Summary for California, Nevada, Washington and Oregon

NOAA El Niño Advisory: There is a greater than 90% chance that El Niño will continue through Northern Hemisphere winter 2015-16, and around an 85% chance it will last into early spring 2016.

During July, sea surface temperatures (SST) anomalies were near +1.0oC in the central equatorial Pacific Ocean, and in excess of +2.0oC across the eastern Pacific. SST anomalies increased in the Niño-3 and Niño-3.4 regions, while the Niño-4 and Niño-1+2 indices decreased slightly during the month. Positive subsurface temperature anomalies strengthened in the central and east-central equatorial Pacific during the month, in association with the eastward movement of a downwelling oceanic Kelvin wave. The atmosphere remained coupled to the oceanic warming, with significant low-level westerly wind anomalies continuing from the western to east-central equatorial Pacific, along with anomalous upper-level easterly winds. Also, the traditional and equatorial Southern Oscillation Index (SOI) were both negative, consistent with enhanced convection over the central and eastern equatorial Pacific and suppressed convection over Indonesia. Collectively, these atmospheric and oceanic features reflect a significant and strengthening El Niño.

All models surveyed predict El Niño to continue into the Northern Hemisphere spring 2016, and all multi-model averages predict a strong event at its peak in late fall/early winter (3-month values of the Niño-3.4 index of +1.5oC or greater. At this time, the forecaster consensus unanimously favors a strong El Niño, with peak 3-month SST departures in the Niño 3.4 region potentially near or exceeding +2.0oC. Overall, there is a greater than 90% chance that El Niño will continue through Northern Hemisphere winter 2015-16, and around an 85% chance it will last into early spring 2016.

Across the contiguous United States, temperature and precipitation impacts associated with El Niño are expected to remain minimal during the remainder of the Northern Hemisphere summer 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

September

Temperatures for much of the four state area should be near normal to slightly cooler than normal. Northeastern Nevada should be moderately cooler than normal.

October

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.

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.

Precipitation

September

Much of California and Nevada should be slightly drier than normal along with a small portion of the southern part of the state. All of Oregon and Washington should be near normal to only slightly wetter than normal in the northwest of Washington for the month.

October

Near normal throughout the region but slightly wetter than normal for nearly all of California and across southern Nevada while much of the rest of the state is should be close to normal for this historical month for the onset of the wetter season. In Washington and Oregon near normal to slightly drier than normal conditions should prevail except in the ranges of northwest Washington where precipitation should be slightly greater than normal.

November

Most of the California and Nevada should be near normal to slightly drier than normal in the north but only slightly to in some cases moderately and this is a rainy season month. The southern half of California and Nevada in contrast could be only slightly wetter than the long-term average although in the southern-most part of California this is a very dry month historically. Washington and Oregon should be slightly to moderately drier than normal.

December

Much of California and Nevada should be slightly to moderately drier than normal. Most of Oregon and Washington should be near normal to only slightly wetter than normal in the northwest of Washington and the northeast of Oregon for the month.

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.

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