Flood Warning For Boise River To Remain For Several Days

May 4, 2012


The Boise River is under a flood warning for the next several days.   Dave Groenert  is a meteorologist with the National Weather Service in Boise. He says that warning will remain at least for the next seven days as temperatures rise. “They (temperatures ) look to peak at the middle of next week Wednesday,” explains Groenert. “And then after that cool back to normal.”

Groenert predicts that highs will rise into the mid-70s to 80s for the Treasure Valley and into the mid-60s to low 70s for the mountains. The warm weather means snow in the mountains will melt quickly. That means more water filling Idaho’s reservoirs, including Lucky Peak.

Already, water managers have lowered the water levels in the New York Canal as irrigation demand has increased. This means the Boise River flow will be around 8,200 cubic feet per second at the Glenwood Bridge gage. But that increased flow isn’t expected to cause any more flooding. The Bureau of Reclamation and the Army Corps of Engineers is managing the flows on the Boise River.

Meanwhile, the USDA Natural Resources Conservation Service released its water supply outlook report on Friday. The report details why Idaho’s rivers and streams are flowing so high right now. You can read an excerpt below:


The high runoff in April was set up by conditions in March. March was warmer than normal and soaking rains fell as high as 7,000 feet. These conditions ripened snowpacks and caused the snow to start melting in early April. Typically snowpacks reach their peak snow water content and linger at that level as the snowpack ripens and slowly begins to melt. This didn’t happen this year, instead like a rollercoaster, the snow water increased steeply through March and then immediately started melting after April 1.


Next, came a heat wave across the West the third week of April. Mountain temperatures reached 70-75 F for several consecutive days and valley temperatures reached into the low 

90s F in Boise. Using long term valley weather station data as a  gauge, this heat wave was likely the hottest in April since 1875. With the snowpack ripe, this heat created record high melt rates of an inch/day in April. Water was flowing out the mid-elevation snowpack and even higher elevation sites at 9,000 feet started melting nearly a month early.

With snowmelt in full swing the heat wave was followed by a cold front that brought heavy rains. Many SNOTEL sites in central Idaho received 1-2 inches of rain on April 26. This combination made streamflows increase like a good day on the stock market. Many streams set new daily high peaks in April. Once the brunt of the cold front’s rain passed and freezing temperatures returned to the mountains, snowmelt slowed and the rivers began to recede.

As of May 1 there is still enough snow in the higher elevations across central, northern and Upper Snake basins to produce another increase in flow when warm temperatures return. It is unlikely, however, that future peak flows in these areas will be higher then what we just saw without help from Mother Nature – either in the form of record high temperatures or an intense rain for several days. ~ USDA Natural Resources Conservation Service