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 August, sea surface temperature (SST) anomalies were near or greater than +2.0oC across the eastern half of the tropical Pacific. SST anomalies increased in the Niño-3.4 and Niño 3-regions, were approximately unchanged in the Niño-4 region, and decreased in the Niño-1+2 region. Large positive subsurface temperature anomalies persisted in the central and east-central equatorial Pacific during the month, with the largest departures exceeding 6oC. The atmosphere remained coupled to the anomalous oceanic warmth, with significant low-level westerly wind anomalies and upper-level easterly wind anomalies persisting from the western to east-central tropical Pacific. Also, the traditional and equatorial Southern Oscillation Index (SOI) were again negative, 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 (3-month values of the Niño-3.4 index of +1.5oC or greater). 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 contiguous United States, temperature and precipitation impacts associated with El Niño are expected to remain minimal during the early Northern Hemisphere fall and increase into the late fall and winter. El Niño will likely contribute to a below normal Atlantic hurricane season, and to above-normal hurricane seasons in both the central and eastern Pacific hurricane basins.

California, Nevada, Washington and Oregon

Temperature

October

Slightly warmer than normal across Washington and Oregon and northern California and Nevada with the rest of California and Nevada near normal to slightly cooler close to the Pacific ocean.

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.

December

Warmer than normal across the western 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

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

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.

Precipitation

October

Near normal throughout the region but slightly wetter than normal for nearly all of central and northern California while much of the rest of the state is should be close to normal to slightly drier in the interior of southern California and all of Nevada. In Washington and Oregon near normal to slightly wetter than normal conditions should prevail except for the far southwest of Oregon where slightly direr than normal conditions should prevail.

November

Most of the California and the southern two thirds of Nevada should be near normal to slightly to in some cases in southern California and southern Nevada moderately wetter than normal. Washington and Oregon should be slightly to moderately drier than normal with only very isolated parts at near normal precipitation in the far south of Oregon and far north of Washington.

December

Much of California and Nevada should be slightly to moderately drier than normal except for the very far corner of southern California and Nevada. Most of Oregon and Washington should be slightly drier than normal with just the far north central part of Washington near normal.

January

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.

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 norther most part of California and far southeast of the state 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.

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