April in the West
Temperatures were near normal across most of the West this month, with some areas of above normal temperatures along the far southern boundary of the region. Precipitation was variable across the West, though with generally wetter than normal conditions across the northern half of the region and drier than normal conditions across southern portions of California, Nevada, and Arizona.
The first half of April saw a continuation of the very active storm track that has persisted throughout the cool season. Portions of northern California, notably along the I-80 corridor and in the Sierra Nevada, experienced over 200% of normal precipitation. Sacramento received 3.36 in (85 mm) precipitation, 258% of normal. In the Feather River basin, Portola observed 5.76 in (146 mm), 420% of normal and the second wettest April since records began in 1915. At some higher elevation Sierra Nevada stations, April snowfall was sufficient to eclipse previous snowpack records. At 8801 ft (2683 m), the Mt. Rose Ski area SNOTEL recorded its largest highest snow water equivalent value on record at 94 in (238.8 cm), surpassing the previous record of 87.1 in (221.2 cm) set in May 1995. SNOTEL observations began at Mt Rose in 1979. Areas in and around the Washington Cascades logged over 200% of normal precipitation this month. Wenatchee recorded 2.15 in (55 mm), 467% of normal and the second wettest April since records began in 1959. Above normal precipitation also occurred in areas of western and central Montana, where Great Falls observed 3.58 in (91 mm), 252% of normal, the 3rd wettest April since records began in 1937. Further south, in northeastern New Mexico, Clayton reported 3.33 in (85 mm), 354% of normal and the 10th wettest April in a 122-year record. Above normal rainfall prompted improvements in drought conditions for eastern New Mexico this month. The Sierra Nevada, Cascades, Great Basin ranges, and northern and central Rockies continued to report above normal snowpack values at the end of April, ranging from roughly 125% to over 250% of normal. The southern Rockies reported near normal snowpack with SWE values, roughly 85-110% of normal.
Drier than normal conditions dominated far southern California, southern Nevada, and much of Arizona this month, not uncommon for the spring season. San Diego, California, recorded only 0.01 in (0.3 m), 1% of normal and tie for 5th driest April since records began in 1939. Both Tucson and Phoenix, Arizona, recorded no measurable precipitation this month, as in many other years in their records. Only 3.8% of the West is currently denoted as having moderate drought conditions or worse; most of this area is in southern California and southwestern Arizona.
Temperatures were slightly (0-4 F/0-2 C) cooler than normal from the Rocky Mountains westward, with the exception of southern portions of California, Arizona, and New Mexico. These areas reported temperatures +2-4 F (1-2 C) above normal. In Los Angeles, California, temperatures averaged to 67.8 F (19.9 C), 4.7 F (2.6 C) above normal, the 4th warmest April since records began in 1877. Phoenix reported an average temperature of 75.3 F (24.1 C), 2.6 F (1.4 C) above normal and the 8th warmest April in an 85-year record. Areas east of the Rockies were generally within 2 F (1 C) of normal with scattered locations reaching 2-4 F (1-2 C) above normal.
April was warmer and drier than normal across Alaska. Stations north of the Arctic Circle experienced the greatest temperature departures from normal; Kotzebue reported an average temperature of 24.3 F (-4.3 C), 11 F (6.1 C) above normal. This was the 3rd warmest April since records began in 1897. In the southern part of the state, Anchorage observed an average temperature of 40.4 F (4.7 C), 3.6 F (2 C) above normal and the 4th warmest April in a 66-year record. April is typically a dry month in Alaska, and this year was no exception. Anchorage received 0.4 in (10 mm), which was 85% of normal. Kodiak was the only long-record station with above normal precipitation at 7.35 in (187 mm), 127% of normal. The breakup of ice on various Alaska rivers typically occurs in April, and this year’s breakups were within a few days of normal. Further south, above normal temperatures were observed at most reporting stations across the state of Hawaii; departures from normal were typically 1-2 F (0.5-1 C). Hilo recorded an average April temperature of 74.2 F (23.4 C), 2 F (1 C) above normal and the 6th warmest since records began in 1949. Precipitation was variable across the state, though most stations on Oahu and several on Maui reported above normal rainfall. Kahului recorded 7.77 in (197 mm), 501% of normal and the 4th wettest April in a 113-year record. Much of Big Island observed drier than normal conditions; 5.08 in (129 mm) of rain fell at Hilo, 44% of normal. The leeward side of the Big Island saw a small area of drought improvement, while abnormally dry conditions were introduced across the rest of the islands. Central Maui and western Molokai were classified as moderate drought this month.
Significant Events for April 2017
April 6-8: Strong late season storm impacted West Coast: High winds (60+ mph/97 kph) downed trees and power lines in northern California and western Oregon, causing temporary power outages for thousands of households. One death was reported in Oregon due to a falling tree. Heavy rainfall associated with this storm initiated a landslide near Oakland, California, destroying three homes. Snowfall of 12+ in (30 cm) was observed in the Sierra Nevada.
April (all month) landslides cause/threaten damage in West: Saturated soils due to the above average wet winter have primed western soils for landslides. A series of large landslides caused closure of Highway 101 in Mendocino County, California. In Washington, geologists are tracking a slow-moving landslide near Oso. This event prompted temporary closure of a state highway and officials have recommended evacuation for several homes.