Drought Monitor: Beneficial showers in the East, Midwest

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Weather Summary:  For the second week in a row, beneficial showers peppered the East.  Much-needed rain also fell across the northern Plains and upper Midwest, although amounts were highly variable.  In contrast, “flash drought” conditions quickly worsened across the remainder of the Midwest, portions of the central and southeastern Plains, and the Mid-South.  The term “flash drought” describes a period of short-term dryness, often accompanied by above-normal temperatures, which has an adverse impact on crops and pastures.  Elsewhere, much of the West—excluding the northern tier of the region—continued to slip deeper into drought under a warm, mostly dry weather regime.

The East:  Once again, appreciable rainfall from the Mid-Atlantic States into southern New England chipped away at dryness (D0) and moderate to severe drought (D1 to D2).  Despite some lingering year-to-date rainfall deficits in locations such as Washington, D.C., drought impacts were quickly diminishing.  Through May 22, Washington’s year-to-date precipitation stood at 9.87 inches (67% of normal).  Farther south, a core region of extreme to exceptional drought (D3 to D4) lingered across central and southern Georgia, northern and central Florida, southern South Carolina, and southeastern Alabama.  On May 19, the first Atlantic tropical storm of the season, Alberto—the earliest named system since Andrea on May 9, 2007—formed about 120 miles south of Cape Fear, North Carolina.  The storm was compact and remained offshore during its entire lifespan, resulting in negligible impacts other than contributing to an increase in convective activity along the southern Atlantic Coast.

The Mid-South:  Rapidly deteriorating agricultural conditions resulted from another week of very warm, mostly dry weather.  During the week ending May 20, the portion of pastureland rated in very poor to poor condition increased by at least 8 percentage points in Arkansas (from 11 to 23%) and Missouri (10 to 18%).  During the same 7-day period, USDA reported that the portion of topsoil moisture rated very short to short skyrocketed from 41 to 66% in Arkansas and 23 to 57% in Missouri.  As a result, moderate to severe drought (D1 to D2) expanded in an area centered on the northern Mississippi Delta and the lower Ohio Valley.

The Midwest:  For the week ending May 20, the portion of topsoil moisture rated very short to short jumped at least 20 percentage points in Iowa (from 9 to 44%), Indiana (15 to 43%), Illinois (12 to 33%), Michigan (7 to 32%), and Wisconsin (6 to 30%).  As a result, there was a fairly large expansion of abnormally dry conditions (D0) across the central and eastern Corn Belt.  Hot weather, short-term dryness, and crop demands were to blame for the rapid depletion of topsoil moisture.  On May 18, high temperatures soared to daily-record levels in St. Cloud, Minnesota (94°F), and Eau Claire, Wisconsin (91°F).  The following day, May 19 featured daily-record highs in Michigan locations such as Traverse City (92°F) and Alpena (91°F).  In contrast, showers developed across the upper Midwest.  Although upper Midwestern rainfall coverage was patchy, drought development was arrested in some areas.  Little rain fell, however, east of a line from southeastern Nebraska to Lake Superior.

The Plains:  Like the Mid-South and much of the Midwest, a continuation of warm, dry weather led to rapid deterioration in crop and pasture conditions.  For the week ending May 20, the portion of Montana’s rangeland and pastures rated in very poor to poor condition jumped from 13 to 24%.  During the 2-week period ending May 20, the portion of the Kansas winter wheat crop rated very poor to poor doubled from 11 to 22%.  However, shower activity began to increase across Montana, Nebraska, and the Dakotas late in the drought monitoring period, helping to slow the expansion of dryness (D0) and moderate drought (D1).  Farther south, warm, dry weather returned to the Oklahoma and Texas early in the period, following the previous week’s drought-easing rainfall.  Still, the May 1-22 rainfall of 9.84 inches (364% of normal) marked San Antonio’s highest May total since 1993, when 12.47 inches fell.

The West:  Both short- and long-term drought continued to affect large portions of the West.  Only the northern tier of the region, from the Pacific Northwest to the northern Rockies, remained largely free of drought.  Worsening drought was noted in parts of Wyoming and the Four Corners States.  During the week ending May 20, the portion of Wyoming’s rangeland and pastures rated in very poor to poor condition leaped from 18 to 33%.  More than half of the rangeland and pastures were very poor to poor in New Mexico (82%), Arizona (69%), and Nevada (51%).  Although nine of the eleven Western States have a buffer against developing drought in the form of abundant reservoir storage, high-elevation snow packs have largely melted out across the southern half of the region.  Reservoir storage is below average for this time of year in Arizona and New Mexico, compounding water-supply issues in those two states.  A new area of extreme drought (D3) in northwestern Colorado is reflective of very low water year-to-date precipitation totals—in the 5th percentile or lower at several locations.  In addition, severe drought (D2) was expanded in several other parts of the Four Corners States.  In recent days, several wildfires have been active in the Southwest.  In central Arizona, both the Gladiator (just east of Crown King) and the Sunflower fires (well north of Mesa) have charred at least 15,000 acres of vegetation.

Hawaii, Alaska and Puerto Rico:  Currently, there is neither dryness nor drought depicted in Alaska and Puerto.  The drought situation across Hawaii’s central and eastern islands continued to gradually deteriorate due to unusually dry conditions since the beginning of the late-spring and summer “dry” season.  On the Big Island at Hilo, April 1 – May 22 rainfall totaled just 10.77 inches (61% of normal).  On the leeward side of the Big Island, deterioration of pastures was reported.

Looking Ahead:  During the next 5 days (May 24-28), daily showers and thunderstorms will linger in parts of the East, particularly across southern Florida and the Mid-Atlantic States.  Meanwhile, a series of disturbances will maintain cool conditions and periods of rain from the Pacific Northwest into the upper Midwest.  Five-day rainfall totals could reach 2 to 4 inches in the upper Midwest and 1 to 2 inches on the northern Plains.  In contrast, mostly dry weather will prevail across the nation’s southern tier, excluding southern Florida.  During the Memorial Day weekend, heat will build across the South, East, and lower Midwest, with many locations expecting multiple days of 90-degree heat.

The NWS 6- to 10-day outlook for May 29 – June 2 calls for near- to above-normal temperatures nationwide, except for cooler-than-normal conditions from the northern Plains into the Great Lakes region.  Meanwhile, near- to below-normal rainfall across the majority of the U.S. will contrast with wetter-than-normal weather in the Southeastern and Atlantic Coast States.

Author: Brad Rippey, U.S. Department of Agriculture

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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