Summary

April 11, 2019 - After a dry March, a series of storms brought much needed precipitation to the Pacific Northwest, staving off further degradations in Washington and resulting in local flooding and broad drought improvements in Oregon. Elsewhere, the West remained largely status quo with the only degradation in drought conditions occurring in the Big Horn Mountains where snowpack has been well below normal all winter. The South and Southeast saw a mixture of improvements and degradations. Locally heavy rainfall brought improvements to parts of Texas, Louisiana, and the Carolinas while areas such as southeastern Alabama saw an expansion of moderate drought. Much of the remainder of the country remains largely free of drought and abnormal dryness.

Northeast

The Northeast saw the development of two abnormally dry regions, in western New York and northeast West Virginia. Western New York has experienced precipitation deficits over the last three months, resulting in low streamflow values. While the deficits in West Virginia have occurred over a shorter time scale, they are more pronounced with stations reporting precipitation totals over the last 30 days that fell within the top three driest in a nearly 200-year period of record.

Southeast

The Southeast experienced warmer than normal temperatures. While much of the region saw above normal precipitation, it generally was not enough to overcome deficits of 5 to 7 inches in southern Alabama and the Florida Panhandle that have been in place since the beginning of the year. Small reductions in abnormal dryness and/or moderate drought occurred in southeast North Carolina, northeast South Carolina, and in south Florida. Moderate drought conditions expanded in parts of southeast Alabama, southwest Georgia, and the Florida Panhandle where deficits have continued to grow and streamflow and soil moisture remain low.

South

Locally heavy rainfall, 4 to 8 inches, fell over parts of central and east Texas, southern Arkansas, Louisiana, and northern Mississippi. Abnormally dry conditions and moderate drought were improved in central and southern Louisiana, with dryness/drought persisting in areas where long-term precipitation and soil moisture deficits still exist. Likewise, Mississippi saw a reduction in abnormal dryness in the south-central portion of the state. Texas saw a mixture of improvements and degradations. Conditions generally improved in central and south Texas where severe drought was eliminated and moderate drought and abnormal dryness were reduced in response to the recent rainfall and improved soil moisture. Degradations generally occurred in the north Texas, which missed out on the surplus rainfall and where precipitation and soil moisture deficits continue to build.

Midwest

Cooler than normal temperatures prevailed across the Midwest last week with near normal precipitation falling across much of the region. The region remained free of drought or abnormal dryness.

High Plains

Precipitation across the High Plains was generally near normal over the last week, with the exception of northeast Nebraska and southeast South Dakota. Temperatures were warmer than normal in all but eastern North Dakota. Temperatures ranged from 3 degrees below normal in Grand Forks to 14 degrees above normal in the Nebraska Panhandle. No changes were made to the map this week and the area remains free of drought and abnormal dryness.

West

With the exception of Wyoming, conditions in the West improved or maintained status quo. A series of storms brought heavy rain and mountain snow to the Pacific Northwest resulting in the elimination of abnormal dryness in northern California and a one-category improvement over much of Oregon. While Washington also received beneficial rains, the amounts were not sufficient to put a dent in the long-term deficits and drought emergencies still exist in several river basins. Elsewhere, reductions in abnormal dryness also occurred in western Idaho, and in northern and east-central Nevada. Moderate drought conditions developed in the Big Horn Mountains of Wyoming where snowpack has been low all winter.

Alaska, Hawaii, and Puerto Rico

Moderate and severe drought continued in southeastern Alaska. This week, the impact designation was changed from “L” to “SL”, to indicate that the area is experiencing short-term impacts and seasonal shortages in precipitation in addition to those caused by long-term dryness. Reduced hydropower caused by low reservoir levels has necessitated the use of diesel generators, negatively affecting air quality in the region. In Hawaii, weekend rain on the windward side of the Big Island was of little benefit to the existing drought areas. Moderate drought conditions spread eastward into the Honokaa and Ookala areas and over the upper slopes of Mauna Kea. Ranchers in the area reported hauling water for cattle due to poor pasture conditions. Moderate drought also expanded near South Point. The leeward areas of Oahu continued to dry out, resulting in the expansion of moderate drought. Dry conditions have been a contributing factor to recent brush fires outside of Honolulu. Rainfall brought some relief to the abnormally dry areas in northwestern Puerto Rico, with the exception of Rincon, Aguada, and Anasco. Abnormal dryness also developed on the southwestern and south-central part of the island which are experiencing elevated fire conditions.

Pacific Islands

Summary by Richard Heim. El Nino and post-El Nino-like dry conditions continued across parts of the USAPI during this USDM week (4/3/19-4/9/19). Inter-Tropical Convergence Zone (ITCZ) activity occurred across southern Micronesia in the form of a near-equatorial trough in the west, with a couple weak disturbances or circulations moving through it, and converging trade winds in the east. A dry trade wind regime blew drier subsiding air from the North Pacific subtropical ridge (the North Pacific High) across northern portions of Micronesia. The ITCZ convection extended south of the equator as the South Pacific Convergence Zone (SPCZ). The SPCZ was manifested as a surface trough near the Samoan Islands, but its influence was weak due to a competing surface ridge which built over the islands. The ITCZ and SPCZ activity was reflected on satellite-based estimates of 7-day precipitation (QPE) as a broken band of rainfall from southeast Micronesia (across the southern Marshall Islands, RMI) extending west-northwest to the Republic of Palau and Yap State. Areas of 2-plus inches of rain were in this band, with 4-plus inches around northern Palau, parts of Yap State, and from Kosrae State to the southern RMI. Little to no rainfall was indicated on the QPE north of this band. The precipitation band extended south of the RMI to about 10 degrees south, then fell apart toward the Samoan Islands.