During the past week, high pressure continued to dominate across much of the region with essentially no precipitation observed except for some light precipitation (generally <1 inch) along coastal Oregon and Washington. On the map, below-normal WYTD precipitation across California led to deterioration across the Sierra Nevada, Central Coast, southern San Joaquin Valley, and areas of Southern California and the Mojave Desert. In the mountains of California, the current statewide SWE for the date (Dec 7) is 36% of normal. Considering the regional breakdown across the state, the current percentage of normal SWE is as follows: Northern Sierra/Trinity–40%, Central Sierra–44%, and Southern Sierra–17%. According to the California Department of Water Resources, the three largest reservoirs in the state were below historical averages for the date with Shasta at 74%, Oroville at 60%, and Trinity at 79%. In the northern Great Basin, areas of Extreme Drought (D2) expanded in northeastern Nevada where snowpack conditions are below normal across the Ruby Mountains, Independence Mountains, and Jarbidge Mountains. Across the Nevada and Utah borders in southern Idaho, areas of Moderate Drought (D1) expanded where below-normal snowpack conditions are being observed in the Bear River Range and the Portneuf Range east of Pocatello, Idaho. In the Pacific Northwest, snowpack conditions at the Sub-region level (4-Digit HUC) ranged from slightly below normal (Lower Snake–78%, Upper Snake–83%, Yakima–84%, Kootenai-Pend Oreille-Spokane–87%, Oregon-Washington Coastal–90%, Upper Columbia–94%, Middle Snake–99%) to above normal (Puget Sound–101%, Willamette–115%, Middle Columbia–117%, Oregon Closed Basins–143%). Across the mountain ranges of the Four Corners states, snowpack conditions are well below normal across with the Little Colorado, Salt, Upper Gila, Rio Grande-Mimbres, Rio-Grande Elephant Butte, Upper Canadian, and Upper Pecos basins—all below ~50% of normal. According to the NRCS (Dec 1), statewide reservoir storage was below normal in Colorado, Nevada, New Mexico, and Oregon while above-average levels were observed in Arizona, Idaho, Utah, Washington, and Wyoming (data not available for California and Montana). Looking at the last 6-month period, the Southwest (Arizona, Colorado, New Mexico, Utah) and West (California, Nevada) climate regions both experienced their hottest and driest June-November period on record, according to NOAA NCEI.

Full Summary