One Down, Three to Go
By Wendilyn Grasseschi
The new year started off with a bang with the biggest storm in five years this week – and that’s just the beginning.
“At least three more storms, including the big one – a large, atmospheric river storm Saturday through Monday, are on their way, and by the time they have exited by the end of next week, the best forecast from the WPC (Weather Prediction Center) puts an additional 18 to 20 inches of precipitation over the Central Sierra by late Friday, Jan. 13,” said Mammoth’s forecaster, Howard Sheckter.
He said Mammoth’s total for the first two weeks of January, when all the storms have passed through, could be 25-30 inches of precipitation.
That might not sound like much to those used to thinking of snow in inches, but that’s not inches of snow, that’s the actual water content within the snow or rain.
For example, the average amount of winter precipitation that falls on Mammoth Pass, which is located at about 9,000 feet of elevation and is used for state survey measurements, is 42 inches. A normal ratio used is 10:1, or ten inches of snow for every one inch of rain, but it depends heavily on how warm the incoming precipitation is.
Thus the average amount of snow that falls on Mammoth Pass each year is somewhere between 25-45 feet of snow.
The 18 to 20 inches new precipitation in the forecast noted above can thus translate to some 15 to 18 feet of snow, depending on how much of the next three storms comes in as rain and how much comes as snow.
The first storm has already made a dent in the Mammoth snowpack, and the next three are going to make an even bigger dent, he said.
“With the first atmospheric river event winding down Thursday, Mammoth Pass recorded 9.14 inches of water as of 12:45 p.m.,” he said. “The Mountain picked up seven feet of new snow. So we are already one third of the way there toward our 25 to 30 inch goal that I set earlier in the week.”
Three more storms are on the way before the storm doors close after next weekend and a drier pattern emerges, but it's the one forecast for this weekend, beginning tomorrow, Jan. 7, that alarms Sheckter and has the entire Town of Mammoth and Mono County now urging residents to take today, Friday, to get ready for a historic storm and flood event.
The reason the incoming storm has so much destructive potential is because it is going to be both very warm and very wet, dropping as much as six to 12 inches of precipitation - not snow, precipitation - on the current snowpack, which is already very saturated from the Tuesday-Thursday storm that just exited the area. The storm, or “Atmospheric River Number Two” as Sheckter calls it, may indeed bring another five to eight feet to Mammoth Mountain.
But it will also be warm enough to drench the Town of Mammoth Lakes and all elevations below 9,500 feet, beginning on Sunday, he said.
“It will be all rain on Sunday, with possible flooding, perhaps serious, during the day, before cooler air moves back into the Town of Mammoth by around midnight, Sunday night,” Sheckter said.
But it will still be mostly a warm storm, with plenty of rain instead of snow.
“Below 10,000 feet it is problematic,” he said. “There is no doubt there is be some loss in snow pack but there will be more gain. I think that the storm, even at 9,000 feet, could bring another two to three feet of wet snow by Monday night.”
The National Weather Service has now issued a Flood Warning for that storm, beginning on Sunday (http://tinyurl.com/h9nz59m).
“I call it a frog strangler,” said Sheckter. “That’s because it’s going to be all rain Saturday night into Sunday afternoon, not snow, enough to drown a frog.
“I am very concerned about localized flooding during this storm, in places prone to flooding, like the Sierra Valley Estates (Mono, Joaquin streets area) and Old Mammoth,” he said. “When the rain hits the snow, if the storm drains are not clear, the water could back up and flood the area. Be sure if you live in one of these areas to watch for this and clear the storm drains.”
He said he talked to the Town of Mammoth Lakes Public Works to alert them to the potential problem, as well.
Then, with barely a breather, it’s time for “AR Storm Number Three.”
“The latest guidance indicates that there may not be much break in the precipitation Monday night (Jan. 9) into Tuesday before the snowfall rates ramp up again Tuesday into Wednesday,” he said.
The storm is quite moist but will move out by Wednesday morning, he said.
“This is not to say that will won’t have high precipitation rates Wednesday, but the wetter part of the atmospheric river will be to our south by then. I think that this is positive and argues for more snowfall over the area Wednesday.”
The last in the series is "Atmospheric River Number Four," which arrives on Thursday, Jan. 12, he said.
“It will hit Thursday mid-morning and will be out of Mammoth about Friday mid-morning,” he said.
The totals from the last two storms are still unclear but he said both are going to be decent storms.
“It is a also a very significant storm that will bring lots of snow to the high country,” he said.
The forecasting for the last two storm noted above are still not concrete in terms of total amounts of precipitation, but Sheckter said that as long as the large ridge of high pressure over the Bering Sea that is allowing the storms to move onshore doesn’t move – and it’s not forecast to move until after Jan. 13 – the storms will arrive.
In other words, the Eastern Sierra is not going back to a dry pattern anytime soon.
“The Bering Sea ridge will drive the weather this week and into next,” he said.
After that, he said, a drier pattern could set up for the following two weeks of January.