June | 2017 | Sage Winds

This past winter and spring had its share of flooding across southeast Oregon and southwest Idaho. Not only did spring runoff bring flooding to rivers and streams, but ice jams and snow melt caused flooding during the winter as well. The stage was being set for an active spring flood season as far back as October 2016, when 150 to 400 percent of normal precipitation occurred across much of the region which moistened the soil profile. The winter storm track brought well above average snowfall to most of southeast Oregon and southwest Idaho, with extreme snowfall across lower valleys. A relatively cool and wet early spring was the final piece of the puzzle to ensure abundant spring runoff. An indicator of how wet this past winter and spring have been, water supply forecasts for the April through September period rank in the top 10 for most of southeast Oregon and southwest Idaho, dating back to 1970. Additionally, all major reservoir systems either have filled or are expected to fill. Record high precipitation was seen across many areas from December 2016 through June 2017, shown in the figures below.

The map below shows March 1 snow pack along with areas where flooding had a significant impact.

Although the threat of snow melt flooding has diminished, summertime thunderstorms can pose a serious flood risk. Areas of steep terrain and areas burned by wildfire are at particular risk for flash flooding due to thunderstorms. For flood safety information, visit http://www.floodsafety.noaa.gov/. For the latest river conditions, see http://water.weather.gov/ahps2/index.php?wfo=boi.

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.

Month: June 2017

Winter 2016 and Spring 2017 Flood Summary

May 2017 Climate Stats