A significant upper-level trough over the central part of the contiguous U.S., accompanied by a slowly moving cold front, brought up to several inches of rain across the eastern and southern states during the past week. The cold front reached the Eastern Seaboard and continued out over the western Atlantic, while the southern portion of this front stalled across the deep South. Later in the week, another upper-level trough moved out of central Canada across the northern High Plains of the United States, before heading east and bringing additional rainfall to the eastern contiguous U.S. In the Southwest, light to moderate precipitation (generally less than 1.5 inches) was observed in association with the summer monsoon. In the northern Rockies and Pacific Northwest, the USDA Forest Service reported approximately 40 large wildfires in progress as of August 26th, as warm and very dry weather persisted.
Hawaii, Alaska and Puerto Rico
Heavy rain (2-5 inches or greater) brought one-category improvements to some areas, though the intensity of rainfall did not permit much soil infiltration, instead going straight to runoff. Pastures remain destocked, since it is too soon for substantial grass regrowth. Nevertheless, abnormal dryness (D0) was removed from the islands of Niihau, Molokai, Lanai, and Kahoolawe. Some of the D0 coverage in Kauai, Oahu, and the Big Island was also trimmed away. No adjustments were made to the drought depiction in Alaska this week. In eastern Puerto Rico, where the drought is most extreme, little if any rain fell in association with the remnants of Danny, which at one time had reached major hurricane intensity. Tropical Storm Erika offers another opportunity for heavy, tropical rainfall for this area in the next few days. The western half of Puerto Rico, however, did receive decent rainfall amounts in association with Danny (generally 0.5-3.0 inches, locally greater). Stream flows are currently near to above-normal in northwestern Puerto Rico, and 30-day PNP values range from about 110-300 percent of normal. Accordingly, D0 in this area was removed. Otherwise, no other modifications were rendered, pending reassessment next week after Erika moves through the region, allowing impacts to be determined.
Lower Mississippi Valley and Southern Plains
Areas of moderate to heavy rain fell over portions of Texas (generally 0.5-4.0 inches, and 5.0-8.0 inch totals near the central Texas coast), which helped to alleviate severe short-term drought. This warranted a nearly complete overhaul of the drought depiction for the Lone Star state. In nearby Louisiana, continuing dryness across the north prompted a number of one-category degradations, while near the Gulf Coast, heavy rainfall (up to 5.0-8.0 inches) justified the removal of the severe drought (D2) area. In west-central and central Mississippi, a one-category degradation was made, which included the introduction of a severe drought (D2) area. In northern Oklahoma, two areas of abnormal dryness (D0) were eliminated from the depiction due to recent rain. In south-central Oklahoma, D0 and D1 coverage was slightly expanded, while a one-category improvement was made to parts of southeastern Oklahoma.
Northeast and mid-Atlantic
Although moderate to heavy rain (0.5-3.0 inches) fell across portions of Pennsylvania, New Jersey, southeastern New York and central Maine within the last 7-days, much of this region has recently (past 30-days) experienced widespread dryness. Other than a one-category improvement across western Long Island, NY, the only alteration made to the drought depiction in this area was to expand abnormal dryness (D0) across northwest Pennsylvania.
Northern and Central Plains
Abnormal dryness (D0) in eastern Montana was expanded south-southwestward due to the ongoing lack of precipitation. No changes were rendered to the depiction in Kansas, as rains that did fall during the week missed the residual D0 area in the northwest part of the state.
Northern Rockies and Pacific Northwest
A slight expansion of severe and extreme drought (D2 and D3) was made to the drought depiction in western Montana, and moderate drought (D1) was expanded across southeast portions of Idaho. The change in the Idaho depiction is based on low stream flows in the Teton and Henrys Fork basins, and precipitation deficits during the last 60-90 days. Extreme drought (D3) coverage was expanded across east-central Washington, and north-central and northeastern Oregon. Some considerations in the D3 expansion across the Northwest include daily record low stream flows, short-term (2-month) Standardized Precipitation Index (SPI) values, and low precipitation amounts from June 1 – present time throughout the region. In some cases, record or near-record dryness was reported for the June 1 – present time.
Several rounds of rain this past week resulted in a widespread, one-category improvement across north-central Alabama. A large portion of this region currently has daily stream flow values above the 90th percentile for this day of the year. In Georgia, targeted one-category improvements were rendered to the drought depiction in the north, due to above-average rainfall within the past 30-days. In the southern part of the state, areas have generally been on the dry side during this same period. Accordingly, one-category deteriorations were made. One-category degradations were also rendered to the depiction in north-central and northeastern North Carolina, along with the expansion of abnormal dryness (D0) into the Tidewater region of southeast Virginia. One-category improvements were made to western parts of North Carolina. The modifications to the depiction in North Carolina were based on such factors as rainfall during the past week, percent of normal precipitation (PNP) for the past 30-days, USGS streamflow and groundwater reports, Corps reservoir conditions, agricultural reports around the state, and Keetch-Byram Drought Index (KBDI) values which provide some measure of wildfire potential.
In Florida, rainfall across much of the state was adequate during the past 7-days, contributing to the removal of D0 from all of northeastern Florida, with the exception of Volusia County. Other parts of the state, however, remained rather dry. The first area is drought-stricken southeastern Florida, where severe and extreme drought areas (D2 and D3, respectively) were expanded slightly northward due to low water levels in the Everglades and the largest, separate, hydrologic unit that feeds into it (Water Conservation Area 3), as well as agricultural areas of southwest Palm Beach County, where groundwater levels are falling rapidly. The second area is the west-central Florida Panhandle, where abnormal dryness (D0) was expanded across the counties of Walton, Washington, Holmes, and Jackson, as well as adjacent counties in extreme southeast Alabama. Some areas within this last region have received less than 2 inches of rain in the past 30-days, at a time when agricultural water demand is 2-3 inches per week. Dryland farms on sandy soils tend to dry very quickly. Portions of the west-central Florida Panhandle counties of Gulf, Franklin, and Liberty remain drought-free, due to adequate rainfall associated with the sea-breeze convergence zone.
Southwest and California
Light to moderate rain (generally less than 1.5 inches) fell across southern sections of both Arizona and New Mexico. In New Mexico, no changes were made to the drought depiction. However, the counties of Curry, Roosevelt, and Lea, in eastern New Mexico (bordering Texas) are being monitored after a fairly dry August (so far) and soil moisture observations. No revisions were considered necessary this week in either the Southwest or California. An Associated Press report (dated August 20th) notes land in central California's agricultural region is sinking quickly because of the state's historic drought. This is forcing farmers to spend millions of dollars upgrading irrigation canals, and putting roads, bridges, and other infrastructure at risk. The extent of Short to very Short topsoil moisture for the state of California as a whole, is generally around 80 percent, a decline of about 5 percent since last week.
Upper Great Lakes region and Midwest
Heavy rains (generally 2-4 inches) during the past week helped to offset deterioration across the northern portion of the Red River Valley of the North Watershed near the Minnesota/North Dakota border, as well as across the Arrowhead region of northeastern Minnesota. The western and northern flanks of the abnormal dryness (D0) in the Arrowhead region were trimmed away accordingly. Along the border between Iowa and Wisconsin, the only alteration made to the depiction was the upgrade from moderate drought (D1) to abnormal dryness (D0) from Dubuque County in Iowa, based on receiving adequate rainfall in the past 7-days. The current North American Land Data Assimilation System (NLDAS) top 1-meter soil moisture anomaly (ensemble mean) ranges between 1-3 inches in this region.
For the upcoming 5-day period, August 27-September 1, attention will be focused on southeastern Florida, which may experience very heavy rainfall early next week in association with what is currently Tropical Storm Erika. Preliminary forecasts from the National Hurricane Center in Miami strengthen Erika to a hurricane either this Sunday or Monday, as it bears down on the southeastern Florida coast. However, Erika is still 4-5 days away from Florida, and its track and intensity may change significantly by then. In the desert Southwest, up to an inch of rain is predicted to fall during this period, which would at least help to offset additional deterioration in many areas. Several inches of precipitation are anticipated across the coastal ranges and Cascades of the Pacific Northwest, an area that could certainly use the moisture. Up to several inches of rain are also forecast for portions of the Midwest/Upper Midwest/Upper Great Lakes region. Depending on exactly where the rain does fall, some reduction in drought coverage is possible.
For the ensuing 5-day period, September 2-6, chances for above-median rainfall are elevated across the Southeast, due to the anticipated approach of Erika near the beginning of the period. Above-median rainfall is also favored across the northwestern and north-central portions of the lower 48 states, in advance of an upper-level trough. Odds for below-median rainfall are elevated across portions of the Northeast, and the southwestern and south-central CONUS. In Alaska, above-median precipitation is favored for much of the northern and western sections of the state, while below-median precipitation is favored along the southern coast from about Kodiak Island to Juneau.