The U.S. Drought Monitor week saw another round of winter storms, bringing snow to the mountainous areas of the West, northern Plains, upper Midwest, and Northeast while lower elevations of the West and parts of the South, Southeast, lower Midwest, and Mid-Atlantic regions saw rain. This week’s precipitation in the Southwest left many areas with accumulations that exceeded 300 percent of normal over the past 14-day period, leading to continued improvements in short-term dryness.
Once again, precipitation in the Northwest was below normal. Many locations have received less than 25 percent of normal over the last 14 days, resulting in the expansion of abnormally dry conditions.
Meanwhile, another dry week in the Southern Plains and below-normal rainfall in the South and Southeast led to expansions in pockets of abnormal dryness and drought.
Rainfall in the Southeast was predominantly below normal last week. While deficits continue to build, they were not enough to warrant degradations in most areas. Exceptions were minor expansions in abnormal dryness (D0) in eastern Alabama and Florida where streamflow has declined and vegetation shows stress.
The South once again saw a mixture of degradations and improvements. Improvements were limited to central Texas, where last week’s rainfall, in excess of 300 percent of normal, resulted in a general one-category improvement.
Meanwhile, the eastern and southern parts of the state continued to dry out with expansions to areas of abnormal dryness (D0) and moderate (D1) and severe (D2) drought. The heavy black line separating drought impact designations was shifted eastward in south Texas to reflect that this area is also experiencing dryness at longer (more than 6 months) time scales.
Eastern Oklahoma also saw degradations with an expansion of D0 as dryness, extending back to September, continued. This dryness comes at a vital time in winter crop cycles, and a continued lack of moisture may cause impacts later. Other degradations include the expansion of D0 and/or D1 in southwest Arkansas, Louisiana, and southwest Mississippi.
The Midwest remains free of abnormal dryness and drought.
Last week’s weather brought continued dryness to the abnormally dry and drought areas of south-central Nebraska, Kansas and eastern Colorado. In Kansas, where moisture deficits have been present for more than three months, abnormal dryness (D0), moderate drought (D1), and severe drought (D2) were expanded to reflect the increasing dryness and its impact on winter wheat. The map was unchanged this week for the remainder of the region.
Another week of above-normal rainfall and mountain snow led to continued improvements in the Southwest. In California and Nevada, rainfall over the last three weeks has helped to make up for the slow start to the water year, resulting in the removal of the abnormal dryness (D0) depiction across most of the state. Pockets of D0 remain in areas that missed the heaviest precipitation or where station data indicate below-normal snow.
In the Four Corners states, the map depiction strives to balance the effect of the recent precipitation with the failure of the monsoon. Changes include a broad 1-category improvement across southern and western Arizona, western Utah, and western New Mexico.
The heavy black line separating drought impact designations was expanded to delineate areas that are experiencing both short- (less than 6 months) and long-term (greater than 6 months) deficits. For example, the designation across southern and western Arizona is “L”, indicating that deficits are only present at longer time scales and in indicators such as groundwater and root zone soil moisture, whereas the designation in eastern Colorado is “S”, indicating more seasonal deficits and impacts to indicators such as surface soil moisture and streamflow.
This week’s rainfall helped alleviate the impacts of a dry autumn in the Northeast. Lingering abnormal dryness (D0) was removed from New Jersey. An area of D0 remains over the Delmarva Peninsula where rainfall deficits, low streamflow, dry soils, and reduced groundwater remain.
Alaska, Hawaii, and Puerto Rico
In Alaska, precipitation was below normal for the week over the long-term drought areas of the southeast where year-to-date deficits in excess of 20 inches remain. While precipitation was above normal for the Kenai Peninsula, longer deficits are still present and snow remains below normal.
In Puerto Rico, no changes were made given the degradations that were introduced last week. Note that deficits continue to build in the eastern part of the island, where deficits of about 4 to 13 inches have occurred over the last 90 days.
In Hawaii, rainfall helped improve conditions on Kauai and the northwest coastal slopes of Molokai. Rainfall in the eastern part of the state was not enough to warrant improvements, and vegetation conditions continue to decline. This week’s map saw the following degradations: an expansion of moderate drought (D1) on Lanai; an expansion of extreme drought (D3) and the introduction of exceptional drought (D4) on Maui; and an expansion of moderate drought (D1) and severe drought (D2) on the Big Island.
The National Weather Service Weather Prediction Center forecast for the remainder of the week calls for moderate to heavy mountain snows extending from the Pacific Northwest to the north-central Great Basin and Rockies. Meanwhile, parts of the northern High Plains, Upper Mississippi Valley, and upper Great Lakes are expected to see snow.
As this storm moves eastward over the weekend, the Southeast, Tennessee Valley, and Mid-Atlantic will see rain, while mixed precipitation is expected in the Northeast. Dry conditions are expected in the Southwest, Southern Plains, and lower Mississippi River Basin.
Moving into next week, the Climate Prediction Center 6 to 10 day outlook (valid December 16-20) favors above-normal temperatures for the central and northern coast of California; parts of the Pacific Northwest, Southwest, and Central Plains regions; and the Florida Peninsula.
Areas with increased chances for below-normal temperatures include parts of the Ohio and Tennessee Valleys and the Northeast region. Precipitation is likely to be above normal over the Pacific Northwest, parts of northern California, and from the Southern Plains, across the Southeast, and into the Mid-Atlantic region.