Tools used in the U.S. Seasonal Drought Outlook (SDO) included the Climate Prediction Center (CPC) temperature and precipitation outlooks for July and July through September 2021 (JAS), 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 related tools from CPC, dynamical models at the monthly and seasonal time scales, the 384-hour total precipitation forecasts from several runs of the GFS, climatology for the JAS season, and initial conditions such as soil moisture. The USDM valid on June 15 was used for initial drought conditions. ENSO-neutral conditions are likely during this outlook period.
Drought remains firmly entrenched across the western CONUS, with nearly 90 percent of the Western Region experiencing drought conditions (D1 or worse) according to the US Drought Monitor valid on 8 June 2021. Recently, the climatological summer ridge shifted to western North America and amplified, resulting in record breaking heat across multiple states and subnormal precipitation for the Northwest. Abnormal heat and dry conditions are favored to continue over the next two weeks based on guidance from the WPC and CPC, and the CPC seasonal outlook favors below-normal precipitation for the Northwest and above-normal temperatures across the entire Western region. The summer dry season in California coupled with below-average snowpack conditions yields little opportunity for drought relief, and the outlooks at all time scales favor drought persistence and expansion across the Northwest. The only region where drought relief is favored is across the southern portions of Arizona and New Mexico, where the CPC seasonal outlook indicates no shift in the climate signal. Monsoon convection typically provides more than 50 percent of the annual rainfall across southern Arizona and New Mexico, so some relief is likely. Due to the spotty nature of the monsoon convection, however, the relief will be localized to some areas, while other areas will experience continued severe to exceptional drought conditions. No drought development is anticipated across Alaska. Across Hawaii, the CPC seasonal outlook indicates enhanced chances for below-normal precipitation. Therefore, continued expansion of drought conditions across the islands is anticipated.
Forecast confidence is moderate to high for the Western Region.
Over the past four weeks, increased wetness improved drought conditions across much of Colorado northward across western Nebraska and South Dakota. Dry weather and warm temperatures resulted in drought expansion across northeastern Nebraska and eastern South Dakota. The JAS period is a wet time of year climatologically for the High Plains, as series of mesoscale convective systems tied to shortwave troughs move over the climatological summer ridge. Precipitation tends to decrease in September. During the next week, the WPC QPF forecast shows generally light accumulations, with the heaviest amounts (0.5 inch) occurring over the far eastern portions of the Dakotas. The Week-2 outlook from CPC shows mixed, low amplitude signals, while the seasonal outlook favors below-median precipitation across parts of the Northern High Plains. Based on the lack of a clear wet signal in the guidance and the long term nature of the drought conditions across the Dakotas, persistence seems to be the most likely outcome. Drought development is possible across southeastern Wyoming, southwestern South Dakota, and northwestern Nebraska based on dry soil conditions and the drier seasonal outlook. The unpredictable nature of high-impact short-term convective events at seasonal time scales reduces outlook confidence in this region.
Forecast confidence is low for the High Plains Region.
Persistent dry weather and periods of above-normal temperatures resulted in drought expansion across parts of the Corn Belt and Great Lakes region. Longer term impacts from drought have begun to set in across the Midwest Region, which makes substantial improvements less likely in the absence of a clear wet signal. Widespread moderate to heavy rainfall (locally exceeding 1.75 inches) is forecast over Iowa, southern Wisconsin, and northern Illinois during the next 7 days, but these amounts are unlikely to substantially dislodge the long term drought conditions. 60-day precipitation departures in the region generally range between 4 and 8 inches. The CPC 8-14 day outlook favors a continuation of above-median rainfall, but probabilities in the core drought area are below 40 percent. The monthly and seasonal outlooks both maintain equal chances for below-, near-, and above-median precipitation. Given the incipient conditions, it is unlikely that climatological precipitation would substantially reduce drought conditions, therefore drought persistence is maintained across the western Corn Belt and Michigan. Since the summer months are a wet time of year and the shorter term outlooks favor wetness, no drought development is indicated. Should a period of hot, dry weather materialize later in the summer, however, flash drought conditions are not out of the question for parts of the central or eastern Corn Belt. Please refer to the monthly drought outlook issued at the end of June for updates.
Forecast confidence is low for the Midwest Region.
In contrast to much of the rest of the CONUS which has experienced dry weather during the past month, parts of the Southern Region, particularly across Texas and the lower Mississippi Delta region experienced copious amounts of rainfall, generating widespread flooding. Small portions of drought remain across far western Texas and central Oklahoma, where rainfall totals were significantly less. In the short to medium term, the National Hurricane Center is monitoring a disturbance over the southern Gulf of Mexico that, regardless of development, is forecast to bring additional heavy rainfall to the central Gulf Coast. Given the wet incipient conditions, short term forecasts showing additional rains, and a wet climatology, no widespread drought development is anticipated in this region. Monsoon convection may help alleviate drought across western Texas, while a lack of a clear wet signal favors persistence of the remaining drought in Oklahoma.
Forecast confidence is moderate to high for the Southern Region.
Subnormal rainfall over the past two months has resulted in pockets of drought in South Florida, parts of the Carolinas and Virginia, northern New England, and eastern Puerto Rico. During the upcoming week, widespread rainfall of 0.75 to 1.5 inches is forecast across the drought areas of New England and the mid-Atlantic, while the summer seabreeze convective regime is anticipated to generate locally higher amounts across southern Florida. Above-median rainfall is slightly favored to continue across the East during Week-2, and both the monthly and seasonal outlooks from CPC favor wetness across the entire Eastern Seaboard. Given these outlooks and the wet climatology, drought removal seems the most likely outcome east of the Appalachians. Summer convection will likely continue to erode drought across Florida and Puerto Rico, and September is the peak of the Atlantic hurricane season. The lowest confidence for drought improvements exists across Maine and far upstate New York, where streamflows are currently very low.
Forecast confidence is high for the Southeast Region, and low to moderate for the Northeast Region.
Forecaster: Adam Allgood
Next Seasonal Drought Outlook issued: July 15, 2021 at 8:30am EDT