Wednesday, June 01, 2016

National Drought Summary for May 24, 2016

Summary

This U.S. Drought Monitor week saw minor improvements in drought conditions in areas of the West including: northeastern California, northern Nevada, northwestern New Mexico, and southeastern Alaska. In Texas, persistent rainfall led to the complete removal of drought conditions from the state. In the Northeast, Northwest, and Southeast, short-term precipitation deficits, low streamflows, and pockets of dry soils led to further deterioration of conditions. Significant rainfall accumulations this week were observed along the western Gulf Coast, portions of the Mid-Atlantic, Northern Rockies, and Southeast. In southeastern Florida, seven-day rainfall totals were impressive with some coastal areas receiving nearly fifteen inch accumulations. Temperatures across most of the conterminous U.S. were below normal during the past week with the largest negative departures across the Central and Southern Plains, lower Midwest and Mid-Atlantic where average temperatures were four-to-ten degrees below normal. Conversely, temperatures were four-to-ten degrees above normal in the North Plains and High Plains of Montana.

The Northeast

On this week’s map, short-term precipitation deficits, low streamflows, and dry soils led to the expansion of Abnormally Dry (D0) in the Adirondacks of New York, southeastern Maine, and northern Vermont. In these areas, 28-day average streamflows were below (10-24th percentile) to well-below (<10th percentile) normal. During the past week, the Northeast remained in an overall dry pattern with no significant rainfall accumulations observed across the region. Average temperatures were two-to-four degrees below normal across the region except for eastern portions of Maine where temperatures were two-to-six degrees above normal.

Mid-Atlantic

On this week’s map, only minor changes were made in the region. Conditions improved in western North Carolina in areas of areas of Abnormally Dry (D0) and Moderate Drought (D1) where recent rainfall and cooler temperatures helped improve groundwater and streamflow conditions. In Virginia, rainfall in May has been consistent with the National Weather Service (NWS) observing station at the Charlottesville-Albemarle Airport reporting measureable rainfall on 21 days this month. For the seven-day period, temperatures were well below normal across the entire region with average temperatures four-to-ten degrees below normal. On Sunday, the NWS Forecast Office in Baltimore/Washington D.C. reported a daily record low maximum temperature of 57° F at Washington Dulles International Airport.

The Southeast

During the past week, temperatures were below normal across much of the region with the exception of Florida where temperatures were a few degrees above normal. Some significant rainfall accumulations were observed in northern portions of South Carolina, southeastern Georgia, and southern Florida. Two-to-four inches of rain and improved streamflow conditions led to the removal of areas Abnormally Dry (D0) in South Carolina and southeastern Georgia. In northern Alabama, short-term precipitation deficits (30 day) and dry soil moisture conditions led to the expansion of areas of Moderate Drought (D1). In Florida, heavy rains fell across southeastern Florida with areas in the vicinity of Vero Beach receiving accumulations in excess of fifteen inches. Improving short-term conditions (30-60 day) led to the removal of an area of Abnormally Dry (D0) in northeastern Florida.

The South

During the past week, the western Gulf Coast region received rainfall accumulations ranging from two-to-six inches. In Texas, the recent wet pattern led to the complete elimination of drought conditions from the state. During the past 30 days, rainfall totals in southeastern Texas have been four-to-twelve inches above normal. Conversely, northeastern Louisiana and northern three-quarters of Mississippi have been quite dry during the past 30 days leading to the introduction of areas of Abnormally Dry (D0). Temperatures were generally below normal across the entire region this past week. According to the NOAA National Centers for Environmental Information Climatological Rankings (NCEI), Texas Climate Division 8 (Upper Coast) experienced its 4th wettest 12-month period (May 2015-April 2016) on record.

Midwest

The Midwest saw some improvements on the map in south-central Kentucky while conditions continued to dry out in northern Minnesota leading to the introduction of areas of Abnormally Dry (D0) where streamflows dipped and soil moisture percentiles were below the 10th percentile, according to the North American Land Data Assimilation System model. Overall, average temperatures were two-to-five degrees below normal across the region with exception of northwestern Minnesota where temperatures were slightly above normal. In general, the region was dry during the past week with exception of some modest rainfall accumulations (one-to-two inches) in southern portions of the region.

The Plains

Across the Plains, only minor changes were made on the map this week including removal of the remaining area of Moderate Drought (D1) from west-central Oklahoma. Overall, the region was relatively dry in western portions while eastern portions received modest rainfall accumulations of generally less than two inches. Temperatures were two-to-ten degrees above average in the Northern Plains while further south below normal temperatures prevailed.

The West

During the past week, average temperatures were below normal across the most of region. Overall, the region was generally dry with exception of areas of northeastern California, northwestern Montana, and south-central Oregon where modest precipitation accumulations were observed (one-to three inches). On the map, improvements were made in an area of Severe Drought (D2) in northeastern California and northern Nevada where overall conditions have continued to steadily improve during the past year. According to the NOAA NCEI Climatological Rankings, Nevada Climate Division 1 (Northwestern Nevada) experienced its 9th wettest 12-month period (May 2015-April 2016) on record. In northwestern Oregon, short-term dryness and degraded streamflow conditions led to the expansion of areas of Abnormally Dry (D0). In northwestern New Mexico, improvements in soil moisture and streamflows led to the reduction of a small area of Moderate Drought (D1). Coming into the summer months, Lake Mead currently sits at 37% full while Lake Powell is slightly higher at 48% full, according to the May 23rd U.S. Bureau of Reclamation’s Lower Colorado Water Supply Report.

Hawaii, Alaska, and Puerto Rico

On this week’s map, minor improvements were made in areas of Moderate Drought (D1) on Kauai and Oahu where field reports indicated improvements in the condition of area vegetation. Overall, the Hawaiian Islands were generally dry during the past week with the exception of two-to-three inch accumulations on the windward side of the Big Island. Average temperatures across the Hawaiian Islands were slightly above normal. In Alaska, areas of Abnormally Dry (D0) were removed from southeast Alaska in response to above average precipitation during the past 30-90 days. During the past week, temperatures were generally above normal across most of Alaska. No changes were made on the map in Puerto Rico this week.

Looking Ahead

The NWS WPC 7-Day Quantitative Precipitation Forecast (QPF) calls for significant rainfall accumulations across the nation’s midsection – primarily focused on Texas, Plains, and western portions of the Midwest with accumulations from three-to-six inches while much of the South and Western U.S. area forecasted to be generally dry. The CPC 6–10 day outlooks call for a high probability of above normal temperatures in the eastern half of the U.S. and Far West while below normal temperatures are expected in the Desert Southwest, extending northward into the eastern Great Basin and Central Rockies. Below normal precipitation is forecasted for the Pacific Northwest, much of California, western Great Basin, and across portions of the Northeast while there is a high probability of above normal precipitation across the Northern Rockies, Plains, Mid-Atlantic, South, and Southeast.

Author(s):
David Simeral, Western Regional Climate Center


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)

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