Northern Plains and Midwest: Unseasonably mild, dry weather persisted in the areas affected by dryness (D0) and drought (D1 and D2). Since this region’s normal winter precipitation is typically very light, changes in the drought depiction have been, and will continue to be, very gradual.
The Southwest: Like the southern High Plains, the southern Rockies were graced with abundant, drought-easing snowfall. By December 27, the water equivalent (SWE) of the high-elevation snow pack generally ranged from 100 to 200% of normal, with a few higher values, in most watersheds across Arizona and New Mexico.
California, the Great Basin, and the Northwest: In stark contrast, extremely dry conditions persisted in northern and central California and the Great Basin, where many basin-level SWE values were less than 25% of normal for late December. Effects have not yet become significantly hydrological in nature; for example, California’s 154 intrastate reservoirs held 125% of their normal water volume for December 1. However, agricultural impacts are beginning to mount, especially in parts of California’s Central Valley. According to USDA, “rangeland had started to deteriorate due to lack of rains” and “supplemental feeding of livestock [will] continue until new vegetation [gains] strength.” Due to short-term dryness, D0 was broadly expanded southward into California and eastward into the Great Basin. The coverage of dryness also increased across the interior Northwest, while some moderate drought (D1) was introduced in an area centered on the California-Nevada-Oregon triple point.
Hawaii: Heavy showers dotted Hawaii’s windward locations, especially on the Big Island. As a result, extreme drought (D3) was eliminated from the southeastern portion of the Big Island. Elsewhere on the Big Island, Hilo’s December 1-27 rainfall climbed to 19.45 inches, 188% of normal. No changes were introduced elsewhere on the Hawaiian Islands.
Looking Ahead: During the next 5 days (December 29, 2011 – January 2, 2012), a pattern change will bring an increase in storminess to the nation’s northern tier, while little or no precipitation will fall across the southern two-thirds of the nation. Five-day precipitation totals could reach 2 to 8 inches in the Pacific Northwest and 2 to 4 inches in the northern Rockies. Generally light precipitation will fall from the northern Plains into the Northeast, with some locally heavier snow in the Great Lakes region. Much of the U.S. will experience near- or above-normal temperatures through week’s end, but colder air will arrive in the East early in the New Year.