Warm February hurt snowpack
March 9, 2016
After four years of disappointing winters, the 2015-2016 season was shaping up to be a return to form. And while the first few months were snowy, Brian McInerney, senior hydrologist for the National Weather Service, said Park City’s snowpack as of this week is at 84 percent of normal.
"Which isn’t terrible," he said. "But when you look at where we’ve been this year, really we were just a bit below normal. We’ve been around 90-95 percent of what we consider normal. The last month, though, has really hurt us bad.
"We haven’t really increased our snowpack by much during that time and if anything, the warmer temperatures have melted off a great deal of the lower elevation snowpack. From 6,500 feet up to 7,000 feet has gone away for the most part."
McInerney said the state of the snowpack is particularly disappointing because conditions early on seemed to be perfect: a record-breaking El Niño and lots of dynamic weather thanks to a friendly atmospheric pressure system. In past years, he said, a high pressure system over the area pushed storms into Canada and split the jet stream. For the first few months of this season, that didn’t happen.
"[The weather] in November was very active all around the West," he said. "And December was great. We were above normal precipitation, it was colder than normal conditions, which is really what we needed. And we were augmenting our snowpack throughout Utah and, really, throughout the Western United States."
It was more of the same in January. Park City, McInerney said, was around 90-95 percent of normal and the feeling was that if the weather kept up, Park City might reach above-normal snowpack.
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"And then February hit," McInerney said.
A ridge of high pressure similar to the one that plagued the Park City area for the past four years came back "in a big way," McInerney said, and did the same thing it had done in prior seasons — it pushed stormy weather north and left Park City with clear skies and above-average temperatures for weeks.
"It was a really depressing occurrence," he said. "We lost up to 20 percent of our forecasted water supply with that one month of very warm temperatures, and had maybe 30-50 percent of normal precipitation during that time. The lack of storminess wouldn’t have really hurt us too bad, but it was the warm temperatures and the increased solar radiation that melted off most of Park City where people live, their snowpack, and brought rain to the ski areas."
Currently the "reservoir contents" for the area are at 60 percent of normal. McInerney said forecasters are predicting they will end up at 65 percent at the end of the spring.
"Reservoir content is the volume of water that comes out of the mountains from April 1 through the end of July," he said. "If you could conceive of filling up your bathtub, putting the drain in on April 1, filling up the bathtub and then stopping at the end of July, then recording how much volume is now stored in the bathtub, that’s what it is. We’re only expecting 65 percent of normal, which is on par with where we were in those poor years."
The problem with snowpack melting off early, as it has been for the past month, is inefficiency, McInerney explained.
"Any time you melt the snowpack prematurely you get an incredibly inefficient melt," he said. "You lose snow water equivalent to evaporation, to transpiration, where the plants come back to life from their dormancy and pull up water through their roots, then transpire it up through their leaves. With warm wind events you can lose half of what you anticipate ending up in the reservoirs if you start melting early in March. And this week we are going to do that."
The ideal runoff happens all at once in May, McInerney said, like a fully soaked sponge that is squeezed dry all at once. He added, though, that there is still time to turn things around.
"It looks like we could have more storminess, but what we need is a continued, cold jet stream parked right over us, and really we need about nine more storms with about a foot for each storm to bring us to where we want to be, and not to melt the snowpack that we’ve already accumulated," he said. "Is that going to happen? Well, there’s a low probability that’s going to occur, unfortunately."
McInerney said as the climate continues to warm, Summit County residents might have to get used to a new normal.
"It’s depressing, but this is our future. This is where we are headed. We are going to see more and more of these types of events as we warm our climate and climate change continues. Around 2035 or 2045, the areas that are 90-100 percent snow-covered now will only be 50 percent snow-covered."