national integrated drought information system

california-nevada 

drought outlook december 2016 

Current Conditions

Drought conditions in parts of Northern 

California and much of Nevada have improved 

since this time last year, and especially since 

Jan. 1, 2016, with as many as four levels 

of U.S. Drought Monitor (USDM) category 

improvements (see map at left). Nevada has 

seen more improvement than California 

in the last year while much of Central and 

Southern California including the Southern 

Sierra remain in drought. As of Nov. 29, 

73% of California and 34% of Nevada 

are in moderate to exceptional drought, 

compared to 97% and 93% at this time last 

year, respectively. 

According to NOAA’s National Centers for 

Environment Information (NCEI), the period 

from October 2014 to October 2016 was the 

warmest and eighth driest period in California, 

and second warmest and 53rd driest period 

in Nevada. The improved USDM categories 

in some locations were due to near- to 

above-normal precipitation last winter, when 

California and Nevada saw their 35th and 30th 

wettest years, respectively. However, after 

years of prolonged drought, this has only put a 

dent in the deficits and longer term hydrologic 

impacts have persisted in both states. 

Since the start of the 2017 water year (Oct. 

1), the West has been warmer than average 

overall. Above-normal temps have been 

recorded across most of California and Nevada 

with the exception of northern portions of 

the Central Valley and the Trinity Mountains. 

Several large precipitation events, including 

atmospheric rivers in October, have done the 

“heavy lifting” to start the water year. 

Atmospheric rivers, or ARs, are narrow 

corridors of high water vapor transport 

in the lowest 2 km of the atmosphere and 

are responsible for most of the horizontal 

transport of water vapor outside of the 

tropics. ARs can produce abundant and 

often intense rainfall, and are especially 

important in California because they can boost 

rainfall storage, but can also result in natural 

hazards such as flooding, intense runoff 

and landslides. While they tend to primarily 

impact California, they can sometimes spill 

over into Nevada, which was the case in midOctober, when two ARs brought rain to far 

northwestern California, the Sierra Nevada, 

and northwestern Nevada. November saw less 

http://droughtmonitor.unl.edu/

Does a Wet October 

indicate a Wet November 

to March? 

By examining past October precipitation 

totals versus November-March 

precipitation totals since 1895, NOAA’s 

Western Regional Climate Center (WRCC) 

has found no significant relationship 

between a wet October and a wet winter 

in California or Nevada. However, the 

number of very wet Octobers is small 

and it is difficult to draw conclusions 

from this sample size.

U.S. Drought Monitor 

Class Change

Dec. 1, 2015 - Nov. 29, 2016

2 Class degradation

1 Class degradation

No change

1 Class improvement

2 Class improvement

3 Class improvement

4 Class improvement

5 Class improvement

average temperature departure 

from average - Water Year so far

Oct. 1 - dec. 5 2016

percent of average precipitation -

Water year so far

Oct. 1 - dec. 5, 2016

http://www.wrcc.dri.edu/

0°F

-4°F

+4°F

+8°F

+12°F

+16°F

50%

25%

70%

90%

100%

110%

130%

150%

200%

5%

Impacts & Updates 

-- California remains under 

a state-declared drought 

emergency.

-- Cachuma Reservoir (Santa -- 

Barbara County) is currently 10% 

of normal. The reservoir supplies 

drinking water for Santa Barbara 

and communities in the Santa 

Ynez Valley.

-- Five years of drought have led 

to a very significant rise in bark 

beetle infestation and historic 

levels of tree die-off. 

-- Based on aerial detection 

surveys conducted throughout 

2016, the Forest Service estimates 

the number of dead trees on 

California’s forested lands grew to 

a cumulative total of 102 million 

on 7.7 million acres since 2010. 

300%
OUTLOOK: PRECIPITATION

DEC-JAN-FEB Mar-apr-may

http://www.cpc.ncep.noaa.gov/

OUTLOOK: TEMPERATURE

DEC-JAN-FEB Mar-apr-may

About this outlook

On December 2, 2016 NIDIS and its partners held a CaliforniaNevada DEWS Drought & Climate Outlook Webinar as part of a 

series of regular drought and climate outlook webinars designed 

to provide stakeholders and other interested parties in the 

region with timely information on current drought status and 

impacts, as well as a preview of current and developing climatic 

events like La Niña.

The presentations from this webinar can be accessed here: 

http://bit.ly/2fFwtbC

contributors

David Simeral, U.S. Drought Monitor author, Western Regional 

Climate Center/ Desert Research Institute

Nina Oakley, Western Regional Climate Center/ Desert Research 

Institute

Doug Boyle, Nevada State Climatologist, University of Nevada 

Reno 

Andrea Bair, National Weather Service

Amanda Sheffield, California Nevada Climate Applications 

Program/Scripps Institution of Oceanography

Alicia Marrs, NOAA/NIDIS

precipitation in the region than October, but in late November 

a weak AR finally brought some much-needed precipitation 

to southern and central coastal California. Nearly an inch fell 

in some areas that are experiencing some of the most intense 

drought impacts, however that rainfall won’t make a significant 

dent in prolonged drought conditions. 

Precipitation in the northern and central Sierra is on a positive 

start to the water year and on track for a record year, with the 

southern Sierra still below normal. However, it is very early in 

the season to make any definitive statements on snowpack, 

especially considering much of the precipitation this season 

has fallen as rain rather than accumulating snowpack due to 

above-average temperatures. 

Soil moisture conditions have seen improvements across 

the northern portions of both states but very dry conditions in 

Southern California and Nevada still persist. 

Overall, streamflows are running normal to above normal 

across both states, with some areas in northeastern California, 

the Salinas River, and the Southern Sierra still below normal. 

Compared to this time last year, reservoir levels have increased. 

However, many reservoirs are still below average, with some at 

levels far below normal where drought has been the most intense. 

Groundwater levels remain low in both California and Nevada; 

for example, near Santa Barbara and San Joaquin Valley in 

California and the Carson Valley and Amargosa Valley in Nevada. 

It is also important to note that reservoir levels are not always a 

clear indicator of drought conditions because they are contingent 

on necessary reservoir operations and available precipitation.

Climate Outlook

Over this past summer, observed El Niño conditions, or 

cooler than normal sea surface temperatures (SST), lessened 

and reached neutral or weak La Niña conditions in the tropical 

Pacific Ocean. Currently, La Niña conditions are present. This 

means that equatorial (Niño 3.4 region) SSTs during the last four 

weeks were below average in the central and east-central Pacific 

Ocean. As of Dec. 2, NOAA’s Climate Prediction Center (CPC) has 

issued a La Niña Advisory. Most multi-model averages indicate 

weak La Niña conditions through the Northern Hemisphere in 

early winter 2016-17 (December-January-February) with La Niña 

slightly favored to persist (~55% chance) with an above-normal 

climatological probability of a return to neutral conditions 

favored in the new year.

Looking at typical La Niña patterns, conditions tend to be 

wetter in the Pacific Northwest and can sometimes extend into 

northern California and northwest Nevada. The effect of La 

Niña on winter precipitation is strongest in Southern California,

where drier than normal conditions tend to develop. This region 

has been one of the slowest to recover from the current drought 

and a La Niña could potentially exacerbate those conditions. 

Historically, past weak La Niña conditions have favored nearnormal or dry winter months with ENSO-neutral events yielding 

more dry winter seasons than normal or wet ones. However, past 

conditions do not guarantee future outcomes. 

The CPC Seasonal Outlooks as of November 17th (above) 

show higher probabilities of warmer than average temperatures 

and slight favoring in the odds of below-normal precipitation 

in Southern California and Southern Nevada through April. 

High uncertainty remains for the remainder of the region with 

equal chances of above, below, and normal precipitation and 

temperature forecasted. Hence, drought is expected to persist in 

the southern and central portions of California and southwestern 

Nevada, with possible improvements in northeast California and 

northwest Nevada.