Western Regional Climate Center


September in the West

September 2013

An active monsoon circulation as well as several storm systems brought extremely wet conditions to the West this month. Several Southwest locations experienced devastating floods. Widespread precipitation helped to alleviate some symptoms of persistent drought in the West, though significant precipitation is still needed in places to remove impacts of ongoing long-term drought. Temperatures were near normal for much of the West, with areas of much warmer than normal temperatures across the northern tier of the region.

Intense monsoon-related precipitation took place during the first half of September in the Southwest. Most notable was the unprecedented and unusually widespread deluge on Colorado’s Front Range between the 11th and 18th. A combination of moist subtropical flow from the south and an upper level low, among other features, induced prolonged intense precipitation in the area. With amounts exceeding thousand year recurrence intervals, Boulder, Colorado broke many rainfall records in its 120 years of data. On the 11th, Boulder received 9.08 in (230 mm) rainfall, exceeding the previous wettest day on record for any month by 90 percent, nearly equal to the previous wettest month. Rainfall totaled 16.48 in (419 mm) in September, shattering the record for any month, 9.59 in (244 mm) in May 1995. Year-to-date, the 31.12 in (790 mm) of rainfall at Boulder has already surpassed the annual record of 29.46 in (748 mm) also set in 1995. Elsewhere in the area, Cheyenne, Wyoming recorded 6.95 in (176 mm) precipitation for the month, crushing the previous September record of 4.52 in (114 mm) set in 1973. Records in Cheyenne began in 1915. Further south, Albuquerque, New Mexico saw 3.97 in (101 mm) of rainfall for the month, the wettest September in a 100-year record. September marks the end of the monsoon season in the Southwest (June 15-September 30). In Arizona, Tucson received 62% of normal precipitation for the season, Phoenix 110%, and Yuma 93%. In Albuquerque, New Mexico, season precipitation totaled 7.16 in (182 mm), 173% of normal.

September is typically one of the drier months in the year in the Northwest, but in 2013 impressive rainfall throughout the region broke many records. The month began with widespread thunderstorms and locally heavy rainfall on the 4th and 5th. Corvallis, Oregon recorded a 24-hr total of 2.94 in (75 mm) on the 6th, the most precipitation received on a September day since records began in 1889. At the end of the month, a strong storm system brought both high winds and impressive rainfall to Oregon and Washington. Three day totals exceeded 9 in (229 mm) in some western Washington locations. Seattle, Washington logged its wettest September on record with a total of 6.17 in (157 mm), with 3.1 in (79 mm) of this on the last three days of the month. Bonners Ferry, Idaho recorded 4.04 in (103 mm) this month, the most in September since the records began in 1907. In Oregon, Portland received 5.62 in (143mm) for the month, easily surpassing the previous September record of 4.3 in (109 mm) set in 1986. Elsewhere in Oregon, 7.08 in (180 mm) fell in Eugene, the wettest September in a 75-year record. Further south, central and southern California received little or no precipitation, typical of September.

The northern tier of the West saw warmer than normal temperatures this month. Quillayute, Washington averaged 61.3 F (16.3 C) for the month, the warmest September in a record that began in 1966. Great Falls, Montana recorded an average 61.9 F (16.6 C), 5.8 F (3.2 C) above normal and the 5th warmest on record. In Billings, Montana, the low temperature on September 4th only dipped to 71 F (21.7 C), the highest minimum temperature recorded in Billings in September. Reno, Nevada also saw its highest September minimum temperature of 66 F (18.9 C) on September 2nd. The previous record was 65 F (18.3 C) set on September 5, 1998. To the east, Colorado Springs, Colorado saw its 3rd warmest September in a 66-year record at 65.5 F (18.6 C).

Dry conditions continued for much of Hawaii this month. On Oahu, Kaneohe only saw 0.05 in (1 mm), 3% of the September normal. On the Big Island, Hilo reported 3.64 in (92 mm), 36% of normal. A few stations reported above normal precipitation such as Honolulu, Oahu at 190% of normal and Lihue, Kauai at 111% of normal. Further north, Interior, South Central and northern Alaska were much wetter than normal this month. Anchorage saw 5.85 in (149 mm) precipitation this month, the 4th highest September total on record. Minor flooding was reported at Anchorage, Yakutat, and Valdez.

Significant Events for September 2013

September (all month): Rim Fire, Yosemite, California: This fire began August 17, cause unknown. It has since charred over 257,000 acres (104,000 hectares) and became the 3rd largest fire in California history. The fire was 92% contained by the end of the month and destroyed 11 residences.

September 10-18: Extremely heavy rains and flooding in Colorado Front Range and New Mexico: Flooding in Colorado’s Front Range resulted in eight confirmed fatalities, over 1,800 homes destroyed and over 5,500 damaged, 30 bridges swept away, and many power and natural gas outages. The governor issued a disaster declaration for 14 counties. In northern and central New Mexico, the flooding had disastrous impacts on residential and commercial structures, transportation, and infrastructure. One fatality was confirmed. Eleven New Mexico counties, including the Navajo Nation, were part of a statewide disaster declaration. Flooding occurred along the Pecos River and the Rio Grande.

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