Tools used in the U.S. Seasonal Drought Outlook (SDO) included the Climate Prediction Center (CPC) temperature and precipitation outlooks for May through July 2018 (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 weeks 3-4 outlooks from CPC, dynamical models at the seasonal time scale, the 384-hour total precipitation forecasts from several runs of the GFS and the Canadian Model, climatology for the MJJ season, and initial conditions (the U.S. Drought Monitor valid April 17, 2018).

In the last month, abundant precipitation has fallen on much of California and northern Nevada, much of which came from one unusually strong storm for this late in the season. Between 10 and 20 inches of precipitation fell in the Sierra Nevada and northwestern sections of the state. Most locations outside the interior southern valley and the southeastern part of the state reported at least 2 to 4 inches. However, drought remains over most of the southern one-third of the state, and since May-July usually brings only 2 to 10 percent of the annual precipitation here, drought persistence is expected with high confidence. Farther east, the seasonal dryness is less marked across Nevada and Utah, where about 20 percent of annual precipitation falls during this forecast period. With below-normal precipitation and above-normal temperatures anticipated for MJJ, persistence is the only reasonable forecast here, though with slightly less confidence. Along the southern tier of states, there is a transition from MJJ being a drier time of year in western Arizona...to one of the wetter seasons in the eastern half of New Mexico. In the short-term, moderate precipitation (approaching 1 inch in spots) is expected through April 25 in much of northern and eastern New Mexico; only a few tenths of an inch at best are expected elsewhere. Odds favor wetter-than-normal weather through both states during the last week of April. Longer-term, there are ehanced chances for a drier than normal May in much of New Mexico and northern Arizona, but no tilt of the odds for MJJ as a whole. Given mixed signals, the forecast leans toward climatology, with drought expected to ease in eastern New Mexico (MJJ climatologically a wetter time of year) while persisting west of there (MJJ a neutral to mildly dry season). Farther north, drought in Oregon should persist given subnormal precipitation anticipated for most time scales (including MJJ as a whole). Some southwestward expansion is forecast into more of southern Oregon and part of northern California, where the low snowpack has the most potential to affect conditions this summer. Drought should continue to ease in eastern Montana, where MJJ usually brings 45 to 65 percent of the annual precipitation. The last half of April looks drier than normal here, but the May forecast favors above-normal precipitation. The MJJ outlook is non-committal. Given climatology and the May outlook, Montana should see additional improvement and removal. Drought will likely develop in parts of Oregon, California, and possibly Nevada by the end of July, but there is not enough confidence in any given location to justify a specific development region.

Forecast confidence for the West is high in California and Oregon; moderate to high in Montana, Utah, Arizona, and eastern New Mexico; moderate to low in the rest of New Mexico. 

Drought should continue to improve in the Dakotas, where MJJ usually brings 45 to 65 percent of the annual precipitation. The last half of April looks drier than normal here, but the May forecast favors above normal precipitation while the MJJ outlook is non-committal. Given climatology and the May outlook, The Dakotas should see additional improvement and removal. Farther south, drought covers all but the northern tier of Kansas and Colorado, with intensity increasing progressively to the south. D3 or worse covers most of the southern tier of the region, with D4 in parts of southwestern Kansas and southwestern Colorado. The outlook reflects climatology, though there are other justifications as well. MJJ is one of the wettest times of year in northwestern Kansas and adjacent Colorado, with nearly half of annual precipitation typically falling during this 3-month period. The marked climatological wetness declines moving away from this area. Between 40 and 45 percent of annual precipitation falls during MJJ in central and southern Kansas, and the proportion drops to between 35 and 40 percent in eastern Kansas and the rest of eastern Colorado. In contrast, MJJ leans slightly dry compared to other times of year in western Colorado. Through April 24, a storm system is expected to drop 0.5 to locally over 1.25 inches of precipitation on the most of the region, with lesser amounts expected in eastern Kansas and western Colorado. Odds favor wetness during the last week of April in central and western Kansas and most of Colorado, but again not in eastern Kansas. The May forecast calls for enchanced chances of subnormal precipitation across Colorado and southwestern Kansas, but for MJJ as a whole, the forecast in nondescript throughout. Given the relative wetness of the seasonal climatology, and that the last half of April is expected to be drier on eastern and western parts of the area compared to the midsection, the forecast calls for persistence in the western half of Colorado and in eastern Kansas, with improvement or removal anticipated elsewhere.  

Forecast confidence for the High Plains is moderate to high except in eastern Kansas and westernmost Colorado, where the consensus of the tools is not as clear. 

MJJ is one of the wetter times of year in western Oklahoma and northwestern Texas, but the difference becomes marginal farther east into central Texas and eastern Oklahoma, and dissapears in southern and southeastern Texas, where MJJ leans neither dry nor wet relative to annual average precipitation. A storm system is expected to push through around April 20, bringing over 0.75 inch of precipitation to Oklahoma and northeastern Texas (including the D4 regions in both Panhandles and western Oklahoma) and 1.5 to 2.0 inches in central and western Oklahoma outside the Panhandle. For some locations, this will be 2 or 3 times as much as during the previous 6 months. The forecast for the last week of April also favors wetter than normal weather. After that, odds favor a drier-than-normal May for both Panhandles and ajacent areas of western Oklahoma and west-central Texas, but MJJ as a whole leans neither wet nor dry. The forecast leans on the short-term storm system and climatology; drought relief is expected in Oklahoma and western Texas, with persistence in southern Texas where the short-term should be drier and the climatological wet season comes later in the year. Development will likely occur in parts of southern and (to a lesser extent) central Texas, but there is not enough confidence in any given location to justify introducing an area of development on the map.

Forecast confidence for the Southern Region is moderate to high in northwestern Texas and Oklahoma. Moderate to low in south-central and Deep South Texas.

Small areas of moderate drought (D1) are designated for parts of the middle Mississippi Valley and northern Minnesota. The official forecasts don't provide definitive guidance for this region. The first seven days of the period should bring a few tenths of an inch of precipitation at best. Thereafter, the odds lean neither dry nor wet for the last week of April, the month of May, and MJJ as a whole. This is a fairly wet time of the year, with 35 to 45 percent of the 12-month precipitation total expected. This would imply a low-confidence forecast for improvement, which is the case in northern Minnesota. Farther south, considering the enhanced chances for above-normal temperatures in the MJJ Outlook, and that some degree of dryness (D0 or worse) has been present in at
 least part of the region each week for more than a year, the forecast leans toward expected MJJ warmth and the protracted (if not particularly intense) nature of the dryness in the middle Mississippi Valley 

Forecast confidence for the Midwest is high for Minnesota, and low in the middle Mississippi Valley. 

Moderate to severe drought cover the central and southeastern sections of both Georgia and South Carolina, and southern Florida. Elsewhere, only patches of moderate drought were noted in southeastern Virginia, southeastern Alabama, and west-central Georgia. During the first seven days of the period, moderate to heavy rain is expected from the Carolinas southward. Amounts should top 1.5 inch in most of South Carolina, Alabama, and Georgia, with over 2 inches expected in central and southwestern South Carolina. Subnormal precipitation is expected during the last half of April, but the pattern looks to turn wetter thereafter. Odds favor a wet May throughout the region, and a wet MJJ from the central Carolinas northward. This season leans wet relative to the rest of the year climatologically in the Florida Peninsula and, to a lesser extent, southeastern parts of Georgia and South Carolina. In particular, MJJ overlaps the early part of south Florida's very reliable wet season. With almost all indicators pointing toward more precipitation than normal, drought improvement or removal is forecast throughout the region, though with less confidence in some areas.

Forecast confidence for the Southeast is high in southern Florida, moderate to high in Georgia and South Carolina, and low to moderate elsewhere.

The Northeast Region is free of drought, and none is expected to develop through mid-summer.

Precipitation will be increasing over the next couple of weeks in the southern Alaska Panhandle, and some impacts, such as hydroelectric power generation, have already eased following moderate preciptation earlier in April. Given the trend in both impacts and precipitation frequency, drought is forecast to be removed by the end of July. It should be noted that the forecast precipitation is not expected to dramatically lower the precipitation deficit that accumulated during the 2017-18 cold season (October-March), one of the driest on record. MJJ leans somewhat dry relative to the rest of the year, so despite expected relief in the short-term, lingering long-term precipitation deficits will leave the region primed for redevelopment. This lowers our forecast confidence.

Hawaii and Puerto Rico are drought-free and none is expected to develop through the end of June.

Forecast confidence for Alaska is moderate.

Forecaster: Rich Tinker

Next Seasonal Drought Outlook issued: May 17, 2018 at 8:30 AM EDT