#Drought news (December 8, 2020): Across the mountain ranges of the #FourCorners states, #snowpack conditions are well below normal

Click on a thumbnail graphic below to view a gallery of drought data from the US Drought Monitor.

Click here to go to the US Drought Monitor website. Here’s an excerpt:

This Week’s Drought Summary

This U.S. Drought Monitor week saw intensification of drought across parts of the western U.S. including California, Nevada, and Colorado where precipitation has been below normal since the beginning of the Water Year (Oct 1). In California, statewide snow water content (SWE) is currently at 36% of the historical average for the date (Dec 7) and Water-Year-to-Date (WYTD) precipitation (statewide) is ranging from the bottom 10% to the bottom 33% with some areas in the Mojave Desert experiencing the driest on record for the period. According to NOAA’s National Centers for Environmental Information (NCEI), the 6-month period from June to November 2020 was the hottest and driest on record for both Arizona and California. Current snowpack conditions across the West are generally reflective of a La Niña-like precipitation pattern with the mountain ranges in the Pacific Northwest and some areas of the northern Rockies observing near-normal to above-normal snowpack conditions. Further south in the Four Corners states, basin-wide (6-digit HUC) SWE is below normal in nearly all drainage basins in the region. Elsewhere on this week’s map, areas of Texas including the Panhandle and central Texas saw some minor deterioration in conditions where both long and short-term precipitation deficits exist. In the Northern Plains, unseasonably warm temperatures and dry conditions continued this week leading to intensification of drought conditions in North Dakota where statewide precipitation for the September-November 2020 period ranked 3rd driest on record, according to NOAA NCEI. In New England, drought-related conditions significantly improved in response to heavy rains and snow associated with a Nor’easter that impacted the region during the weekend. The storm delivered heavy rains and strong winds to coastal areas as well as heavy snowfall in the mountains of New Hampshire and northern Maine…

High Plains

On this week’s map, areas of the region—including southwestern North Dakota and central Nebraska—saw modest expansion in areas of Severe Drought (D2) as well as expansion in areas of Moderate Drought (D1) in southwestern North Dakota in response to a combination of factors—short-term precipitation deficits, lack of seasonal snow cover, depleted soil moisture, and unseasonably warm temperatures (12 to 20 degrees F above normal)—during the past week. In the eastern Plains of Colorado, areas of Extreme Drought (D3) and Exceptional Drought (D4) expanded where long-term precipitation deficits continued to mount…

West

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... South

On this week’s map, areas of drought intensified and expanded in the Panhandle and central Texas where both long and short-term precipitation shortfalls exist. In these areas, 6-month precipitation deficits ranged from 4 to 8+ inches. Conversely, above-normal precipitation during the last 30-day period led to improvements on the map in areas of Moderate Drought (D1) and Abnormally Dry (D0) along the Coastal Plain region of Texas. According to the USDA for the week of November 29, 61% of topsoil moisture in Texas was rated short to very short and 34% of the winter wheat crop was reported to be in poor to very poor condition. Elsewhere in the region, short-term dryness during the past 30-day period led to expansion of areas of Abnormally Dry (D0) across portions of Louisiana, Arkansas, Mississippi, and Tennessee. Average temperatures for the week were well below normal (4 to 10+ degrees F) across the entire region…

Looking Ahead

The NWS WPC 7-Day Quantitative Precipitation Forecast (QPF) calls for light-to-moderate liquid accumulations ranging from 1 to 2+ inches across a swath extending from east Texas and the Lower Mississippi Valley northward to eastern portions of the Midwest. Out West, moderate-to-heavy liquid accumulations are forecast for areas extending from Northern California to western Oregon and Washington including the Olympic Mountains of Washington, Cascades of Oregon and Washington, and the central/northern Sierra. Lighter precipitation (generally <1-inch liquid) is expected across the ranges of the northern Great Basin, the Rockies, and along the Mogollon Rim and “Sky Island” mountain ranges of southeastern Arizona. In northern portions of New England and the Southeast, light precipitation accumulations (generally <1 inch of liquid) are expected. The CPC 6–10 day Outlook calls for a moderate-to-high probability of above-normal precipitation across most of the northern tier of the western U.S., Northern Plains, Upper Midwest, and the Northeast while normal temperatures are expected across much of Southwest Texas, the Midwest, the Northeast, and the Mid-Atlantic states. Conversely, there is a moderate-to-high probability of drier-than-normal conditions forecast for much of California, the central and southern Rockies, and the Southwest. Likewise, dry conditions are expected in Texas, the central and southern Plains, much of the Midwest, and Florida. In terms of temperature, there is a moderate-to-high probability of above-normal temperatures across most of the West, the Plains states, and the Northeast while below-normal temperatures are expected across the South and Southeast.

US Drought Monitor one week change map ending December 8, 2020.

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