Western Regional Climate Center

PROVIDING CLIMATE SERVICES SINCE 1986

May in the West

Most locations in the West varied in temperature from well above to well below normal throughout May, averaging near normal for the month. A closed low pressure system mid-month brought helpful but insufficient precipitation to Southern California, the Sierra Nevada, and the western Great Basin. During the last third of May, a persistent low pressure system set up over the Pacific Northwest bringing cool temperatures and ample precipitation to the area. Late May also brought very wet conditions to eastern Montana.

May began with increasing temperatures for much of the West. Coastal areas of California saw a smattering of daily record high temperatures throughout the month. San Francisco recorded a trio of record daily highs of 89 F (31.7 C), 85 F (29.4 C) and 84 F (28.9 C) on May 2nd-4th. Five daily high temperature records were set at Camarillo, California during the first half of the month. Temperatures at Camarillo averaged out to 67.2 F (19.6 C), 5.8 F (3.2 C) above the May norm. Further east, Tucson recorded its 2nd warmest spring with an average 71.5 F (21.9 C), but only its 10th warmest May at 78.8 F (26 C) in an 83-year record. Tucson typically logs four days over 100 F (37.8 C) in May, but recorded none this month. This was their first May since 2004 to have no days over the century mark. In the western Great Basin, Tonopah recorded its 4th warmest spring with an average 53.2 F (11.8 C) but only 19th warmest May. Further north, Spokane, Washington saw seven consecutive days with temperatures higher than 80 F (26.7 C) on the 6th through the 12th. This is the longest such stretch this early in the warm season at Spokane, where records began in 1889. May started off a bit cooler in the Rockies. The 19 F (-7.2 C) reading at Denver, Colorado Airport on the 2nd is the second lowest May reading since the station was installed in 1995.

A closed low developed over the Southwest during the first week of the month, bringing scattered precipitation across the region. Over 4 days, May 5th-8th, Reno, Nevada, received 0.65 in (17 mm) of rain, more than the combined total of the previous four months. Bishop, California received 0.47 in (12 mm) precipitation on the 6th and 7th, the first measurable precipitation since December 26th and tied May 6 1972 for latest observance of first measurable precipitation in a calendar year. Many Southwest locations such as Phoenix and Las Vegas recorded no precipitation, not atypical for May. The Pacific Northwest began the month with warm temperatures and clear skies. Wet, cool weather then dominated the latter half of the month as a low pressure system posted over the region. Vancouver, in southwestern Washington, recorded its wettest May in a 123-year record at 4.89 in (124 m), 198% of normal. Even so, for the year, 2013 is the 4th driest on record there with 13.23 in (336 mm), 71% of normal. Further east, Yakima, Washington logged its 3rd wettest May at 2.48 in (63 mm), 428% of normal for the month. In eastern Montana, Miles City recorded 6.69 in (170 mm) precipitation, 307% of normal and the 3rd wettest May on a 76-year record. Parts of eastern Montana recorded over 10 inches of rain.

April’s below normal temperatures continued through the final week of May for Alaska’s interior. Fairbanks began the month with temperatures more than 10 F (5.6 C) below normal and ended with temperatures over 10 F (5.6 C) above normal. Fairbanks recorded an average 44.3 F (6.8 C) for the month, the 5th coolest May in a 63 year record. Portions of southern Alaska saw abundant precipitation and snowfall this month. Valdez recorded 10.61 in (270 mm) precipitation, 378% of normal and the wettest May in a record that began in 1917. Valdez also logged its snowiest May on record, receiving 27.3 in (69.3 cm) total for the month.

Significant Events for May 2013

May (all month): Fires in the West: Several large fires occurred throughout the month in Alaska, California, New Mexico, and Arizona. One of the most destructive was the Springs Fire in Ventura County, California. Ignited on May 2, the blaze spread quickly due to strong Santa Ana winds and dry fuels. Over 24,000 acres (9,700 hectares) were consumed, 10 outbuildings destroyed and 12 structures damaged. No homes were destroyed.

May (throughout month): Drought conditions in the West: Precipitation helped to alleviate drought conditions in a few locations along the northern tier of the West. Drought conditions worsened in New Mexico, Arizona, and northern California, where below normal precipitation was observed this month. According to the US Drought Monitor, the area of the West with no drought designation decreased from 20% to 14% in May. Areas in extreme drought status rose from 4% to 6%. This increase occurred in southeastern Colorado and New Mexico.

May 23: Dry air over Boise, Idaho: Radiosonde observations from Boise recorded only 0.05 in (1.3 mm) precipitable water, the driest atmosphere recorded on any day in Boise since radiosonde observations began.

May 27: Flooding in Alaska: Colder than normal temperatures this spring has slowed melting of ice along the rivers of Alaska’s interior. This has resulted in ice damming and flooding at some locations. On May 27, an ice jam on the Yukon River caused flooding in the town of Galena, prompting evacuation of many of the town’s 470 residents.

May 2013 Departure from Normal Temperature and Percent of Normal Precipitation for Western United States

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