Winter 2012-13 Recap

Winter 2012-13 was really a tale of two seasons for northern California.  November and December
were wetter than normal, when an active Pacific jet stream brought series of moisture-rich systems into the region.  January through March were much different, when a persistent upper-level ridge of high pressure over California deflected incoming storm systems well north of the state.  As a result, San Francisco recorded its driest January to March period on record with only 2.31 inches of rain, or over 9 inches below normal.  This record is also impressive due to the fact that records in San Francisco date back to 1850.  The heavier precipitation in November and December was very promising given the preceding very dry winter of 2011-12; unfortunately, this winter too will go down in the record books as another dry one for California. 

High elevation snow in the Sierra has been equally disappointing this winter.  Late March to early April is normally the peak in snow depth for California's mountains.  However, the most recent data show that California's snow pack currently holds only about 50% of normal for this time of year.  This is extremely concerning for agricultural and ecological concerns in the state, not to mention the upcoming fire season, especially following the dry winter last year.  Leading seasonal climate indicators for California weather, such as ENSO, have generally been neutral this season, with no preference toward unusually wet or dry conditions.  It's also implausible to pin the two consecutive dry winters on climate change, as California has experienced its share of dry winters in the historical record.  Climate research shows varying results in regards to future precipitation amounts for California, but the general consensus is for fewer but stronger winter time storm systems, which would likely result in more winters at both ends of the precipitation spectrum - either very dry or very wet.

Since the vast majority of California's precipitation falls between November and March, the state stands little chance of making a dent this spring in the current precipitation deficit.  Last year, despite the lack of rainfall, we were still able to benefit on the coattails of the wet 2010-11 winter season.  This year, California has no such luxury.