Tools used in the U.S. Monthly Drought Outlook (MDO) included the Climate Prediction Center (CPC) temperature and precipitation outlooks for April 2021, various short- and medium-range forecasts and models such as the 7-day quantitative precipitation forecast (QPF) from the Weather Prediction Center (WPC), the 6-10 day and 8-14 day CPC extended-range forecasts (ERFs), the Week 3-4 outlooks and tools from CPC, dynamic models at the monthly time scale, the 384-hour total precipitation forecasts from several runs of the GFS, climatology for April, and initial conditions for parameters such as soil moisture. Existing drought areas in the forecast are based on the March 30, 2021 U.S. Drought Monitor. Forecasts currently reflect the presence of a moderate La Nina, which is expected to remain throughout most or all of April, as there is a ~60 percent chance that conditions will begin transitioning toward ENSO-neutral into the spring months. Therefore, ENSO's influence remains a factor in the April 2021 MDO.

In the West, snow water equivalent (SWE) and reservoir levels are above-normal for the season leading up to April in the Pacific Northwest and northern Great Basin, falling quickly to below-normal southward in the Western Region. However, March saw below-normal precipitation across the West, leading to some expansion of moderate drought (D1) in some locations in eastern Washington and northern Montana. Odds for below-normal temperatures indicate existing drought conditions will not likely be exacerbated further during April. Additionally, the lack of a precipitation signal, coupled with surplus snowpack and above-normal reservoir levels, suggests no major improvements either. As such, persistence favored for much of the Pacific Northwest, with improvement favored along the western Cascades. Further south, drought persistence is also likely, with no additional development, as temperature and precipitation signals are lacking along the West Coast and western portions of the Great Basin. Further east, in the eastern Great Basin, below-normal precipitation is favored in areas already experiencing moderate to exceptional drought, indicating persistence is likely.

Forecast confidence is moderate to high for the Western Region.

The Northern Plains in the High Plains Region is a victim of below-normal seasonal snowfall and above-normal temperatures (6-10°F above-normal). This has resulted in drought expansion and intensification across the Dakotas and into the upper Midwest in the months leading up to April. The Dakotas are favored to experience above-normal precipitation (33% - 40% chance), with the greatest chances during the first half of the month. Additionally, the Great Plains begins its transition into a wetter time of year climatologically toward the end of April, in addition to a typical slight enhancement of wet precipitation signals across the region during La Nina years. Despite the potential for above-normal precipitation, lower probabilities indicate lower confidence, and any precipitation received will need to be much above-normal to overcome antecedent, long-term severe (D2) and extreme (D3) drought conditions across the Dakotas. However, some removal is favored in areas experiencing moderate (D1) drought in the eastern Dakotas, as drought indicators show weaker signals leading into the April period, suggesting any precipitation received will be more impactful. However, it should be noted that any potential improvements in the Dakotas will be slow to develop. Further south, the Central Plains experienced a major winter storm system in mid-March, which dropped 2-3 feet of snow in portions of eastern Colorado and southeastern Wyoming and anywhere from 5-10 inches of rainfall from the Front Range eastward to the Midwest, which brought major drought improvement. However, with above-normal temperatures and below-normal precipitation favored for the western High Plains, drought conditions are likely to persist during April. Furthermore, drought development is likely in abnormally dry (D0) areas, including those affected by the strong March storm system, as these areas are prone to high-wind events and conditions are favored to dry out again during April.

Forecast confidence is low for the Northern Plains and moderate elsewhere for the High Plains Region.

In the Midwest, portions of the Corn Belt have seen beneficial rainfall in the weeks leading up to April, resulting in drought removal across central Illinois. Elsewhere, however, below-normal precipitation has led to drought expansion across southern Michigan and northern portions of Ohio. Drought development also occurred across northern Minnesota. Above-normal precipitation is weakly favored for much of the Midwest during the next 6 to 10 days, transitioning to below-normal during Week-2 (8 to 14 days). Due to increased odds of above-normal precipitation early in the period, and above-normal precipitation favored in the April precipitation outlook in the upper Midwest, drought removal (D1) is likely across Minnesota. Additionally, standardized precipitation indices (SPIs) have shown gradual improvements in recent months, suggesting above-normal precipitation is likely to have more immediate impacts (although to a lesser extent in farther west in Minnesota and the eastern Dakotas, where dry signals in drought indicators are more pronounced). However, in portions of western and southern Michigan and northern Ohio, drought persistence, with additional expansion into abnormally dry (D0) areas, is likely, with above-normal temperatures strongly favored and precipitation signals transitioning to below-normal eastward toward the eastern Great Lakes and Northeast.

Forecast confidence is moderate for the Midwest Region.

The Texas Panhandle, northern and northwestern Oklahoma, the Tennessee Valley, and portions of the middle and lower Mississippi Valley experienced above-normal precipitation and drought removal during March. This beneficial improvement will be much needed during April, as equal chances of above or below to below-normal precipitation is favored throughout the Southern Region. Predicted weak mid-level height patterns during the middle part of the month increases uncertainty a bit in which location could see continued improvement versus degradation. As such, drought persistence is favored across the Southern Region, with development likely in abnormally dry (D0) areas across portions of west-central and southeastern Texas and southwestern Oklahoma, as well as the Texas and Oklahoma Panhandles. However, further eastward toward the lower Mississippi Valley, greater uncertainty among the model precipitation signals makes persistence (northeastern Louisiana) with no further development likely.

Forecast confidence is moderate for the Southern Region.

Heavy precipitation across the Southeast during the latter half of March led to some drought removal across areas of the Deep South. However, dryness has persisted in Florida, resulting in drought development in southern portions of the Peninsula in the past couple of weeks. In addition to April being a climatologically dry month for Florida, enhanced odds of above-normal temperatures and below-normal precipitation are favored, increasing the likelihood of additional drought expansion across the Florida Peninsula during April.

Forecast confidence is moderate to high for the Southeast Region.

In the Northeast, long-term drought has slowly diminished in recent months. However, D0 to D2 standardized precipitation indices (SPIs), locally D3, are still prominent, extending from western Pennsylvania to northern New England. Unfortunately, relief is not likely to come during April, as below-normal precipitation is favored through the first half of the month. Additionally, recent medium-range model solutions point toward equal chances for above and below to below-normal precipitation at longer leads. Coupled with increased odds of above-normal temperatures and plant growth being ahead of schedule (increasing evapotranspiration and water uptake in the root zones), this is likely to exacerbate existing dryness, suggesting drought development is likely in the driest areas from the Shenandoah Valley into western Pennsylvania, northern and western New York, New England, and western Maine.

Forecast confidence is moderate to high for the Northeast Region.

D0 currently covers much of northern Alaska, extending across the North Slope and Brooks Range southeastward to the Yukon Flats. Basin SWE estimates are currently below-normal (near 60% of normal for the period of record) across central Alaska. However, above-normal precipitation is favored throughout the period across the western Mainland, with equal chances for above or below elsewhere, which will help to stave off drought development throughout April. In Hawaii, many areas received heavy rainfall in recent weeks, with several locations experiencing flooding. As the wet season winds down during April, the state is expected to continue to see above-normal precipitation, making drought removal likely for the entire state. Moderate drought (D1) is currently depicted in northwestern Puerto Rico. Despite above-normal temperatures favored during April, above-normal precipitation is also favored. Coupled with continued improvements in SPIs in recent weeks, this area is primed for continued improvement, making complete drought removal likely for the island.

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

Forecaster: Adam Hartman

Next Monthly Drought Outlook issued: April 30, 2021 at 3:00 PM EDT.