Map released Dec. 10, 2020 | Data valid Dec. 8, 2020
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 six-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 (six-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.
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, six-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 Nov. 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.