Sunday, November 30, 2014

The Winter Outlook for the Western U.S.

The big question right now for outdoor enthusiasts in the western U.S. is whether there will be enough snow for outdoor recreation this winter.  Last year was a  mixed bag, with snow drought conditions in California and southern Utah, while Washington State, Idaho, and Montana made up for a dry fall to end up above normal snowpack by early spring.

 The latest snowpack information from the USDA Snotel network indicates well below normal snowpack over the Sierra and Cascades, but near normal conditions over Colorado, Wyoming, Montana, and Idaho.

But what will happen now?   Meteorologists' most useful tool for predicting the nature of western U.S. winters is the correlation between El Nino/La Nina and regional weather.   El Nino years are associated with warmer than normal tropical Pacific waters and  often bring warmer than normal conditions to the western U.S., less snow in the Northwest, and more precipitation in the southwest U.S.

It appears that his winter that we will be in a weak El Nino pattern and  forecasters at the National Weather Service's Climate Prediction Center are predicting a winter with El Nino characteristics.   More precipitation over the southern tier of of the U.S. and drier than normal over the Northwest.

They forecast warmer than normal conditions from the Rockies to the West Coast.  Keep in mind that such long-range forecasts have imperfect skill, analagous to weighting a coin, so that heads occurs perhaps 70% of the time.

The bottom line prediction for snow lovers?  

Below-normal snowpack over the Northwest.   More precipitation in California than last year, which will allow more snow in the high Sierra. Normal year for Colorado.  This forecast has imperfect skill, but it is the best we can do at this point.