There were big changes in the Drought Monitor depiction of dryness and drought this week compared to last, primarily across the contiguous U.S. east of the Mississippi River.
Inundating tropical rains literally washed away the entrenched moderate to severe drought that had covered southern Florida. The opposite was the case farther north across most of the eastern states. Rainfall has been generally below-normal across a majority of this region for the past one to two months, with subnormal rainfall dating back three or more months in some areas. Increasingly, above-normal temperatures have accompanied the dryness, which has added to the rate of surface moisture depletion.
Temperatures have had the greatest impact on conditions in the climatologically-hotter areas across the South until late this past week, when excessive heat started to engulf the Great Lakes and Northeast. Declining streamflows and dropping soil moisture started to become obviously apparent over large sections of the East. As a result, there was an expansive increase in new D0 coverage east of the Mississippi River and north of central Florida, with only small spots in Georgia and Maine experiencing any discernable relief.
Farther west, although changes were not as expansive, both south-central and north-central portions of the Plains and Rockies also saw significant areas where dry conditions developed or intensified. There were other areas of heavy rain outside southern Florida, but most of it fell on sections of the Upper Midwest that have received consistently above-normal precipitation for at least several weeks, thus bringing no changes to areas of dryness and drought.
West of the Mississippi River, limited improvement was introduced in relatively small swaths in northeastern Arkansas, central and western Kansas, southern Nebraska, southwestern Montana, and a few adjacent locales.
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
New, relatively small areas of D0 were brought into south-central Tennessee and part of east-central Tennessee, with abnormal dryness expanding from the areas covered last week into somewhat larger parts of north-central Mississippi, and portions of northern and western Arkansas.
In contrast, light to moderate rains (up to 1.5 inches) eased brought just enough relief to prompt 1-category improvements in parts of northeastern Arkansas. Scattered moderate rains (1 inch or more) with isolated heavy amounts (up to 3 inches) moistened parts of the northeastern fringes of the D0 region in central Texas, and some patches in eastern New Mexico and western Texas.
Meanwhile, growing short-term deficits have begun to quickly reduce surface moisture levels in western Oklahoma east of the Panhandle, so this entire region has been placed in moderate drought. Streamflows declined significantly this past week, with several locations reporting flows more indicative of D2 to D4 conditions if no other parameters were considered, especially over the southern half of this area.
Declining streamflows and increasing short-term rainfall deficits prompted new D0 areas in parts of northern and western Arkansas where little or no rain fell last week, and similarly low streamflows were observed in parts of this region as well.
Midwest
Heavy rains fell on extreme northern and western Iowa, parts of central and northwestern Missouri. Almost none of these areas, however, were assessed with any degree of dryness last week, so improvements on the Drought Monitor were limited to small parts of northeastern Missouri.
Several tenths of an inch of rain, at best, fell on the rest of the region. Across the southern tier of the Midwest region, conditions the past few weeks have progressed similarly to many locations in the northeast and southeast regions, with persistently below-normal precipitation increasingly aggravated by periodic hot weather (especially late this past week) leading to a relatively quick decline in surface moisture and a simultaneous increase in 30- and 60-day precipitation deficits, all of which became limpid across a large area over the course of the last seven days.
Broad new areas of D0 were introduced across Iowa and Missouri also saw areas of D0 expansion. Almost all of the new D0 areas are experiencing significantly low 30-day precipitation totals and some degree of 60-day shortfalls as well. Farther northwest, antecedent D0 conditions are lingering across central and northeastern Iowa.
High Plains
Moderate to heavy rains soaked a sizeable part of the High Plains Region this past week. Most fell on locations not experiencing antecedent dryness and therefore provided no relief, but several areas that have been entrenched in drought did record enough rainfall to consequentially improve conditions.
Heavy rainfall totals of 2 to locally 4 inches were fairly common over a fairly broad swath from northeastern to southwestern Kansas, making this one of the few states to experience more relief than deterioration last week. Patches of 1-catregory improvements were introduced where heavier rains fell, continuing a general trend of decreasing dryness observed since mid-May.
At that time, almost one-third of the state was covered by severe drought (D2) or worse. Four weeks later, less than 8% of the state is similarly dry. Farther north, heavy rains also affected parts of areas experiencing antecedent dryness in southern Nebraska. Generally 1 to 3 inches of rain eliminated moderate drought in south-central Nebraska, and whittled away some D0 in some other parts of south-central Nebraska. Moderate to heavy rains also ended D0 conditions in a few small areas in central South Dakota as well.
Farther west, however, continued dry and warm weather engendered areas of deterioration in central portions of the Rockies and High Plains, as has been scattered across these areas occasionally for the past several weeks. Burgeoning 60- to 90-day precipitation shortfalls along with acute root-zone moisture and ground water deficits led to a broad expansion of moderate drought in eastern Wyoming and western Nebraska.
The dry week compounded by recent heat and increasing short-term precipitation shortfalls also led to some lesser D0 and D1 expansion in other parts of Wyoming and a few areas across Colorado and the central and western portions of South Dakota.
West
Conditions were seasonably dry in this broad region, so in sharp contrast to areas farther east, very few changes were made. But one area of deterioration was in part of New Mexico, based on high wildfire danger and ongoing fires that are threatening dwellings and other structures near the town of Ruidoso.
Unusually dry, hot, and windy weather combined with low fuel moisture are abetting favorable conditions for the rapid development and spread of wildfires near and south of Ruidoso, so the D1 through D3 areas in this region were expanded somewhat to the northwest. Meanwhile, improving soil moisture and some recent light to moderate precipitation—especially at higher elevations—prompted improvement from moderate drought (D1) to D0 in southwestern Montana and a small part of adjacent Wyoming.
Looking ahead
In the 24 hours after the valid period for this Drought Monitor ended (7 a.m. central time June 18), excessive to historically heavy rains fell on the central Oklahoma Panhandle and some adjacent locales in Texas and, to a lesser extent, Kansas. Over 7 inches of rain inundated some sites in the central Oklahoma Panhandle during the 24-hour period.
Climatologically, these amounts are expected only once every few hundred years, at most, in this region. During the next five days (June 20-24), moisture from the first named tropical system in the Atlantic basin this year (Tropical Storm Alberto) is expected to stream into southern Texas, dropping 3 to locally 8 inches of rain from Webb County (north of Laredo) and San Patricio County (north of Corpus Christi) southward into Mexico. An inch or more is possible as far north as Del Rio and East Matagorda Bay.
Farther north, heavy to excessive rains of 3 to 6 inches are expected to drench a swath from southeastern South Dakota through much of southern Minnesota and into part of northern Wisconsin —an area frequently affected by heavy rains over the past several weeks—and a smaller area over southwestern Colorado.
Amounts exceeding 1.5 inches are forecast from parts of the north-central Great Plains eastward through the upper Mississippi Valley and scattered higher elevations in northern New Mexico and western Colorado.
In contrast, fairly dry weather—featuring a few tenths of an inch of precipitation at best— is expected in the areas of dryness and drought affecting the Far West, Intermountain West, central and northern Texas, most of Oklahoma, and interior portions of the lower Mississippi Valley. Other locations across the contiguous United States are forecast to receive near typical amounts for a week in mid-June.
Most of the contiguous states are expected to average warmer than normal for the five-day period, with all areas north and east of the middle and lower Mississippi Valley, the immediate Gulf and South Atlantic Coasts, and Florida forecast to average at least 2 degrees Fahrenheit above normal.
Similar anomalies are anticipated in the central and south-central Plains, the northern half of the Rockies, the Intermountain West, and the Far West. Parts of interior California, the northern Great Basin and adjacent northern Intermountain West, south-central Great Plains, and a large swath from the middle Mississippi Valley eastward through the mid-Atlantic and adjacent regions are expected to average 6 to 10 degrees above normal.
Subnormal mean temperatures should be confined to Deep South Texas, much of the Rio Grande Valley, and much of the Big Bend, part of the upper Mississippi Valley.
The Climate Prediction Center’s 6- to 10-day outlook, valid June 25 to 29, favors a continuation of above-normal temperatures over a vast majority of the contiguous states, with the greatest odds (over 80%) across much of the Four Corners region.
A large part of the contiguous states also show elevated chances for above-normal precipitation, although in most areas the shift of the odds is modest. There is a 33 to near 50% chance of surplus precipitation in the Four Corners region, and from the Plains eastward through the Mississippi and lower Oho Valleys, Great Lakes region, southern Appalachians, Southeast, and Florida.
Odds for wetter than normal weather exceed 50% in much of Arizona and New Mexico. Neither abnormal wetness nor dryness is favored in the Northeast, mid-Atlantic region, northern Rockies, and Southwest while drier than normal conditions are only favored in the Great Basin and adjacent areas in the northern Intermountain West and California.
Richard Tinker is with the National Oceanic Atmospheric Administration, National Weather Service, National Centers for Environmental Prediction, and Climate Prediction Center.
