Tools used in the U.S. Seasonal Drought Outlook (SDO) included the official Climate Prediction Center (CPC) temperature and precipitation outlooks for September through November (SON) 2017, 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), Weeks 3-4, dynamical models (CFSv2, NMME, IRI, IMME, and ECMWF), the 384-hour total precipitation forecasts from several runs of the GFS, the four-month Palmer drought termination and amelioration probabilities, climatology for September and the SON season, and initial conditions (the 8/15/2017 U.S. Drought Monitor). ENSO-neutral conditions are favored into the Northern Hemisphere 2017-18 winter.
Little to no drought is currently in place across the Northeast and Southeast climate regions. Over the past few weeks, moderate drought (D1) developed across eastern Maine due to below-normal summer precipitation, which has impacted agriculture and short term streamflow levels. Abnormal dryness also expanded during the past four weeks across parts of Virginia and North Carolina, though recent rainfall has kept deteriorating impacts at bay in some locations, and eased dryness in others. The WPC 7-day QPF shows no rainfall across New England, which will promote short term drought expansion. The CPC 8-14 day outlook favors precipitation falling in the middle tercile of the climatological distribution, and the September monthly outlook and the SON seasonal outlook both show no shift in the climatological precipitation distribution. Therefore, beyond the Week-1 period, the impact of typical fall precipitation is the best indicator of the drought vector. Soil moisture levels usually increase across the Northeast during the fall, as diminishing sun angles and vegetation entering dormancy reduce evapotranspiration rates. Therefore, drought removal is forecast for the D1 areas in Maine. Confidence in this forecast is reduced somewhat, as long term (12 month) precipitation deficits remain, which may act to resist complete moisture recharge. Forecasts at all time scales favor above-average precipitation for the Southeast, so no drought development in that region is anticipated.
Confidence is low for the Northeast region and moderate to high for the Southeast region.
Precipitation was highly variable for the Plains and the Midwest during the last 30 days. Widespread above-average rainfall led to drought-free conditions across all of Oklahoma and northern Texas, with locally heavy rainfall further east causing flooding in parts of eastern Texas and Louisiana. Several inches of much needed rainfall eased drought across parts of Nebraska and the Dakotas as well. Drought expanded and intensified in other regions where below-average precipitation was observed, however, including central Kansas, Iowa, northwestern Minnesota, and other parts of the Dakotas. Climatological precipitation decreases across the Plains during the fall months, limiting the potential for substantial drought relief, although decreased evapotranspiration rates allows any precipitation that falls to more effectively recharge the soils ahead of the winter freeze. In contrast, September is a wet time of year for southern Texas, due in part to tropical activity. During the upcoming week, the WPC 7-day QPF shows widespread heavy rainfall across the eastern Plains and Midwest, excluding the Dakotas and southern Texas. This short term forecast favors additional drought reductions for Kansas, northern Nebraska, eastern South Dakota, Iowa, and Missouri. During Week-2, the CPC ERF forecast favors above-normal rainfall for the central and southern Plains, with below-normal rainfall anticipated across the Great Lakes region. The CPC monthly and seasonal outlooks both favor enhanced precipitation for the Southern region. Based on these outlooks, drought improvement and removal is anticipated for southeastern South Dakota, Kansas, most of Nebraska, Iowa, Missouri, and Texas. Drought persistence is favored for the rest of the Dakotas and northern Minnesota.
Confidence is moderate for the Southern region, and moderate for the High Plains and Midwestern regions.
Below-normal precipitation continued to plague the northern parts of the Western region, promoting drought expansion and intensification across Montana. Impacts from persistently dry, hot weather began to emerge across Idaho, Washington, and Oregon, with abnormal dryness (D0) expanding westward over the past 30 days. In contrast, robust monsoon convection promoted drought relief for central and southeastern Arizona and New Mexico. Drought conditions remained unchanged for southwestern Arizona and California. The Southwest monsoon winds down early in the period, and since the winter wet season peaks beyond the SON period, drought persistence is favored across the Southwest, as well as lingering drought areas of Utah. For the Northwest, little to no precipitation is anticipated over the upcoming week, and the CPC 8-14 day outlook favors below-normal precipitation. The monthly and seasonal outlooks both maintain equal chances for precipitation to fall in the lower, middle, or upper terciles of the climatological distribution. Based on the short term outlooks, drought is anticipated to persist or intensify across Montana, and expand westward across the northern Rockies and Northwest. Precipitation climatology ramps up across the Northwest during the fall months, which may ease impacts later in the period, particularly across Washington and Oregon. Therefore, drought development is indicated on this outlook for the remainder of Montana that is not currently in drought, the northern two-thirds of Idaho, and far western Washington and northeast Oregon. Although possible in the early part of the period, drought development is not indicated at this time for the Pacific Northwest due to the wet climatology in late fall.
Confidence is moderate for the Western region.
Recent above-average precipitation eased drought across Alaska, with no remaining D1 areas as of the latest US Drought Monitor. Precipitation climatology decreases across much of interior Alaska during the fall months, as does daylight and temperatures. Therefore, drought redevelopment is not anticipated. Drought has developed over the past several months across much of Hawaii, and with the core of the wet season falling largely beyond the outlook period, persistence is the most likely outcome by the end of November. A small area of moderate drought has expanded across southern Puerto Rico. Dynamical models indicate enhanced chances for above-normal precipitation over the next few weeks, possibly tied to tropical cyclone activity. Based on the model forecasts and a wet climatology, drought removal is anticipated for Puerto Rico.
Confidence is high for Alaska, and moderate for Hawaii and Puerto Rico.
Forecaster: Adam Allgood
Next Seasonal Outlook issued: September 21, 2017 at 8:30 AM EDT