NWS Flood Projections Look Good for Glasgow

The National Weather Service in Glasgow is projecting a mild flood season for Spring, 2019. According to meteorologist Patrick Gilchrist, the projected flood risks for the area are minor flooding at 35 percent, moderate flooding at five percent and major flooding at less than five percent.

Gilchrist told the Courier that the projections are favorable for a number of reasons. First is that the snowpack that does exist is low in water content. Gilchrist called this the “snow-water equivalent” which changes based on the temperature when the snow is created. Right now there is a lot of snow but not a lot of water in that snow.

Second is that not all of the Milk River run-off basin contains a large amount of snow-water equivalent. “If you look at the maps, there is a lot of snow from Glasgow to Havre but then not that much snow as you head up into Canada,” explained Gilchrist. The issues for Glasgow then will be localized flooding. According to Gilchrist, because a large number of creeks converge with the Milk at or near Glasgow, the largest risk comes if those creek valleys melt at the same time and all that water converges in the river.

Gilchrist clarified, though, that the projections does not show much of that happening. The third reason flood projections are so favorable is that much of the water is leaving the area slowly. In the last two weeks, the snow-water equivalent at Glasgow has gone from 1.9 inches to 1.2 inches, caused by some melt off and a process called sublimation (when a solid turns directly into a gas), which Gilchrist said happens this time of year.

“The forecast is for a slow warm up,” said Gilchrist, “which will slowly even out the snow pack.” That means unless some major event occurs the snow will leave the region slowly and avoid moderate to major flooding. “A dramatic shift could occur.” explained Gilchrist, “If a large rain event occurred over the top of the snow, that would change the equation.”

A risk of the colder temperatures, though, is threat of ice jams. The cold keeps the ice thick as it starts to break up, causing large ice jams along the river. Gilchrist explained that ice jams are frequent along the river but usually break up and move on rapidly.

“If you live along the river, it takes 30 days for flood insurance to take effect,” said Gilchrist, urging those who are weary of possible floods to take action now to be better prepared. “Just have a plan. If you live in an area you know will have minor flooding, plan ahead,” said Gilchrist adding that residents should ask themselves what they would do if there was a flood or if they were cut off and start planning for that event.

Minor flooding is described as 25 feet at the US Highway 24 bridge, moderate is 29 feet and major is 31 feet. The largest-recorded flood event in Glasgow was 34.1 feet. To access more information about flood projections or to see the effects of minor, moderate and major flooding visit: water.weather.gov/ahps2/hydrograph.p?wfo=ggw&gage=glwm8&hydro_type=2.