NOAA Drought Outlook Monthly – December

La Niña conditions have developed and are expected to continue during the Northern Hemisphere winter 2021-22.

Based on 4-week changes in the Drought Monitor through November 23, drought changes were a mixed bag of improvement and deterioration, depending on location.

Beneficial precipitation fell on the Northwest and northern California, where severe (D2) to exceptional (D4) drought has been entrenched since late spring. Still, D2 to D3 conditions cover most of this area, with D4 persisting in areas that received lesser amounts of precipitation.

Conditions also generally improved from the central Great Plains through the upper Midwest and northern Mississippi Valley, as did portions of the central Rockies and around eastern Oklahoma. Smaller sections near the Atlantic Coast of Georgia and northern Florida, and also across far upstate New York and northernmost New England.

Meanwhile, drought intensified across a broad region covering the central and southern High Plains, scattered patches from the lower Mississippi Valley to the Carolinas, the northern Great Lakes, and north-central Montana east of the Front Range.

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Beyond the contiguous 48 states, drought persisted or intensified across much of Hawaii and scattered portions of Puerto Rico. These changes still left large swaths of D3 to D4 from the High Plains westward to the Pacific Coast, as well as northeastern Minnesota, and the central and southern Hawaiian Islands.

By the end of the year, additional areas of improvement are expected across the Pacific Northwest, northern Intermountain West, and western Wyoming. Drought is also expected to ease up across northern parts of Wisconsin and Michigan, where lake-effect and lake-enhanced snowfall is most common climatologically.

In contrast, the large majority of American drought-affected areas should persist essentially unchanged or deteriorate slightly. This includes the remainder of the broad drought area extending from the High Plains to the Pacific Coast and in the less-widespread areas of drought through the Great Plains, upper Midwest, lower Mississippi Valley, Southeast, and Hawaii.

Furthermore, drought should expand into many of the abnormally dry (D0) areas across the southern Plains and the Southeast. Drought areas in Hawaii and Puerto Rico are also expected to get no notable improvement.

Forecast confidence is high for the Western Region.

• Drought covers the vast majority of the Western Region, as it has for many months. Much of this drought is deep, long-standing, and firmly entrenched. Almost half of the Western Region is covered by extreme (D3) or exceptional (D4) drought.
• The December monthly CPC outlook favors above-normal precipitation from the Pacific Northwest through the northern Rockies, likely bringing modest improvements to those regions.
• December is one of the wetter months of the year for the West Coast states, with over 15 percent of the annual precipitation recorded from the Cascades westward.
• However, the December contribution to the annual total decreases east of the Cascades. In eastern sections of Montana and New Mexico, December is one of the driest months of the year, producing less than 4 percent of the annual total precipitation on average.
• Enhanced chances for surplus precipitation during one of the wetter months of the year leads to an increased likelihood for improvement or removal.
• Farther east, where December is climatological above-normal precipitation indicate any meaningful improvements to long-term precipitation deficits. So persistence is expected farther east despite the wetness favored by the December outlook.
• Outside the Northwest, neither a wet nor dry December is favored, leaving very little chance that enough precipitation will fall to move the entrenched drought conditions.

Forecast confidence is moderate in the Rockies of Colorado and Wyoming, and high elsewhere for the High Plains Region.

• In the High Plains Region, drought covers much of Wyoming and Colorado, but drought is generally less widespread and less intense farther east in the High Plains Region. In eastern Wyoming and most of Colorado eastward, December is one of the drier months of the year climatologically, typically contributing less than 2 percent to the annual total precipitation from the Dakotas southward to Kansas.
• The December outlook shows enhanced chances for above-normal precipitation in western Wyoming, warranting improvement and removal, where December is not markedly drier than other times of the year.
• Farther east, neither above nor below- normal precipitation is favored over the Dakotas and most of Nebraska, but odds favor a drier than normal December across Kansas and a large portion of eastern Colorado. But in areas where there are equal chances or enhanced odds for a dry December, in addition to climatology, persistence is forecast.
• Along the southern fringes of Kansas and Colorado, where the December outlook shows the greatest likelihood of subnormal precipitation, drought is expected to expand slightly into the abnormally dry areas (D0) in the Drought Monitor.

Forecast confidence is high in most of the Midwest Region, but moderate in Wisconsin and Michigan.

• In the Midwest Region, drought persistence is likely in northwestern areas from the western Great Lakes Region through portions of Minnesota, northern Iowa, and northern Illinois. Elsewhere, only a few patches of D0 at worst are identified.
• The December outlook shows enhanced chances for surplus precipitation. From central Wisconsin and the Minnesota Arrowhead eastward.
• December is a drier time of year in most of Minnesota and Iowa, which receive 3.5 percent or less of their annual total precipitation on average.
• Farther east, December is still drier than most other months, but not as significantly, particularly from Michigan eastward (climatologically receiving up to 7 percent of normal annual precipitation).
• In areas where there is no tilt of the odds toward a wet or dry December in the Monthly Outlook, drought persistence is favored during a drier time of year.
• In areas where surplus precipitation is favored, the fact that December is a drier time of year limits any potential improvement.
• So most of these areas should expect persistence, except in the northern reaches of Wisconsin and Michigan in areas where lake-effect or lake-enhanced snowfall is most common.

Forecast confidence is high in the Southern High Plains in Southern Region, and moderate from eastern Texas to Mississippi.

• In the Southern Region, moderate to severe drought is established over and near the Texas Panhandle, western Oklahoma, parts of the Big Bend and southern Texas, and some sections of the ArkLaTex region and western Mississippi.
• In the December outlook, subnormal precipitation is favored almost everywhere in the region, with the greatest tilt toward below-normal precipitation odds over eastern New Mexico, Texas, most of Oklahoma, Louisiana, and the southern half of Mississippi. Persistence is forecast for all areas of drought, although confidence is reduced somewhat because some deterministic models bring moderate precipitation from eastern Texas through Mississippi around mid-month, though this is far from certain.
• Drought is forecast to expand into current D0 areas in the Southern Plains, but farther east, with the potential for moderate precipitation mid-month, there is little confidence that conditions will deteriorate sufficiently to bring drought into areas where it doesn’t currently exist.

Forecast confidence is moderate for the Southeast Region.

• After being drought-free earlier in the year, moderate drought has developed in southern Virginia and central and eastern sections of the Carolinas, with patches of abnormal dryness extending southwestward through Alabama.
• The December outlook favors deficient precipitation region-wide, with the best chances in Florida, southern Georgia, and some coastal areas in the Carolinas. With precipitation fairly uniformly distributed throughout the year, seasonality is less of a consideration here. So with odds tilting toward a drier than normal December, persistence is forecast in areas of ongoing drought.
• Some expansion into areas currently experiencing abnormal dryness is expected given a dry December outlook. However, no expansion is forecast from central Alabama westward, where some deterministic models show the potential for moderate precipitation around mid-month.

Forecast confidence is low for the Northeast Region.

• In the Northeast, drought is restricted to parts of western Maine. Most December forecasts are nondescript, and there is no indication that a storm might bring potentially drought-busting precipitation to the region, so conditions should persist to the end of the year.

Forecast confidence is high for Alaska, moderate for Hawaii, and low for Puerto Rico.

• Alaska is drought-free presently and none is expected to develop during December as the state moves into a drier and colder time of year.
• Across Hawaii, surplus precipitation is favored for December in the monthly outlook, but conditions are well-established in most current areas of drought, so the precipitation is not expected to be sufficient to engender notable improvement.
• And in Puerto Rico, small areas of moderate drought are noted in southwestern and northeastern parts of the Commonwealth, with broader areas of D0 in other areas. Few tools point toward a wetter-than-normal December, so drought persistence is anticipated. However, given the uncertainty of December conditions, no specific location seems likely to deteriorate into drought by the end of December.