Although only half of the normal monthly precipitation fell at the Boise Airport, and measurable rain was recorded on only 7 days. Nevertheless, strong thunderstorms did occur in our region on the 5th, 12th, and 16th. Most of the severe weather missed Boise, but high winds, large hail, and brief heavy downpours hit a number of locations in eastern Oregon and southwest Idaho.
Temperatures averaged close to normal. The high of only 49°F on the 17th was the only record. It was the coolest maximum temperature ever recorded on that date, breaking the old record of 51°F set in 1896. The last freezing temperature of the season was 31 on the 13th. The average date of the last 32 degree reading is may 8.
The first official 90 degree high of the season occurred on the 30th. The last time 90 degrees was reached was September 29, 2016.
Typical of spring, changing weather patterns brought a succession of warm and cool periods. Upper level high pressure ridges with above normal temperatures were displaced about every 6 days by cold fronts followed by upper level troughs with unseasonably chilly north Pacific air, gusty northwest winds, and showers.
The most noteworthy of these weather systems arrived from the Gulf of Alaska on the 16th, passing directly over the Boise area that afternoon. It was ushered in by a thunderstorm which formed over the lower Treasure Valley and dropped half an inch of rain on the Boise Airport. Small hail was seen in some parts of town.
During the late afternoon of the 30th, a dry thunderstorm rolled off the Owyhee Mountains and arrived at the airport just before 7 pm, with gusty winds and blowing dust. A peak gust of 45 mph was measured at 6:58 pm MDT.
On the 31st, isolated afternoon showers and early evening thunderstorms developed west of Boise and intensified as they moved north ahead of an approaching Pacific cold front. They had little effect on the upper Treasure Valley, but the front ended the five day stretch of summer-like weather.