Tools used in the U.S. Monthly Drought Outlook (MDO) included the official Climate Prediction Center (CPC) updated temperature and precipitation outlooks for August 2014, various short- and medium-range forecasts and models such as the 5-day and 7-day precipitation totals from the Weather Prediction Center, 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 (CAS) moisture, dynamical models (CFSv2, NMME, IMME, and IRI), the 384-hour total precipitation forecasts from several runs of the GFS, climatology, historic modeled soil moisture changes during the month, June 24-30 observed precipitation (not included in the July 29 Drought Monitor analysis), and initial conditions.
During the previous 30 days, areas of thunderstorms yielded above-average rainfall and improved abnormally dry conditions across parts of southeastern Alabama, central Georgia and the Carolinas. Other parts of the Southeast missed out on significant rainfall, however, especially southern Georgia, northern Florida, and central and southern Alabama, where some locations received less than 25 percent of normal rainfall for the month (corresponding to more than 4 inches below normal rainfall in some locations). The dryness prompted the expansion of abnormal dryness (D0) and the introduction of small areas of moderate drought (D1) over central Alabama and southern Georgia on the July 29 U.S. Drought Monitor. Although D0 conditions were expanded into the Florida Panhandle, moisture surpluses from an excessively wet spring offset the shorter term dryness, slowing the advance of drought conditions. Based on these dry initial conditions, the region is vulnerable to continued drought development during August if there is a continuation of below normal rainfall. Cotton, peanut, and corn crops all require substantial moisture during August for proper development, and the latest Weekly Weather and Crop Bulletin (published by the USDA) noted reports of crop stress in southern Georgia. During the upcoming week, showers and thunderstorms along a frontal boundary are likely across the Southeast, although the focus for heaviest rainfall is expected to be along the Atlantic coast. The WPC 7-day QPF outlook indicates a potential for 1-2 inches of rainfall across southern Georgia and Alabama, which would be timely but insufficient to erase short term deficits. The CPC 8-14 day outlook places southern Georgia in an area of anticipated near normal rainfall between a forecast favoring below-median rainfall across the Florida peninsula and above-median rainfall across the Piedmont, southern Appalachians, and interior Southeast. The CFS August outlook favors below normal rainfall, although the updated CPC monthly outlook maintains equal chances for below, near, or above-median precipitation. Downstream impacts from one or more recurving typhoons in the western Pacific may promote a return to a highly amplified pattern with frontal intrusions into the southern U.S., but it is too soon to determine where any areas of heavy rainfall would set up. Based on the dry initial conditions across southwestern Georgia, southeastern Alabama, central Alabama, and west-central Georgia, and a lack of a clear signal favoring enhanced precipitation during August, this outlook favors drought development for existing D0 areas.
Forecast confidence for the Southeast is low.
During July, below normal rainfall (25-75 percent of normal) fell across much of Missouri and southwestern Illinois as an unusually amplified pattern suppressed seasonal convection to the south. Periods of below normal temperatures reduced the rate of evapotranspiration, which aided maintenance of soil moisture levels for agricultural needs. Further east, much below normal rainfall promoted the development of moderate drought (D1) across western Kentucky and far northern Tennessee. The dry initial conditions increase the potential for drought development across Missouri during August during any periods of below normal rainfall or above normal temperatures. While little rainfall is indicated by the WPC 7-day QPF outlook, the CPC 6-10 and 8-14 day outlooks both tilt the odds towards above-median rainfall during the first half of August. The CPC updated August outlook tilts the odds towards below median temperatures as well, which would help to ease stress on crops. While below normal temperatures over Kentucky and Tennessee would help prevent a rapid degradation of drought conditions, the incipient dryness and short term forecasts indicating a continued dry pattern make further degradations likely. Therefore, drought persistence is forecast across west-central Missouri, with no additional development, while drought development is forecast for existing D0 areas in western Kentucky and northern Tennessee.
Forecast confidence for the Midwest and the Ohio and Tennessee Valleys is low.
During July, several heavy rainfall events boosted moisture across northern and eastern Texas, Oklahoma, and southwestern Kansas. Drier conditions prevailed across western and southern Texas and the remainder of Kansas. Late in the month, another heavy rainfall event brought significant rainfall to much of Oklahoma, boosting soil moisture in regions that have experienced a multi-year drought. During the upcoming week, additional rainfall is forecast across far western Texas, the southeastern Plains, and the Mississippi Valley. The CPC 8-14 day outlook maintains enhanced chances for a wet pattern over the south-central Plains, while below normal precipitation is favored for South Texas. The updated August outlook tilts the odds towards above median precipitation across the south-central Plains as well, due to an anticipated continuation of frontally enhanced rainfall with monsoon interactions. Based on these outlooks, continued drought improvement or removal is forecast for much of Kansas, Oklahoma, and northern Texas. Persistence is anticipated across the remainder of Texas, while development is forecast for southern Texas. Drought persistence is also favored for a thin stripe across the drought areas in southern Nebraska, northern and eastern Kansas, and western Missouri as the mean frontal position is expected to remain generally south of these areas.
Forecast confidence for the southern and central Plains is moderate.
While late spring brought widespread heavy rainfall to the northern Plains, conditions were drier during July. Soil moisture remained adequate in most areas due to the earlier precipitation; however, pockets of moderate drought (D1) developed over northeastern Nebraska and southeastern South Dakota, where 30-day rainfall deficits were the greatest. Light to moderate precipitation is forecast during the upcoming week, with accumulations generally below an inch. The CPC 8-14 day outlook indicates near normal rainfall through mid-August. An anticipated continuation of below-median temperatures favors reduced evapotranspiration, which would help to prevent rapid drought expansion. A continuation of rainfall deficits during August, however, would promote gradual drought expansion over existing D0 areas in southeastern South Dakota and northeastern Nebraska.
Forecast confidence for the north-central Plains is moderate.
Enhanced monsoon activity and upslope flow along a frontal boundary brought widespread heavy rainfall to New Mexico and southeastern Colorado during June, reducing drought conditions that have persisted for years in some areas. On July 29, 3 to 5 inches of rainfall fell across southeastern Colorado and northeastern New Mexico, causing localized flooding. Monsoon thunderstorms were more widely scattered across much of Arizona and Utah, where drought conditions primarily persisted during the past four weeks. A complicated precipitation pattern, both temporally and spatially, is forecast during August. Additional widespread heavy rainfall is expected during the upcoming week across New Mexico, Colorado, and to a lesser extent southeastern Arizona, which would promote a continuation of drought reduction. However, the CPC 6-10 day outlook favors wetness across Colorado and eastern New Mexico but dryness in western New Mexico and Arizona, and for the 8-14 day period odds are neutral or lean toward favoring dryness throughout the region. Meanwhile, the updated August outlook tilts the odds towards above-median precipitation from central Arizona eastward. Based on these outlooks, further drought improvement is forecast across New Mexico and Colorado, while persistence is more likely for Arizona and Utah.
Forecast confidence for the Four Corners states is moderate across Arizona and Utah, and high across New Mexico and Colorado.
Mostly dry and hot weather prevailed across the West, promoting a northward expansion of extreme to exceptional drought conditions in California, and further degradations over the Northwest. Scattered thunderstorms developed over the Great Basin, although some cells produced numerous lightning strikes with little rainfall, sparking wildfires. The Carlton Complex fire in Washington surpassed the 1902 Yacolt Burn as the largest wildfire in Washington state history, and has burned more than 400 square miles of land while destroying hundreds of homes. Increased thunderstorm activity later in the month provided some assistance to firefighting activities as well as additional lightning strikes. Little change to the pattern is anticipated during the first half of August, with above-median temperatures favored and seasonal dryness continuing. One or more recurving tropical cyclones over the western Pacific may promote a renewed amplification of the downstream pattern, which could yield additional periods of above normal temperatures for the western U.S. The CPC updated August outlook maintains enhanced odds for above-median temperatures across the Pacific states. Based on these outlooks and climatology, drought persistence or intensification is anticipated, with further expansion possible across parts of Oregon.
Forecast confidence for the West is high.
A pattern of suppressed convection continued across much of the Caribbean, promoting continued drought expansion across southern Puerto Rico. A low frequency climate signal evolving towards El Niño conditions favors suppressed convection over the Caribbean and reduced tropical cyclone activity across the central Atlantic. Based on initial conditions and the potential for continued dryness, drought development is anticipated across eastern Puerto Rico.
Forecast confidence for Puerto Rico is high.
A small drought area remains on Hawaii's Molokai Island. August is a climatologically dry time of year, which would promote drought persistence. There is a potential, however, for tropical cyclone activity in the central Pacific to bring enhanced rainfall to parts of Hawaii.
Forecast confidence for Hawaii is moderate.
Forecaster: A. Allgood
Next Monthly Drought Outlook issued: August 31, 2014 at 3:00 PM EDT