A tandem of winter storms impacted the country during the week, bringing cold temperatures, heavy snow, and strong winds to the mountainous areas of the west, northern Plains, upper Midwest, and Northeast. Lower elevations and latitudes dealt with a combination of weather impacts, including moderate to heavy rainfall in the Southwest, showers and thunderstorms across the South and lower Midwest, and freezing rain to the Mid-Atlantic regions. Another week of above-normal precipitation in the Southwest continued to alleviate the effects of a sub-par monsoon season. In contrast, relatively little precipitation fell in the Northwest, continuing dryness-related impacts such as low streamflow, dry soils, and poor snowpack. Farther east, rain continued to chip away at lingering dryness in the southern Ohio River Valley, Mid-Atlantic, and parts of the Southeast while rainfall amounts in Gulf Coast states were generally not enough to stave off developing dryness.
Alaska, Hawaii, and Puerto Rico all saw changes to the map this week. In Alaska, abnormal dryness (D0) was reduced in the south-central part of the state in response to recent precipitation and a general lack of impacts this time of year. D0 remains over the Kenai Peninsula where a snow dearth continues and ephemeral ponds remain dry. Additionally, a continual lack of snowpack in southeast Alaska has resulted in the area remaining in D0 and D1 (moderate drought). Hawaii saw a combination of improvements and degradations. After a dry start to November, rainfall brought relief to parts of Kauai, Niihau, the Big Island, and the southeast lower slope of Maui. Meanwhile, Molokai, the windward slopes of Maui, and Kahoolawe all saw degradation. Puerto Rico also saw a combination of improvements and degradations. While conditions improved on the southwest part of the island, another week of below-normal precipitation left the eastern third of the island with deficits of more than eight inches of rainfall over the past 60 days, resulting in the introduction of moderate drought.
Last week’s winter storms brought widespread snow and winds to the northern Plains leaving the Dakotas. Farther south, precipitation in southern Nebraska and northern Kansas was enough to avoid degradations, but not enough to warrant improvements. Southwest Kansas saw an expansion of abnormal dryness (D0) and moderate drought (D1) in response to continued developing dryness, low streamflow conditions, and impacts to winter wheat. Eastern Colorado was the one area in the region that saw improvements (to areas of D0 and D1) as the result of cold, wet conditions in November.
More than two inches of rain fell along the eastern border of Kentucky last week, eliminating the remaining area of abnormal dryness (D0) and reducing lingering moisture deficits. The remainder of the region remains drought free after last week’s winter storms.
The winter storm near the close of the Drought Monitor week helped alleviate the impacts of a dry November, resulting in the removal of lingering abnormal dryness (D0) from central New Jersey and along the border of West Virginia and Kentucky.
The South saw a mixture of degradations and improvements. Last week’s rainfall resulted in a general one-category improvement across central Texas, while the eastern part of the state continued to dry out with expansions to areas of abnormal dryness (D0) and moderate drought (D1). An area of extreme drought (D3) was also introduced as precipitation deficits continue to build and impact rangeland. Northwest Oklahoma also saw degradations with an expansion of D0 and D1 as continued dryness combined with last week’s high winds resulted in a wildfire outbreak. Additionally, the U.S. Department of Agriculture reports that the dry weather has dried out topsoil and left winter wheat underdeveloped. Additionally, Arkansas saw expansions to D0, while Louisiana saw expansions in D0 and D1. These areas missed out on the heaviest precipitation and continue to accumulate moisture deficits.
This week’s rain continued to reduce coverage of abnormal dryness (D0) and moderate drought (D1) from Virginia to northern Alabama. The two lingering pockets of D2 in northern Georgia saw minimal improvement and persist due to rainfall deficits at timescales longer than 90 days and low streamflow. In contrast, southern Alabama, south Georgia, and Florida all saw an expansion of abnormal dryness as rainfall amounts generally continued to remain below normal. An area of D1 was introduced in South Florida where rainfall amounts have been less than 50 percent of normal over the last 90 days, resulting in low streamflow and dry soils.
The two storms brought record-breaking precipitation to the Southwest, resulting in widespread one-category improvements across southern and central New Mexico, southern and western Arizona, southern California, southern Nevada, and southwest Utah. Heavy precipitation helped erase short-term precipitation deficits, replenished soil moisture, and improved streamflow conditions. Remaining drought and abnormally dry areas in these regions have been designated with an “L” to denote that dryness is only apparent in longer-term (greater than 4 months) indicators. While beneficial, these events were not enough to allow for improvements to the Four Corners area, which has been experiencing deficits for nearly a year. Despite the significant precipitation, much of California was left in D0 (abnormal dryness) after consultation with the state drought monitoring team. While the precipitation has helped improve conditions, water year to date deficits remain. In contrast, dryness continued to develop in the Pacific Northwest, with parts of Oregon and Washington experiencing among the driest Novembers on record. Precipitation over the last 60 days is less than 50 percent of normal across much of the region, resulting in the expansion of D0.
According to the National Weather Service Weather Prediction Center forecast for the remainder of the week, a storm is expected to bring rain and higher elevation snow to the West Coast, with the highest totals focused over northern California, the southwest corner of Oregon, and the Sierra Nevada. Other areas of the West will likely see lesser amounts. Farther east, cold air moving over the Great Lakes is expected to generate bands of lake effect snow. Elsewhere, dry conditions should be in place for the remainder of the week. By early next week, precipitation will begin to develop over the eastern half of the country with the heaviest amounts favored over portions of the Tennessee Valley, southern Appalachians, and parts of the Ohio River Valley and Mid-Atlantic.
The Climate Prediction Center 6 to 10 day outlook for December 9-13 calls for an outbreak of cold arctic air across the across the lower 48 with temperature departures approaching -15 degrees Fahrenheit. The weather pattern favors above-normal temperatures over Alaska and the West Coast. Variable temperatures are expected along the East Coast. Precipitation is expected to be above normal for most of country, with the exception of California and the Southwest.
Deborah Bathke, National Drought Mitigation Center
Ahira Sanchez-Lugo, National Drought Mitigation Center