U.S. Drought Outlook: Improvement is Limited
Since the release of the previous Drought Outlook issued on April 5, warm and dry weather caused drought to intensify and expand from the Gulf Coast and the south Atlantic states northward along the Eastern Seaboard. Farther west, conditions intensified to drought status in relatively small sections of western Kentucky, central Illinois, and the central High Plains.
Overall, the current Drought Outlook is not optimistic. Substantial improvement is expected only in southern Maine, the southern half of Florida with the onset if its rainy season, and western North Dakota. Meanwhile, limited surface moisture improvement is anticipated in the rest of the Northeast, North Carolina, the immediate southern Atlantic coastline, northern Florida and adjacent Alabama, and the upper Midwest.
In addition, late-period monsoonal rains could bring limited improvement to southern sections of New Mexico and Arizona. Drought should persist where it exists elsewhere (including Hawaii) and may expand to cover the central Rockies. It should be noted that the Drought Outlook is hampered by uncertainty regarding the track and intensity of a storm system that could drop heavy precipitation on part or all of the Atlantic Seaboard during April 21 – 23. This Drought Outlook assumes, as a compromise, a storm of moderate strength that affects the entire East Coast.
Forecast confidence for the Southeast is moderate, and for the Northeast is low.
Given all of the uncertainties, the outlook boils down to two factors: First, improvement is expected in southern Florida where there is a significant climatological increase in rainfall and summer progresses. Second, all other things being equal, drought has the best chance of persisting where the intensity and duration are currently the greatest and where there is no sharp climatological increase in rainfall – along the Delmarva Peninsula, and across South Carolina, Georgia, and adjacent areas away from the immediate Atlantic and Gulf Coasts. The limited improvement expected elsewhere is a reflection of the fact that extant drought is of lesser intensity and shorter duration in these areas, and not the result of a wetter forecast.
Forecast confidence for the upper Midwest and northern Plains is low.
In the upper Midwest and northern Plains, May – July is climatologically one of the wettest times of the year. Typically 35 to 45 percent of annual precipitation falls during this 3-month period from the eastern Dakotas eastward through Iowa and Minnesota, climbing to between 45 and 60 percent in the northern Plains. Near- to above-normal precipitation is expected for the remainder of April – especially along the northern tier – and the sum of indicators does not lean significantly toward dryness or wetness for May – July. However, both constructed analogs and CFS output leans wet in the northern and eastern tiers of the region, especially in western North Dakota, and toward dryness across western Nebraska.
This information translates into a forecast for improvement in western North Dakota (where indicators and climatology lean the wettest) and for persistence in western Nebraska (where forecasts on all time scales lean drier) and northeastern Minnesota (home of the region’s most entrenched drought conditions). Limited improvement is anticipated in other drought areas. It should be noted that since this is a wet time of year for the region – particularly in the western reaches – the lack of a convincing preponderance of indicators implies a large range of possible outcomes by the end of the period.
Forecast confidence across the southwestern and western parts of the nation is high.
For most of the southwestern and western part of the country, drought is expected to persist in most locations and expand into the central Rockies. This is a relatively wet time of year for the southern High Plains and neutral to dry farther west, especially in the desert Southwest and California.
Some precipitation is expected in northern parts of the region in late April, but thereafter the odds lean toward a drier-than-normal May – July through the northern half of the area. There is no discernible tilt of the odds farther south. Surface moisture is depleted in late spring and summer across this region due to the frequency of hot, dry, and windy weather. In addition, mountain snowpack, the source of a lot of the region’s moisture, is starting off below normal, and as a result summer stream flows are expected to be abnormally low.
In addition, May – July is expected to be warmer than normal, potentially enhancing the typical surface moisture depletion that always happens during this time of year. The result is a forecast for persisting drought that could expand into the central Rockies if there is sufficiently enhanced seasonal surface moisture draw-down. The only exception is in southern sections of New Mexico and Arizona, where the onset of monsoonal rains in July should bring some surface moisture back.
Forecast confidence in Hawaii is high.
Finally, Hawaii is transitioning into its drier time of the year, and there is little chance for any lasting drought improvement.