Tools used in the U.S. Seasonal Drought Outlook (SDO) included the Climate Prediction Center (CPC) temperature and precipitation outlooks for May and May through July 2021 (MJJ), various short- and medium-range forecasts and models such as the 7-day quantitative precipitation forecast (QPF) totals 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, dynamical models at the monthly and seasonal time scales, the 384-hour total precipitation forecasts from several runs of the GFS, climatology for the MJJ season, and initial conditions such as soil moisture. The April 13 USDM was used for initial drought conditions. ENSO-neutral conditions are likely during this outlook period. 

Long-term drought remains entrenched throughout a majority of the West with D2 (severe) to exceptional (D4) drought designated for parts of Oregon, California, and the Southwest. As of mid-April, snow water equivalent remains below normal for California, the Great Basin, and the Four Corners region. Water-year-to-date (Oct 1, 2020 to Apr 12, 2021) averaged less than 75 percent of normal for these same areas. Farther to the north across Washington, short-term drought expanded due to a lack of precipitation during the past 30 to 60 days. Persistence is likely for California as May-June-July is a dry time of year. The Southwest is also entering a dry time of year until monsoon rainfall begins later in July. Therefore, persistence is forecast for the Southwest and any potential improvements related to monsoon rainfall are not expected until late July or August. Drought is expected to expand northward across parts of the Pacific Northwest and northern Rockies based on: below normal precipitation during the past 30 to 60 days, low soil moisture conditions, and elevated probabilities of below normal precipitation and above normal temperatures for MJJ. Also, longer term precipitation deficits dating back a year or more across eastern Oregon and Washington is another factor to support development for these areas. Based on the seasonal precipitation and temperature tools, ongoing drought is likely to persist across Montana and potentially intensify if spring rainfall averages below normal. 

Forecast confidence for the Western Region is high for persistence and moderate for development. 

Widespread, heavy precipitation (2 to 8 inches, liquid equivalent) during March resulted in 1 to 3-class improvements to drought conditions across Colorado, Kansas, Nebraska, and Wyoming. The eastern two-thirds of Kansas and Nebraska are currently drought-free with soil moisture above the 70th percentile. Soil moisture declines rapidly to the north across northern South Dakota and North Dakota where drought continues to intensify after a lack of snowfall this past winter. According to the USDA's National Agricultural Statistics Service for the week ending on April 11, topsoil moisture is rated as short to very short across 83 percent of North Dakota. Based on a dry signal among precipitation tools from week-2 through the seasonal time scale along with the likelihood of above normal temperatures, persistence is forecast for a majority of the long-term drought across the central to northern Plains. However, this region is entering their wettest time of year when 40 to 65 percent of its annual precipitation occurs from May through July. This wet climatology reduces forecast confidence of persistence. The most likely area for improvement or removal is across eastern North Dakota where the seasonal outlook calls for equal chances of below, near, or above normal precipitation. Although additional improvements are expected across Colorado during April, the MJJ outlook favors below normal precipitation and above normal temperatures. Therefore, persistence is forecast for long-term drought across Colorado and Wyoming with development favored for areas designated with abnormal dryness (D0). 

Forecast confidence is low for the High Plains Region.
 
Drought varies in intensity across Oklahoma and Texas with the lowest soil moisture (below the 5th percentile) affecting western and southern Texas. According to the USDA's National Agricultural Statistics Service for the week ending on April 11, topsoil moisture is rated as short to very short across 77 percent of Texas. Although rainfall during mid to late April may prompt minor improvements across central Texas, broad persistence is most likely as seasonal tools support elevated probabilities of below normal precipitation and above normal temperatures. Development is favored in parts of west-central Texas due in part to the large probabilities (above 60 percent) of above normal temperatures forecast in the MJJ outlook. Since May is one of the wettest months of the year across the southern Plains and the dynamical model guidance has a strong dry signal for May, development is also forecast for parts of Oklahoma and northwest Texas where 60-day precipitation deficits (more than 2 inches) exist. The southern Plains will be closely monitored in the monthly drought outlooks through the summer. Moderate drought recently developed across northeast Louisiana due to inadequate precipitation during the past 30 to 60 days along with periods of above normal temperatures. Since this is a short-term drought area, heavy rainfall (1 to 3 inches) during the next week and the lack of a dry signal at the seasonal time scale favors drought removal for northeast Louisiana. Removal is also forecast for parts of the short-term drought area in southeast Texas, based on heavy rainfall forecast during mid to late April. Recent heavy rainfall and saturated soils make drought development unlikely throughout the lower Mississippi Valley and Tennessee Valley. 

Forecast confidence is low for the Southern Region.

The most severe long-term drought across the Midwest remains centered across northwest Iowa, based on 6 to 12-month SPI values. Given the long-term duration of this drought area, persistence is most likely but forecast confidence is low since the spring and early summer are a relatively wet time of year. Removal of moderate drought is more likely across northwest Minnesota based on: recent heavy rainfall, the absence of a dry signal at the seasonal time scale, and a wet climatology. Since mid-March, changes to coverage of abnormal dryness (D0) and moderate drought (D1) have varied throughout the Corn Belt, upper Mississippi Valley, and Great Lakes. Although below normal precipitation is favored for the Midwest during the next two weeks, cooler-than-normal temperatures are expected to limit any additional development this month. Based on elevated probabilities of above normal precipitation in the MJJ outlook, removal is forecast for ongoing drought areas across the Great Lakes. The Corn Belt will be closely monitored in the monthly drought outlooks through the summer. 

Forecast confidence is low for the Midwest Region.

Only small areas of abnormal dryness (D0) and short-term moderate drought (D1) are designated for parts of Alabama, Georgia, and Florida. Due to the lack of any dry signal among seasonal tools, development is unlikely for the Southeast. Recent heavy rainfall, a wet pattern during the next two weeks, and the onset of the convective season during June strongly favor removal of short-term drought across south Florida. 

Forecast confidence is high for the Southeast Region.

Moderate drought (D1) is ongoing across parts of southern New England, the central Appalachians, and eastern Great Lakes where soil moisture and 28-day average streamflows are below the 20th percentile. 30 to 60-day precipitation deficits exceed 2 or 4 inches across these D1 areas. During the latter half of April, an amplified 500-hPa trough over eastern North America favors above normal precipitation. Therefore, drought may begin to ease during the next couple of weeks. Since the seasonal precipitation outlook for MJJ calls for elevated probabilities of above normal precipitation for much of the Northeast, drought removal is forecast by the end of July. 

Forecast confidence is moderate for the Northeast Region.

Due to a lack of snowfall this past winter, abnormal dryness (D0) is designated for parts of northern and eastern Mainland Alaska. Based on an increasingly wet climatology later in the spring and early summer, this D0 area is unlikely to worsen to moderate drought (D1). Alaska is likely to remain drought-free through July. 

Forecast confidence is high for Alaska.

Although heavy to excessive rainfall during March resulted in 1 to 3-category improvements to drought conditions across Hawaii, abnormal dryness (D0) and moderate drought (D1) exists across the leeward slopes of the Big Island. Drought is forecast to develop for leeward parts of the Big Island of Hawaii with increasing chances of development across Lanai and Molokai later in the outlook period.

Forecast confidence is moderate for Hawaii.

Drought coverage continues to decrease across Puerto Rico, due to above normal rainfall during the past month. Inputs to the North American Multi-Model Ensemble feature large differences in their seasonal precipitation outlooks. Since May is one of the wetter months of the year, drought removal is favored. 
 
Forecast confidence is moderate for Puerto Rico.


Forecaster: Brad Pugh
 
Next Seasonal Drought Outlook issued: May 20, 2021 at 830am EDT