Idaho’s terrain is all over the place, which means its weather just can’t make up its mind either. The northern panhandle sits in thick mountain forests, while the south stretches out into desert plains. Each area gets its own distinct seasonal changes that really shake up temperature, precipitation, and the overall climate.
Idaho’s monthly weather is a wild ride, honestly. Winters hit hard in the mountains with heavy snow, while summers get hot and dry almost everywhere. Spring and fall? Those are the sweet spots, usually. Idaho sits up in the northwestern U.S., so it has this continental climate vibe—four pretty clear seasons. But how intense those seasons get really depends on where you are and how high up.
If you want to get through an Idaho year, you need to know these monthly patterns. Residents and visitors have to brace for everything: winter storms that dump feet of snow and summer heat waves that push into the 90s.
The state’s weather swings through dramatic seasonal shifts and wild temperature differences—sometimes 30 degrees between cities. Most of the moisture comes in winter and spring, so if you’re hoping for rain in July, good luck.
Overview of Idaho’s Climate
Idaho’s climate is all over the map, mostly because of the crazy terrain and elevation changes. The state packs in everything from semi-arid deserts to subarctic mountain climates. Elevation really calls the shots on what kind of weather you’ll get.
Climate Zones in Idaho
Idaho has three main climate zones that make the weather feel totally different depending on where you are. The south? That’s a semi-arid desert climate—hot, dry summers and winters that are pretty mild.
Central Idaho sits in a continental climate with bigger swings between seasons. Think Boise, where July can hit 92°F and January drops to 25°F.
Up north, the humid continental climate takes over, thanks to moisture from the Pacific. Sandpoint is a good example—cooler summers around 82°F and more steady rain year-round.
Mountains bring in subarctic conditions at the high spots. Winters get colder, and snow piles up like crazy.
Elevation and Its Impact on Weather
Elevation really mixes things up across Idaho. Go above 8,000 feet and you’re in subarctic territory, where the average year barely hits 37°F.
You lose about 3-5°F for every 1,000 feet you climb. That’s why mountain towns are way cooler than the valleys in the summer.
As you go up, you get more precipitation. Moist air rises and cools, so mountain areas can see 30-50 inches of rain and snow a year, but the valleys might only get 10-15 inches.
Snow piles up fast the higher you go. Valleys might get 2-4 inches a month in winter, but mountain peaks can rack up 8-12 inches on the regular.
Annual Weather Patterns
Idaho’s seasons are pretty clear-cut, with wet and dry stretches. Winter (December through February) brings most of the snow and the coldest days.
Spring creeps in with warmer temps and more rain. March through May gets a little soggy as the snow starts melting down low.
Summer is bone dry. July and August barely see half an inch of rain, and most days are sunny.
Fall cools things down again and brings a bit more rain. From September to November, clouds roll in and you start to feel winter coming back.
Month-by-Month Weather Breakdown
Idaho’s temperatures bounce around a lot during the year. Winters get brutally cold with mountain snow, while summers can sizzle into the 90s. The state’s mix of elevations means each region gets its own weather flavor.
Winter Weather: December to February
Winter in Idaho? It’s rough. Harsh conditions move in, and January averages 23°F. In the mountains, it can sit anywhere between 10°F and 30°F.
Mountains get buried in snow during these months. The Sawtooth and Bitterroot ranges pull in heavy snowfall, and winter sports fans love it.
Down in Boise and the Snake River Plain, it’s milder but still plenty cold. Sometimes you’ll get snow, other times freezing rain.
December kicks off the cold stretch. Temps average 26°F, and snow starts piling up in the mountains while valleys brace for their first big storms.
January is the coldest. Mountain snowpack builds and ski resorts are in full swing.
February hangs onto the chill, averaging 28°F. Snow keeps falling up north and in the mountains, while the south might get a mix of rain and snow.
Spring Weather: March to May
Spring is unpredictable. Conditions change fast, with temperatures climbing from 36°F in March to 55°F in May as the snow melts down low.
March is when you first notice things warming up—temps from 25°F to 45°F. Mountains hang onto their snow, but valleys start to thaw out.
Rivers swell up as the snow melts. Rain showers show up more often, especially in the valleys.
April warms things up even more, with temps jumping from 35°F to 60°F. Valleys lose most of their snow, but mountains keep their white peaks.
Wildflowers pop up in lower elevations. Spring rain picks up, so you might want to grab a rain jacket if you’re heading outside.
May really feels like spring, with temps from 45°F to 70°F. Valleys turn green and rivers run full, since most of the snow is gone.
Summer Weather: June to August
Summer in Idaho is hot and dry. July is the peak, averaging 72°F, but southern regions often break into the 90s.
June starts things off, with temps from 55°F to 80°F. Rivers are still high from melting snow, perfect for rafting or fishing.
Rain almost disappears during summer. Long, sunny days make it prime time for outdoor adventures.
July is the hottest, with temps from 60°F to 90°F. Southern Idaho really bakes, while mountains give you a break from the heat.
You might get a quick thunderstorm, but they’re usually short and spotty.
August keeps the heat going, with temps from 58°F to 88°F. Nights start to cool down a bit, hinting that summer’s winding down.
Fall Weather: September to November
Fall is just gorgeous here. Temperatures feel great, and the scenery explodes with color. September averages 61°F, but by November it’s down to 35°F.
September brings perfect weather—temps from 50°F to 75°F. The crowds thin out, but it’s still awesome for hiking and camping.
Higher elevations start showing off those autumn colors. Nights get cooler, but days stay warm for a while.
October is when the fall colors hit their peak, with temps from 40°F to 65°F. The weather is usually dry and sunny, making it a great month to explore.
Mountains might see their first snow. Most days stay clear and crisp, though.
November gets colder, with temps dropping to 30°F-50°F. Snow starts coming back, especially up north and in the mountains.
Monthly Temperature Trends
Idaho’s temperature swings are no joke. Winter lows can drop way below freezing, and summer highs climb into the 90s. Northern Idaho stays cooler all year, while the southern valleys heat up more.
Average Highs and Lows by Month
Winter is the coldest season. In January, Boise averages a high of 38°F, Idaho Falls sits at 29°F, and Sandpoint hits 35°F. Lows? Boise drops to 25°F, Idaho Falls to 14°F, and Sandpoint to 25°F.
Spring starts warming up in March and keeps going through May. By May, Boise averages 72°F, Idaho Falls 67°F, and Sandpoint 66°F. Nighttime lows in May are 48°F in Boise, 41°F in Idaho Falls, and 42°F in Sandpoint.
Summer peaks in July. Boise tops out at 92°F, Idaho Falls reaches 86°F, and Sandpoint gets to 82°F. Even nights are comfortable—62°F in Boise, 52°F in Idaho Falls, and 50°F in Sandpoint.
Fall cools off slowly. By October, highs drop to 65°F in Boise, 60°F in Idaho Falls, and 56°F in Sandpoint.
Record Temperatures for Each Month
Idaho’s seen some wild extremes. The record high? 118°F. The record low? -60°F. Ouch.
Summer heat waves come when high pressure just parks over the region. Sometimes, temps jump 15-20 degrees above normal for days in a row.
Winter cold snaps roll in when Arctic air pushes south through the valleys. These can hang around for weeks, especially up north or at high elevations.
Spring and fall can be unpredictable too. Late spring freezes sometimes wreck crops, and early fall cold snaps can show up right after a warm spell.
Temperature Variations Across Idaho
Elevation is the big difference-maker. Mountain spots are 10-15 degrees cooler than the valleys all year.
North vs. south is another clear split. Sandpoint averages about 10 degrees cooler than Boise in summer. Winter differences are smaller but still there.
Valleys like Boise and the Snake River Plain get the warmest weather. Lower elevation and some shelter from mountains help keep things toasty.
Mountain towns stay cold, even in summer. At night, it can still freeze up high.
Precipitation and Snowfall Patterns
Idaho’s precipitation is all over the place. Mountains grab way more moisture than the valleys, and winter snow really shapes the state’s water and recreation.
Monthly Precipitation Averages
Precipitation in Idaho depends on where you are and what time of year it is. The west gets more rain thanks to the Pacific, while the east is drier.
Spring (March-May) brings moderate rain as snow melts down low. April usually kicks off increased precipitation in a lot of regions.
Summer is dry, especially in southern Idaho. The Snake River Plain barely gets any rain in July and August. Mountains might get a stray thunderstorm, but it’s rare.
Fall and winter bring most of the year’s precipitation. November through February dumps the heaviest snow, especially in the mountains. Western and northern Idaho get more winter moisture than the south.
Most places get 10 to 20 inches of precipitation a year. Mountains can rack up over 40 inches, but some valleys don’t even hit 10 inches.
Snowfall Patterns in Different Regions
Mountains across Idaho get a ton of snow—20 to 60 inches a year in many spots. The highest peaks can see more than 100 inches during big winters.
The Sawtooth, Bitterroot, and Clearwater Mountains usually get the most snow. Snow sticks around from December through March or April.
Lower spots like the Snake River Plain don’t get as much. Most valleys see 10 to 30 inches each winter.
Northern Idaho pulls in more snow than the south, mostly because it’s closer to Pacific storms. The panhandle hangs onto snow cover longer, too.
Snow starts piling up in the mountains by November. The deepest snow usually happens in February or March, then it melts fast in spring.
Wettest and Driest Months
December through February are the wettest months for most of Idaho. Winter brings most of the snow to the mountains and a mix of rain and snow to the valleys.
January often ends up as the single wettest month. Mountains can get several feet of snow during this stretch.
July and August are always the driest. Some areas go weeks without a drop of rain, especially in the south and east.
September and October see moderate rain as fall sets in. These months bridge the gap from dry summer to wet winter.
The contrast between wet and dry seasons is sharpest in the valleys, where summer drought is pretty normal.
Humidity and Sunshine in Idaho
Idaho usually has low humidity, especially during the summer. Most of the year feels pretty dry. The state enjoys abundant sunshine, with plenty of spots getting more than 300 sunny days each year.
Monthly Humidity Levels
Thanks to its inland position and continental climate, Idaho keeps humidity low for most of the year. Summers, especially from June through August, can get downright arid, with afternoon humidity sometimes dropping below 30%.
Seasonal Humidity Patterns:
- Winter (Dec-Feb): 65-75% relative humidity
- Spring (Mar-May): 45-60% relative humidity
- Summer (Jun-Aug): 25-40% relative humidity
- Fall (Sep-Nov): 50-65% relative humidity
Western Idaho, a bit closer to the Pacific, tends to feel just a touch more humid than the east. Mountain valleys sometimes trap extra moisture, so you might notice pockets of higher humidity there.
Humidity usually peaks in the morning. As the day heats up, those numbers drop fast.
Average Sunshine Hours by Month
Idaho gets a ton of sunshine, honestly. Depending on where you are, the state racks up between 2,800 and 3,200 hours of sunshine every year.
Monthly Sunshine Averages:
- January-February: 4-5 hours daily
- March-April: 6-8 hours daily
- May-August: 10-12 hours daily
- September-October: 7-9 hours daily
- November-December: 3-4 hours daily
You’ll see more sunshine in southern Idaho than up north. Boise, for example, averages 211 sunny days a year, while places farther north get about 174.
Summer days stretch long, and July often brings 12 or more hours of daylight. Winter days are shorter, but you can still catch some clear skies between storms.
Clouds tend to roll in more often during winter, which cuts down on sunshine. Spring and fall, though, offer plenty of sun and comfortable temps.
Regional Weather Variations
Idaho’s mix of mountains, valleys, and plains leads to some pretty distinct weather patterns. Elevation and latitude really shake things up. The north is cooler and wetter, while the south stays warmer and drier.
Weather Differences Between Northern and Southern Idaho
Northern Idaho definitely sees more rain and cooler air than the south. For example, Sandpoint up north gets about 2.1 inches of rain in January, while Boise only picks up 1.2 inches that month.
Temperature differences can be pretty dramatic. In July, Sandpoint’s highs reach 82°F, but Boise cranks up to 92°F. Winters show big gaps, too, with January lows of 25°F in both Sandpoint and Boise, though the chill can feel different depending on the wind and humidity.
Snowfall is a whole different story in the north. Sandpoint piles up 8.6 inches of snow in January, while Boise gets just 2.5 inches. Those northern mountains? They’re a dream for winter sports thanks to all that snow.
Cloud cover changes a lot depending on where you are. In January, Sandpoint only gets clear skies about 23% of the time, but Boise enjoys clear weather 42% of winter days.
Climate of Major Cities and Towns
Boise stands out as the warmest of Idaho’s major cities. In July, highs can hit 92°F, but January lows drop to 25°F.
Summers in Boise stay pretty dry. The city usually gets just 0.2 inches of rain in both July and August.
Idaho Falls lands somewhere between northern and southern climates. July brings highs of 86°F, but in January, lows can fall to 14°F.
Idaho Falls sees a fair amount of snow in January, with about 4.1 inches.
Wind speeds jump around a lot from city to city. Idaho Falls gets the wildest winds, averaging 8.0 mph in January.
Sandpoint, on the other hand, is much calmer at just 3.8 mph. Boise sits in the middle with winds around 6.5 mph.
None of these cities really deal with muggy days. Idaho’s urban areas keep humidity low all year, which honestly sounds pretty nice.