National Drought Monitor for July 8, 2014
Summary
During the past 7-days, heavy rain (greater than 2 inches) fell in parts of the Northeast, eastern North Carolina, the Florida peninsula, the Great Lakes region, northern and central portions of the Mississippi Valley, and parts of the southern Great Plains and Southwest. An unusually strong cold front for early July moved across the eastern contiguous U.S. early in the period, approaching the Atlantic Seaboard as a Category-2 hurricane (Arthur) was moving across the Outer Banks of North Carolina. As the hurricane accelerated to the northeast, it gradually became incorporated into the larger-scale cold front and associated low pressure system, resulting in heavy rains across portions of the Northeast. Meanwhile, the onset of the Southwest summer monsoon across Arizona and New Mexico brought moderate precipitation (0.5-2.0 inches) to portions of the Four Corners region.
Alaska, Hawaii, and Puerto Rico
Based largely on June rainfall data, D0 was expanded across the western one-half of the island of Molokai. D0 was introduced to the western slopes of Lanai, and on the Big Island, D0 was expanded to include the northwest slopes from the Kona International Airport to the Hawi/Pololu Valley. Most of Kauai and Oahu were wet in June, and drought is not an issue at this time for these two islands. In Puerto Rico, deteriorating conditions warranted the expansion of abnormal dryness, and the introduction of moderate drought (D1) in south-central and northeast Puerto Rico. This is based on low stream flows, and the 60-, 30-, and 14-day DNPs and PNPs. Drought is not an issue at this time in Alaska.
Mississippi Valley
This past week was much drier in Iowa, with the exception of 3-inch amounts in far southwest Iowa, which is almost three times the weekly normal. The latest USDA NASS report has only 6 percent of the southwest Iowa crop district as short or very short of subsoil moisture. Accordingly, the D0 was removed from this area. In southeast Iowa, the area covered by D0 received near-normal precipitation this past week. Year-to-date (YTD) rainfall deficits range only between 1.0-3.5 inches, with normal YTD precipitation nearly 20 inches. Therefore, this area of D0 is mostly a longer-term remnant of the very dry second half of 2013. Farther south, in southwest Arkansas and adjacent northwest Louisiana, hot temperatures, increased evaporation rates, and 90-day PNPs favor the expansion of abnormal dryness across this region.
Northeast and mid-Atlantic
A complex low pressure system involving two cold fronts and several waves of low pressure, along with moisture from hurricane Arthur, resulted in the deposition of moderate to heavy rainfall (generally 0.5-4.0 inches, locally heavier) across portions of the Northeast and mid-Atlantic region. The area of abnormal dryness (D0) over southeastern New England on the drought depiction was split into two unequal parts, with some D0 being removed where the heaviest rain fell. AHPS depicted rainfall departures of 2-4 inches above normal for the past 7-days. Though 0.5-1.0 inch of precipitation was measured over the southern Delmarva Peninsula, the depiction remains unchanged from last week. In southwest Virginia, the coverage of abnormal dryness (D0) was expanded, to be more consistent with significant AHPS Departures from Normal Precipitation (DNP) during the past 60-, 30-, 14-, and 7-days, stream flows within the lowest quartile, and the Vegetation Drought Response Index ( VegDRI) plot. Six to nine inches of rain is estimated by the Long Term Palmer Drought Severity Index (PDI) to end the drought (bring the PDI to -0.5) in southwest Virginia. Danville (Pittsylvania County) recorded its third driest June on record (1948-2014) with 1.23 inches of rain. The first driest was 1.06 inches in 2008, and the second was 1.13 inches in 1985.
Ohio/Tennessee Valley
Drier conditions returned to much of Kentucky and Tennessee during the past 7-days. Stream flows are generally near to below average in Kentucky, and near-average in Tennessee. Moderate drought (D1) was introduced to parts of southeast Kentucky based on stream flows and 90-day Percent of Normal Precipitation (PNP) being around 60 percent of normal. In northern Kentucky, D0 was expanded eastward along the Ohio River, in response to 30- and 60-day rainfall deficits. In contrast, the small area of D0 in western Kentucky (which was considered marginal to begin with) was removed after very recent rain. In southeast Tennessee, abnormal dryness (D0) was trimmed back to account for rainfall deficits (DNPs) during the last 60-, 30-, and 14-days.
Southeast
30-day PNPs, and declining soil moisture and pasture conditions suggest the early stages of a developing flash drought in this region. The AHPS 30-day PNPs reveal a long, broad swath of 50-percent of normal rainfall from the Florida Panhandle to the Delmarva Peninsula, with values ranging from 25 to 75 percent of normal. Forty-two percent of the state of Georgia reported Short or Very Short Topsoil Moisture, with North Carolina reporting 38 percent, South Carolina 60 percent, and Florida 17 percent. The extent of Subsoil Short or Very Short Moisture is 32 percent in both Georgia and North Carolina, 56 percent in South Carolina, and 16 percent in Florida. Pasture conditions are declining as well, with now just 40 percent rated Good to Excellent in South Carolina, and 50-60 percent in North Carolina, Virginia, Delaware, and Kentucky. Based on these indicators, and low stream flows (lowest quartile of historical distribution), abnormal dryness (D0) was added to the drought depiction in the westernmost counties of South Carolina, as well as a sizable portion of eastern South Carolina. D0 was also expanded in central North Carolina (which largely missed out on the heavy rainfall associated with an unusually strong cold front and Hurricane Arthur this past week), and north-central Georgia. In southeast Alabama, D0 was added to the counties of Coffee, Dale, Henry, Barbour, Geneva, and Houston, based on similar indications for the other Southeastern states. According to the National Weather Service’s Southeast River Forecast Center, the southern part of the Chattahoochee River at the W.F. George Lake and Dam (U.S. Army Corps of Engineers) has a current (July 9) river stage of 101.99 feet, far below the nominal flood stage value of 134 feet. In addition, D0 was also introduced to portions of Jefferson and Shelby Counties in north-central Alabama.
Southern and Central Plains
A relatively narrow band of heavy rain (greater than 2 inches) was observed from near Lubbock to Wichita Falls in Texas, while a fairly concentrated area of heavy rain was reported from about Houston to Victoria in eastern Texas. About a dozen relatively minor revisions were made to the depiction in Texas this week, some degradations and some improvements. No changes were made in Oklahoma, Kansas, or Nebraska this week, in part due to widespread areas of well above-normal precipitation in the past 30-days (3-6 inches, locally greater, especially in Kansas and Nebraska). Another reason for not making alterations this week is to better assess the impacts from recent precipitation, and to consider areas ripe for downgrades next week. In eastern South Dakota, no changes were rendered this week either to the drought depiction. However, the coverage of abnormal dryness in this area will need to be revisited next week, along with the possibility of introducing some moderate drought (D1). In Wessington Springs, corn still looks okay, but surface water is lacking and grasses are drier.
Southwest and California
The initial moisture surges of the summer monsoon commenced on schedule across Arizona and New Mexico this past week. River Forecast Center rain gauge data depicts a few widely scattered 2-3 inch rainfall amounts, but much of Arizona and New Mexico reported moderate amounts of precipitation (0.5-2.0 inches). In northwest New Mexico, which missed out on the significant rainfall this past week, extreme drought (D3) was expanded eastward across all of San Juan County, and continuing across the western one-third of Rio Arriba County. In south-central Colorado, a one-category downgrade was made, based on very dry short-term SPI’s (less than -1.5), and on VIC soil moisture model considerations. In southeast Colorado (western Kiowa County), conditions are still deplorable with little vegetation on the ground, and there is also the occasional dust storm kicking up. In Otero County, where better moisture conditions exist, a one-category improvement was made to the depiction. In Baca County, a one-category improvement was rendered based on June-early July precipitation, SPI values near and slightly above zero, and reports that the wheat harvest is looking better than it has in this county for several years. No other modifications were made throughout the Southwest or California. As an important side note, according to the Federal Bureau of Reclamation, southern Nevada’s Lake Mead is expected to fall this week to its lowest level since 1937, when the manmade lake (the largest reservoir in the United States) was first being filled.
The Pacific Northwest
No alterations were made to the depiction this week. In southwest Idaho, the flow of the Owyhee and Bruneau Rivers is near record lows for the second consecutive summer, while record low Water-Year-To-Date (WYTD) precipitation has fallen at various SNOTEL sites in central Idaho.
Looking Ahead
During July 10-14, 2014, a broad band of moderate precipitation (0.5-2.0 inches) is expected from Arizona and New Mexico northeastward and eastward across the north-central Plains, the north-central Mississippi Valley, the Ohio Valley, and interior Northeast. A band of moderate to heavy rainfall (1.0-3.5 inches) is forecast for the central and eastern Gulf Coast states, and the southern Atlantic states from Florida to Delaware.
For the ensuing 5-day period, July 15-19, 2014, there are enhanced odds of above-median rainfall in the Southwest, the Southeast, and over northern and southwestern Alaska. There are enhanced odds of below-median rainfall in the Pacific Northwest, from eastern Montana to Michigan, southern Texas, southern Louisiana, and over south-central and southeast Alaska including the Panhandle.