California Drought

I touched on it briefly in this week's State of the Atmosphere, but wanted to take a closer look today at the ever worsening drought conditions across California and portions of Oregon.

San Francisco
San Francisco recorded an all time record dry year in 2013. According to the National Weather Service (NWS), San Francisco recorded less than half the rainfall of Phoenix in 2013. In a given year the city usually receives about 10 to 35 inches of precipitation, in 2013 that number was just 3.39 inches.

Snow Cover
As of January 15, 2015 (right), snow cover for the Western Coastal region as defined by the NWS is at just 2.6%. Compare that to the same date in 2013 when 25.7% of the area had snow cover. What is almost more compelling is that where there is snow, there's not much of it. The max snow depth this year for the region is 6.8 inches, while in 2013 that number was 150 inches. Even 2012, which boasted snow cover levels similar to this year had max snow depths greater than 40 inches where there was snow.

With the lack of snow cover comes an uncanny risk of wildfire for January. Elevated risks exist for the entire Sierra Nevada range, as well is in and around the Bay Area, with critical risk across a broad swatch of southern California.

Unfavorable Weather Pattern Continues
Unfortunately the extended outlook does not look all too favorable for precipitation across California and the west. The same weather pattern that has kept snow out of Denver by and large this winter is the same pattern that is keeping the snow out of California. A dominant ridge of high pressure over the west forces the storm track to travel up and over California, before diving south once more with the trough in the east. The ECMWF ensembles show little rest for the weary over the next week or two.

There are some indications that the ridge in the west begins to retrograde as we head into February. This is actually typical as we head into the springtime months for ridging in the east to return as a more favorable storm pattern to set up in the west. The question will be how far west the ridge retreats, and if California can finally catch a break. In the meantime, everyone do a snow dance for California.

Brendan Heberton

Brendan is founder of Weather5280. He is co-founder of FreshyMap, and develops software for geospatial data analysis and visualization.

Denver, Colorado
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