Western Drought Relief Under Way ... Here's Why

Quincy Vagell
Published: November 5,2015
California and much of the West have been experiencing a long-term drought over the past few years, but a recent storm system has brought much-needed moisture to the area and further relief is possible in the weeks and months ahead.
When it comes to drought relief, the pattern so far in early November may be the ideal solution: small doses of moisture over time, rather than an enormous amount coming all at once.
While lack of rainfall is an obvious factor driving the drought, in the West snowfall plays a much larger role in maintaining water supply.

April 1 percent of average snow-water equivalent of California snowpack compared to April 1 average from 2005-2015. The April 1, 2015 snow-water content set an all-time low for April 1.
(Data: National Resources Conservation Service)

The Importance of Snow

Spring snowmelt is crucial to replenishing water supplies in California. The combination of below average rainfall and significantly below average snowfall has been allowing drought conditions to worsen.
The snowpack typically reaches a peak in early spring in the Sierra Nevada. This past April, the snow-water content was at an all-time low, just 5 percent of average, or 95 percent below average.
(MORE: California's Snowpack at Record Early-April Low)
The trend for a lack of snow has been ongoing since the winter of 2011-12, with California seeing less and less snow each season to melt in the spring and replenish reservoirs.

Signs of Change

A recent change in the jet stream pattern is allowing for cold air to drain down into much of the western United States. This has quickly reverted the pattern from unseasonable warmth to near and even below average temperatures in some locales.

The general weather pattern to start November has brought a dip in the jet stream across the west, allowing for cooler air and more snow across the region.

Snow has also fallen across many mountain ranges of the West to start November. Snow-water levels are already running considerably above average across the Sierra Nevada. Although it is early in the season, snow-water levels in parts of the Sierra Nevada were observed well over 200 percent above average as of Nov. 4.
Although snow-water levels across most of the Cascades and parts of the northern Rockies are generally running below average so far this season, even many of those areas have seen an improvement from this time last year.
(MORE: First Widespread Snow Cover in Lower 48 of the Season)
Computer model guidance suggests that a similar snowy setup may evolve early next week, which could bring more fresh powder to the higher elevations of California.
In addition to the snow that is helpful for replenishing reservoir levels in the spring, some lower elevation rain is in the forecast. The long-range European computer model ensemble forecasts indicate that the jet stream pattern could bring a series of shots of cold air and snow to the West through much of November.
(Forecast: Redding | Reno, Nevada | Sacramento
What makes this setup particularly helpful is that the low-elevation rain is not flooding out California. It is going to take a great deal of precipitation to erase the water deficit, possibly more than one wet season can provide, as a large portion of California is experiencing a severe to exceptional drought.

The U.S. Drought Monitor analysis valid Nov. 5, 2015, for the western United States. Darker shades of red indicate the most severe to exceptional drought conditions.

When too much rain falls over a short period of time, especially over dry soil, it can result in flooding. While this happened in Texas recently, a similar scenario is not anticipated in California, at least not in the short term.
(MORE: Flooding in Texas Leaves 6 Dead)
With smaller, more manageable bouts of rain likely on the way, this might be just what California needs. It will be a slow process, but there are indications that drought-relieving precipitation should continue to fall across parts of the area over at least the next couple of weeks.

Winter Weather Woes

The general weather pattern over the past few winters has been characterized by a massive ridge of high pressure across western North America. This ridge has kept warmer than average temperatures locked in over the West, pushing the active storm track largely north and east of the region.
(MORE: Winter Weather 2014-2015 Recap)

Through much of the winter of 2014-2015, a large ridge pushed the jet stream north into western Canada, resulting in generally warm and dry conditions across the West.

The result was one of the warmest and least snowy winters on record across California and surrounding states in 2014-15.
For the upcoming winter, although forecasts suggest that above average temperatures may be the rule over the West, precipitation forecasts call for above average precipitation for roughly the southern two-thirds of the Golden State.
Regardless of how much of this falls as snow or rain, the end result could mean much-needed moisture returns to the region.
Furthermore, NOAA's U.S. Drought Outlook calls for some improvement with central and southern California's drought through January. The outlook also predicts that further relief is possible into February and March.
(MORE: Winter 2015-2016 Outlook: 5 Things to Expect)
Based on the evidence, there is reason to believe that at least some drought relief can be expected in California in the weeks and months ahead.
Given the El Nino pattern, we cannot rule out a major storm system causing heavy rain and flooding later this fall or winter across the West. The best-case solution to the drought is a series of smaller storm systems, much like the ones recently observed and predicted coming up.
Either way, the drought will not disappear overnight, but steps in the right direction are certainly being observed.
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