Tools used in the U.S. Seasonal Drought Outlook (SDO) included the official Climate Prediction Center (CPC) temperature and precipitation outlooks for August through October (ASO) 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 August and ASO season, and initial conditions (the 7/18/2017 U.S. Drought Monitor). ENSO-neutral conditions are likely into the Northern Hemisphere 2017-18 winter.

Currently, no drought (albeit a few small D0 areas) exists on the latest Drought Monitor in the Northeast (New England and mid-Atlantic) and Southeast regions, and no drought is forecast to develop in any specific areas within these regions; however, due to medium- to long-term precipitation shortfalls in parts of coastal New England, the mid-Atlantic, and small areas of the Southeast, these areas will be monitored closely over the next few months as periods of heat and sub-normal precipitation could cause drought to develop and intensify quickly. At this time, a warmer-than-normal August and ASO period is forecast, with rainfall expected to be near or above normal through the last half of July and no tilt of odds (EC) toward either wetness or dryness for August and ASO in the Northeast and Southeast, except for some ASO wetness in AL, GA, and the southern Appalachians. In addition, the wild card factor of an Atlantic or Caribbean tropical system(s) is always possible during ASO.

Confidence is moderate for the Northeast and Southeast regions (eastern third of Nation).

Variable precipitation and near-normal temperatures during the past 30-days allowed for a mixture of drought improvement and deterioration in the South, although overall, more degradation occurred, especially in western Oklahoma and the Texas Panhandle. Fortunately, the climatology is wet in Texas and Oklahoma during September and October (less so in August), and wet for ASO in western Texas and Oklahoma. Although the 7-day QPF is mostly dry, the ERFs favor near- to above-median rainfall, as does the Week 3-4 and ASO precipitation outlooks. Although conditions may degrade in the short-term, there are enough tools in the medium- to long-term that suggest improvement should be expected by the end of October across Texas and Oklahoma, along with no drought expected to develop in the lower Mississippi Valley (AR, LA, MS).
 
Confidence is moderate for the South region.

Similar to the Northeast and Southeast regions, the past 30-days brought wet and cool conditions to most of the Midwest, effectively erasing or easing drought and abnormal dryness throughout much of the region.  As of the 7/18 USDM, there were no drought (D1 or drier) areas east of the Mississippi River; instead, only some areas of D0 were found in Illinois and southern Michigan. In contrast, conditions were mostly drier west of the Mississippi River since mid-June, with subnormal precipitation occurring in portions of Minnesota, Iowa, and Missouri (plus central Illinois). Fortunately, temperatures averaged below normal during the period, tempering agricultural impacts as evapotranspiration rates were lower than usual. Nevertheless, drought expanded (but also decreased) in parts of Iowa while decreasing in northwestern Minnesota. With no official guidance to go on from the August and ASO precipitation outlooks (EC), the drought outlook forecast relied on current conditions and trends, short-term forecasts (7-day QPF), climatology (wet during July-September, but October dry), and experimental 1- and 3-month drought and soil moisture forecasts (NLDAS – 3 models, MSU using CFSv2 and ESP-based, NASA GEOS5, SPI3 from 6 NMMEs), with the drought models all showing gradual improvement for the northern and central Plains by late October. As a result, no development is expected in the Midwest (although in the short-term some drought could occur in Illinois and increase in Iowa), while improvement is expected in Minnesota and Iowa by the end of October.

Confidence is moderate in eastern sections of the Midwest, low to moderate in western areas.

Since the spring and summer months are normally a wet time of year for the High Plains, especially the northern Plains, the lack of substantial precipitation, windy conditions, and occasional heat rapidly spread and intensified the abnormal dryness (D0) in the central Dakotas in mid-May to envelop most of North and South Dakota as well as eastern Montana and northern Minnesota by mid-July with drought (D1-D4).  Unfortunately, their wet season gradually ends by August, and October is rather dry throughout the northern and central Plains, thus limiting when substantial precipitation can usually occur. Similar to the Midwest where there was no official guidance from the 1- and 3-month precipitation outlooks (EC), this outlook relied on current conditions and trends, short- and medium-term forecasts, climatology, and the experimental 1- and 3-month drought and soil moisture forecasts. Unfortunately, with the short- and medium-term forecasts all pointing toward sub-median precipitation and above-normal temperatures, a climatology with decreasing precipitation into October, and no clear cut forecasts that showed improvement for the northern Plains (except for the experimental models), persistence was left in eastern Montana and the western Dakotas. Improvement was made to the eastern Dakotas as more favorable conditions, climatology, and forecasts (see Midwest) lend themselves for improvement than in western areas, albeit the confidence was low. It is possible, however, for the northwestern High Plains to show improvement by the end of October since northeastern Montana, western North Dakota, and north-central South Dakota are at D3 (2-5%ile) and D4 (0-2%ile), and near normal precipitation could easily bring percentiles up to D2 (5-10%ile) and D3 (2-5%ile) in the near future, although impacts and drought would still linger into the fall.

Confidence is low in the eastern High Plains, low to moderate in the western High Plains.

In the West, May into early July is typically dry and warm, with no significant rainfall expected during this time (from end of the winter wet season to start of summer monsoon). Fortunately, drought was limited to small sections of the Southwest as this year’s extremely wet winter effectively erased drought from much of the West.  Excessive heat (30-day temperatures averaging 4 to 8 degF above normal), however, plagued much of the western quarter of the Nation since mid-June, expanding abnormal dryness across much of the Southwest and Four Corners region, including the introduction of a few small D1 areas.  Mid-July through September, however, is a very wet time of year across most of the Southwest, with over half of annual rainfall typically falling during the JAS period in the drought areas east of Yuma, AZ (October is much drier). Farther west, southern California typically receives little if any monsoonal rainfall, especially outside far southeastern areas. In addition to a wet climatology, the forecast is also based upon wet short (7-day QPF) and medium-term (6-10 and 8-14 day ERFs) forecasts, a wet August precipitation forecast, and current conditions (widespread monsoon showers). Therefore, with such overwhelming support, improvement is expected in the Southwest (southern Arizona, Utah, southwestern New Mexico), but persistence for southern California where the climatology is drier and in southwest Arizona where precipitation forecasts have lower odds for wetness. Farther north in the northern Rockies (northwestern Montana), recent dryness plus heat has greatly degraded conditions, and with no expected precipitation in the near future plus slight odds for sub-median ASO precipitation in the Northwest, drought development was added to this area where D0 already existed.
 
Confidence for the West is moderate (Southwest and northwest Montana) to high (southern California).

Drought developed across interior southwestern Alaska in early June and has lingered, with USGS June stream flows among the lowest on record in this area. Fortunately, the summer is a relatively wet time of year there, with 40-50% of the annual precipitation typically observed. In addition, there are enhanced chances for above-normal precipitation in western Alaska in both the 6-10 and 8-14 day ERFs and the 1- and 3-month precipitation LLFs. Furthermore, previous Alaskan spring droughts have been alleviated by October, thus the forecasts and past drought history gives high confidence for improvement by the end of October. Drought also covers most of the western Big Island of Hawaii, where removal is anticipated in climatologically wetter sections across the windward (eastern) locations, especially as the fall approaches, and persistence is forecast at leeward (western) areas. Drought should persist in the northwest portion of the Big Island (leeward South Kohala District) as their start to the wet season (usually October) has been delayed the past 5-10 years, with November and December a more likely time for significant rain. Lastly, a wild card for Hawaii is moisture from Pacific tropical systems (like last year) that could quickly provide drought relief. No drought development is expected in Puerto Rico.
Confidence is high in Alaska and moderate in Hawaii.

Forecaster:  David Miskus

Next Seasonal Outlook issued: August 17, 2017 at 8:30 AM EDT