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 8-14 day CPC extended-range forecasts (ERFs), the weeks 3-4 outlook from CPC, dynamical models at the monthly time scale, the 384-hour total precipitation forecasts from several runs of the GFS, climatology, and initial conditions (the U.S. Drought Monitor valid on April 24, 2018).
May is a relatively wet month in Montana, but in most other parts of the western region, it is either drier than most other months, or approximately neutral compared to the rest of the year. May usually contributes less than 4 percent of the annual precipitation total across most of California, southern Nevada, Arizona, and western New Mexico. The official outlook for May 2018 features enhanced chances for below-normal precipitation in Oregon, as do forecasts on most other time scales. Persistence is forecast there, with some expansion anticipated into adjacent areas over the rest of central and southeastern Oregon. Farther south and east, above-normal May precipitation is favored across Utah, and with a neutral climatology relative to other times of the year, drought improvement or removal is anticipated in northeastern parts of the state, but a drier climatology coupled with more protracted drought conditions led to persistence being forecast in the rest of the state. Farther south and west, where May climatology contributes less to the annual precipitation total, persistence is forecast.
Forecast confidence is high for the southern and western tiers of the region, moderate in the Great Basin and much of Utah, and low in northeastern Utah.
In the High Plains climate region, drought covers the western Dakotas, Kansas, and much of Colorado, with Extreme Drought observed in southwestern Kansas. May is wet relative to other seasons throughout the region outside western Colorado, where it is neither a dry nor wet time of year. The May outlook favors above-normal precipitation from Kansas northward through South Dakota, and in most of Colorado. Conditions are expected to improve across central Colorado and in eastern and northern sections of Kansas, but despite the forecast favoring a wet May, persistence is anticipated through southern Colorado and roughly the southwestern one-third of Kansas. In these areas, drought is more intense and has lasted longer than in other areas, and there are some indications, at least in the short term, that this region may not receive as much precipitation as areas to the north and south.
Farther north in the western Dakotas, this is a wet time of year, especially in western South Dakota. In addition, odds favor above-normal precipitation in the May outlook in western South Dakota, but neither dryness nor wetness is favored farther nort. These two factors lead to a forecast of improvement in South Dakota drought areas, but persistence farther north.
Forecast confidence is moderate to high across most of Kansas and Colorado, and in South Dakota; moderate to low in central Colorado and North Dakota.
In the South Region, Extreme to Exceptional Drought covers part of southwestern Texas, areas near the Texas Panhandle, and western Oklahoma. Conditions improve markedly farther east, and the region is drought-free from central sections of Oklahoma and Texas eastward. May precipitation odds favor above-normal precipitation in most of the drought areas outside the westernmost Texas and Oklahoma Panhandles, and in the short-term, amounts of 1.0 to locally 2.5 inches are forecast for the first week of May in most of Texas and Oklahoma east of the Panhandles. This is a relatively wet time of year in the drought areas outside the Big Bend in Texas, but this must be weighted against the D3 to D4 conditiions in the Panhandles region that have existed for several months in some areas. Drought is expected to improve in South Texas and along the eastern tier of the drought region through central parts of Texas and Oklahoma. In western parts of these states, where drought is more intense and lesser short-term precipitation amounts are forecast, drought should persist.
Forecast confidence for the Southern Region is moderate.
Small areas of moderate drought (D1) are designated in parts of the middle Mississippi Valley and northern Minnesota. Heavy precipitation is favored during May across southern Iowa and northern Missouri, and 1.0 to 2.5 inches are expected for the first week of the month. Removal is expected in this region, though the long-term nature of the drought tempers confidence some. In northern Minnesota, this is one of the wetter months of the year, but forecasts don't favor surplus precipitation on any time period, so persistence is forecast but with reduced confidence.
Forecast confidence for the Midwest is low in northern Minnesota and moderate farther south.
May climatologically is a relatively dry time of year across most of Florida and the adjacent Southeast, though not as markedly as in some areas farther west. May precipitation odds lean dry across the interior Southeast, with equal chances forecast elsewhere. For the first 1 to 2 weeks of the period, surplus precipitation is slightly favored in most drought areas south of Virginia. Without much confidence, persistence is expected in southwestern Florida and for the drought areas in Georgia and Alabama, where either the monthly outlook favors drier than normal weather or conditions early in the period don't look as wet as in some other areas. Farther east and north, improvement or removal is anticipated in southeastern Florida, South Carolina, and southern Virginia where substantial precipitation appears more likely, especially early in the period.
Forecast confidence for the Southeast is low.
In the Northeast Region, the small area of moderate drought near Washington, DC is expected to be removed due to precipitation early in the month and recent subnormal temperatures.
Forecast confidence in the Northeast is moderate.
Hawaii, Alaska, and Puerto Rico are drought-free and none is expected to develop through the end of May.
Forecast confidence for Alaska, Hawaii, and Puerto Rico is moderate.
Forecaster: Rich Tinker
Next Monthly Drought Outlook issued: May 31, 2018 at 3 PM EDT