The Boise area, also known as the Treasure Valley, is drier and warmer than other parts of southern and central Idaho where summers can seem short, the winters bleak. The average annual precipitation is just 11.7 inches per year. It’s also milder than other arid regions of the western US, where summer feels like an oven every other day. The distinct four seasons in the Treasure Valley also offer year-round activities with something for everyone to enjoy.
What’s the Winter Weather Like in Boise?
Winter Snow? Of course. The average winter season snowfall, mainly mid-November through early February, is 21 inches. While that can sound like a lot, many locals will tell you most of the snow falls one inch at a time, at night, and melts away the same day. In fact, the coldest days of the season are normally from December 21st to January 6th, but the normal high for those days is 36 degrees, including Christmas and New Year’s Day.
December is the wettest month of the year in Boise, with a monthly average of 5½ inches of snow and about an inch of rain (measured as 1.55 inches of total precipitation). If you’re dreaming of a white Christmas, you just might find it here. In the last decade, snow was falling and/or on the ground for seven Christmases. Four times there was one inch, the other three of those holidays it was four or more inches of snow.
January gets an average of seven inches of snow per year, but the average daily high temperature is about 38 degrees. December’s average high is just under 37.5 degrees. But it does get colder. For the last 20 years, the temperature has dipped below 0 degrees 9 times each in December and January. In terms of annual occurrences, that translates to .43 days below 0 per year in each of the two months.
February’s average high temperature is 44 degrees, and usually, a little more than four inches of snow will fall. Snowfall can linger into the spring, with the average last measurable snow in any given year on March 24th. November can get about two inches of snow in an average year, March about 1½ inches.
What’s the Spring Like in Boise?
Spring Showers? You betcha. March, April, and May each experience between 1¼ and 1½ inches of precipitation in an average year. While this doesn’t sound like much, it’s quadruple what falls during July or August. Average temperatures rise steadily through the spring, with average highs of 55, 62, and 72 degrees in the three months. The average high on Easter is 61 degrees.
Spring also gets leftover snow and some frost. In the last 20 years, there has been measurable snow in March 16 times, but only 6 times in April, and none in May. There have been traces of snow in May and even June, but not enough to measure. In an average year, the last day of a hard freeze (28 degrees) is April 19th, and the last day for frost (32 degrees) is May 8th.
What’s the Summer Like in Boise?
Summer Storms? Not that many. July and August are the driest months of the year, with an average rainfall of just 1/3 inch and ¼ inch, respectively. Thunderstorms do occur, but the monsoon moisture that brings summer showers to states south and east of here avoid Boise.
July and August are also the hottest months of the year, with daily average high temperatures of 91 and 90 degrees. These mid-summer months also experience the most frequent days with 100+ degree temperatures. For the last 20 years, there was an average of 10.3 occurrences of 100+ degrees each year, 64% were in July (6½ times per year) and 24% were in August (2½ per year). On the 4th of July, expect an average high of 89 degrees, with sunset at 9:29 PM.
June, September, and October are also fairly dry, each seeing only ½ to ¾ inch of rain per year. The dry air and light summer rain make the Treasure Valley an ideal place to grow vegetable seeds, such as corn, onions, and carrots.
What’s the Fall Like in Boise?
Fun in the Fall? For sure! Fall is a beautiful season in Boise. The least windy time of year and the overall most pleasant weather is from mid-September through October. Temperatures are beginning to drop in October, however. In average years the first day of frost (32 degrees) is October 10th, and the first day of hard freeze is October 23rd.
Although the first frost and hard freeze occur before the end of October, Halloween itself usually has a low of 35 and a high of 56 degrees. The crisp fall air makes the day feel just right.
The average first day of measurable snow in Boise every winter is just in time for Thanksgiving, November 22. Thanksgiving’s annual forecast calls for a high of 44 degrees and a low of 27, just right for football. An average November sees 2.6 inches of snow, but there is usually no snow on the ground for Thanksgiving.
Windy City? Not really. The Treasure Valley runs from the northwest at Ontario, Oregon, 90 miles to southeast at Mountain Home, Idaho, and is about 45 miles wide. The Boise Mountains to the northeast and Owyhee Range to the southwest frame the Treasure Valley and each have peaks above 8,000 feet. This creates a regular wind pattern of flows from northwest to southeast – and vice versa. Because Boise and the other towns in the Treasure Valley area also lower than the Boise Foothills, higher winds often stay aloft.
But that doesn’t mean there aren’t ever any strong winds. On the contrary, especially in Ontario or Mountain Home. As in many locations, spring is the windiest time of year with unsettled air masses moving over the continent. In winter the Treasure Valley can also experience inversions, trapping cold hazy air close to the ground while milder air passes over. The least windy time of year is from mid-September through October.
What Else? We can talk about the weather all day, but you can’t find a better four-season climate than right here. Experience it for yourself!