Thunder and rain in Boise this weekend, along with the usual heat? Check out the forecast

The National Weather Service in Boise recorded its first measurable rain in 50 days on Tuesday.

Granted, it was only 0.01 inches of rain, but hey, it was measurable nonetheless.

It also seems to have signaled the start of a more active weather period for the Treasure Valley.

Boise has a slight chance of thunderstorms Friday evening and night, according to National Weather Service meteorologist Spencer Tangen.

“We’re in more of a pattern where we’re getting flow out of the south,” Tangen said. “And so that’s bringing in monsoonal moisture from the desert southwest.”

Following Friday’s clouds and storm possibilities, Boise will endure its usual summer weekend: hot and dry, peaking at 97 degrees on Sunday, according to the weather service. Another system from the West Coast will move into the area on Tuesday, and with it will come the chance of rain showers.

Boise’s hot, dry summers

Around 75% of Boise’s annual precipitation comes during the winter and spring months, and since 1940, the city averages only about a quarter-inch of rain in July and the same in August.

But looking at historical rainfall data for the area, a 50-day dry streak with no measurable precipitation is still abnormal for the region. That’s partly because of the Owyhee Mountains to the south of the Treasure Valley, according to previous Statesman reporting, which pushes dry air into the valley and is almost a barrier to stormy weather.

When storms do come from the south — such as the system that will bring a 20% chance of storm activity to the Treasure Valley on Friday — Boise is actually too far away from the Owyhees to benefit from rain that does make it past their peaks.

The mountains are a big reason why Twin Falls and other areas of south-central Idaho have a 50% chance of storms on Friday night compared to Boise’s much lower outlook.

“(Twin Falls) have the mountains that are closer to them to the south,” Tangen said. “Storms form over the mountains and then drift into the lower elevations, but they’ll weaken once they get off the mountains. It’s not as far from the mountains to Twin Falls as it is from the Owyhees to Boise.”

Smoky skies

The Weather Service has also included the term “patchy smoke” in its forecast for Friday evening. Smoke from wildfires in Northern California is being pushed northeast toward Idaho, but it is expected to primarily affect areas north of Ontario, Oregon, up toward McCall.

“Generally, we’ll put that in the forecast when you know when you look outside, and you can see some smoke,” Tangen said. “There is a little bit of smoke, so it’s kind of patchy; that’s the lowest category of smoke in the forecast.”

The Idaho Department of Environmental Quality has issued a yellow air quality advisory for the Treasure Valley, meaning those unusually sensitive to air pollution are the ones at risk.