Mount Shasta Avalanche Center column: For the period of December through January, the National Weather Service in Medford, Ore., is expecting increased chances of above normal precipitation and above normal temperatures for the Mt. Shasta area.

For the period of December through January, the National Weather Service in Medford, Ore., is expecting increased chances of above normal precipitation and above normal temperatures for the Mt. Shasta area.

This generally warmer and wetter weather than normal has the potential to continue into the spring, resulting in some and, possibly, significant drought relief across northern California. However, higher than normal snow levels and the magnitude of precipitation deficits mean that the area is still, most likely, going to remain in drought going into the summer of 2015.

State of the drought

Despite some minor drought relief from near normal precipitation during the September through November 2014 time period, the Mt. Shasta area is currently in “Extreme” to “Exceptional” drought, as depicted by the US Drought Monitor shown on the web at: http://droughtmonitor.unl.edu/.

The drought was brought on, in large part, by an exceptionally warmer and drier than normal 2013. It was the driest year on record in Mount Shasta City, with a mere 10 inches of total precipitation recorded. The previous driest year on record was 1976, when 14.21” fell.

The 1981-2010 normal precipitation for Mount Shasta City is 43.21.”

Warmer than normal temperatures in 2013 also led to a snowpack restricted to high elevations. The 2013-2014 Wet Season was the warmest on record by a full degree, with an average temperature of 52.8F. The previous record warmest was 1958-59.

This season’s forecast

The mostly warmer than normal conditions observed across the Mount Shasta area since 2013 are likely the result of the combined effects of both natural climate variability and anthropogenic climate change.

One plausible theory explaining how climate change may be impacting the area is Arctic Amplification (http://onlinelibrary.wiley.com/

doi/10.1029/2012GL051000/abstract). In short, this theory indicates that global warming is generally resulting in a slower jet stream across the Northern Hemisphere since declining Arctic sea ice is resulting in a decreased temperature difference between equatorial areas and the poles. The slower jet stream results in a higher amplitude jet stream during some seasons and a northward shifted storm track.

Warmer than normal water off the west coast of North America is one factor that favors higher than normal snow levels for this winter. The warmer than normal water is related to the warm phase of the Pacific Decadal Oscillation (PDO). This phase of the PDO often enhances the atmospheric effects of El Niño conditions across the Pacific Northwest (www.nature.com/srep/2014/141017/

srep06651/full/srep06651.html). Thus, an El Niño-like atmospheric pattern is generally expected this winter, with a predominantly more south and southwest flow storm track along the west coast.

Above average sea surface temperatures in the Equatorial Pacific Ocean in an area termed the Nino 3.4 Region and forecasts of those temperatures indicate a weak to low end moderate El Niño is likely to develop this winter. An El Niño Watch is in effect: www.cpc.ncep.noaa.gov/.

Archived climate data for Mount Shasta City indicates no correlation with winter precipitation from weak El Niños alone, and a slight increase in chances for wetter than normal conditions from moderate ones. Correlation with precipitation is significant for strong El Niños, with wetter than normal conditions likely during strong El Niño events. Thus, the El Niño forecast for this winter, by itself, means little for Mount Shasta.

The pattern expected this winter is generally anticipated to be consistent with the negative phase of the Arctic Oscillation (AO) for January and February. This pattern also favors warmer than normal conditions for the western US. The forecast transition from the current neutral to positive Arctic Oscillation to the negative phase has been tied to antecedent autumnal snow cover in Eurasia (www.aer.com/node/740).

Snow and climbing impacts

What all this boils down to for the Mt. Shasta area snowfall and snowpack is that elevations above about 7,000 feet are likely to experience near to above normal snow and snow pack this winter. For areas below about 6,000 feet, warmer temperatures are likely to mean less snowfall as well as less snow than normal persisting on the ground.

It should be noted that, while this is the expected general state of conditions for the season, it does not mean snow will not fall and be significant, at times, below 6,000 feet. In fact, one of the primary climate models used for seasonal forecasting has been indicating that January may very well be near normal for temperatures with above normal precipitation for the area, though it also predicts the DJF (December-February) period, as a whole, to be warmer than normal. Thus, snow may very well occur all the way into town, at times, but it is generally expected to be less than average for the winter season.

Nick Meyers, director of the Mount Shasta Avalanche Center, says climbers are looking at a good season on Mt. Shasta. If the precipitation continues as forecast, Meyers says it “will mean an ample snowpack to remain into April, May, June and possibly July. These months are the best months for climbing Shasta, and good climbing conditions, simply stated, means snow on the mountain. Less snow equals more rockfall and more difficult footing for climbing.”