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Drought Monitor: Precipitation in the Four Corner States

USDA | Updated: 12/08/2011

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Weekly Weather Summary: As the week commenced, a strong storm system in the Northeast quickly departed, bringing tranquil weather to the East and Southeast for the remainder of the week. In the Southwest, however, an upper-air low developed and intensified, generating strong winds in the Southwest, especially southern California, and gradually spreading precipitation and colder air into the Four Corner States. Parts of Arizona, New Mexico, and southern Colorado received between 1 and 2.5 inches of precipitation. As this system tracked eastward into the Nation’s midsection over the weekend, moderate to heavy precipitation (more than 2 inches) fell from central Texas northeastward into the eastern Great Lakes by Tuesday morning. Heavy rains (more than 4 inches) were reported in parts of northeastern Texas, northwestern Louisiana, southern and eastern Arkansas, western sections of Tennessee and Kentucky, and southeastern Missouri. A second band of light to moderate precipitation (1 to 2 inches) occurred from central Kansas northeastward into southern Wisconsin. In contrast, little or no precipitation fell on the West, northern Plains and upper Midwest, and Southeast (from southeastern Louisiana eastward to the Carolinas). Temperatures averaged below normal in the western half of the Nation and in the Southeast, while milder weather was limited to the Northeast, Great Lakes region, and northern Plains.

Southeast: After last week’s beneficial (and torrential in some areas) precipitation in most of the Southeast, much drier weather returned to southern and eastern sections. Heavy rains, however, were not absent from the South as western and northern Louisiana, Arkansas, northwestern Mississippi, and western Tennessee received 2 to 4 inches of rain, with local totals to 6 inches. Short-term deficits (30- and 60-days) were effectively eased or erased in western Louisiana and southern Arkansas, but medium (6 to 12 months) to long-term (more than a year) departures still remained (20 to 30 inches). As a result, a 1-category improvement was made to the D4 area on the Louisiana and Texas border where 6-month and year-to-date deficits were noticeably less than surrounding areas. In contrast, the SPI blend indicated that D4 still remained in this region. Elsewhere, D0 to D3 1-category improvements were made further north were recent conditions have been wetter, this week’s precipitation totals were greater (3 to 5.5 inches), and long-term deficits were smaller. In northwestern Alabama, another week with light to moderate precipitation (0.7 to 1.5 inches) effectively alleviated the D0(S). At 12-months, a large precipitation anomaly gradient existed between northern Arkansas (20 inch surplus) and northwestern Louisiana (20 inch deficit).

In contrast, much different weather prevailed to the east as locations from southeastern Louisiana to Florida and northward into the Carolinas saw little or no rain. In southeastern Louisiana, southern Mississippi and Alabama, and parts of southern Georgia and the Florida Panhandle, 60 and 90-day precipitation has been less than half of normal, with accumulated shortages of 5 to 10 inches. Many USGS averaged stream flows at 7-, 14-, and 28-days were below the tenth percentile as of Dec. 6. With this information, D0 and D1 was expanded slightly northward, and D2 spread into southeastern Louisiana. Some slight expansion of dryness and drought was made in counties (Wakulla, Jefferson, Taylor) near Tallahassee, FL, which is flirting with its driest year on record (since 1893), and in northeastern Florida (Alachua County) where short-term (and long-term) deficits are accumulating and affect prairie wildlife. Farther north, growing short-term (out to 90-days) precipitation deficiencies called for expansion of D0(SL) into the central and southern Coastal Plains of North Carolina.

Southern and Central Plains: Widespread welcome precipitation fell across much of Texas, Oklahoma, and Kansas as the recent bouts of precipitation (since mid-September) have greatly eased or eliminated short-term deficiencies. Unfortunately, long-term deficits remained, especially after the driest 12 months on record (Oct 2010-Sep 2011) in Texas and near-record 12-month dryness in surrounding states (OK, LA, NM) that was exacerbated by the record summer heat, which will take time and continued surplus precipitation for major improvement. Nevertheless, 2 to 4 inches of rain from central Texas northeastward into southeastern Oklahoma, plus 1 to 2 inches in parts of northern Texas, southern Oklahoma, and central and northern Kansas, were enough to make a dent in some of the severe, extreme, and exception drought areas. In addition, 0.5 to 1 inches in the Texas Panhandle and the remainder of Oklahoma and Kansas also brought some modest improvements. But not all areas of Texas saw relief from the rains. For example, although parts of central and eastern Texas received between 1.5 and 3 inches of rain, SPI blends, long-term deficits (at 18-months, 25 to 35 inches), and soil moisture values still at D4 levels, and conditions were kept status-quo there. Farther north, where recent conditions have been better and long-term shortages were not as great as further south, the light to moderate precipitation (1 to 2 inches) provided a general 1-category improvement in most of Kansas. In western, southwestern, and southern Texas, the precipitation was light enough (less than 0.5 inches) to prevent deterioration, but not large enough for improvement.

Midwest and Northern Plains: For the second week in a row, light to moderate precipitation (1 to 2 inches) fell on southern and eastern sections of the Midwest, except this week’s 1 to 2 inch amounts were shifted a bit farther to the north and west. This allowed for improvement of short-term D0 and D1 areas in northern Missouri, southwestern, southeastern, and extreme northeastern Iowa, and southeastern Nebraska. The recent wet spell has eliminated precipitation shortages out to 90-days (where D0 was erased), and greatly diminished short-term deficits where the remaining D0 and D1 were.

In contrast, weekly totals sharply dropped off to the north and west, and little or no precipitation was observed in the Dakotas, most of Minnesota, northeastern Nebraska, and extreme northwestern Iowa. Although fall and winter normal are generally low in the northern Plains and upper Midwest, an extremely dry autumn and early December called for an expansion of D1 into areas with 25 to 50 percent of normal precipitation during the past 90 days (e.g. east-central and northwestern Minnesota). Elsewhere, no changes were made.

The Southwest: Early in the period, a strong upper-air low developed and intensified across the region. The low initially brought strong winds to parts of the region, including Santa Ana winds gusting to near 100 mph in southern California. Later, the storm generated widespread light to moderate precipitation (0.3 to 1.5 inches), enough to prevent deterioration but not enough to improve conditions (e.g. status quo). Some exceptions to this were in central Arizona (up to 2.6 inches) where 90- and 180-day deficits were close to zero (D1 to D0), in southwestern New Mexico (two straight weeks of 0.5 to 1.5 inches of precipitation) where small surpluses existed out to 180-days (D3 to D2), and in northwestern New Mexico (0.5 to 1 inches this week, 0.2 to 0.5 inches last week) where the Water Year SNOTEL Snow Water Content (SWC) stood at 124 percent of normal in the Rio Chama Basin. So far this water year, the mountain basins in central Arizona and northern New Mexico have observed above normal basin average precipitation and SWC. Accordingly, a general one-category improvement was made on the D0 to D2 areas.

The Northwest: In stark contrast to last week’s moderate to heavy precipitation from the Cascades westward, much quieter and cooler weather prevailed across the Northwest this week. Although it is still early in the water year (since October 1), precipitation has averaged about half to two-thirds of normal in the SNOTEL mountain basins of Oregon, California, and Nevada, according to the USDA/NRCS. And in the Intermountain West, precipitation has been even more spotty and minimal. During the past 90- and 180-days, 25 to 50 percent of normal precipitation, and in some locations 10 to 25 percent, have fallen, and these D0 “watch” areas were expanded to include northeastern California, northwestern Nevada, and south-central Washington. Fortunately, normal are generally low in this region thus generating relatively small deficits. Precipitation, however, will be needed soon during the normally wet winter months to prevent degradation of conditions.

Hawaii: Early in the period (Tuesday through Friday), scattered light showers (daily totals between 0.25 to an inch, locally 1 to 3 inches) occurred mainly on the windward side of the islands while little or no rain fell on the leeward locations. By the weekend, shower activity greatly diminished across all of Hawaii, with most stations reporting no rain the rest of the week. On Oahu, subnormal November rainfall over the Koolau Range resulted in the spreading of D0 there. On the Big Island, spotty leeward November rainfall in the upper elevations of South Kohala and in the Pohakuloa region of the Hamakua District led to USDA/FSA reports of conditions similar to 2010 (bad). Ranchers have been destocking pastures and selling replacement heifers which will have long-term effects. Accordingly, D3(S) was extended southwestward from the northwestern portion into the central part of the island.

In contrast, some pasture regrowth occurred from Kepuni to Kaupo on southeast Maui from early November rains, but missed the southwestern section. As a result, D3(S) became D2(S) in southeastern Maui. On the Big Island, over 20 inches of rain in November on the east-facing slopes alleviated D0 there. There were no changes made for Kauai, Molokai, and Lanai.

Looking Ahead: For the ensuing 5 days (December 8-12), a storm system will track off the East Coast by late Thursday, bringing moderate to heavy precipitation to the mid-Atlantic and New England, with snow possible in parts of the central and northern Appalachians. Once this system departs, much quieter and colder weather will envelop the lower 48 States. The exceptions to this include light to moderate rain in southern Texas and most of Florida, especially the Atlantic side. A weak clipper system may bring light precipitation from the northern Rockies to the lower Great Lakes region, and a cold front will approach the West Coast late in the period.

The CPC 6-10 day outlook (December 13-17) indicates enhanced odds for above-normal precipitation in the lower and middle Mississippi, Tennessee, and Ohio Valleys, Great Lakes region, and Alaska. Subnormal precipitation is favored from the central Pacific Coast and Great Basin eastward into the northern and central Plains, and in Florida. Temperatures are expected to average below normal in the western third of the U.S. and above-normal in Alaska and the eastern third of the Nation.

Author: David Miskus, NOAA/NWS/NCEP/Climate Prediction Center

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)