Weather in Boise in August

A good month. August works. It is not the peak, but nothing about it fights you. Highs average 33.9 °C, lows 18.2 °C, and rain falls on 1 days — nothing in the month is working against you.

August ranks 6 of 12 in Boise: past the worst of the year but short of September, which is the month to book if the dates are open.

Rain falls on only 1 days, so an itinerary with no wet-weather fallback is a reasonable risk. Pack for 33.9 °C days and 18.2 °C nights; the spread matters more here than any single number.

What the averages hide

Averages flatten a month, and this one hides a few things: 14 days clear 35 °C, so a serious heatwave is normal rather than notable; the day swings 15.6 °C from low to high, which means one bag has to cover both. Across the twenty years measured, the hottest August day reached 43.5 °C and the coldest night fell to 8.5 °C.

August is dependably dry, and that reliability is the point: across the twenty years measured, the wettest August on record still only managed 30 mm, and the driest managed 0 mm. There is no meaningful variability to plan around, which makes this one of the few months anywhere that you can build a fixed outdoor itinerary against without a fallback. The wettest single day in twenty years of Augusts brought 12 mm. Rain simply is not the variable that decides this trip — heat, crowds and cost are.

Wind is light at 7.3 km/h, so the temperature on the page is close to the temperature on your skin, and the air is dry at 29% humidity, which makes the heat far more bearable than the same figure somewhere humid — and dehydrates you faster than you expect.

How August sits in the year

Temperatures hold steady either side: 35.1 °C in July, 33.9 here, 27.9 in September. Nothing about the timing within the month matters much.

Daylight in August

14 hours of daylight, losing 1.3 hours across the month. That is between Boise's extremes of 15.4 and 9 hours, so days are long enough not to constrain the plan.

An inland climate

With no coast nearby, the year swings a fair way — 38.7 °C between the warmest afternoons and the coldest nights, wider than any coastal city at this latitude would manage. At 823 m the air is thin enough to matter — sun that burns faster than the temperature suggests, and nights that cool off quickly. Within August itself the daily swing is 15.6 °C, so mornings and afternoons need different clothes.

How busy it gets

Busy. Popular without being frantic; book the things you care about, improvise the rest.

Crowd levels are estimated from climate desirability and school-holiday calendars, not from visitor numbers.

August in Boise versus nearby

If Boise is one option among several, the nearby comparison is worth making. Tri-Cities is close enough to be a coin toss — within a degree on temperature, 1 day more rain. Spokane is a better bet in August — 4.6 °C cooler, 2 days more rain.

So: August is a compromise. September is 24 points better and is what Boise is actually like at its best — worth moving the trip for if that is possible, and worth adjusting expectations for if it is not.

Every month in Boise

See all twelve months in Boise, or where else to go in August.