Saturated soil plus 147 percent snowpack could equal significant flooding

Weather experts, comfortable forecasting five to seven days into the future, are trying to figure out the next six to eight weeks given the high probability of flooding in northern Utah. Utah water experts are very concerned about Logan River, Blacksmith Fork and the Weber River in Kamas. Brian McInerney, hydrologist with the National Weather Service, spent time in Cache Valley this week visiting with government officials. He said a higher-than-normal potential for flooding exists, given the snow pack plus the current moisture in the soil. “We have snow pack that is at 147 percent of normal and the snow is lying on soil that is extremely saturated,” said McInerney. “The third part of the equation is: how will the spring weather shape the volume of runoff coming out of the mountains?” He said it is a given that the volumes, or the amount of water coming out of the mountains, is going to be very high. “When we did a forecast on peak flows it indicated we have a pretty good probability of reaching flood stage and having some damage in Logan Canyon at some of the summer homes. Whether it will damage some places within the city limits remains to be seen.” He said that would depend on debris in the creek channels that might jam up the culverts under the road. “My feeling is we will have some flooding near the confluence down by the Blacksmith Fork and Logan River. If the weather turns warm and dry without any significant rainfall, we could come through this with no river flooding whatsoever.” McInerney explained that would still mean high flows but the peaks wouldn’t be so high. However, he said if there are cold and wet temperatures in April and May with a couple of significant thunderstorms, that could lead to problems. “What we need right now are three or four days in the 70s to melt off some of this low elevation snow. Low elevation snow has been hanging around two weeks past what it should. What you want is an orderly melt; you want the low elevation to melt off then the mid-elevation then the high elevation.” He said the wildcard is always a thunderstorm of any certain magnitude adding more water to an already swollen hydrologic system. “That’s when we would see damage. “On an average day during the runoff in late-May, we’ll have an inch to an inch and a half of melt per day. A thunderstorm on top of that kicks off increased peak flows, jumps the banks, and starts producing damage.” McInerney said he’s met with public utilities people in the valley and they are now busy cleaning out channels as fast as they can to get rid of debris already in the channels.

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