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, and climatology for May. Initial conditions such as soil moisture, 28-day streamflows, and Snow Water Content (SWC) were also considered.

The Advanced Hydrologic Prediction Service (AHPS) Percent of Normal Precipitation (PNP) values for the past 30-days range from 200-400 percent of normal in Montana and New Mexico, down to 5-25 percent of normal in Arizona, southern Utah, and central and southern portions of California, including neighboring portions of Nevada. SWC is well above average in the California Sierras (ranging from 175% to 245%), above average in the Wasatch Mountains (115% to 144%), and below average in the Cascade Mountains (60% to 91%). Across the West, 28-day streamflows from the U.S. Geological Survey depict values in the lowest quartile of the historical distribution for this time of year in western Washington, far southern California, central Arizona, and in other very scattered locations. May precipitation climatology favors increasing dryness across the West Coast states and the Southwest (pre-monsoon), and relatively wet conditions in Montana. Precipitation outlooks for the next 30-days favor relatively wet conditions across the Four Corners drought area (including southeast New Mexico), and relatively dry conditions for north-central Washington. Accordingly, drought conditions are likely to be improved or removed across the southern Rockies/Four Corners region during May, though drought conditions are likely to persist and expand in Washington state.

Forecast confidence is high for continued improvement/removal for the southern Rockies/Four Corners region, and moderate for Washington state. 

The High Plains region is mostly drought-free, though there are two small areas of moderate drought (D1 on the U.S. Drought Monitor) currently indicated in Wyoming; one in north-central Wyoming, and the other in extreme southwestern Wyoming. For the first area (Big Horn Mountains), SWC is only about 70 percent of average, while for the second area (extreme southwestern Wyoming), SWC is near 110 percent of average. Precipitation for nearly all time-scales out to a month in advance is expected to be above normal. These precipitation outlooks and May climatology favor the removal of drought in southwestern Wyoming, but it will be harder to erase the drought in north-central Wyoming because of the lower SWC and related longer-term hydrological impacts. Elsewhere, above average precipitation this winter resulted in major flooding along the banks of the Middle and Lower Missouri River. Drought development is unlikely by the end of May since soil moisture ranks above the 90th percentile from South Dakota into Kansas. Although development is not anticipated across northern North Dakota by the end of May, this region will be closely monitored later this spring since 30-day precipitation has averaged between 50-75 percent of normal.

Forecast confidence is high for most of the High Plains region, though low for northern North Dakota.

Only three small areas of moderate drought remain in the South, all in southern and southwestern Texas. May climatology, a relatively wet April, soil moisture ranking between the 80th and 85th percentiles, and above normal precipitation forecast at most time ranges out to 30-days in advance, all point to drought removal in this region.

Forecast confidence is moderate to high for the South.


Widespread flooding continues across parts of the Midwest region, especially along the banks of the Mississippi River and the Red River of the North. During the past 60 days, precipitation surpluses range from 2 to 6 inches throughout much of the Midwest with soil moisture ranking in the 95th-99th percentiles for this time of year. Based on these wet initial conditions, and the expectation of near to above-normal precipitation at all timescales out to 30-days, drought development is unlikely during the outlook period.

Forecast confidence is high for the Midwest Region.

Abnormal dryness (D0) and moderate drought (D1) affected the area from Alabama to South Carolina during April. Sixty-day precipitation deficits range from 2 to 4 inches in these D0 and D1 areas, and 28-day streamflows fall within the lowest quartile. May precipitation climatology favors a slight tilt toward dryness in this region. Climatologically, sea-breeze induced and/or pulse convective activity in this area ramps up significantly by about mid-June, which is beyond the range of this drought outlook. Most precipitation outlooks during the next few weeks to a month out favor a slight tilt toward above normal rainfall. Despite this, the predicted precipitation amounts are not expected to be enough to erase longer-term deficits. Therefore, drought persistence (and even some development) is considered more likely.

Forecast confidence is moderate for much of the Southeast Region; but low along and near the South Atlantic Coast. 

The Northeast region has remained drought-free since early November 2018. During the last 30-days, widespread precipitation surpluses have been observed across most of the Northeast, and soil moisture ranks above the 80th percentile for nearly all of this region. Based on these initial soil moisture conditions, a wet April, and the absence of a dry signal for all time ranges out to the end of May, development is unlikely to occur. 

Forecast confidence is moderate to high for the Northeast Region. 

Moderate to severe drought (D1 to D2) coverage remained nearly steady along the southern Alaska Panhandle this past month. Since May is a relatively dry month, and there is not a wet signal in the constituent precipitation outlooks that comprise the monthly accumulation (including almost all of the input models that go into the North American Multi-Model Ensemble), persistence is forecast for the southern Alaska Panhandle.

Forecast confidence is moderate to high for Alaska.

Abnormal dryness (D0) and moderate drought (D1) returned to Hawaii during the last 30 days. The North American Multi-Model Ensemble indicates below normal precipitation during May, and the archipelago is entering its dry season with a weak El Nino in progress. These factors support drought persistence for the leeward slopes of the Hawaiian Islands.

Forecast confidence is high for Hawaii.

Drought coverage dropped from 30.38 percent in late March to 12.61 percent in late April across Puerto Rico. The large reduction in drought and abnormal dryness occurred over the western third of the Commonwealth in early to mid-April, as heavy rains affected that area. In contrast, conditions have been deteriorating farther east. Sixty-day precipitation deficits range from 4 to 8 inches in the interior portion of central Puerto Rico, and dryness/drought is expanding towards the southeast coast. Aquifers in eastern parts of the south coast of Puerto Rico (Guayama-Salinas and Santa Isabel areas) are reaching critical levels, according to the Department of Natural Resources. Although climatology becomes increasingly wet during late spring, it may not be enough to erase the longer-term deficits noted above. Therefore, drought persistence is expected in Puerto Rico.

Forecast confidence is moderate for Puerto Rico.

Forecaster: Anthony Artusa

Next Monthly Drought Outlook issued: May 31, 2019 at 3 PM EDT