April in the West
The snow season typically declines significantly in the West as April ushers in a transition to warmer temperatures. A few precipitation events brought much needed moisture to California and added to the near-normal water year totals in the Pacific Northwest, while the Desert Southwest remained mostly dry.
Periods of anomalously low and high temperatures averaged to near normal for the month as a whole for the coastal states, while more inland locations saw higher than average temperatures. The first week of the month gave a smattering of record lows west of the Rockies. April 5th and 6th saw back-to back record lows in Sacramento, CA at 35 F and 34 F (1.7 C and 1.1 C). On the 7th, Portland, Oregon hit a record daily low of 31 F (-0.6 C). Several other locations throughout California, Idaho, and Oregon also saw record daily lows during this period. A ridge built up the following week, bringing temperatures up to a daily record of 70 F (21.1 C) in Seattle, Washington on April 8, and setting three consecutive daily records at Idaho Falls, Idaho of 73 F, 76 F, 76 F (22.8 C, 24.4 C, and 24.4 C) on April 9-11. A stronger upper level ridge near the end of the month pushed the temperature at Reno, Nevada to 90 F (32.2 C) on April 22. This was the first 90 F (32.2 C) or greater day Reno has seen in April since airport records began in 1937, and earlier than the previous “first 90” by 8 days. Many daily records were set elsewhere in the Desert Southwest as well. At Death Valley, California temperatures soared to 110 F, 113 F, and 113 F (43.3 C, 45 C, and 45 C) on April 21, 22, and 23 setting a record at that location for most days over 110 F (43.3 C) in April. The previous record of two days occurred in both 1989 and 2007; records at Death Valley began in 1911. After a cold and snowy winter, temperatures in Alaska were mild and near normal for April. Several daily record highs were set at various locations throughout the state during the latter half of the month.
April 10-14 brought copious amounts of precipitation to Central and Southern California. Several daily precipitation records with totals over 1 in (25.4 mm) were set throughout the region for this period. San Francisco airport received a total of 2.79 in (70.9 mm) of rainfall for the month, making this the 10th wettest April in the station’s 65-year record. The Pacific Northwest had a week of moderate precipitation between the 15th and 21st of April, followed by lighter rains at the end of the month. Over April 14th and 15th, Flagstaff, Arizona received 10 in (254 mm) of snowfall, setting a daily record and helping the location reach a precipitation total just over normal for the month.
The Great Basin and Desert Southwest saw dry conditions and persistence or development of drought in April, with most locations well below normal precipitation values. Due to low snowpack and rapid melt of existing snowpack, spring and summer stream flow forecasts for these areas are at 50% of normal or less for these regions. Fire conditions in the Great Basin in April were already comparable to those normally experienced during the peak of summer. After a rainy March, Hawaii returned to dry conditions with Hilo, Big Island, only receiving 6.67 in (169.4 mm) for the month, 57% of normal. To the northwest, Lihue, Kauai received 0.37 in (9.4 mm) 19% of normal, though the location’s year-to-date total of 31.75 in (806.5 mm) remains well above average thanks to the high March totals.
Significant Events for April 2012
April 7: Anchorage, Alaska season snowfall record: On Saturday, April 7, Anchorage, Alaska received 4.3 in (109.2 mm) of snowfall, bringing the season total (since water year’s beginning on Oct 1, 2011) to 134.5 in (341.6 cm) and setting a record for greatest season snowfall at that location. This total narrowly eclipses the previous record of 132.6 in (336.8 cm) observed in 1954-55; snowfall records have been kept in Anchorage since 1915.
April (all month): Fires in Western Great Basin: Due to the dry winter and warm April, the Western Great Basin has experienced over 60 fires so far this year, four times the usual number of fires for this region. Vegetative dryness this low is usually not seen for another 3-4 months.