California and National Drought Summary for May 19, 2015

Summary

Nearly coast-to-coast storminess reduced drought’s footprint across the nation’s mid-section but triggered lowland flooding from the southeastern Plains and the western Gulf Coast region into the mid-South. Farther east, however, only light showers, if any, dampened the eastern U.S., except for some briefly heavy rain in the northern Mid-Atlantic region. In the Northeast, where little precipitation has fallen during the spring, another mostly dry week raised concerns about a lack of soil moisture and declining streamflows. Meanwhile, cool, wet weather in the upper Midwest provided much-needed moisture, following a period of rapid planting progress. In fact, below-normal temperatures dominated much of the country, with widespread freezes noted across the north-central U.S. from May 18-20. Elsewhere, broadly unsettled weather prevailed in the West, with the heaviest precipitation falling across the northern Intermountain region and the central and southern Rockies. The Western precipitation boosted topsoil moisture, aided winter grains, and reduced irrigation requirements. Beneficial showers dampened parts of California and Nevada, but failed to dent the Far West’s serious hydrological drought.

Great Plains

Frenetic weather led to further reductions in drought coverage. Late-season snow briefly blanketed several areas, including parts of North Dakota on May 17-18 and western Nebraska on May 19-20. Farther south, multiple rounds of heavy showers and locally severe thunderstorms led to flooding, particularly across the southeastern Plains. Several gauging points, including the Red River near DeKalb, Texas, and the Poteau River near Panama, Oklahoma, climbed to their highest levels since May 1990. The Red River near DeKalb rose 4.51 feet above flood stage on May 13, while the Poteau River near Panama surged 14.54 feet above flood stage on May 12. By May 20, cumulative storage in Texas’ reservoirs climbed to 24.78 million acre-feet (78.5% of capacity)—the highest in more than 4 years. Only a month ago, Texas’ storage was 22.53 million acre-feet, or 71.4% of capacity. Six months ago, on November 20, 2014, storage stood at just 19.43 million acre-feet, 62.0% of capacity.

On the southern Plains, month-to-date rainfall has already exceeded a foot in many locations, including Oklahoma City, Oklahoma (13.88 inches, or 508% of normal), and Wichita Falls, Texas (12.43 inches, or 570%). Record-high May totals in those two locations are 14.52 inches (in 2013) in Oklahoma City and 13.22 inches (in 1982) in Wichita Falls. In the Plains’ cotton belt, incessant rains have hampered fieldwork. For example, only 19% of Texas’ intended cotton acreage had been planted by May 17, compared to the 5-year average of 36%.

Farther north, spring precipitation arrived mostly too late to revive winter wheat but has aided rangeland, pastures, and summer crops. By May 17, roughly one-third of the winter wheat was rated in very poor to poor condition in South Dakota (36%), Nebraska (31%), and Kansas (30%). The damage to wheat was caused much earlier due to a combination of drought and winter weather extremes. Meanwhile, South Dakota’s rangeland and pastures—which were rated 33% very poor to poor on May 3, improved to 24% very poor to poor by May 17. Spring wheat, grown primarily in six Northern States from Washington to Minnesota, was off to a good start, with 65% of the crop rated good to excellent (and only 4% very poor to poor) on May 17.

Hawaii, Alaska and Puerto Rico

No changes were made in Alaska and Puerto Rico. It is worth noting, however, locally heavy showers in parts of western and northeastern Puerto Rico staved off drought expansion. Areas that missed most of the mid-May rainfall remain dry. In San Juan, for example, rainfall from March 1 – May 19 totaled just 3.15 inches (31% of normal). Meanwhile in Hawaii, water restrictions were eased (from 10% mandatory to 10% voluntary) on Molokai, contributing to the removal of D1. On Maui, however, short-term dryness (D0) and moderate drought (D1) expanded, mainly due to worsening pasture conditions.

Midwestern and Great Lakes States

Significant rainfall pushed as far east as the upper Mississippi Valley but tapered to light showers east of the Mississippi River. As a result, substantial improvements in areas affected by dryness and drought were limited to the upper Midwest. St. Cloud, Minnesota, received 5.19 inches of rain during the first 18 days of May, followed by consecutive freezes (30 and 31°F, respectively) on May 19-20.

Southeast

Pockets of abnormal dryness (D0) dotted the Southeast, with moderate drought (D1) confined to southern Florida. Southern Florida continues to await the arrival of its summer wet season, with drought-related impacts expected to diminish once rains arrive. Elsewhere, patchy Southeastern dryness was promoting spring fieldwork but reducing streamflows and increasing stress on pastures and summer crops. In Tennessee, 59% of the pastures were rated good to excellent on May 17, down from 70% a week earlier. Similarly, Georgia’s pastures rated good to excellent declined from 70 to 63% during the week ending May 17.

The Northeast

Aside from a couple bursts of thundershowers in the Mid-Atlantic States, mostly dry weather again prevailed. Stream data from USGS indicated extremely low flows for this time of year from the northern Mid-Atlantic region into southern New England. Moderate drought (D1) was introduced in two areas—one stretching from parts of eastern Pennsylvania into New England, and the other covering much of northern New York. In many of the driest areas, spring precipitation has been scarce. From March 1 – May 19, precipitation totaled less than two-third of normal in locations such as Boston (5.64 inches, or 56% of normal), New York’s Central Park (7.12 inches, or 63%), and Providence (7.39 inches, or 65%).

West

Cool, occasionally showery weather across much of the western U.S. reduced irrigation demands, boosted topsoil moisture, and benefited rangeland, pastures, winter grains, and spring-sown crops. However, the late-season moisture failed to significantly alter the bleak hydrological situation in drought-affected areas, including California. By April 30, reservoir storage as a percent of average for the date was significantly below normal in Arizona, California, Nevada, New Mexico, and Oregon. Storage in California’s 154 reservoirs stood at 18.0 million acre-feet (64 percent of average) on May 1, about 1.6 million acre-feet lower than a year ago. With little snow in the mountains above California’s lakes, further inflow will be negligible, meaning that the reservoir recharge season has ended early.

An exception to the West’s cool, damp pattern was the Pacific Northwest, where abnormal dryness (D0) expanded to cover western Washington. During the first 19 days of May, rainfall totaled just 0.65 inch (20% of normal) in Quillayute, Washington. Farther inland, USDA on May 17 rated only a little more than one-third of the winter wheat crop in good to excellent in Washington (39%) and Oregon (34%). In addition to less-than-ideal crop conditions, snowpack and streamflows remain at extremely low levels in most of the Northwest. As a result, severe drought (D2) was introduced across portions of northeastern Washington and northern Idaho, while moderate drought (D1) was expanded. Farther south, recent precipitation has been heavy enough in southern Idaho to prevent significant drought expansion, although hydrological concerns persist.

Despite atypically heavy showers for May in California, Nevada, and Arizona, the drought depiction remained effectively unchanged. Simply stated, the late-season rain and snow showers have improved the appearance of the landscape but have left the underlying, long-term drought virtually untouched. Even with the showers, California’s topsoil moisture was rated 85% very short to short on May 17, while subsoil moisture was 90% very short to short. Similarly, Nevada’s topsoil moisture was 65% very short to short, while subsoil moisture was 85% very short to short. Nevertheless, locations reporting their wettest May day on record included San Diego, California (1.63 inches on May 14; previously, 1.49 inches on May 8, 1977), and Phoenix, Arizona (0.93 inch on May 15; previously, 0.91 inch on May 4, 1976).

More widespread precipitation has fallen in recent weeks across the central and southern Rockies and environs. In fact, the water content of the high-elevation snowpack climbed above the mid-May average in several river basins in the Rockies of Colorado and New Mexico. Due to the extensive precipitation, improved water-supply prospects, and boost in soil moisture, another round of sweeping improvements in the drought depiction were introduced in Colorado and New Mexico, extending northward into southern Wyoming and westward into eastern Utah. Through May 19, month-to-date precipitation has totaled 200 to 300% of normal in locations such as Grand Junction, Colorado; Salt Lake City, Utah; Denver, Colorado; and Evanston, Wyoming. Parts of New Mexico have been even wetter in recent weeks, relative to normal, with May 1-19 totals reaching 5.45 inches (524% of normal) in Clayton and 1.50 inches (484%) in Albuquerque.

Looking Ahead

During the next several days, a parade of storms will continue to emerge from the western U.S. As a result, 5-day precipitation totals could reach 1 to 2 inches from Oregon and northern California to the Intermountain West. Meanwhile, totals of 2 to 5 inches or more can be expected across the central and southern Plains and parts of the mid-South. In contrast, little or no rain will fall in the eastern U.S. and across the nation’s northern tier. Most of the country, excluding the Southeast and Northwest, will continue to experience cool weather.

The NWS 6- to 10-day outlook for May 26 – 30 calls for likelihood of above-normal temperatures along the Pacific Coast, in the Northwest, and east of the Mississippi River. Meanwhile, cooler-than-normal conditions will cover the central and southern High Plains and parts of the Southwest. A wet pattern will persist nearly nationwide, with drier-than-normal weather likely limited to the northern Pacific Coast, southern Florida, and a small area near the Canadian border centered on northern North Dakota.

Author(s):
Brad Rippey, U.S. Department of Agriculture

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Dryness Categories

D0 ... Abnormally Dry ... used for areas showing dryness but not yet in drought, or for areas recovering from drought.

Drought Intensity Categories

D1 ... Moderate Drought

D2 ... Severe Drought

D3 ... Extreme Drought

D4 ... Exceptional Drought

Drought or Dryness Types

S ... Short-Term, typically <6 months (e.g. agricultural, grasslands)

L ... Long-Term, typically >6 months (e.g. hydrology, ecology)