Tools used in the U.S. Monthly Drought Outlook (MDO) included the Climate Prediction Center (CPC) temperature and precipitation outlooks for May, 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 time scale, the 384-hour total precipitation forecasts from several runs of the GFS, climatology for May, and initial conditions such as soil moisture. The U.S. Drought Monitor, valid on April 27 at 12Z, was used for the initial drought conditions. 


Long-term drought remains entrenched throughout a majority of the West. According to the U.S. Drought Monitor valid on April 27, nearly a third of this region is designated with severe (D2) to exceptional (D4) drought. Since May begins the dry season for much of the West, persistence is likely. Based on low soil moisture (below the 20th percentile) and the May outlook calling for elevated probabilities of below normal precipitation, development is forecast for southern Idaho and eastern Oregon. 

Forecast confidence for the Western Region is high.  


The wet March continued into April across the Front Range of the Colorado Rockies and adjacent high Plains where 30-day precipitation surpluses are 1 to 3 inches. Based on improving conditions such as soil moisture, generally above the 20th percentile, and additional precipitation forecast during the first week of May, drought removal is likely for northeast Colorado along with south-central Wyoming. Please note that the seasonal outlook (May-June-July) favors below normal precipitation and above normal temperatures. Therefore, worsening drought conditions may return later in June or July. The remainder of the north-central Rockies and Great Plains have received near to below average precipitation during April. Persistence is more likely for the northern and central Great Plains as it is expected to take more than a month for broad improvement to occur for these long-term drought areas. However, forecast confidence is low since May is one of the wetter months of the year when the northern and central Great Plains receive 14 to 20 percent of their annual precipitation. The one exception to the persistence is southeast South Dakota where conditions have improved this spring. Based on this factor and the wet May climatology, removal is favored for that part of South Dakota. Drought is expected to return to southwest Kansas by the end of May due to elevated probabilities of below normal precipitation and above normal temperatures during May. 

Forecast confidence is high for removal in northeast Colorado but low for the remainder of the High Plains Region. 
 

Widespread, heavy rainfall (1 to 3 inches, or more) from April 27 to 30 along with additional rainfall at the beginning of May are likely to result in drought improvement or removal across central and eastern Texas. Farther to the west and south, including the Rio Grande Valley, persistence is forecast for areas that largely missed out on this beneficial rainfall and soil moisture is below the 5th percentile. Following an end to the drought across northwest Oklahoma and parts of the Texas Panhandle earlier this spring, April became increasingly dry. Based on this recent dryness and elevated probabilities of below normal precipitation and above normal temperatures during May, drought is expected to return to northwest Oklahoma and expand across the Texas Panhandle. 

Forecast confidence is moderate for the Southern Region. 


Long-term drought is more likely to persist across parts of northern  Iowa. However, forecast confidence is low given the wet time of year and mixed precipitation forecasts at various time scales. Farther to the east across the Great Lakes, the May outlook favors above normal precipitation albeit with relatively low probabilities. Removal is most likely from northeast Illinois eastward to southern lower Michigan and northern Ohio where probabilities exceed 40 percent for above precipitation in the updated May outlook. Persistence is favored for the remainder of Michigan and southern Wisconsin. This south to north depiction of removal to persistence is consistent with predicted rainfall amounts during the first week of May. Near to above normal rainfall expected during the first half of the month preclude designation of any development for the Midwest. 

Forecast confidence is low for the Midwest Region.



Abnormal dryness (D0) expanded across parts of the Carolinas and Georgia due to increasing 30 to 90-day precipitation deficits. Based on a relatively dry first half of the month along with periods of above normal temperatures, development is expected for most of the current D0 area. Along and west of the Savannah River, development is less likely as those areas are not quite as dry. Removal is forecast for the small D1 (moderate drought) area in southwest Florida which is consistent with the May precipitation outlook. As the convection season ramps up around the beginning of June, any lingering dryness across the Florida Peninsula is likely to be short-lived. 

Forecast confidence is moderate for the Southeast Region.

 
Beneficial rainfall at the end of April along with a likely wet first half of May favor removal for northwest Pennsylvania and New York. Persistence is more likely across New England due to larger precipitation deficits (more than 8 inches) dating back 6 months. Although small areas of removal may occur across Massachusetts, New Hampshire, and Vermont with any heavy rainfall, broad persistence is more likely given the longevity of the drought conditions.  

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 during May, this D0 area is unlikely to worsen to moderate drought (D1). Alaska is likely to remain drought-free.

Forecast confidence is high for Alaska.

 
Abnormal dryness (D0) expanded in coverage across the Hawaiian Islands during April. Forecast confidence is too low to designate development for any specific area on a monthly time scale, but degradation to moderate drought is expected through the early summer. Persistence is likely for the ongoing drought area on the Big Island. 

Forecast confidence is low for Hawaii.


During late April, moderate drought (D1) was introduced to eastern Puerto Rico and Vieques and slightly expanded across southwest Puerto Rico. Since the latest model guidance indicates a continued drier-than-normal pattern through at least early May, persistence is favored. Development is most likely across southern and eastern Puerto Rico where 28-day average streamflows are the lowest. 
 
Forecast confidence is moderate for Puerto Rico.


Forecaster: Brad Pugh
 
Next Monthly Drought Outlook issued: May 31, 2021 at 3pm EDT