Western US weather expert

Record Snow Brings Flood Threat to Utah and the West/Lake Mead

5/12/2011, 2:14:24 AM

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The Sierra has not been the only place where record winter snow fell this year. Utah north to Wyoming and Montana also had abundant snow. Here is an example of the abundant snow that still exists from much of the northern to the southwestern Utah mountains. This graph shows the snow water equivalent as a percentage of normal as of today from the National Resources Conservation Service.

All this snow is going to melt, of course, and this is where we have the good news and bad news scenarios.

The bad news is that the threat for flooding, and in some areas major flooding, is high, and how bad it gets will be determined by how quickly the snow is going to melt. It is not a question of whether there will be flooding, because there will be flooding. Rather, the question is how bad is it going to get. The current snowpack is well above what it was in 1983 when massive floods occurred in northern Utah, causing $250 million in damage, with crops wiped out, along with homes and businesses. Flooding is a given, and a quick warm-up could cause catastrophic flooding. This is what is worrying many officials. What is happening today and tonight will not help matters. Rain is likely at lower elevations, and heavy snow is likely in the mountains, with a foot or more above 7,000 feet.

Flooding is also a possibility in Wyoming, Montana and California. Rivers fed by the California snowpack melting will run high and very cold well into summer. Here, too, flooding is of major concern. At the lower elevations fed by the rivers from the Sierra, there is an added problem. Rivers will run fast, deep and very cold well into the summer months. While the weather is not warm now, it will get hot again and stay hot in the Central Valley and foothills. This means people will flock to the rivers and be tempted to cool off in the water. Due to how cold the water is, this could lead to drowning due to rapid onset of hypothermia. If that weren’t bad enough, the fast currents will add to a second drowning threat from people being swept off their feet and downstream. I urge anyone heading to the rivers this summer to use extreme caution.

The good news is the state of reservoirs. I have already covered the status of California reservoirs in an earlier posting. However, there are some interesting statistics for Lake Mead, a huge water source from Las Vegas down through the lower Colorado River between Arizona and California. Early in April, the Department of the Interior said that due to the excessive snowpack in the northern Colorado River Basin, an extra 3.33 million acre feet (maf) of water will be released from Lake Powell; this is in addition to the 8.23 maf that was already going to be released through the summer. The projected April through July inflow of water into Lake Powell is 120 percent of normal, the best year in the last decade, even exceeding 2005 and 2008. The water released from Lake Powell will raise the level of Lake Mead in Nevada by close to 20 feet by the end of September from what it was in October 2010. This is great news for Las Vegas and areas downstream that may have been looking at water restrictions this summer, had last winter not been so wet. This will go a long way in assuring plenty of water, even well into 2012. Here are the Lake Mead water levels since early in December. Current water inflow into Lake Mead is over 150 percent of what it was last year, and running over 126 percent of normal.

The views expressed are those of the author and not necessarily those of AccuWeather, Inc. or AccuWeather.com

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Western US weather expert