April in the West
Large-scale circulation patterns this April continued to favor precipitation in the eastern Great Basin, Rockies, and far northwest at the expense of the Sierra Nevada and Southwest. Much of the southern tier of the West experienced less than 25% of normal precipitation. Eastern Oregon and southern Idaho also saw dry conditions. Persistent upper level troughs over the High Plains brought colder than normal temperatures to the far northeastern portions of the region, the Rocky Mountain states and inland Northwest, while the Southwest saw above normal temperatures.
After a fairly dry start to the winter season, March and April brought significant snowfall to Colorado’s Front Range. Boulder recorded its snowiest April in a 120-year record with 47.6 in (121 cm) snowfall. The previous record was 44 in (112 cm) in 1957. Much of this snowfall occurred over the 15th-18th with consecutive strong storms. Colorado’s statewide average snowpack climbed to 92% of average, with basins in the northern part of the state near to above average while basins in the southern part of the state remained 60-80% of average. Despite the record snowfall, total precipitation at Boulder fell short of record values, totaling 4.16 in (106 mm), 145% of normal. Western Washington also received ample precipitation this month. Sea-Tac Airport recorded 5.8 in (147 mm) precipitation this month, the second wettest April in the location’s 65-year record. Several other western Washington locations reported one of their top-10 wettest Aprils as well. Washington snowpack was doing well at month’s end, with all basins over 90% of normal. Elsewhere in the West, precipitation and snowpack were not so abundant. With very little snowfall and warm temperatures this month, snowpack in the Sierra Nevada fell to 18% of normal by the end of the month. Snowpack also dwindled in southern Oregon, southern Utah and northern Nevada. Montana saw its 4th consecutive month of below normal statewide average precipitation, making for nine out of the past 12 consecutive months with below normal precipitation. Further south, Los Angeles recorded its 5th driest rain season (July 1-April 30) total of 5.14 in (131 mm). This is the 5th driest since records began in 1877 and 9.44 in (240 mm) below normal for this period. The total January-April precipitation is the least on record over much of central and northern California and western Nevada, parts of western Oregon and Washington, and in southwest Montana, eastern Idaho, and northwest Wyoming.
Above normal temperatures dominated the Southwest this month. Average April temperatures of 5-6 F (3-4 C) above normal made for many top-10 warmest Aprils in southern California. Las Vegas, Nevada and Phoenix, Arizona recorded their 7th warmest Aprils on record at 70.1 F (21.2 C) and 75.3 F (24.1 C), respectively. In Las Vegas, a high of 99 F (37.2 C) on the 29th tied for the highest April temperature on record. Records began in Las Vegas in 1937 and in Phoenix in 1895. Elsewhere in the West, colder conditions prevailed. In Montana, a 21-city mean monthly temperature averaged 38.1 F (3.4 C), 4.9 F (2.7 C) below normal and the 11th coldest April for Montana in the past 133 years. Denver, Colorado and Cheyenne, Wyoming both saw their 6th coolest Aprils on record at 41.7 F (5.4 C) and 35.7 F (2.1 C), respectively.
Unusual cold dominated Alaska this month with average temperatures ranging 12-15 F (6-8 C) below normal at inland locations. Fairbanks logged an average 18 F (-7.8 C) for the month, 14.5 F (8 C) below normal and the coldest April in its 64-year record. Further south, trade wind frequency was below normal this month in Hawaii, leading to dry conditions on the windward sides of Maui and Big Island. Hilo, on the Big Island, recorded only 2.97 in (75 mm), making for the second driest April on record. Meanwhile, with the passage of two cold fronts over the northwestern part of the state, Lihue, Kauai, recorded 3.05 in (77 mm) for the month, 136% of average and the wettest April since 2000.
Significant Events for April 2013
April 7-8: High winds: A passing cold front brought high winds to many locations in the West. Mammoth Lakes at 9875 ft (3010 m) in southeastern California recorded a 115 mph (185 kph) gust on the 7th. Further north, Nevada’s Washoe Valley recorded a gust of 63 mph (101 kph). Gusts of over 50 mph (80 kph) were recorded in Pendleton, Oregon on the 7th. Winds downed a light pole in Las Vegas on the morning of the 8th.
April 14-16: Dust storm in southern Nevada, northern Arizona: High winds across the Southwest lifted and transported dust from the deserts of southeastern California and the Colorado plateau, northeastward into Colorado. Visibility was reduced to 5 miles (8 km) in Las Vegas, Nevada, on the 14th and 50 feet (15 m) in northern Arizona on the 16th. Interstate 40 was closed between Winslow and Winona, Arizona. Wind gusts reached 68 mph (109 kph) in Winslow on the 16th.