July 2017 Drought Report

Issued 4 August 2017

Contents Of This Report: National Drought Overview Detailed Drought Discussion Overview Synoptic Discussion Palmer Drought Index Standardized Precipitation Index Agricultural & Hydrological Indices and Impacts Regional Discussion Regional Climate Center Reports Pacific Island Drought State/Regional/National Moisture Status Drought Indicators Contacts & Questions

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Please note that the values presented in this report are based on preliminary data. They will change when the final data are processed, but will not be replaced on these pages.

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National Drought Overview

Based on the Palmer Drought Index, severe to extreme drought affected about 4 percent of the contiguous United States as of the end of July 2017, an increase of about 3 percent from last month. About 9 percent of the contiguous U.S. fell in the severely to extremely wet categories. About 9 percent of the contiguous U.S. fell in the moderate to extreme drought categories (based on the Palmer Drought Index) at the end of July. On a broad scale, the 1980s and 1990s were characterized by unusual wetness with short periods of extensive droughts, the 1930s and 1950s were characterized by prolonged periods of extensive droughts with little wetness, and the first decade of the 2000s saw extensive drought and extensive wetness (moderate to extreme drought graphic, severe to extreme drought graphic).

A file containing the national monthly percent area severely dry and wet from 1900 to present is available for the severe to extreme and moderate to extreme categories. Historical temperature, precipitation, and Palmer drought data from 1895 to present for climate divisions, states, and regions in the contiguous U.S. are available at the Climate Division: Temperature-Precipitation-Drought Data page. These filenames begin with "climdiv". According to the weekly U.S. Drought Monitor, about 11.8 percent of the contiguous U.S., and about 11.0 percent of the U.S. including Alaska, Hawaii, and Puerto Rico, was classified as experiencing moderate to exceptional (D1-D4) drought at the end of July.

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Detailed Drought Discussion

Overview

During July 2017, very few troughs and closed lows moved across the southern CONUS in the upper-level circulation. Although the relative dearth of vigorous low-pressure systems is a common summer occurrence, the overall monthly pattern for July 2017 had even more ridging than normal across the western United States, enhancing this effect. The western ridge resulted in warmer-than-normal conditions across most of the U.S., more dramatically in the West, and in drier-than-normal weather across the Northern Rockies and Northern Plains. The frequent presence of frontal boundaries in the mid-Atlantic and upper Ohio Valley facilitated above-normal precipitation and cooler-than-normal afternoons to those regions. Tropical cyclones played a neglibile role in CONUS July precipitation, with the exception of Tropical Storm Emily, which made landfall very late in the month, and affected an area already devoid of drought. The placement of significant precipitation in areas not experiencing drought led to only very minor improvement of drought during July, generally among and adjacent to the Southern Rockies. In contrast, drought intensification and expansion in the Plains and Northern Rockies was significant, particularly in the areas where above-mornal temperatures and below-normal precipitation coincided.

As of the USDM analysis for July 18^th, Exceptional Drought, or D4, emerged in North Dakota and Montana. This was the first occurrence of D4 anywhere in the Nation since January 2017. For the third consecutive month, the expansion of drought was greater than the contraction, with the USDM-based national moderate-to-exceptional drought footprint across the CONUS increasing from 8.0 percent at the end of June to 11.8 percent by August 1st (from 7.8 percent to 11.0 percent for all of the U.S.).

Percent area of the CONUS in moderate to exceptional drought, January 4, 2000 to present, based on the U.S. Drought Monitor.

Drought conditions at the end of the month, as depicted on the August 1^st, 2017 USDM map, included the following CONUS core drought and abnormally dry areas:

• Abnormal dryness (D0) through extreme (D3) drought generally expanded, and some exceptional (D4) drought was introduced, in the northern Plains — The worsening conditions were reflected in several drought indices and indicators, most notably those related to evapotranspiration (Evaporative Drought Demand Index [EDDI], Evaporative Stress Index [ESI]), soil moisture in the root zone and surface soil moisture. U.S. Department of Agriculture (USDA) reports of soil moisture conditions revealed very dry conditions in the northern Plains. According to July 2^nd USDA reports, 93 percent of the topsoil moisture and 90 percent of the subsoil moisture were short to very short (dry to very dry) in Montana. These same statistics were 79 percent for topsoil and 77 percent for subsoil in South Dakota, 73 percent for topsoil and 66 percent for subsoil in South Dakota, and 62 percent for topsoil and 60 percent for subsoil in Nebraska. The USDA reports indicated that pasture and rangeland were in poor to very poor condition for 78 percent of North Dakota, 71 percent of South Dakota, and 60 percent of Montana.
• Abnormal dryness and some amount of moderate drought (D1) expanded in parts of the Northern Rockies and Northwestern U.S., with short-term drought impacts being more prevalent than long-term drought impacts. Several large wildfires developed in these regions, concomitant with the encroachment of abnormally dry and moderate drought conditions.
• On average, drought conditions worsened slightly in the Southern Plains, with parts of central Kansas, central Oklahoma, and South Texas showing deterioriation.
• Drought improvement was observed in a fairly limited area of the Southwest, stretching from southern portions of Arizona and New Mexico into west Texas.

Palmer Drought Index

The Palmer drought indices measure the balance between moisture demand (evapotranspiration driven by temperature) and moisture supply (precipitation). The Palmer Z Index depicts moisture conditions for the current month, while the Palmer Hydrological Drought Index (PHDI) and Palmer Drought Severity Index (PDSI) depict the current month's cumulative moisture conditions integrated over the last several months. While both the PDSI and PHDI indices show long-term moisture conditions, the PDSI depicts meteorological drought while the PHDI depicts hydrological drought. Through July 2017, the PDSI and the PHDI map show similar depictions for the Nation's major drought areas, while the PHDI displays some lingering long-term wetness and dryness in other areas not picked up by the PDSI.

The Palmer Z Index map show that short-term dry conditions occurred across a wide swath of the U.S. northern tier, into the central Plains and Rockies and in South Texas. This short-term dryness was associated with areas that witnessed drought expansion in the USDM during July.

Standardized Precipitation Index

The Standardized Precipitation Index (SPI) measures moisture supply. The SPI maps here show the spatial extent of anomalously wet and dry areas at time scales ranging from 1 month to 24 months.

The SPI maps illustrate how moisture conditions have varied considerably through time and space over the last two years. July 2017 (the 1-month SPI map) showed contrasting areas of wetness and dryness, generally consistent with areas of above- and below-normal precipitation for the month. The dryness in the northern Plains at the 1-month time scale was a continuation of dryness which extended to the 9-month time scale in places, with a few areas dry at the 24-month time scale. The dryness extended into the central and parts of the southern Plains at the 1- to 3-month time scales, and the early summer dryness in the West is reflected at the 3-month scale as well. Generally, the eastern CONUS is generally ut not unviersally wet beyond the 3-month scale, and the prolific Southeastern drought of mid-to-late 2016 has started to fade from the 12-month SPI analysis. Wetness, in or approaching the extreme, is pervasive at nearly all scales in the immediate vicinity of the Great Lakes, and the summer deluges along the Northern Gulf Coast appear plainly as wetness at the 3-month scale.

Regional Discussion

CONUS Agricultural & Hydrological Impacts:

Drought conditions at the end of July 2017 were reflected in a number of meteorological, hydrological, and agricultural indicators, both observed and modeled. These include: evapotranspiration (EDDI, ESI), and soil moisture (GRACE root zone and surface soil moisture, CPC model, VIC model, SMOS satellite-based analysis).

On a national scale, as of August 1^st, 2017, non-trivial portions of the agricultural areas of the CONUS were affected by drought. Driven largely by the situation in the Dakotas, 16% of corn production was in drought, the largest footprint in more than a year. Drought also affected 16% of soybean production as of early August. One month prior each of the values for corn and soybeans were in single-digit percentages. Approximately 17% of hay acreage was within an area experiencing drought, as well as 15% of cattle inventory and 14% percent of winter wheat production. Each of these were higher than the values for the end of June, reflecting the worsening drought conditions in the Northern Plains, and to a lesser extent, Central and Southern Plains and Northern Rockies.

Hawaii: July 2017 had a mixed precipitation anomaly pattern across the Hawaiian Islands. As was generally the case in May and June, dryness was evident over the southern islands during the last three months. Hilo, in particular, continued its dry 2017 year-to-date, which stood, as of July 31^st as the eighth-driest year-to-date of its 1950-2017 record. At longer time-scales (last 6, 12, 24, 36 months), conditions are generally — with some exceptions — slightly-dry-to-near-normal across most of the Hawai'ian Islands. On the USDM map, drought worsened across northern portions of the Big Island, with more of the island depicted in severe (D2) drought conditions. Moderate (D1) drought was introduced to much of Maui and Moloka'i. Moderate to severe (D2) drought covered 69% of the state's land area as of the August 1^st, 2017 USDM analysis.

Alaska: Record and near-record warmth, combined with near-record to record dryness to expand abrnormal dryness (D0) and introduce some moderate drought (D1) into central Alaska. This drydown in central Alaska continues back to the three-month time scale. The rest of the state remained depicted similarly to the end of June. Notably, snow water equivalent (SWE) of the remaining snowpack, relative to July norms, was quite low at all high-elevation stations in southern Alaska. As of the August 1^st USDM, about 7% of the state was analyzed as experiencing moderate drought.

Puerto Rico: Precipitation anomaly maps for Puerto Rico were not available this month. San Juan had its seventh warmest and 17^th wettest July of its 62-year (19576-2017) record. Soils in southern Puerto Rico continued to dry down, continuing a trend seen in June. The combination of relative warmth and a continued drydown led to the introduction of abnormal dryness (D0), and, later in July, moderate drought (D1) conditions in the southern quarter of the island. By the end of the month, about 7% of the territory was depicted in moderate drought.

CONUS State Precipitation Ranks:

July 2017 was drier than normal across much of the Northwest, Northern Rockies and Great Plains, south Texas and California - although California is typically very dry during July. On a statewide basis, 13 states ranked in the driest third of the historical record with Montana ranking second driest in the 123-year record and Washington fifth driest.

At the 3-month time scale, dryness was evident in the northern and central Plains, Northern Rockies and Northwest. Thirteen states ranked in the driest third of the 1895-2017 record, including Montana and North Dakota, which had their third- and fourth-driest May-July, respectively.

The dryness persisted at the 6-month time scale in the northern Plains, with three states there ranking in the driest third of the historical record. North Dakota had its third driest January-July.

On the twelve-month time scale, only North Dakota had a precipitation in the dryest third of its history, at 31^st driest on record.

NOAA Regional Climate Centers:

A more detailed drought discussion, provided by the NOAA Regional Climate Centers and others, can be found below.

As described by the High Plains Regional Climate Center, July provided little relief to areas dealing with drought this past spring and summer, as most of the High Plains ended the month with below-normal precipitation and above-normal temperatures. The Northern Plains drought continued to spread and intensify, reaching farther across the Dakotas and southward into northern and central Nebraska. Crop stress increased in severity and became more widespread, as much of the corn and soybean crops in this region did not get adequate moisture when it was needed most. Impacts to livestock and ranching were evident during July as well. Pasture conditions worsened, and by the end of the month more than two-thirds of pastureland in the Dakotas was in poor to very poor condition. Furthermore, the quality of water in livestock ponds declined, causing livestock to become ill and die. The USDA approved additional Conservation Reserve Program (CRP) land for emergency haying and grazing to alleviate drought impacts to livestock. Despite the widespread dryness, above-normal precipitation occurred throughout portions of eastern Colorado, central and eastern Nebraska, and eastern South Dakota. These conditions favored the development and intensification of corn disease in some areas. For instance, warm nighttime temperatures and high relative humidity caused the spread of southern rust. Heat was a common feature throughout the High Plains, resulting in several top 10 records for warmest July. Near-record-low relative humidities were reported in areas of drought, especially across portions of Montana, and contributed to the high temperatures as well as exacerbated drought conditions. High temperatures combined with high humidity to create high heat index values and dangerous conditions in the eastern part of the region. July temperatures ranged from near normal in the southern High Plains to 4.0-6.0 °F above normal in the northern part of the region. The greatest departures occurred in the western Dakotas where drought has been present this summer. The majority of the High Plains region was dry during July, and little relief was provided to drought-stricken areas. Less than 50 percent of normal precipitation fell across North Dakota, central South Dakota, the Nebraska panhandle, and much of Wyoming and Kansas. The dryness resulted in Pierre, South Dakota having its 2nd driest July on record, while it was the 5th driest for Cheyenne, Wyoming. Meanwhile, a few areas were particularly wet during July. Monsoon conditions brought excessive precipitation to eastern Colorado, which led to Alamosa and Colorado Springs having their wettest and 3rd wettest Julys on record, respectively. Excessive precipitation across central Nebraska and eastern South Dakota helped relieve dryness in these regions. Widespread dryness and above-normal temperatures contributed to the depletion of soil moisture across much of the region in July - a time when moisture is critical for row crops, such as corn and soybeans. Topsoil moisture conditions deteriorated in all six states with Kansas and North Dakota showing the largest increases in percent short to very short. Over the past several months, flooding has been an issue along areas of the Wind River and its tributaries in Wyoming, as well as the North Platte River in Nebraska. Although flood waters have receded and streamflows are returning back to normal along the North Platte River, streamflows continued to be above normal in much of the Wind River Basin. In other areas of the region, heavy monsoonal precipitation across eastern Colorado and western Kansas caused much-above-normal streamflows, while persistent drought conditions in the western Dakotas caused the continuation of much-below-normal streamflows. Low streamflows in southwestern Nebraska throughout the month indicated drought development, which was reflected in the U.S. Drought Monitor's drought depiction of that region by the end of July. Drought continued to expand and intensify throughout the High Plains during July, as weather conditions provided little relief. According to the July 25th release of the U.S. Drought Monitor, nearly one-third of the region was experiencing drought conditions, compared to just under 20 percent at the end of June. The Northern Plains drought intensified in the Dakotas and expanded southward into northern Nebraska. Exceptional drought (D4), the highest category of intensity depicted on the U.S. Drought Monitor, was introduced to portions of western North Dakota. While Nebraska was drought-free at the end of June, drought expanded to cover approximately 40 percent of the state by the end of July. Abnormal dryness (D0) and small pockets of moderate drought (D1) slowly spread across parts of Kansas, Colorado, and Wyoming as well. Agricultural impacts from the drought have become widespread, particularly in the Dakotas. The U.S. spring wheat crop took a big hit this year, as the drought-stricken states of Montana, North Dakota, and South Dakota contain major wheat-growing areas. For the week ending July 29th, the USDA Weekly Weather and Crop Bulletin reported the following percentages of spring wheat in poor to very poor condition: South Dakota (75%), Montana (58%), and North Dakota (44%). Some of the destroyed crop was turned into hay for feed. Corn and soybean conditions also began to deteriorate during July. South Dakota was faring worst as soybeans and corn were rated 35% and 39% poor to very poor, respectively.

As explained by the Southern Regional Climate Center, precipitation values for July varied spatially across the Southern Region. Parts of southern Oklahoma, and northern and western Texas were 300% of normal precipitation. Central Tennessee, northern and western Arkansas, southern Mississippi, western and southern Oklahoma, and northern, eastern, and western Texas reported 150 - 300% of normal precipitation. In contrast, parts of northern Mississippi, southeastern Louisiana, southeastern Arkansas, northern Oklahoma, and western and southern Texas were 0 - 50% of normal precipitation. Drought conditions improved for some parts of the region, such as areas in eastern Texas and northeastern Mississippi. In contrast, drought conditions worsened in the panhandles of Texas and Oklahoma, central Oklahoma, and southern Texas. Currently there are areas of severe drought present in Oklahoma and Texas. At this time there are no areas of extreme or exceptional drought. Parts of Oklahoma and southern Texas became abnormally dry whereas parts of northwestern Louisiana, northeastern Mississippi, and central Texas improved from abnormally dry to normal conditions.

As summarized by the Midwest Regional Climate Center, July temperatures in the Midwest were close to normal. July precipitation in the Midwest ranged from less than 1 inch in some locations in Iowa and Minnesota to more than 6 inches for a large swath of the region extending from the southeastern tip of Minnesota, through parts of Wisconsin, Iowa, Illinois, and Kentucky, and across most of Indiana and Ohio. Totals exceeded 8 inches along the Illinois-Wisconsin border and in central Ohio. Viewed as a percentage of normal, some locations were at less than 25 percent of normal while large parts of Indiana and Ohio, along with the Illinois-Wisconsin border area, had more than 150 percent of normal. Drought expanded in the Midwest in July, especially in Iowa. At the beginning of the month less than two percent of the region was in drought. This rose to nearly eight percent by the end of the month and included an area of severe drought in south central Iowa. Parts of northwestern Minnesota, east central Missouri, west central Illinois were in drought along with a big chunk of Iowa extending from the northwestern part of the state to the southeastern part and slightly into northern Missouri. Crop conditions were better than some years but worse than others when compared to the past five years. 2012 was worse in nearly all locations but was not the only year topped by the current year. Most locations had a better year or two among the past five years as well. The factors causing stress on the crops varied by location with dryness and wetness both being a factor along with hail and wind damage in some locations. Some locations still had effects from late planting or replanting due to wetness in the spring.

As noted by the Southeast Regional Climate Center, temperatures were near average to above average across the Southeast region during July, with extreme warmth occurring at several locations. Precipitation was highly variable across the Southeast region during July, with a few wet and dry extremes recorded. The driest locations were found across broad portions of Upstate South Carolina, central North Carolina, and central Virginia, where monthly precipitation totals were 50 to less than 25 percent of normal. In contrast, the wettest locations were found across portions of the Florida Peninsula, northern Alabama, southeastern Georgia, central and coastal South Carolina, western and northeastern North Carolina, northern Virginia, and the District of Columbia. Monthly precipitation totals ranged from 150 to nearly 300 percent of normal in these areas. With the removal of a localized area of moderate (D1) drought in northeastern Georgia at the beginning of July, drought conditions (D1 and greater) were not observed across the mainland portion of the region during the remainder of the month. However, below-average precipitation caused abnormally dry (D0) conditions to develop across broad portions of North Carolina and Virginia, with below-normal streamflows also recorded in these areas. A narrow strip of moderate (D1) drought developed across the southern coast of Puerto Rico at the end of the month. Dryland crops and pastures thrived from timely rainfall and few days of extreme heat across much of the region, but detrimental impacts were reported in some areas. A persistence of heavy rainfall, especially during the first half of July, continued to delay winter wheat harvesting, hay cutting, and soybean planting across portions of Alabama and Georgia. Several wheat fields in northern Georgia were lost due to the excessive wetness, which could also prevent a subsequent planting of soybeans in those fields. High humidity and abundant rainfall resulted in fungal disease issues for several crops across the region, particularly fruit and vegetable products in Georgia and South Carolina, tobacco in parts of North Carolina and Georgia, and cotton in multiple states. Some farmers in Alabama, Georgia, and Florida were unable to spray fungicides and remove weeds in their saturated fields. A period of hot, dry weather during mid-to-late July stunted the growth of crops, hay fields, and pastures across portions of North Carolina and Virginia. Wilting of corn and soybean plants was prevalent in these areas, and some livestock fatalities in central Virginia were attributed to the unusual dryness. Plentiful rainfall and near-average temperatures during the month contributed to a bumper crop of watermelons in South Carolina, with some farmers reporting double their normal yields.

As explained by the Northeast Regional Climate Center, July averaged out to be slightly warmer than normal in the Northeast. The states were split, with six wrapping up the month on the cold side of normal and six on the warm side of normal. It was the fifth wetter-than-normal month in a row for the Northeast. The region received 5.12 inches of rain (130.05 mm), 120 percent of normal, making it the 18th wettest July since recordkeeping began. Just like with average temperature, the states were split in terms of precipitation. For the drier-than-normal states, precipitation ranged from 78 percent of normal in Maine to 93 percent of normal in Vermont. For the wetter-than-normal states, precipitation ranged from 125 percent of normal in West Virginia to 205 percent of normal in Delaware. The U.S. Drought Monitor released on July 6 showed abnormally dry conditions for 3 percent of the Northeast, including portions of coastal Maine, eastern Long Island, southern Delaware, south-central Pennsylvania, and central and southern Maryland. During the month, dryness eased in Pennsylvania, Delaware, and most of Maryland but expanded in Maine and Long Island. In West Virginia, abnormal dryness was introduced mid-month but eased slightly by month's end. The U.S. Drought Monitor released on July 27 showed abnormally dry conditions for 7 percent of the Northeast.

As summarized by the Western Regional Climate Center, near record to record-breaking temperatures were observed in the Great Basin, Inland Northwest, and some parts of California this month, with near normal temperatures across the Southwest. Widespread monsoonal rains during the latter two-thirds of the month brought above normal precipitation and flooding to some areas of the Southwest. The Southwest Monsoon had a relatively late start this year for much of Arizona, though a series of storms beginning mid-month brought above normal, and in some cases record-breaking, precipitation to many areas of the state. Other areas of the Southwest and southern Great Basin experienced above normal precipitation as well. Outside of the Southwest, much of the West received little to no precipitation, typical of July for areas west of the Rockies. Drier than normal conditions persisted across central and eastern Montana this month. Dry conditions coupled with above normal temperatures intensified drought conditions in Montana this month; 38% of Montana is experiencing severe to exceptional drought, all in the eastern half. Northern and Interior Alaska observed well above normal temperatures this month, while other parts of the state saw less extreme temperatures. Precipitation was generally above normal in western and southeastern Alaska. Dry conditions in Hawaii this month prompted expansion of drought conditions, such that nearly all of Hawaii and Maui counties are in moderate or worse drought according to the US Drought Monitor.

U.S. Affiliated Pacific Islands:

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State/Regional/National Moisture Status
A detailed review of drought and moisture conditions is available for all contiguous U.S. states, the nine standard regions, and the nation (contiguous U.S.):

States

alabama	arizona	arkansas	california	colorado	connecticut
delaware	florida	georgia	idaho	illinois	indiana
iowa	kansas	kentucky	louisiana	maine	maryland
massachusetts	michigan	minnesota	mississippi	missouri	montana
nebraska	nevada	new hampshire	new jersey	new mexico	new york
north carolina	north dakota	ohio	oklahoma	oregon	pennsylvania
rhode island	south carolina	south dakota	tennessee	texas	utah
vermont	virginia	washington	west virginia	wisconsin	wyoming

Regional

northeast u. s.	east north central u. s.	central u. s.
southeast u. s.	west north central u. s.	south u. s.
southwest u. s.	northwest u. s.	west u. s.

National

Contiguous United States

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Contacts & Questions