Low snowpack means a dry summer for the West
The winter of 2012 produced more apocalyptic records than hip-hop MCs on the eve of Y2K. March was the warmest on record for the Lower 48, averaging 8.6 degrees Fahrenheit above the 20th century average. In the West, La Niña predictably soaked and chilled the Northwest while leaving the Southwest warm and dry. The positive phase of the Arctic oscillation -- a belt of high atmospheric pressure around the mid-latitudes -- exacerbated everything, keeping frosty temperatures up north and blocking winter storms from dipping much farther south than Wyoming. Snowpacks suffered, with Colorado seeing its driest March on record; warm temperatures caused early melt-off there and in Utah, Nevada and California -- as much as 30 percent was lost in one month. In the Colorado River's upper basin, people who depend directly on tributaries and small reservoirs might feel the pinch, but water in the river system's big main-stem reservoirs has increased over the past seven years, allowing roughly 30 million users at least temporary relief.
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