California and National Drought Summary for April 25, 2017

Summary

PLEASE NOTE – The Drought Monitor reflects observed precipitation through Tuesday, 1200 UTC (8 am, EDT); any rain that has fallen after the Tuesday 1200 UTC cutoff will be reflected in next week’s map.

April 28, 2017 - During the 7-day period (ending Tuesday morning), widespread heavy rain eased drought but caused local flooding from Oklahoma to the Carolina Coast. In contrast, dry, hot conditions caused drought to intensify over the lower Southeast, though tropical downpours afforded some drought relief in southern Florida. Additional improvements to drought intensity and coverage were noted in the Northeast and Mid-Atlantic in response to late-spring rain as well as recovering groundwater levels. Conditions also improved on the central Plains, while drought remained largely unchanged elsewhere.

Northeast

Widespread showers continued the region’s slow recovery from long-term drought (denoted by an “L” on the map). Rain during the period totaled 0.5 to 1 inch in the north, while amounts locally topped 2 inches from southern New York into West Virginia. Although short-term dryness is currently not a concern, slower-to-recover drought impacts remained. In particular, groundwater levels remained unfavorably low (10 to 25th percentile, locally below the 10th percentile) in the region’s lingering Abnormal Dryness and Moderate Drought (D0 and D1) areas, and additional soaking rainfall will be needed to recharge the region’s aquifers as water demands increase in response to seasonally warmer weather.

Southeast

Heavy to excessive rainfall alleviated drought but triggered flooding across interior portions of the region, while hot, dry weather caused drought to intensify and expand farther south. A slow-moving storm system coupled with abundant subtropical moisture generated 2 to 8 inches of rain from northern portions of Alabama and Georgia into the Carolinas and Virginia. As a result, 1- to 2-category reductions in drought were noted over the interior Southeast. Furthermore, with saturated soils, elevated streamflows, and local flooding, the remaining drought in the interior Southeast was changed to long-term (“L” on the map), indicating little — if any — dryness in the shorter term (6 months or less), but longer-term deficits remained. For example, 12-month precipitation stood at 60 to 75 percent of normal in the interior Southeast’s Moderate to Extreme Drought (D1 to D3) areas. Meanwhile, warmth (4-8°F above normal) and dryness led to additional expansion of D0, D1, and D2 from northern Florida into southern Alabama and Georgia. Rainfall over the past 90 days has totaled a meager 20 to 40 percent of normal in the most severe drought areas, enhancing the risk for wildfires and depleting soil moisture supplies for crops and pastures. As of April 23, topsoil moisture stood at 64 percent short to very short in Florida, according to USDA-NASS. Despite the dry weather pattern, tropical downpours (2-8 inches) were reported in southeastern Florida, providing some localized drought relief.

South

Heavy rain in northern portions of the region contrasted with dry conditions closer to the Gulf Coast. A slow-moving storm system was responsible for 2 to 8 inches of rain from central Oklahoma into Tennessee, resulting in widespread 1- and 2-category reductions in drought. Precipitation over the past 30 days has topped 10 inches (locally more than a foot) in northeastern Oklahoma, while 8- to 10-inch totals are common over the same period in Tennessee. Additional heavy rainfall — on top of the rain that has already fallen after the Tuesday morning data cutoff— expected over the weekend (April 29-30) will likely necessitate further reductions in drought if the forecast verifies. Conditions remained largely unchanged across the Gulf Coast States, as near- to below-normal-temperatures accompanied this week’s generally dry weather.

Midwest

Rain in southern portions of the region further reduced the remaining Midwestern drought footprint. During the 7-day period, rainfall totaled 2 to 5 inches over the southern third of Missouri, easing or eliminating Abnormal Dryness and Moderate Drought (D0 and D1). More heavy rain is expected over the ensuing 7 days, likely providing additional relief from dryness and drought.

High Plains

Wet weather brought drought relief to the southern half of the region, while conditions remained unchanged on the northern High Plains’ long-term drought areas (denoted by an “L” on the map). Precipitation amounts were highly variable, but well-placed moderate to heavy rain and wet snow (1-3 inches liquid equivalent, locally more) led to reductions of Abnormal Dryness (D0) and Moderate Drought (D1) over southern-most portions of Wyoming, northern and northeastern Colorado, as well as the northwestern and southeastern corners of Kansas. Additional D1 and D0 reductions were made from eastern Colorado into southwestern Kansas despite lighter rainfall (half inch or less), as precipitation totals over the past 90 days were now mostly well above normal, with 30-day totals locally more than three times normal. Meanwhile, despite recent wet weather, long-term deficits linger in the north’s D1 and D0 areas; 12-month precipitation stood at 65 to 80 percent of normal in northeastern Wyoming and adjacent portions of the Dakotas, though some parts of southwestern South Dakota were closer to normal and may be removed from D0 in the near future.

West

As the region’s climatological wet season draws to a close, there were no changes made to the drought depiction from the Rockies into the Southwest. Farther east, well-placed moderate to heavy rain and wet snow (1-3 inches liquid equivalent, locally more) led to reductions of Abnormal Dryness (D0) and Moderate Drought (D1) over southern-most portions of Wyoming as well as northern and northeastern Colorado. Additional D1 and D0 reductions were made in eastern Colorado despite lighter rainfall (half inch or less), as precipitation totals over the past 90 days were now mostly well above normal, with 30-day totals locally more than three times normal.

Alaska, Hawaii, and Puerto Rico

In Alaska, there were no changes made to the state’s Abnormal Dryness (D0), as mostly dry but cool weather (up to 3°F below normal) prevailed everywhere save for encroaching warmth (up to 10°F above normal) in the western tier . In Hawaii, moderate to heavy rain (locally more than 1 inch) on the southern coast of the Big Island led to a small reduction of Severe Drought (D2). Additional moderate to heavy rainfall (1-5 inches) fell over the rest of the Hawaiian Islands, and further reductions of Abnormal Dryness (D0) and Moderate Drought (D1) may be forthcoming pending impact assessments from the field. Puerto Rico remained free of drought or dryness concerns.

Looking Ahead

The focus for heavy rainfall will shift to the nation’s mid-section over the next 5 days. An area of low pressure and its attendant cold front will produce moderate to heavy showers and thunderstorms as it moves from the Mississippi Valley toward southern Canada and the Atlantic Seaboard, though rain from this system will largely bypass the East Coast States. In its wake, another storm system will develop over the south-central U.S. during the weekend and lift slowly northeastward, producing heavy rain from the central Gulf Coast into the central Great Lakes Region; moderate to heavy wet snow is likely in the colder air on the northwest side of the storm over central and southern portions of the Rockies and High Plains. Combined, these two storms are expected to produce a large swath of 1- to 3-inch precipitation totals from the central Plains to the Great Lakes and Mississippi Valley, with excessive rainfall (4-12 inches) possible from the northern Delta into the central Corn Belt. The NWS 6- to 10-day outlook for May 2 – 6 calls for above-normal precipitation across much of the nation east of the Mississippi as well as central and northern portions of the Rockies and High Plains. Conversely, drier-than-normal conditions are expected from Texas into the upper Midwest and from the Great Basin into the Northwest. Colder-than-normal conditions from the western slopes of the Appalachians to the High Plains will contrast with warmer-than-normal readings along the Atlantic Coast as well as California and the Southwest.

Author(s):
Eric Luebehusen, 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)
Source: National Drought Mitigation Center