Tools used in the U.S. Monthly Drought Outlook (MDO) included the updated Climate Prediction Center (CPC) temperature and precipitation outlooks for August, 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), Week 3-4 outlooks, CFSv2 monthly forecasts of temperature and precipitation, the 384-hour total precipitation forecasts from several runs of the GFS, climatology for August, and recent precipitation. The July 25 U.S. Drought Monitor (USDM) was used to identify existing drought areas (D1 or drier) in the MDO. For consistency, MDO regional write-ups will be based upon the 7 regions in the U.S. Drought Monitor summary.
In the Northeast, only a few small areas of D0 existed on the 7/25 USDM (Maine, Long Island, southeast WV). Moderate to heavy (2-6 inches) rains fell on much of the mid-Atlantic during late July, eliminating concerns of D0 development. Although the most recent 7-day QPF shows little or no precipitation for coastal New England and in southeast WV, the 6-10 day ERF tilts toward above-median precipitation and subnormal temperatures for the Northeast, and EC for both temperature and precipitation for the 8-14 day ERF. EC precipitation is also favored in the Week 3-4 outlooks and 1-month LLF. With no consistent indication for subnormal August precipitation, drought development was not expected in the Northeast.
Forecast confidence for the Northeast is moderate (coastal New England) to high (mid-Atlantic).
In the Southeast, D0 encompassed parts of Virginia and a small area around Wilmington, NC. Moderate to heavy (1.5-3 inches) rains during late July fell on most of Virginia except extreme south-central sections, and will probably lead to some D0 removal in central Virginia in the next USDM. Light to moderate rains also occurred near Wilmington, NC. Although the 7-day QPF has light precipitation in northern sections of the Southeast (with heavy rains along the Gulf and southern Atlantic Coasts and in Florida), the 6-10 and 8-14 day ERFs have EC precipitation but favor subnormal temperatures, Week 3-4 tilts toward above-normal temperatures and precipitation, and EC August temperature and precipitation. With mixed but more so wet precipitation signals in the Southeast during August, no drought development was made.
Forecast confidence for the Southeast is moderate (Virginia) to high (rest of region).
In the South, small areas of D1 and D2 existed in parts of Oklahoma and Texas due to spotty rains and above-normal temperatures during the past 30- and 60-days. Light to moderate rains have fallen on parts of the Texas and Oklahoma Panhandles during late July (after the 7/25 USDM cutoff time), while the 7-day QPF was forecasting 1-3 inches of rain in most of western Texas and Oklahoma. The 6-10 and 8-14 day ERFs, Week 3-4, updated 1-month and 3-month LLFs all showed enhanced chances for above-median precipitation. With a good precipitation consensus in all of the forecasts out to a month, drought improvement or removal is likely in the southern Plains. Farther east in the lower Mississippi Valley (LA, MS, AR), no D0 or drought was present in the 7/25 USDM, but 30-day shortages appeared across southern Arkansas, northern Mississippi, and northeastern Louisiana. At longer time periods, however, conditions were wet, so it would take additional prolonged subnormal August precipitation before abnormal dryness or drought develops. Based upon the QPF, ERFs, Week 3-4, and updated 1-month precipitation LLF, the guidance favors submedian precipitation early in the month but above-median rainfall later on. With mixed precipitation signals, no development is expected in the lower Mississippi Valley by the end of August.
Forecast confidence is moderate to high in the southern Plains and lower Mississippi Valley.
In the Midwest, drought was limited to northwestern Minnesota and across parts of Iowa in association with the drought extending southward and eastward from the northern Plains. Abnormal dryness also existed across the remainder of Iowa, parts of Missouri into central Illinois, and southeastern Michigan. The August precipitation climatology is fairly wet in Iowa and Minnesota and less so farther east. Based upon July 25-30 rains (mostly dry except for light to moderate rains in southwestern Minnesota, western Iowa, and central sections of Missouri and Illinois), the 7-day QPF (1-3 inches in southern Minnesota and northwestern Iowa), 6-10 day ERF (subnormal temperatures and near- to sub-median precipitation odds), 8-14 day ERF (subnormal temperatures and near- to above-median precipitation chances), and EC at both Week 3-4 and the updated August precipitation, the MDO consensus was to show some improvement in western Iowa (in association with improvement in the High Plains southeastern South Dakota and Nebraska) but persistence across the rest of Iowa and northwestern Minnesota as the tools and outlooks were not convincing enough to depict improvement there. Fortunately, with the odds favoring subnormal temperatures during the first half of August, any dryness that may occur would be tempered by the cool conditions. In addition, the mixed precipitation signals in the Ohio Valley are not enough to show drought development in the existing D0 areas. The forecast confidence, however, is low as summertime convection is difficult to predict due to the variability of areal coverage and widely-varying amounts.
Forecast confidence is low for the Midwest (northwestern Minnesota and Iowa).
In the northern High Plains, drought has continued to expand and intensify southward, eastward, and westward since the last MDO (and the 6/27 USDM). A 1-class degradation has occurred across most of Montana (with some 2- and 3-class downgrades in northeastern sections), western North Dakota, most of South Dakota and Nebraska (including some 2-class degradations), and central Kansas. In contrast, a few pockets of above-normal 30-day rainfall allowed for a one category improvement in small areas of eastern North Dakota, north-central South Dakota, and southern Nebraska. Unfortunately, the precipitation climatology for the northern Plains begins to dry out after August as the fall months are typically dry, thus hope for improvement in the near future greatly decreases after August. As mentioned in the Midwest summary, however, late July rains and the 7-day QPF does show some promise of relief in southern and eastern sections with 1-3 inches of rain in central parts of Kansas and Nebraska, the eastern Dakotas, and most of Minnesota. The ERF precipitation odds are mixed, with sub-median amounts at 6-10 days but near- to above-median at 8-14 days, and both ERFs with good odds for subnormal temperatures. The Week 3-4 is mainly EC for both temperature and precipitation, while the updated August precipitation tilts slightly sub-median in northwestern areas (Montana and western North Dakota), and EC elsewhere. Therefore, with a drier August climatology in western areas, lower chances for above-median precipitation during August and a more intense and longer drought in northern sections, persistence was forecast for much of the northern Plains. Farther south, however, with recent rains, favorable short-term forecasts for precipitation, good odds for subnormal temperatures during the first half of August, and more of a shorter-term drought, some improvement was made in southern sections (southeastern South Dakota, Nebraska, and Kansas).
Forecast confidence is moderate for the northern High Plains (Montana and Dakotas) and low in the central High Plains (Nebraska and Kansas).
In the West, August typically brings abundant albeit scattered monsoonal showers, with some areas of Arizona, New Mexico, and southern Colorado receiving 11.5% up to 26% of their ANNUAL precipitation. During the past 30-days, monsoonal showers have been frequent and with above-normal totals across most of Arizona, southern halves of Nevada and Utah, most of Colorado, and parts of New Mexico, bringing a 1-category improvement to some areas. The 7-day QPF forecasts moderate to heavy (1-3 inches) rains across most of Arizona, New Mexico, western Texas, and Colorado, with minimal rains in Nevada and Utah. Odds favor above-median rains from Arizona and Nevada eastward toward mid-month, along with the updated 1-month LLF (Week 3-4 precipitation was EC). Farther west, August is normally drier in southern California as compared to areas to the east, thus is not typically affected by the monsoon. Farther north, recent dryness and warmth has impacted pastures and ranges in western Montana, leading to the recent introduction of D1 there. With the QPF showing no precipitation, nearly all of the forecasts favoring dryness, and most outlooks tilting toward above-normal temperatures, additional degradation is possible, hence the development in western Montana. Farther south, based on the climatology, recent rains, short- and medium-term forecasts, and updated August and the ASO precipitation outlooks, drought removal is expected in central Utah and southeastern Arizona, with persistence anticipated to the west (southwestern Arizona and southern California).
Forecast confidence is high for the West (southern California), and moderate in southern Arizona, central Utah, and western Montana.
In the OCONUS (Alaska, Hawaii, Puerto Rico), abnormal dryness and drought has increased in coverage across Hawaii during July, with drought covering nearly all of the Big Island, Maui, and western Molokai. The summer months are normally a dry time of year, changing during the Fall when the trade winds typically increase and enhance showers on the windward sides. A wild card during August would be moisture from a Pacific tropical system (like last year). But without any signs of an impending tropical system, persistence is forecast to the end of August. In Alaska, precipitation normally increases during the summer, with July and August the wettest months of the year, and JAS the wettest season (3-months). Precipitation rapidly decreases during the fall months in most locations except the far southeastern Panhandle, so the best time for drought relief is now. With most medium- and long-range outlooks tilting toward above-median precipitation, drought elimination in southwestern sections should occur by the end of August. In Puerto Rico, recent dryness along southern sections led to the introduction of D0. With the summer months normally rainy due to Atlantic tropical systems and increased convection, and a forecast for above-normal Atlantic tropical activity, development of drought in Puerto Rico is unlikely by the end of August.
Forecast confidence for the OCONUS is moderate for Hawaii, and high for Alaska and Puerto Rico.
Forecaster: David Miskus
Next Monthly Drought Outlook issued: August 31, 2017 at 3pm EDT