National Drought Summary for December 20, 2016
Summary
Streaks of heavy precipitation fell from the Ohio Valley into the Northeast and across the lower Southeast. Stormy weather also prevailed in the West, particularly in California and southwestern Oregon—but also extending inland to the Rockies. Amid the active weather pattern, an Arctic outbreak peaked on December 17-18, sending temperatures as low as -40°F across northern portions of the Plains and Intermountain West and below 0°F as far south as the panhandles of Oklahoma and Texas.
Northeast
Precipitation totaled more than 3 inches in non-drought areas of southwestern Pennsylvania, while 1- to 2-inch amounts were common throughout the Northeast. The precipitation fell in many forms, including snow, sleet, freezing rain, and rain. On December 17, daily-record snowfall totals were observed in several Northeastern locations, including Hartford, Connecticut (6.5 inches), and Newark, New Jersey (3.0 inches). Snow squalls raged at times downwind of the Great Lakes, with 10.6 inches—a daily record—occurring on December 15 in Rochester, New York. All of the precipitation contributed to general reductions in the coverage of dryness (D0) and drought (D1 to D3) across the Northeast. Despite the December improvement, year-to-date precipitation deficits through December 20 remained greater than 10 inches in locations such as Hartford, Connecticut (12.84 inches below normal); Islip, New York (11.17 inches); and Boston, Massachusetts (11.10 inches).
Southeast
Florida’s peninsula has been unusually dry—even by dry-season standards—for the last 2 months, and USDA’s topsoil moisture statistics continued to reflect significant short-term dryness. On December 18, Florida’s statewide topsoil moisture was rated 46% very short to short, compared to the 5-year average of 35%. Agricultural impacts of Florida’s short-term dryness included heavy irrigation requirements in the Citrus Belt to keep moisture in the ground and on the trees. In addition, deteriorating pasture conditions (31% very poor to poor, statewide) are resulting in many of Florida’s cattle producers to use supplemental feeding. Finally, farmers in parts of Florida are reporting that conditions are too dry for the planting of winter grains and cover crops. Accordingly, D0 (abnormal dryness) was introduced across much of Florida’s peninsula.
Farther north, much of the remainder of the Southeast continues to exhibit gradual improvement in the wake of a historically warm, dry autumn. In fact, recent rainfall has been heavy enough to eradicate drought in parts of western Florida, southeastern Alabama, and southwestern Georgia. Dothan, Alabama, received 10.04 inches of rain, 312% of normal, during the first 20 days of December. The streak of heavy rain extended westward to the central Gulf Coast, where substantial reductions in the coverage of dryness and drought were also noted. Across the interior Southeast, some of the improvements were based on further assessment of the effects of previously fallen rain, such as robust streamflow response and soil saturation. Despite widespread rainfall in the last 3 weeks, year-to-date rainfall deficits of 10 to 20 inches are still common across the core extreme to exceptional drought (D3 to D4) area of the interior Southeast. For example, January 1 – December 20 rainfall totaled just 32.08 inches (63% of normal, or 18.75 inches below normal) in Rome, Georgia, and 31.39 inches (65% of normal, or 16.93 inches below normal) in Anniston, Alabama.
Midwest
The Ohio Valley received heavy precipitation, with Louisville, Kentucky (2.22 inches), and Cincinnati, Ohio (1.76 inches), reporting daily-record totals for December 17. Accordingly, coverage of dryness (D0) and moderate to severe drought (D1 to D2) was reduced or eliminated where heavy rain fell. Farther west, however, coverage of abnormal dryness expanded in the middle Mississippi Valley and environs, while some additional moderate drought (D1) crept into southern Missouri. December 1-20 precipitation totaled less than one-third of an inch (12 to 16% of normal) in Missouri locations such as Springfield, Joplin, and West Plains. Several weeks ago, on November 27—prior to the December dryness—topsoil moisture was rated 50% very short to short in southwestern Missouri.
The Plains
With much of the region heading into a “deep freeze” during the weekend of December 17-18, there were only small changes in the drought depiction. Much of the nation’s mid-section received snow in advance of the Arctic outbreak, but liquid totals were relatively light in areas affected by dryness and drought. In the last week, some of the most significant deterioration was noted in eastern Oklahoma and neighboring areas, where drought signals were apparent in both long- and short-term indicators and where both agricultural and hydrological impacts continue to mount. The Arctic outbreak resulted in a multitude of daily-record lows, shortly after a brief burst of warmth had spread across the southern Plains. In South Dakota, consecutive daily-record lows were set on December 17-18 in locations such as Aberdeen (-32 and -37°F); Watertown (-29 and -37°F); and Mobridge (-28 and -26°F). Other places on the Plains setting consecutive record lows included Valentine, Nebraska (-27 and -31°F); Pueblo, Colorado (-19°F both days); Tribune, Kansas (-14 and -13°F); and Dalhart, Texas (0 and -8°F). Dalhart’s record-setting lows followed a daily-record high of 73°F on December 16. Similarly and elsewhere in Texas, December 16 daily-record highs of 85°F in Childress, 78°F in Lubbock, and 76°F in Borger were followed 2 days later by daily-record lows of 7°F, 4°F, and -3°F, respectively.
The West
Recent colder storms have significantly improved Western snowpack, especially across the northern Great Basin, Intermountain West, and Pacific Northwest. As a result, areas where the heavy snow has overlapped with dryness or drought—such as northwestern Wyoming and parts of Utah—have experienced some improvement—although it is still early in the season. Meanwhile, California weathered some impressive storminess, although high-elevation snowpack continues to lag normal for this time of year. According to the California Department of Water Resources, the average water content of the Sierra Nevada snowpack stood at 5 inches on December 20—roughly two-thirds of average but less than 20% of the typical April 1 peak. At the same time, basin-average precipitation since October 1 in the Sierra Nevada watersheds has totaled roughly 150 to 200% of normal. Some of the discrepancy is due to the barrage of “warm” storms that hit northern California during October. Despite the lagging snowpack, there has been ongoing drought recovery in much of northern California. Areas not dependent on snowpack, such as California’s northern coastal ranges, have seen the greatest recovery from long-term drought. Even before December’s precipitation, California’s 154 reservoirs held 18.5 million acre-feet of water by November 30, an improvement of nearly 7.6 million acre-feet from a year ago. The end-of-November statewide storage was 88% of the historic average (for this time of year) of 21.1 million acre-feet.
Alaska, Hawaii, and Puerto Rico
There was no change to the depiction of abnormal dryness (D0) across the southeastern mainland of Alaska. Much of Alaska had been cold during the first half of December, followed by a warming trend and an overall increase in precipitation. Fairbanks reported its highest temperature of the month to date—13°F—on December 16, followed the next day by a 5.2-inch snowfall. Farther south, a general increase in Hawaii’s rainfall coverage and intensity in recent weeks has led to a reduction in drought coverage. In fact, drought was removed entirely from Oahu, Lanai, and Molokai, while coverage was reduced across Kauai, Maui, and the Big Island. On the Big Island, Hilo’s month-to-date rainfall through December 20 stood at 17.13 inches, 217% of normal.
Looking Ahead
Mild weather will continue in many areas of the U.S., following the recent cold snap. During the weekend, however, colder air will engulf the West and return to the northern High Plains. For Thursday, precipitation highlights will include light snow spreading into the Northeast and rain developing in the Southwest. Precipitation associated with the Southwestern storm will overspread portions of the southern and eastern U.S. by Saturday. Meanwhile, a much more potent storm should arrive in northern California on Friday and reach the central High Plains by Christmas Day. Significant precipitation, including high-elevation snow, should occur throughout the West. Wind-driven snow can be expected late in the holiday weekend across the northern and central Plains and upper Midwest.
The NWS 6- to 10-day outlook for December 27 – 31 calls for the likelihood of below-normal temperatures in the West, while warmer-than-normal weather should prevail across the South, East, and lower Midwest. Meanwhile, near- to above-normal precipitation in most of the country will contrast with drier-than-normal conditions across the lower Southeast and portions of the Rockies and High Plains.
Author(s):
Brad Rippey, U.S. Department of Agriculture
Dryness Categories
D0 … Abnormally Dry … used for areas showing dryness but not yet in drought, or for areas recovering from drought.
Drought Intensity Categories
D1 … Moderate Drought
D2 … Severe Drought
D3 … Extreme Drought
D4 … Exceptional Drought
Drought or Dryness Types
S … Short-Term, typically <6 months (e.g. agricultural, grasslands)
L … Long-Term, typically >6 months (e.g. hydrology, ecology)