August - October 2014

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Latest Seasonal Assessment - Widespread June rainfall over the Plains and Corn Belt continued to improve drought conditions across Iowa, Nebraska, Kansas, Oklahoma, and Texas. In contrast, severe to extreme drought expanded across New Mexico and southern Colorado due to somewhat poor coverage of monsoon convection. Abnormal dryness expanded across the Southeast, Tennessee Valley, and southern Mid-Atlantic due to short term dryness, and abnormally hot conditions over the western States exacerbated ongoing drought conditions. In addition, suppressed convection over the Caribbean basin promoted expansion of abnormal dryness and moderate drought in southern and eastern Puerto Rico.

The seasonal drought outlook valid for July 17 through October 31, 2014 is based on analysis of initial conditions, short-, medium-, and long-range outlooks, and climatology. Climate anomaly composites based on El Niño conditions were also considered, though these impacts typically become more pronounced during the winter, after the outlook period. Decreased soil moisture due to below normal rainfall increases the potential for rapid drought development across parts of the Southeast, southern Mid-Atlantic States, and the Tennessee Valley. An anticipated wet pattern during the latter half of July, however, may mitigate the development of drought conditions, so no areas of development were included in this outlook. Recent locally heavy rainfall over southeastern Kentucky in addition to this wet forecast may result in removal of D1 conditions. Drought development is favored across southern and southeastern Texas, based on recent below average precipitation and a tilt towards dryness in the 8-14 day, monthly, and seasonal outlooks. Persistence is forecast across central Texas, while short term forecasts of heavy rainfall along a frontal boundary, as well as enhanced probabilities for above-median precipitation during the seasonal period, increase the potential for drought improvement or removal across far north Texas and the remainder of the Plains. Monsoon convection across the Four Corners states is anticipated to bring areas of localized drought relief. Across the West, drought persistence is forecast through the end of October based on climatological dryness, and additional development is possible over parts of the Northwest due to a forecast continuation of abnormally hot conditions. A dry climatology favors persistence of remaining drought in Molokai, Hawaii, while a low frequency tropical convective climate signal (trending towards El Niño conditions) is anticipated to continue a regime of suppressed convection across the Caribbean, favoring continued drought degradation across Puerto Rico.

Tools used in the U.S. Seasonal Drought Outlook (SDO) included the official Climate Prediction Center (CPC) temperature and precipitation outlooks for August 2014 and August–October 2014, various short- and medium-range forecasts and models such as the forecast 5-day and 7-day precipitation totals from the Weather Prediction Center (WPC), the 6-10 day and 8-14 day CPC forecasts, the NAEFS precipitation outlooks, the soil moisture tools based on the Constructed Analog on Soil Moisture (CAS), dynamical models (CFSv2, NMME, IRI, and IMME), the 384-hour total precipitation forecasts from several runs of the GFS, the four-month Palmer drought termination and amelioration probabilities, climatology, and initial conditions. An El Niño Watch is currently in effect, with the July 10 ENSO update indicating an almost 70% chance of El Niño during the summer season.

Recent rainfall deficits and decreasing soil moisture promoted the rapid expansion of abnormal dryness (D0) across eastern Alabama, Georgia, the Carolinas, southern Virginia, Tennessee, and Kentucky. Additionally, small areas of moderate drought (D1) developed during the past month across parts of the southern Appalachians. Widespread thunderstorms across the Southeast on July 15 brought localized relief to southeastern Alabama, south-central Georgia, and the Carolinas; however, 14-day rainfall deficits exceeding 2 inches remained along the border between central Georgia and Alabama. The greatest short term rainfall deficits extend across the Florida Panhandle, though surpluses remain on a longer time scale (90 days). Agricultural demands and high evapotranspiration rates are normal during the summer; a continuation of below-normal precipitation over these areas could result in rapid drought development. During the remainder of July, a mean frontal boundary extending across the Southeastern U.S. is forecast to provide focus for widespread precipitation. The 12Z July 16 7-day precipitation outlook from the WPC indicates widespread precipitation totals exceeding 1 inch across the Southeast, with potentially greater amounts across South Carolina. The CPC 8-14 day outlook also indicates enhanced chances for above-median precipitation across the entire eastern U.S. The August monthly outlook, however, tilts the odds towards below-median precipitation across the Gulf Coast and southern Appalachians. The 3-month outlook valid for August-September-October (ASO) provides no signal. It is possible that rainfall during late July may mitigate the potential for drought development. Any areas where precipitation deficits remain by the end of July, however, are at risk for drought development during August. Since climatological precipitation decreases over the Southeast during the fall, any drought areas that develop during August may persist through the remainder of the forecast period. Based on the potential for widespread precipitation during the remainder of July, no areas of drought development are indicated in this outlook, but persistence is indicated for existing drought across eastern Tennessee. Improvement is forecast for eastern Kentucky, where recent locally heavy rainfall has increased moisture. Drought development will be considered for the August monthly drought outlook across any areas where significant rainfall deficits remain by the end of the month.

Forecast confidence for the Southeast, the southern Mid-Atlantic States, the southern Appalachians, and the Tennessee Valley is low.

During the past 30 days, above-normal rainfall fell across the Texas Panhandle and parts of north central Texas, while generally below-normal rainfall was observed across central, southern, and eastern Texas. Drought improvements occurred where precipitation amounts were near to above normal, however, moderate to severe drought (D1-D2) developed across far southern Texas, and abnormal dryness (D0) expanded across the northeastern part of the state. During the upcoming week, areas of soaking rains are forecast to push southeast across much of northern Texas. The WPC outlook indicates widespread accumulations exceeding 2 inches during this period, with some areas exceeding 3 inches. In contrast, the CPC 8-14 day outlook indicates enhanced odds for below median precipitation. The August monthly outlook continues the enhanced chances for below median precipitation across eastern Texas, while maintaining equal chances for near, below, or above-median precipitation for the rest of the state. The ASO seasonal outlook tilts the odds towards above median precipitation for northern and western Texas, while maintaining enhanced chances for below along the Gulf Coast. Based on these outlooks, drought improvement is anticipated across far northern Texas, while persistence is maintained elsewhere. Drought development is possible across southern and southeastern Texas as well. Drought improvement is possible across far western Texas due to monsoonal activity.

Forecast confidence for Texas is moderate.

Across the remainder of the southern and central Plains and the Corn Belt, widespread rainfall during the previous 30 days promoted areas of drought relief across Iowa, Nebraska, Kansas, and Oklahoma. In contrast, small areas of abnormal dryness developed across far eastern Oklahoma and parts of South Dakota, where precipitation deficits remained. During the upcoming week, a swath of widespread rainfall is forecast from southeastern Colorado and western Kansas through Oklahoma and the southern Mississippi Valley. The heaviest rainfall is expected in southern Oklahoma, where localized amounts exceeding 5 inches are possible. The forecast rainfall, and recent moisture increases are anticipated to result in continued drought reduction across the central and south-central Plains. Although the CPC 8-14 day outlook indicates enhanced chances for below median precipitation, the seasonal outlook tilts the odds towards above-median precipitation across the Plains.

Forecast confidence for the remainder of the Plains is moderate.

Monsoon convection was widely scattered during June and early July, bringing little relief to drought areas across Utah, Arizona, New Mexico, and southern Colorado. Extreme drought (D3) expanded across parts of New Mexico, while moderate drought (D1) developed over south-central Colorado. Monsoon activity is not anticipated to increase during the remainder of July. The CPC 8-14 day outlook tilts the odds towards below median precipitation across the Four Corners states. Longer range tools, however, support the potential for more robust monsoon convection during the remainder of the season. The CPC monthly and seasonal outlook both maintain enhanced chances for above median precipitation across the Southwest monsoon regions. Enhanced sea surface temperatures across the eastern Pacific may promote enhanced tropical cyclone activity, which can aid surges of Pacific moisture into the Southwest. September and October remain a relatively wet time of year for eastern monsoon areas (New Mexico, Colorado, and western Texas), whereas the monthly percent of annual precipitation drops significantly across Arizona and southern California by October. Therefore, drought improvement is indicated across Utah and Arizona along a line consistent with where the CPC August outlook maintains a greater than 40% chance of precipitation falling in the upper tercile. Across Texas and New Mexico, drought improvement is indicated for areas where the CPC ASO seasonal outlook maintains a greater than 40% chance of enhanced precipitation. Since the forecast is based on convective monsoonal precipitation, drought improvements are likely to be localized in nature, with wide variability of impacts across the region.

Forecast confidence for the Four Corners States is moderate.

Mostly dry weather continued across the West, which is seasonable. Periods of hot weather, however, exacerbated drought conditions across parts of California, Nevada, Oregon, and Washington. During the upcoming week, widely scattered thunderstorms may produce localized flash flooding across parts of the western Great Basin, while abnormally hot weather is forecast to continue. Near to below-median precipitation is anticipated during the 8-14 day period, while above normal temperatures are favored across parts of Nevada and California. The CPC 1- and 3-month outlooks both tilt the odds towards above median temperatures across the West, with the August outlook maintaining odds greater than 50% for monthly temperatures in the upper tercile across parts of northern California, northwestern Nevada, central Oregon, and south-central Washington. Based on these temperature outlooks, further drought degradation is possible, with additional development favored across parts of the Northwest. Despite the potential for El Niño development during the fall months, climatological precipitation remains very low through the end of October, so drought improvement is unlikely.

Forecast confidence for the West is moderate to high.

A small area of moderate drought (D1) remains on Hawaii’s Molokai Island. The summer months are climatologically dry for this region, and reservoir levels have begun to drop. The CPC August monthly outlook indicates no shift in precipitation probabilities, while the ASO outlook only slightly favors above-median rains. Although there is a correlation between El Niño conditions and below-normal rainfall across Hawaii, this relationship is more pronounced during the winter months than in the fall. Based on climatology, current conditions, and outlooks, drought persistence is anticipated.

Forecast confidence for Hawaii is moderate to high.

CPC analyses of 10-day OLR (outgoing longwave radiation) anomalies indicate that a regime of generally suppressed convection has persisted over the western and central Caribbean during the past 60 days. The dry weather has promoted development of abnormal dryness and moderate drought (D0-D1) across much of southern and eastern Puerto Rico. A plume of tropical moisture associated with a mid-level trough brought widespread rainfall to northwestern Puerto Rico during mid-June, increasing soil moisture in that region. CFS precipitation anomaly forecasts for the upcoming three months indicate a potential for continued near to below normal precipitation across the Caribbean basin. This forecast is consistent with the low frequency tropical convective signal that is gradually evolving towards El Niño conditions. Based on this outlook, drought persistence and development is anticipated across southern and eastern Puerto Rico.

Forecast confidence for Puerto Rico is moderate to high.