterways are ideal for relaxing in the hot summer. Tourists visit the multitude of museums, historical sites, and unique destinations like Shoshone Falls to quench the summer thirst. The abundant number of rainbow trout keeps fishing enthusiasts away from the competition. July mornings in Idaho are perfect for hiking the alpine zone or traversing through 400 miles of nature trails in Sun Valley.
Weather in August
August is warm to hot in the summer of Idaho, with mostly clear skies. Days register in the warm to hot zone of 79°F (26.1°C) to 94°F (34.4°C), while nights are comfortable between 33°F (0.6°C) to 59°F (15°C). Little precipitation occurs in the north and east, but windstorms and forest fires are a threat to the tree-covered mountain slopes. White water rafting is enjoyable in the morning sun on the Boise River. Mountain biking is popular with the vast number of trails and loops. Falcons, hawks, eagles, and other birds in the wild keep the interests of the bird watchers and hobbyists alive. Catch the time after sunrise for the best pictures. Wear sunscreen and avoid midday heat when temperatures can reach 100°F (37.8°C). Light summer clothing keeps perspiration at bay during the day, but layered clothing is better to counter the drop in temperatures during the night. Expect temperatures to cool off gradually by the end of summer in August in Idaho.
Weather in September
September sees a transition to the beautiful autumn season in Idaho, with average high temperatures in the 69°F (20.6°C) to 83°F (28.3°C) range. The nights are on the colder side in the average zone of 26°F (-3.3°C) to 43°F (6.1°C) and even freezing in the hills. Lewiston in the north registers between 51°F (10.6°C) to 78°F (25.6°C), while Driggs in the east is relatively cooler between 37°F (2.8°C) to 69°F (20.6°C). Thunderstorms occasionally extend to the early fall season, but the rainfall is moderate at best. The daily sunshine lasts for 8 hours, which makes summer clothing relevant in early fall days. Fall is the time to explore colors and enjoy the beauty of nature. The conditions cool down significantly by mid-September, which makes it an ideal time to soak in one of the many hot springs. Scenic byways and rural roads offer unmatched natural beauty but wear a jacket or sweater during the breezy evenings. A September visit to Idaho offers one of the best weather conditions of the year.
Weather in October
October is warm to cold in the fall season of Idaho and full of brilliant colors. The average high temperatures are in the range of 55°F (12.8°C) to 70°F (21.1°C), while the average low temperatures are between 26°F (-3.3°C) to 45°F (7.2°C) statewide. Fall colors are at their peak by mid-October, and the refreshing air, scenic wilderness, and abundant wildlife make the conditions lively. Hues of yellow, orange, red, and purple color the beautiful landscape. The hunting and fishing and seasons are in full swing, with plenty of deer, elk, mountain sheep as well as trout, bass, and salmon for company. The harvest season brings ample sugar beets, potatoes, onions, apples, pumpkins in the numerous farmers' markets of the countryside. Rain is negligible, but jackets and long pants offer comfort in the autumn than shorts and t-shirts of summer. Pack in layers if the objective is to explore the colors in the mountains in October in Idaho.
Weather in November
November ends the autumn season in Idaho, with cold temperatures in the average range of 11°F (-11.7°C) to 53°F (11.7°C) across the state. Coeur d'Alene in the north experiences freezing nights with temperatures between 32°F (0°C) to 44°F (6.7°C), while Boise in the southwest has mild days between 32°F (0°C) to 48°F (8.9°C). The precipitation picks up to register 3" (76.2mm) to 5" (127mm) in the north, but the east is relatively dry between 1" (25.4mm) to 2" (50.8mm). November sees the first signs of snow in the high mountains. Sunny days are rare by the end of November as the trees begin to show bare limbs. The conditions are unpredictable, with shades of sunny, cold, or icy weather in different regions. The Sawtooth Scenic Byway along state highway 75 has some of the wildest forests in the country, with abundant wildlife sightings during the fall season. Lake Coeur d'Alene has many miles of forested shoreline, sandy beaches, coves, and bays that make it an ideal fall getaway. November is the last month in Idaho with comfortable day temperatures.
Weather in December
December is bitterly cold in Idaho with the average high temperatures in the 27°F (-2.8°C) to 42°F (5.6°C) range and the average low temperatures in the freezing zone of -2°F (-18.9°C) to 28°F (-2.2°C). The eastern parts of the state, such as Preston, are regularly below freezing and register between 15°F (-9.4°C) to 32°F (0°C). The north and central parts are snowier than the rest of the regions and receive between 5" (127mm) to 15" (381mm). The winter brings cold air masses from the polar region that reaches the far south. The landscape turns white as the mountains turn into icy playgrounds. There are plenty of sites in all regions for skiing, snowboarding, and snowmobiling. The top barley producer state is home to a multitude of craft brews with plenty of breweries to serve delicious pints and keep warm. Warm winter coats, caps, and gloves are in demand during the cold season, especially during Christmas and New Year's Eve. Expect December to be icy in Idaho.