Summary for California, Nevada, Washington and Oregon

NOAA El Niño Advisory: There is an approximately 95% chance that El Niño will continue through Northern Hemisphere winter 2015-16, gradually weakening through spring 2016.

During September, sea surface temperature (SST) anomalies were well above average across the central and eastern Pacific Ocean. The Niño indices generally increased, although the far western Niño-4 index was nearly unchanged. Also, relative to last month, the strength of the positive subsurface temperature anomalies decreased slightly in the central and eastern Pacific, but the largest departures remained above 6oC. The atmosphere was well coupled with the ocean, with significant low-level westerly wind anomalies and upper-level easterly wind anomalies persisting from the western to the east-central tropical Pacific. Also, the traditional and equatorial Southern Oscillation Index (SOI) values became more negative (stronger), consistent with enhanced convection over the central and eastern equatorial Pacific and suppressed convection over Indonesia. Collectively, these atmospheric and oceanic anomalies reflect a strong El Niño.

All models surveyed predict El Niño to continue into the Northern Hemisphere spring 2016, and all multi-model averages predict a peak in late fall/early winter. The forecaster consensus unanimously favors a strong El Niño, with peak 3-month SST departures in the Niño 3.4 region near or exceeding +2.0oC. Overall, there is an approximately 95% chance that El Niño will continue through Northern Hemisphere winter 2015-16, gradually weakening through spring 2016.

Across the United States, temperature and precipitation impacts from El Niño are likely to be seen during the upcoming months. Outlooks generally favor below-average temperatures and above-median precipitation across the southern tier of the United States, and above-average temperatures and below-median precipitation over the northern tier of the United States.

California, Nevada, Washington and Oregon

Temperature

November

Warmer than normal across the entire four state region with temperatures in the mountainous areas at close to 1 degree C (1.8 degree F) above normal. Only coastal areas near or slightly below normal.

December

Warmer than normal across the eastern half of the four state region with temperatures at close to 1 degree C (1.8 degree F) above normal. The western parts of Washington, Oregon and California should be close to normal to slightly cooler than normal especially in the coastal zone.

January

Warmer than normal across the eastern half of the four state region with temperatures at close to 1 degree C (1.8 degree F) above normal. The western parts of Washington, Oregon and California should be close to normal to slightly cooler than normal especially in the coastal zone.

February

Slightly to moderately cooler than normal across much of the four state area with the exception of southernmost California and central Washington.

March

Slightly to moderately cooler than normal across much of the four state area.

April

Slightly to moderately cooler than normal across much of the four state area except for central Washington and southern California that should be slightly above normal along with parts of northern Nevada.

Precipitation

November

Most of the California and the southern two thirds of Nevada should be near normal to in some cases in southern California and southern Nevada slightly wetter than normal although drier than normal in extreme southern California. Washington and Oregon should be near normal to slightly drier than normal.

December

Much of California and Nevada should be slightly to moderately drier than normal except for southern California and Nevada that should be slightly to moderately above normal. Most of Oregon should be slightly drier than normal with just the northeastern portion near normal. Nearly all of Washington should be near normal to slightly wetter than normal except the central Washington that should be slightly drier than normal.

January

In California, the southern half of the state should be slightly wetter than normal along with southern Nevada. The northeast coastal ranges and northern Sierra should be slightly drier than normal while much of the northern half of Nevada should be slightly to moderately drier than normal. The coastal ranges of Oregon should be slightly drier than normal along with eastern Oregon while central Oregon should be near normal to slightly wetter than normal. Most of Washington State should be near normal to only slightly wetter than normal in the central regions.

February

In California, the Central Valley and the southern half of the state should be slightly wetter than normal along with southern Nevada. The northeast coastal ranges and northern Sierra should be slightly drier than normal while much of the northern half of Nevada should be slightly to moderately drier than normal. The coastal ranges of Oregon should be slightly drier than normal along with eastern Oregon while central Oregon should be near normal to slightly wetter than normal. Most of Washington State should be near normal to only slightly wetter than normal in the central regions.

March

Much of California and Nevada should be slightly to moderately drier than normal Only small areas in the northern most part of California and southern third of the state along with southernmost Nevada should be near normal to slightly wetter than normal. Most of Oregon and Washington should be near normal to only slightly wetter than normal in the central regions.

April

Much of California and Nevada should be slightly to moderately drier than normal Only small areas in the northern most part of California should be near normal. Most of Oregon and Washington should be near normal to only slightly wetter than normal.

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