Western Regional Climate Center


May in the West

May is typically a month in which temperatures increase and precipitation totals have begun to wane in the coastal and southern West as the Pacific storm track edges northward and the Southwest Monsoon system has yet to develop. May 2012 showed few exceptions to this trend. Many Southwest locations received no precipitation at all, and only a smattering of stations in the Northwest and along the Mexico border recorded average to above-average precipitation. The northern tier of the region experienced cooler than normal average temperatures this month, while in the Southwest, average temperatures were generally above the May mean. Severe fire weather dominated the Southwest, leading to the rapid development of several large wild land fires and New Mexico experiencing its largest fire on record.

Many locations the Southwest were dry this month, not uncommon in Mays past. For the 31st time in the last 75 years, Las Vegas, Nevada received no measureable precipitation (less than 0.01 in / 0.25 mm) in May. Further west, Santa Barbara, California has 25 years in its 71-year record with no measurable May precipitation. Other zero-precipitation locations this month include Yuma and Flagstaff, Arizona and Palm Springs, California. To the north, central Washington and Oregon have seen drought development over the last few months. This month, Spokane, Washington received only 0.69 in (17.5 mm) rainfall, the 28th driest May in the station’s 112-year record. Western Washington and Oregon fared better, with Seattle, Washington and Portland, Oregon notching several daily precipitation records toward month’s end. Rainfall at Portland totaled 3.37 in (85.6 mm), tied for 14th wettest May since records began in 1938. Glasgow, Montana also saw above average precipitation, receiving 3.06 in (77.7 mm) and 11th wettest May in a 57-year record. Mid-month thunderstorm activity along the US-Mexico border helped to alleviate exceptional drought conditions in some specific locations. Las Cruces, New Mexico received 0.58 in (14.7 mm) of rain, tying for the 22nd wettest May in the past 120 years at that location.

Temperatures in the Northwest and along the coast this month were 2-4 F (1-2 C) below normal, similar to but less cool than May 2010 and 2011. Average May temperatures do not show recent warming or cooling in the Northwest, though the past two years were anomalously cool. The Southwest saw temperatures 2-6 F (1-3 C) above normal, breaking the cool May pattern of 2010 and 2011, and back to the general trend of increasing May temperatures in the Southwest over the past 30 years.

A significant consequence of the continued warm and dry March, April, and May has been a drastic lowering of the expected summer snowmelt in the Intermountain West. Forecasts of Colorado River inflow to Lake Powell have dropped very far, and now rank among the 3rd or 4th lowest in the past century.

Significant Events for May 2012

May (all month): Fires throughout Southwest: Critical fire conditions (low relative humidity, high wind, drought conditions) were in place for most of May in the southwest, allowing wildfires to develop and spread rapidly.

New Mexico: The Whitewater-Baldy Complex Fire, ignited by lightning on May 16, has become New Mexico’s largest fire on record. As of June 1, 216,650 acres (87,865 hectares) had burned and the fire was only 10% contained. Arizona: The Gladiator Fire, approximately 20 mi (32 km) north of Phoenix, Arizona began May 16 and had burned 16,240 acres (6,572 hectares) and was 45% contained as of June 1. The fire was a human-caused structure fire and forced mandatory evacuation of the town of Crown King, Arizona. The Sunflower Fire, 30 mi (48 km) north of Mesa, Arizona began May 12 and had consumed 17,618 acres (7,129 hectares) and stood at 80% contained on June 1.

Nevada: The Topaz Ranch Estates Fire, 60 mi (97 km) south of Reno, Nevada, began May 22 and burned 7,152 acres (2,894 hectares). The human-caused fire destroyed two residences and 17 structures.

Colorado: The Hewlett Fire in the Roosevelt National Forest began May 14 and burned 7685 acres (3,110 hectares) before containment. The Sunrise Mine Fire began May 25 4 mi (6 km) north of Paradox, Colorado. By June 1 it had consumed 6,192 acres (2,505 hectares) and was 85% contained. Both fires were human-caused.

May 26: Four Corners Dust Storm: Southwest winds in excess of 50 mph (80 kph) associated with a deep trough drove a dust storm into the Four Corners region. The dust, combined with smoke from fires in New Mexico, reduced visibility to less than a mile (1.6 km).

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

© Western Regional Climate Center