Tools used in the U.S. Seasonal Drought Outlook (SDO) included the Climate Prediction Center (CPC) temperature and precipitation outlooks for September through November (SON) 2020, various short- and medium-range forecasts and models such as the 7-day quantitative precipitation forecast (QPF) 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 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 SON season, and initial conditions such as soil moisture. The August 18th U.S. Drought Monitor drought areas were used. Conditions currently reflect ENSO-neutral, but a La Nina watch continues to be in effect, with ~60% chance for La Nina development during the Fall. If La Nina develops, there is a 50-55% chance that it will remain through the winter.

The Northeast region has seen drought conditions deteriorate slightly in parts of New England and western Pennsylvania in the last 30 days. On the contrary, the extratropical transition of Hurricane Isaias aided in drought removal in eastern New York near the beginning of August, with parts of eastern New York seeing 2-5" of rainfall during its passage. The ERFs show probabilities for above-normal precipitation through Week-2, which bodes well for at least some improvement in the near-term. However, precipitation signals in the long-range statistical guidance are absent in much of the Northeast during the SON period and the SON precipitation forecast depicts equal chances. In addition, precipitation anomalies have high spatial variability during years when La Nina conditions are present, with a trend toward wetter conditions in more recent La Nina years for all of the Northeast. Despite above-normal temperatures favored throughout the valid period, some drought improvement (D2 and worse) and removal (D1) is favored, in support of probabilities of above-normal precipitation in the extended range and a wetter trend during La Nina years.
 
Forecast confidence is moderate for the Northeast Region.


The Southeast has experienced large variability in drought and abnormal dryness coverage over the past month. With the potential for La Nina development looming this Fall, this may act to increase odds of below-normal precipitation, particularly in the Lower Mississippi Valley. However, with the peak of the Atlantic hurricane season a few weeks away and the potential for it to coincide temporally with the shift of the active phase of the Madden-Julian Oscillation (MJO) over the Atlantic, no drought development or continuation is favored in the Southeast. In further support, the seasonal outlook also favors above-normal precipitation during the SON period.

Forecast confidence is moderate for the Southeast Region.


The Southern Region experienced a mixture of drought improvement/removal (northern Oklahoma, Texas Panhandle, and northeast New Mexico) and development/intensification (central and western Texas) in the last month. La Nina development could translate to below-normal precipitation for much of the southern tier states, extending into the Lower Mississippi Valley. Also, long-range statistical guidance and the seasonal outlooks favor above-normal temperatures and below-normal precipitation west of the Mississippi River (Arkansas and Louisiana westward). As such, drought persistence is favored for areas currently in D1 drought or worse throughout the Southern Region. Development is favored across much of central and northern Texas and western Oklahoma. Development was not extended into eastern Oklahoma, toward areas of persistence in Kansas and Missouri, due to the climatological southward shift of the storm track into that region during the Fall. Eastern Oklahoma, southeastern Kansas, and southern Missouri remain a wild card due to the juxtaposition of a wetter climatology in the first half of the SON period and the dry signal in this region for the season as whole. Development was also not expanded further eastward toward the Lower Mississippi Valley due to favorable conditions for an active peak to the hurricane season during September, and its potential to coincide with the active phase of the MJO moving into the Atlantic.

Forecast confidence is low to moderate for the Southern Region.


Similar to the rest of the eastern CONUS, the Midwest has experienced a combination of drought improvement/removal and development/deterioration in the last month. D1 and D2 removal occurred in Minnesota while D0 and D1 removal occurred in much of the Corn Belt. Drought developed in Ohio, with several locations seeing 90-day precipitation deficits of 2-4". A localized region of western Iowa saw drought intensification, with 90-day rainfall deficits of 6-12" for locations currently experiencing extreme drought (D3). Long-range outlooks depict equal chances for above- and below-normal precipitation for the entire region. Although the Midwest is favored to experience above-normal temperatures during the SON season, the transition into the Fall season brings with it lower evapotranspiration (ET) rates, coupled with wider-spread synoptic events. As such, drought improvement (D2 and worse) and removal (D1) are favored in the Midwest Region.

Forecast confidence is moderate for the Midwest Region.


In the High Plains Region, drought expansion and intensification was prevalent in Colorado, Wyoming, and western and eastern Nebraska in the past month, mainly due to above-normal temperatures and high ET rates. The Dakotas also had a couple of isolated spots where D1 expanded slightly, and intensified (D2 in central North Dakota). Although some short-term relief is predicted in the Week-2 period for the northern Rockies and Northern Plains, areas in the eastern Rockies and the along the Front Range favor above-normal temperatures and below-normal precipitation at longer ranges. Equal chances for above- and below-normal precipitation is favored elsewhere in the High Plains Region during the SON period. As such, drought is expected to persist for Wyoming, Colorado, western Nebraska, and extreme western Kansas. Meanwhile, the Dakotas and eastern Nebraska are favored to see reductions in drought coverage and intensity, due to the aforementioned lower ET rates and climatologically wider-spread synoptic events during the Fall.

Forecast confidence is high for the eastern Rockies and Front Range, and moderate elsewhere for the High Plains Region.


Widespread drought persisted last month across much of the Western Region and expanded in coverage, increasing from 47.81% on July 14, 2020 to 63.85% coverage as of August 11 (~16% increase). Much of the expansion in drought coverage (D1 and worse) took place in New Mexico and Arizona due to below-normal precipitation resulting from a suppressed monsoon season. The outlook for much of the West looks bleak with the highest probabilities for above-normal temperatures and below-normal precipitation favored in the southern Rockies and Southwest. The only region where drought improvement/removal is favored resides in the Pacific Northwest, with odds for above-normal precipitation stretching from Washington and northern Oregon eastward through northern Montana. The potential onset of La Nina might also act to enhance the above-normal precipitation signal. As such, some removal (D1) and improvement (D2) is predicted in Washington and extreme northern Oregon, corresponding to odd of above-normal precipitation. Additional removal and improvement was extended southward in western Oregon, as this region is entering into a wetter time of year. Meanwhile, persistence is favored elsewhere in the West, with drought development favored in portions of Arizona, New Mexico, and southern California.

Forecast confidence is high for the Western Region.


Abnormal dryness (D0) persisted across the Kenai and Alaska Peninsulas since the previous seasonal drought outlook, with some eastward expansion of D0 along the southern coast. Fortunately, during autumn the upper-level westerlies typically strengthen and shift southward, helping to focus the mean storm track and associated precipitation across the southern coast of Alaska. CPC's monthly and seasonal precipitation outlooks favor equal chances to above-normal precipitation over this region. Therefore, no drought development is favored in Alaska during the SON season.

Forecast confidence is moderate to high for Alaska.


Gradual reduction in drought coverage occurred across portions of Oahu, Maui, and Hawaii Counties in Hawaii last month, with removal occuring in Kauai. Luckily, the Fall months are when Hawaii begins its transition into a climatologically wetter time of the year. In addition, if La Nina conditions materialize, it may further increase odds for above-normal precipitation, particularly for the latter half of the SON period. Therefore, removal (D1) and improvement (D2) is favored in Hawaii.

Forecast confidence is moderate to high for Hawaii.


Above-normal precipitation and the passing of Isaias eliminated drought conditions in Puerto Rico last month. Abnormally dry (D0) conditions still remain across southern and eastern portions of the country. Long-term statistical guidance depicts a wet signal during the SON season. In addition, an increased potential for a continued active hurricane season further support these increased odds for above-normal precipitation. As such, no drought development is likely.

Forecast confidence is high for Puerto Rico.


Forecaster: Adam Hartman

Next Seasonal Drought Outlook issued: September 17, 2020 at 8:30 AM EDT