Latest Seasonal Assessment -
Although the water supply situation in drought-affected areas of the West is not expected to change significantly
before the snowpacks start to build in late fall or early winter, the seasonal outlook does show limited improvement
over large parts of the Rockies and the Plains, as well as relatively greater improvement in the Northwest and
Alaska. Most of the Southwest will see persisting drought into November. The winding down of the monsoon during the
forecast period reduces the odds for improvement as much of the Southwest and southern Great Basin enter a seasonally
drier period. In contrast, cool, wet weather expected from late August into early September farther north and east
should boost soil moisture, benefit grasslands, reduce the wildfire threat, and limit the need for irrigation
water. Prospects for improvement are relatively greater in the Northwest, where both short-term rainfall and the
typical increase in storm activity expected by the end of November contribute to the likelihood for increased
moisture. In Alaska, the trend toward cooler weather and the prospects for increased storm activity as winter
approaches should reduce the fire danger, which has been the main drought impact this summer. Although a weak El
Niño is likely this fall and winter, impacts should be minor going into late autumn. El Niño's do not guarantee
drought improvement but, if an El Niño persists into winter, there should be a slight increase in the chances for
above-normal precipitation and increased streamflows over the Southwest this winter and early spring.
Tools used in the Drought Outlook included the official CPC long-lead precipitation outlook for
September-November, the drought termination and amelioration probabilities for November, various medium
and short-range forecasts and models such as the 6-10 day and 8-14 day forecasts, and the soil moisture tools based on the GFS model and
the Constructed Analogues for the season.
The drought forecast for the interior West considers the wet and cool conditions forecast by the medium-range
products as the broad upper air trough retrogrades westward during the next week. The most recent runs from the
GFS model have been consistent in showing a tendency for an upper level trough to be located near the West Coast
or the interior West into early September. The 2-week soil moisture forecasts based on the GFS model show
significant increases in moisture over the Northwest into western Montana and southward into northeastern
Nevada, northern Utah, and western Wyoming, and northern Colorado. The forecast only shows limited improvement
for much of this area because rainfall during late summer and early fall is not very critical to the long-term
water supply situation, since significant snowpack rarely builds up before late November. Nevertheless, the forecast
moisture and unseasonably low temperatures should benefit the wildfire situation and enhance growth of grasslands
while reducing the need for irrigation, resulting in less use of reservoir storage. The areas with the greatest
chance for improvement, as shown in Washington, western Montana and central Idaho, tend to begin to experience
seasonal precipitation from winter-like storms by the end of November, so there are prospects for improvement from
both a short and long-term perspective. However, little improvement to the reservoir situation by late November
can be anticipated in the areas shown as improving in Montana and Idaho.
In the Southwest, the latter stages of the monsoon will provide some scattered heavy rains in this area during the
forecast period, but the odds for overall drought improvement tend to diminish during autumn. Climatologically,
southern California usually does not see much drought improvement before December. Drought is largely expected to
persist for the southern Great Basin and over the Southwest from Southern California into Arizona.
In Alaska, the seasonal drop in temperatures along with increased storm activity should ease drought in the eastern
part of the state, where several large fires were still burning as of mid-August.
Elsewhere, the first half of August was abnormally dry in several areas in the central and interior eastern parts of
the country, including east Texas and much of Illinois, Indiana, and Nebraska, but there were no strong indications
from the long-range or medium-range forecasts that drought would develop in any of these areas.
A weak El Niño is expected to develop shortly, but El Niño impacts are expected to be either too weak or too ambiguous
to be considered a major part of the outlook through November. If an El Niño does develop, its potential impacts
should be increasingly important for future drought outlooks as winter approaches. Traditionally, an El Niño tends to
improve drought conditions in the Southwest, but improvement can be limited, as seen during the last event in 2002-2003.
See the Climate Prediction Center's latest long-lead seasonal outlooks for the current thinking on the precipitation
outlook through winter and beyond.