May 29, 2017

Quiet early summer conditions; thoughts on the season ahead

California
USA
by
Daniel Swain
,
California Weather Blog
How does the 2017 snowpack compare to 1983? Image: Center for Western Weather and Water Extremes
How does the 2017 snowpack compare to 1983? Image: Center for Western Weather and Water Extremes

Weather-wise, conditions across most of California have been rather quiescent in recent weeks. Despite a record-wet Water Year to date across much of Northern California, it has been a dry (and warm) spring across Southern California. Some early season warmth (in some spots, marginally record-breaking) has allowed for an acceleration in Sierra Nevada snowmelt, and many snow-fed rivers in California and Nevada are currently running high and cold. So far, though, only minor flooding has resulted from snowpack melting in recent days. This is partly because a lot of the snow on the ground has already melted at lower elevations, despite a hefty upper-elevation snowpack–in fact, relatively warm temperatures led to lower elevation snowmelt even during the middle of winter earlier this year.

The rather striking graphic above demonstrates just how strong this elevational snowpack gradient has been in 2017–with near-record snow water equivalent comparable to 1983 at the highest elevations and dramatically less accumulation further down the slopes. While not as visually dramatic as the near-total lack of snow in 2015, 2017 featured at least the fifth consecutive winter where a below-average fraction of precipitation fell as snow (as opposed to rain). A flurry of recent research strongly suggests that recent observations like these are indeed linked to California’s long-term warming trend–and that snowpack losses are expected to accelerate further over the next few decades.