Latest Seasonal Assessment -
The first half of September saw abundant rains bringing drought relief to many parts of the country, including the
Southwest, southern Plains, the Rockies, and portions of the central and northern Plains and the Southeast. Indications
are that further improvement will take place over many remaining drought areas in the Great Plains. The odds for
overall improvement during the next season diminish toward the Northwest. Despite good rains expected during the last
half of September for much of the region, as well as below-normal temperatures, drought development by the end of
December remains a distinct possibility over interior parts of the Pacific Northwest, as precipitation during
October-December is expected to be below normal over Washington, Oregon, and Idaho. The progressive seasonal increase
in precipitation should improve the recently-developed drought in western Washington, and the near-term trend toward
wetter and cooler weather should ease the wildfire threat over the Northwest in general. In the Southwest, a record
summer monsoon ended drought over New Mexico and parts of Arizona. Through December, some limited additional
improvement is anticipated over remaining drought areas in Arizona, northwestern New Mexico, and southwestern
Colorado. The expectation that recently-developed El Niño conditions should persist through the end of the calendar
year makes it very unlikely the upcoming snow season will see anything resembling the dearth of snow observed last
winter across the Southwest, and that should benefit water supplies. Elsewhere, some improvement is likely for
drought areas from northeastern Texas into Missouri, and also across the Southeast. In Hawaii, drought has developed
in parts of Oahu and Maui, but heavy seasonal rains should offer some improvement by December.
Tools used in the Drought Outlook included
the official CPC long-lead precipitation outlook for October-December, the four-month drought
termination and amelioration probabilities, 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 Analogue on Soil moisture.
In general, the Drought Outlook is consistent with last month's Outlook in calling for improvement over many areas of the Great Plains, with more limited improvement in the Southeast and from northeastern Texas into Missouri. In the Southwest, the ending of the monsoon, which was one of the wettest on record, should decrease the odds for thunderstorms during this forecast period, but moisture from Pacific tropical weather systems cannot be ruled out for the next several weeks. Later on, Winter storms could loom large in the Southwest and southern Rockies.
The onset of El Niño conditions, which should continue through winter, increases the odds for wetness across the southern tier of the U.S., and this Outlook calls for improvement in Texas as a result. Improving conditions, however, do not necessarily translate into drought elimination, and with low water supplies affecting many areas, it could take a long time and a lot of precipitation to end the drought completely. Farther north, long-range forecast models and El Niño composites show a tendency toward drier weather for the season from northeastern Texas through Missouri, so the Drought Outlook shows more limited improvement in this region despite the wetness forecast for the last half of September. In the Southwest, El Niño conditions usually induce above-normal rain and snow during the winter, but significant additional improvement could be relatively limited through December.
In Washington, drought improvement is forecast west of the Cascades despite the expectation of below-normal precipitation through the end of the calendar year. This is because ample rains are expected during the latter half of September, and because November-December precipitation is typically quite heavy, even when somewhat below normal. However, the climate is drier farther to the south and east, where the forecast for below-normal precipitation for the season can more easily result in drought. The objective drought indicator blends helped to delineate the areas in the Northwest most vulnerable to drought in fall and early winter. These monitoring tools already indicated very dry conditions in the Northwest in September, consistent with the large wildfires reported in the region. There were 34 large fires across the nation on September 19, most of them burning in Washington, Oregon, and Idaho.
The drought indicator blends also implied that relatively little additional moisture is needed to end drought across the eastern Dakotas and northwestern Minnesota, which factored in to a bullish outlook for improvement in these areas, as did wet 2-week forecasts.
In the Southeast, conflicting signals from various short and long-term forecast tools led to the outlook anticipating some improvement. Recent medium-range forecasts showed normal rainfall in parts of the Southeast, and a slight tilt of the odds toward wetness came from a few long range models, such as the CFS.
El Niño conditions tend to be associated with dryness in the Ohio Valley, and this area will be monitored for drought development later in the year. However, current conditions and wet medium-range outlooks argue against forecasting development at this time.
In Hawaii, October and November can bring heavy rain, even during El Niño episodes. If these rains do not develop, however, then winter dryness associated El Niño conditions could induce drought development toward the end of the year.