October in the West
Storms began marching across the Pacific Northwest mid-month, providing the first relief from a summer dominated by below normal precipitation and developing drought. Dry conditions persisted throughout the Southwest with the exception of southern Nevada, where a slow moving low-pressure system generated heavy precipitation and thunderstorms.
A storm system with a tap into subtropical moisture brought substantial precipitation to Washington, northern Oregon, the Idaho Panhandle, and western Montana on the 29th-31st, pushing many of these regions into one of their top 10 wettest Octobers on record. The windward side of the Olympic range in Washington received 7.5 to 9 in (190-230 mm) of rain during the 3-day event. After receiving no measurable precipitation for 84 days (July 21-Oct 12), Wenatchee, Washington recorded 1.56 in (39.6 mm) this month, 354% of normal and Wenatchee’s 3rd wettest October on record. Seattle-Tacoma Airport, Washington recorded its 4th wettest October in a record beginning in 1948 with 6.71 in (170.4 mm), 193% of normal for the month. Further east, Missoula, Montana logged 1.82 in (46.2 mm) total precipitation and 4 in (10.2 cm) snow, making for the 6th wettest and 7th snowiest October in a record that began in 1893. Despite high precipitation totals this month, 60% of Montana remains in moderate to extreme drought.
Las Vegas, Nevada saw its 9th wettest October in a record beginning in 1888 with a total of 0.73 in (18.5 mm). In just 3 months, August 1-October 31, 2012, Las Vegas received 4.19 in (106.4 mm) of precipitation, equal to the location’s 30-year normal for annual precipitation. In contrast, the first 6 months of 2012 saw only 0.25 in (6.35 mm) in Las Vegas, the 6th driest January-June period on record. The same storm system that brought precipitation to the Las Vegas area also provided rainfall to Colorado’s Front Range, helping to alleviate the persistent drought in this region. A cold front passed through the Front Range late in the month, bringing over 5 in (12.7 cm) of snowfall to Denver, bringing the city’s total to 1.22 in (31.0 mm) of precipitation for October, 119% of normal. Wyoming also received some drought relief this month from the aforementioned storm systems. Normal to slightly above normal precipitation fell in the western and southeastern portions of the state, though at month’s end, 97.8% of Wyoming remained at some level of drought. In the Southwest, Albuquerque, New Mexico recorded only trace precipitation this month, tying the 2nd driest October since official records began in 1933.
In addition to dry conditions, above normal temperatures dominated the Southwest. Phoenix, Arizona recorded its 8th warmest October at 78.8 F (26.0 C), and Albuquerque, New Mexico noted its 10th warmest at 60.8 F (16 C). Records at Phoenix date back to 1895 and at Albuquerque to 1892. On October 6th, Ely, in northeastern Nevada, saw its second latest autumn freeze in an 89-year record, behind October 13, 1963. On the heels of its warmest August and September on record, Reno, Nevada posted an average October temperature of 58 F (14.4 C), the 5th warmest in a record beginning in 1888.
Much further north, most of interior and southeast Alaska saw near or below normal temperatures this month. In contrast, the North Slope recorded average monthly temperatures 8-10 F (4-5 C) above normal. Barrow posted an October average of 27.5 F (-2.5 C), 10.3 F (5.7 C) above normal and the warmest since records began in 1949. This warmth is likely associated with the smallest measured summer minimum of polar ice extent, well below the former 2007 record. Out in the Pacific, Lihue, Hawaii set an all-time October high temperature record of 91 F (32.8 C) on October 9th. Lihue also recorded its driest October in a record that began in 1950, receiving only 0.39 in (9.9 mm) of rainfall, 9% of normal. Hilo, Hawaii also had a dry October at a total of 2.91 in (73.9 mm), its 3rd driest on record. All reporting stations in Hawaii received 75% or less of their normal October rainfall, further exacerbating the persistent drought conditions on the lee sides of the Islands.
Significant Events for October 2012
Sierra Snowfall: In a 4-day event beginning October 22nd, the Sierra Nevada received its first significant snowfall of the season. The Central Sierra Snow Lab two miles west of Donner Summit reported a maximum snow depth of 29 in (74 cm) on October 25th. This is the highest October snowfall total in the last 8 years at this location. October is typically hit-or-miss as the start to the winter snow season in the Sierra, with many station records for the region showing a mix of zero-snowfall Octobers and totals over 1 ft (30.5 cm).