Western Regional Climate Center

PROVIDING CLIMATE SERVICES SINCE 1986

October in the West

October saw a startup of the winter storm season and the 2011-2012 water year. The first such storm arrived during the early days of October, followed by another significant event about mid-month, and providing above normal precipitation for much of the West. Temperatures were near normal throughout most of the West, with areas of above normal temperatures throughout Montana, Wyoming, eastern California, Nevada, and southern Arizona.

The greatest positive temperature anomalies this October occurred in eastern Montana, northern Wyoming, and southern Arizona. Tucson’s October average was 83.3 F (28.5 C), the 13th warmest October on record. Billings, Montana experienced a monthly average of 51.9 F (11 C), the 9th warmest October since 1948. In the midst of warm October temperatures in the inland Northwest, record low temperatures on individual days were recorded with the passage of cold fronts. On October 27th Laramie, Wyoming had a record low of -16 F (-26.7 C), shattering the previous daily record of 7 F (-13.9 C) set in 1970.

Precipitation was near normal for most of the West, with pockets above normal. Many above normal values were recorded in the inland Northwest, setting or tying previous precipitation records. Missoula, Montana experienced its 4th wettest October on record with a rainfall total of 2.4 in (60.9 mm). Pocatello, Idaho and Boise, Idaho both experienced their 6th wettest Octobers on record with rainfall totals of 1.99 in (50.5 mm) and 1.79 in (45.5 mm) respectively. One of the most impressive records occurred at Riverton, Wyoming on October 8th. Riverton received a daily total of 1.14 in (29 mm) rainfall, well beyond the previous record for the date of 0.11 in (2.8 mm) set in 2010, and above the October monthly average at that location of 0.91 in (23 mm).

Western Oregon and southern Arizona and New Mexico were drier than normal at most stations. October 2011 was the 16th driest year on record at Eugene, Oregon airport, with a precipitation total of 1.81 in (46 mm), or 51% of the 3.54 in (90 mm) October average. Tucson, Arizona received 0.06 in (1.5 mm), only 7% of the average 0.87 in (22 mm) for that location, making it the 29th driest October on record at Tucson. The low precipitation in the Southwest allowed drought conditions and extent to persist for Arizona and New Mexico throughout October.

Significant Events for October 2011

October 6-8: Winter Storm: The first winter storm of the 2011-2012 water year passed through the West October 6th through 8th, providing precipitation throughout the region and dropping 1 to 2 ft (30.5 cm-61.0 cm) of snow at some locations the Sierra and Rockies.

October 26, 27: Colorado Snowstorms: Heavy snowstorms dropped up to 18 in (45.7 cm) of snow in the foothills west of Denver, and 5-8 in (12.7 cm-20.3 cm) in the Denver metropolitan area. The heavy, wet snow felled many trees leaving 200,000 without power.

October (all month) Late first freezes: Warm temperatures dominated throughout the West in October. Many locations saw much later than average first freezes. Ely, Nevada experienced its first freeze October 5. The only later freeze at that location was October 13, 1963. Spokane, Washington and Boise, Idaho experienced their first freezes on October 25, more than two weeks later than their average freezes of October 8th and October 10th respectively.

October 2011 Departure from Normal Temperature and Percent of Normal Precipitation for Western United States

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