Heat causes degradations in drought map

This U.S. Drought Monitor week saw degradations across the areas of the Plains, Upper Midwest, and Florida, while rainfall during the past week led to improvements in drought-affected areas of the South, Southeast, Mid-Atlantic, and Northeast.

In the West, a mix of improvements and degradations occurred on the map with improvements across areas of Idaho and Montana in response to above-normal rainfall during the past 30-day period. Conversely, areas of eastern Colorado and southeastern Wyoming saw degradation in response to dry conditions and excessive heat and elevated evaporative demand.

Likewise, hot and dry conditions prevailed across the central and northern Plains leading to expansion and intensification of drought, with temperatures ranging from 2 to 10+ degrees Fahrenheit above normal and reports of poor rangeland conditions.

In the South, another round of heavy rainfall in the Hill Country of Texas led to continued improvement in the long-term drought situation as well as severe flash flooding, with widespread rainfall accumulations ranging from 5 to 10 inches and isolated areas receiving totals in excess of 15 inches.

In terms of reservoir storage in the West, California’s reservoirs continue to be at or above historical averages for the date (July 21), with the state’s two largest reservoirs, Lake Shasta and Lake Oroville, at 110% and 100% of average, respectively.

In the Southwest, the U.S. Bureau of Reclamation is reporting (July 19) Lake Powell at 22% full (34% of average for the date; lowest on record for the date in the last 30 years), Lake Mead at 27% full (45% of average for the date; lowest on record for the date in the last 30 years), and the total Colorado River system (July 19) at 33% of capacity (compared to 39% of capacity the same time last year).

The U.S. Drought Monitor is jointly produced by the National Drought Mitigation Center at the University of Nebraska-Lincoln, the U.S. Department of Agriculture and the National Oceanic Atmospheric Administration. (Map courtesy of NDMC.)

South

Improvements were made in drought-affected areas of Texas and Arkansas. In terms of precipitation during the past week, moderate to heavy rainfall accumulations (ranging from 5 to 15+ inches) were observed in the Hill Country of Texas bringing much-needed relief to the long-term drought situation and low reservoir levels.

However, the torrential rains also led to severe and dangerous flash flooding across areas of the region. Looking at the reservoir situation, Water Data for Texas (July 22) reports statewide reservoirs at 78% full, with eastern reservoirs in good condition while numerous western and southern reservoirs remain below normal.

Looking at climatological rankings for the past 30-days, record to near-record precipitation was observed in areas of the region, including in Junction, Texas, (2nd wettest on record; +5.44 inch departure), San Angelo, Texas (9th wettest; +2.49 inches), Del Rio, Texas (3rd wettest; +5.86 inches) and Shreveport Airport, Louisiana (wettest; +8.36 inches). Average temperatures for the week were above normal across most of the region (1 to 5 degrees).

Midwest

On this week’s map, degradations were made across areas of Minnesota and Iowa in response to above-normal temperatures and precipitation shortfalls during the past 30-day period.

Elsewhere in the region, conditions continued to improve in Kentucky where precipitation has been well above normal during the past month. Temperatures were near normal across the southern tier of the region, while the northern extent logged anomalies ranging from 2 to 6 degrees.

High Plains

Drought-related conditions deteriorated across the region including in the Dakotas and Nebraska with reports of rapidly deteriorating conditions. The recent anomalously hot temperatures and deteriorating drought-related conditions led to the South Dakota governor issuing a drought emergency executive order.

In terms of drought impacts, the National Drought Mitigation Center’s Condition Monitoring Observer Report drought impacts reporting system is showing numerous impact reports across the Dakotas during the past 30 days. For the week, average temperatures were 4 to 10+ degrees above normal across the Dakotas and Nebraska. Looking at climatological rankings for the past 30-day period, several locations logged near-record dryness including Omaha, Nebraska (third driest on record; -3.16 inches); Grand Island, Nebraska (fifth driest; -3.05 inches); and Rapid City NWS Weather Forecast Office, South Dakota (fifth driest; -1.48 inches).

West

On the map, drought-related conditions continued to deteriorate in areas of eastern Colorado and southeastern Wyoming while improvements were made in Montana where short-term conditions (past 30 days) improved.

In the Southwest, monsoonal thunderstorms delivered much-needed moisture to isolated areas of the Four Corners states. In the Colorado River Basin, Lake Powell is 22% full, while Lake Mead is 27% full, according to the U.S. Bureau of Reclamation.

Other reservoirs in the region are experiencing low levels including at Elephant Butte Reservoir in New Mexico (2% of capacity) and Blue Mesa Reservoir in southwestern Colorado (32% full). Looking at climatological conditions for the past month, record or near-record precipitation was observed at the following locations: Great Falls, Montana (wettest on record; +2.29 inches); and Glasgow Airport, Montana (third wettest; +2.88 inches.

Looking ahead

The NWS Weather Prediction Center 7-Day Quantitative Precipitation Forecast calls for the heaviest precipitation accumulations across portions of the Mid-Atlantic states, where precipitation accumulations generally ranging from 2 to 7+ inches are expected.

In isolated areas of the central Plains, precipitation accumulations generally ranging from 1 to 2 inches are expected. In Texas, light to moderate accumulations (2 to 4 inches) are expected in areas of the south Texas plains.

In the West, the higher elevations of areas of the central and southern Rockies and portions of the Southwest, including the Mogollon Rim of Arizona, localized precipitation accumulations of 1 to 2+ inches are expected.

The National Weather Service’s 6– to 10-day temperature outlook (valid July 27 to 31) favors above-normal temperatures across most of the contiguous United States, with the highest probabilities centered across the central and southern Rockies, Plains states, Texas, and western portions of the Midwest. Above-normal temperatures are also favored across much of the South regions.

The NWS precipitation outlook favors above-normal precipitation across portions of the Southwest and central Rockies. Below-normal precipitation is favored across eastern portions of the central and southern Plains, Texas, South, and Midwest.

David Simeral is with WRCC/DRI.