Lake Tahoe, known for its incredible blue water, expansive forests and snowy peaks, is currently experiencing a dry spell with warm temperatures that are impacting local snowpacks. Although , the area benefited from a very active pattern that resulted in a number of major storms in late December and early January, bringing the snowpack back to average. Baker Perry, Ph.D., State Climatologist, professor of climatology in the College of Science, and faculty at the Tahoe Institute for Global Sustainability, explained that these patterns of snowfall are typical for the area, but that lower-elevation regions are experiencing more rainfall than usual.
In an interview with the , Perry answered questions about weather patterns, snow science and climate forecasting across the Sierra.
What is a state climatologist, and what do you do in the role?
The job of state climatologist entails being very familiar with what's happening across the state with weather and climate and specifically involves writing monthly drought reports and communicating this to key partners and stakeholders, as well as quarterly climate reports that provide a summary of what the climate has been over the most recent months and sometimes longer. We do quite a bit of research across the region and interface with partners at the National Weather Service, with the Nevada Snow Survey, and other water-related organizations. We have several surface-based instruments, rain gauges, weather stations and snow sensors that we are collecting a lot of data with. One major active area of research is to help improve forecasts for precipitation, which is a major forecasting challenge here in Reno and across western Nevada.
Why do we need good forecasts in this region?
We need good forecasts because the weather has a big impact on everyone. Certainly, in wintertime, we must think of the impacts of snow on the roads. It is also a consideration of if there will be snow or rain on the ski slope, which has a big impact on winter tourism. More broadly, the amount of precipitation that spills over the Sierra crest has a huge impact on water resources, drought conditions, soil moisture, reservoirs and water resource availability.
Snow is important to predict for our snowpacks. Rain, when it falls, infiltrates into the ground and runs off relatively quickly. Snow, on the other hand, especially if it's falling in the heart of the winter months, is going to build a snowpack, especially at higher elevations. In the spring and early summer months, the snowpack is a resource that melts slowly and sustains vegetation and communities and moves into those reservoirs to provide a much longer lasting benefit than just rain.
Can you describe what La Niña and El Niño weather patterns are?
La Niña patterns refer to a large area of below normal water temperatures, what we call “sea surface temperatures,” across the tropical Pacific Ocean. That usually means storm tracks are favored into the Pacific Northwest. Here in Northern California and Western Nevada, it means that – although variable – we're on the southward extent of those storms, even though the bulk of them go into the Pacific Northwest into southwestern Canada.
El Niño patterns, on the other hand, mean that the water temperatures in the tropical Pacific Ocean are much higher than normal. Normally, during an El Niño year, we have more active storms that move into Southern California and into the southwestern United States.
What are the different kinds of snow in this region, and what does it imply for snowpacks?
Here in our region, we tend to have snow that is a bit wetter and denser than other regions. That is because we're very close to the Pacific, which is the primary moisture source for the region, and it means that a lot of our storms are relatively warm and provide water-heavy snow. This is not the classic powder that you might find in the Northern Rockies or colder locations, but it builds a great base that builds a strong snowpack that will melt slowly for more continuous water supply later in the season. From a water resource perspective, the amount of water that we have in an inch of snow here in the Sierra is typically much greater than in other places, which means that when it does eventually start to melt, it has a lot of value.
We can, however, get powdery snow in the Tahoe region, especially if one goes to higher elevations where it's colder. When storm systems are colder, and especially if they're coming in from the northwest or the north, it usually means that the snow will be less dense, providing the region with very nice powder. Having some powder on top of Sierra cement can be tremendous for skiing and tourism.
What is Sierra cement?
Sierra cement is a name given to the very dense snow and snowpack that develops here in the Sierra. It is a product of having super cooled liquid water that freezes on the outside of the snowflakes as they're falling through the clouds, creating a denser snowpack. Because we have systems that produce so much snow in a single storm, that amount of snow ends up compacting itself and making the snowpack denser. It's one of those characteristics of our region that helps build a fantastic snowpack that can last, especially at higher elevations, through the spring and even into the summer in many locations.
What can we expect for the future of snow in this area?
As the climate has warmed, we have certainly seen some changes in snowpack and winter conditions in the Tahoe region. One of the most notable changes is increased rainfall and less snow, especially here in the Western Nevada valleys. Even in years with normal to above normal precipitation, those middle elevations at 6,000 to 7,000 feet experienced that precipitation as rain, which meant that there was not much of a snowpack that built up. We think this may be a harbinger of what's to come. Especially as storms get warmer and the climate in general continues to warm, it's going to be harder for those lower and middle elevation regions to enjoy as much snow as they have in the past.
If you go up high enough, the storms are going to continue to come, and it's still going to be cold enough for snow to fall. Ultimately, there's going to be a real dependence on elevation in terms of how the Sierras and Tahoe region see changes to snow with respect to a warming climate.
