A series of winter storms have dumped much-needed snow across much of California, including over two feet in parts of Tahoe which have been dubbed a “Christmas miracle.”
These systems have provided a welcome boost to the state’s snowpack, which was lagging headed into the season amid a “snow drought,” with higher-than-average temperatures causing much precipitation to fall as rain.
The storms also came shortly after California water officials conducted their first manual snow survey of the year at Phillips Station near Lake Tahoe, which found the snowpack at 50% of average. The statewide snowpack, which is monitored electronically, was at 71% of average.
Dr. Andrew Schwartz is the Director of UC Berkeley’s Central Sierra Snow Lab at Donner Summit.
He spoke with Insight Host Vicki Gonzalez about what the latest storms mean for the state’s snowpack, and the implications for California’s water supply for the rest of the year.
This interview has been edited for length and clarity.
Interview highlights
How have the past couple weeks been up at the summit?
Snowy, thankfully. We’ve had about seven-and-a-quarter-feet of snowfall in the last one to two weeks, it's been really fantastic. It's like Dec. 23 hit and then we've had nothing but winter storms since.
Officials at the Department of Water Resources recently conducted their first manual snow survey of the year, and the statewide snowpack was also measured at 71% of average. How does this compare to recent years or historical totals?
We've seen patterns like this happen before. In fact just a couple years ago, we had a relatively slow start to the season where I think had worse numbers for the Jan. 1 measurement. There's so much variability in our early season that it's hard to say where we should be for average. It’s kind of funny; we had that measurement, a lot of people were worried, and here we are right back up to [the] median here at the Central Sierra Snow Lab.
The snowpack is also different from water content. Can you talk about that difference?
We measure snowfall — how much snow has fallen, the snowpack — in depth above the ground. And then snow water equivalent is the amount of water that will get out of the snowpack when we melt it. Even though we may have gotten seven feet of snow, generally fresh snow means that it's about 10 inches of snow to one inch of water. So that’ll produce seven inches of water when it melts.
Conditions aren't the same across California, which parts of the state are faring better?
Down south is where we see the best snowpack. We have about 114% of normal snowpack in the southern Sierra. Up north though, not quite as good. We're at 61% here in the central Sierra, kind of like last year we're right in the middle.
Is there a region of the Sierra that is more preferable to having a more robust snowpack, does it matter?
It does a little bit. So much of our water comes from the northern Sierra or the central Sierra. As those rivers like the San Joaquin and the Sacramento get shipped south, we want those to have plenty of water, of course. So generally speaking, we do want more water around northern and central California because that's where a lot of our water throughout the state comes from. That said, there’s not a bad place within the state to have a good snowpack.
Just a month ago California was in a “snow drought” with a lot of rain falling due to warmer weather. What are the consequences of having all that rain as opposed to snow?
We started the year warm. We have actually about 160% of average rain and snowfall at the lab, meaning that the rain's really paying dividends. The challenges for that being that our reservoirs are used also as flood mitigation, which means we can't store every drop that comes in. The way we can get around this and really help with our water resources is when we go into winter, our snowpack builds up and that means that water isn't immediately going downstream and into our reservoirs where we might have to release it.
It’s a good thing to have that rain, it helps wet our soil so that our snowpack doesn’t have to go into the soil before it runs off, but we definitely want to see snow.
What if there is more higher elevation snow at this point? If we have more rainfall as opposed to snow, does that hurt the snowpack?
It can. Honestly, this is one of the areas we don’t understand about snow super well. The New Year’s Day floods in Yosemite Valley in 1997 were a result of rain falling on fresh snow. There were massive floods that happened in Reno at that same time. But there's been other rain on snow events that have even happened in the last few years where it'll rain a ton, but we just get a little pulse up in our rivers.
It's kind of challenging for us to know which one will occur when we get a rainstorm. But that said, obviously we're hoping that it'll seep into the snowpack and bulk it up rather than cause these catastrophic floods by melting it.
What do our reservoirs look like as of today?
They look really good, most if not all are at average or above average for this time in year. Those last several above-average or average years in our snowpack and our water intake with rain have really paid dividends to keeping us in a good spot moving into this winter.
How fast can conditions change?
We are still early in the season. January through February, those are our snowiest months and they can change on a dime. We were very, very dry going into these last two weeks, and the models are looking like we could be dry for the next two weeks. It's hard to say with any certainty what the rest of the season will look like because things are always up in the air… but we hope that it balances out when all is said and done.
Are you concerned about this extended dry period being forecasted?
Not necessarily. We see these dry periods occur a lot in January with regards to snowfall. They're becoming more common and they delay things even further. We have these big high pressure systems that set up and really prevent us from getting snow in the second half of January, and it tends to happen a lot.
Now, if that all of a sudden goes into February and we start getting these really long periods without precipitation, that's when we're going to start to worry because we can see dry periods during January, we don't want it to be for the rest of the season.
