Western Regional Climate Center


August in the West

An active monsoon doused the southern Great Basin this month, while drier conditions dominated the Northwest, favoring development of numerous large and destructive wildfires. Average August temperatures ranged from 2-6 F (1-3 C) above normal over most of the West, with some locations recording their hottest August on record. Only the coastal regions of northern California and southern Oregon and a few other isolated locations averaged cooler than normal for the month.

A persistent upper level ridge and strong surface heating over the Great Basin and desert Southwest facilitated moisture transport into the area, supporting monsoon activity. The southern Great Basin saw most of the action, with numerous accounts of flash flooding, and several instances of record daily precipitation. Rainfall at the Las Vegas, Nevada airport totaled 2.31 in (58.7 mm), the second wettest August since records began there in 1937 (behind 2.59 in / 65.8 mm in 1957). Las Vegas also tied its record number of 12 thunderstorm days in August, set in 1955. Farther north, the airport at Tonopah, Nevada recorded 1.94 in (49.3 mm), its fourth wettest August in a record beginning in 1954. Many locations in the Southwest that receive a large portion of their annual precipitation during the summer monsoon (Las Vegas, Nevada and Phoenix, Yuma, and Tucson, Arizona) recorded above or near average August precipitation totals and are on track to meet the monsoon season (June-Sept) average at their respective locations. In contrast, New Mexico was dry in August, and statewide has experienced its driest 18 consecutive month period on record. By mid-August, 89% of the pasture and rangelands there were rated as poor, one of the highest percentages in the nation. Farther north, Reno Nevada experienced the third driest water year to date in its 75-year airport record.

The Pacific Northwest, which typically experiences low rainfall totals in August, was exceptionally dry this month. August 31st marked 42 days without measurable precipitation in Portland, Oregon, the 14th longest streak of this type on record. Billings, Montana experienced its driest first 8 months of the year since records began in 1934, only receiving 5.08 in (129 mm) in that time, 52 percent of average and below the previous minimum of 5.82 in (147.8 mm) in 1946.

Triple digit temperatures and record high minimum temperatures dominated much of the Southwest this August. Temperatures at Reno, Nevada airport averaged 79.0 F (26.1 C) for the month, 5.8 F (3.2 C) above normal and the hottest August on record since 1888. Reno reached 100 F (37.8 C) on 11 days, tied with 1970 and 2 days fewer than the 1972 record. In southern California, Lancaster recorded 23 consecutive days (July 29-August 20) of triple-digit F (over 37.8 C) heat, breaking the 2009 streak of 20 days. The average maximum temperature in Lancaster in August is 95.7 F (35.4 C).Various locations in southwest California hit daily high minimum temperature records on more than half the days in August. Further east, Phoenix, Arizona recorded its third warmest August minimum temperature of 84.9 F (29.4 C).

Significant Events for August 2012

August (all month) Fires throughout the Northwest: Hot, dry, and windy conditions primed the region for wildfires this month. In conjunction with the fires, poor air quality prevailed in many areas, notably Idaho, Montana, and the northwestern Great Basin. The following are several fires that had significant impacts. Washington: The Taylor Bridge Fire in central Washington burned 23,500 acres (9,510 hectares) along with 51 homes and 26 other structures. The fire did an estimated $8 million in damage. Montana: The 19-Mile Fire, 10 miles southeast of Butte, Montana, consumed 14 homes and six structures over the last few days of August. At month’s end, 4,141 acres (1,675 hectares) had burned and containment stood at 64%. Idaho: The Trinity Ridge Fire, near Featherville, Idaho, consumed 144,430 acres (58,448 hectares) and stood at 22% contained on [give the date]. The resort towns of Featherville and Pine were evacuated for a time due to the fire. Nevada: On August 5 the state reported that 200,000 acres (80,972 ha) had burned, a total that had jumped to 800,000 acres (323,887 ha) three weeks later. Northern California: The lightning-caused Ponderosa Fire in Shasta County destroyed seven homes, threatened 3,000 and caused an emergency declaration for the county. Further east near Quincy, CA, the Chips fire burned 75,217 acres (30,439 hectares) in August. That fire was 100% contained at the end of the month.

August 2012 Departure from Normal Temperature and Percent of Normal Precipitation for Western United States

© Western Regional Climate Center