Large-scale rain event hit many regions in country

Heavy to excessive rainfall impacted significant parts of the contiguous United States this past week.

Amounts of 4 to locally over 8 inches of rain were common across south-central and southeastern Georgia, northeastern Florida, the Florida Panhandle, portions of the immediate Gulf Coast, and a swath from central Texas through the middle Red River (South) Valley.

This brought an abrupt end to a protracted spell of hot and dry weather across the southern Great Plains that dated back through most of the summer. Dallas, Texas, recorded 4 inches of rain from Sept. 30 through the first week of October, including a daily total of 3.47 inches on Oct. 1.

Prior to that, Dallas recorded only 0.01 inch of rainfall July 16 through Sept. 29 (76 days), and a total of 2.27 inches going back to June 8. Elsewhere, a few broad areas recorded at least 2 inches for the week, including a large stripe through central and adjacent eastern Texas, central through southeastern Oklahoma. Also numerous patches from southeastern Colorado and much of Kansas through southeastern Nebraska, portions of Iowa, and northern Missouri received beneficial rain. In some of the wetter locations across the central Plains and adjacent Front Range, impacts improved substantially enough to justify 2-cagegory improvements on the Drought Monitor.

Meanwhile, several patches across northern Arkansas and southeastern Missouri also received 2 or more inches of rain. Moderate totals exceeding 0.5 inch, with localized totals topping 2 inches, affected areas from the central High Plains and southern half of the Great Plains that extended east and north of the region.

Meanwhile, light precipitation at best was observed through most of the northern Great Plains, and most areas from the High Plains to the Pacific Coast outside Kansas, Colorado, and northern New Mexico. Many existing areas of drought that were impacted by the heavy precipitation experienced marked relief, but despite expansive areas receiving little or no measurable precipitation, drought intensification was limited in extent, largely due to the lower temperatures and the typical autumnal decline in human and environmental water demand.

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

A variable precipitation pattern was observed across northern and northwestern Arkansas with increased moisture deficits and deterioration scattered across southern and eastern Arkansas.

Farther west, across Texas and Oklahoma, broad areas recorded heavy to excessive precipitation, resulting in several sizeable areas of widespread improvement. Multiple inches of rain—for the second consecutive week in some areas—induced improvements across most of southeastern and Deep South Texas, and in a swath from central Texas through much of the Red River (South) Valley into central Oklahoma.

Farther west, across the Big Bend and the Texas and Oklahoma Panhandles, light to moderate precipitation following the excessive amounts recorded last week led to widespread one-category improvements. Enough precipitation was observed to support 2-category improvements at a few locations in Deep South Texas, south-central Oklahoma, and the western Oklahoma Panhandle.

There were a few patches in southwestern Texas and the northern interior missing the heavy precipitation that hit most locations over the past couple of weeks, resulting in scattered spots of deterioration. Improvement was far more common across Texas and Oklahoma; however, as opposed to the mixed bag of changes noted farther east.

Midwest

Dryness and drought continued affecting the southern and northern tiers of the region this past week while persistently wet weather over the past few months has a void of dryness and drought stretching from Iowa and northern Missouri eastward north of the Ohio River and south of the Great Lakes States.

Drought remained essentially unchanged over most of Minnesota, with only isolated changes noted.

Along the southern tier of the Midwest Region, continued subnormal precipitation allowed for areas of deterioration across parts of southern Missouri while locally higher amounts prompted limited improvement in west-central Missouri.

High Plains

Widespread heavy precipitation abetted robust improvement across eastern Colorado, central and western Kansas, and parts of southern Nebraska.

Numerous locations reported 3 to locally over 6 inches of rain, which was sufficient to support 2-category improvements in portions of southeastern Colorado and the western half of Kansas. Precipitation amounts declined abruptly north of a line from central Colorado through northeastern Nebraska, and only a few tenths of an inch at best was observed beyond this delineation.

Still, improvements were introduced in parts of the central and northern Dakotas where earlier precipitation may have been more beneficial than initially assessed. The only areas of deterioration noted were in northeastern Colorado and part of north-central Wyoming, which consistently have been north and/or west of the heaviest precipitation. Elsewhere, dryness and drought intensities did not markedly change from last week.

West

Moderate to heavy precipitation (0.5 to locally approaching 2 inches) fell early in the period across north-central and northeastern New Mexico, but conditions were quiet across the rest of the West Region.

There were scattered small areas reporting a few tenths of an inch of precipitation last week, primarily in Montana and the lower Four Corners sates, while most sites observed no measurable amounts.

Despite the predominantly dry week, fairly substantial areas of improvement were noted as the environmental response to earlier above-normal to heavy precipitation continued. Improvement was most common across New Mexico and Montana.

Looking ahead

During Oct. 7-12, Tropical Storm Isaias in the southwestern Gulf is expected to intensify into a category-2 hurricane and head northeastward and then northward toward the United States.

After peaking in intensity and beginning to weaken, landfall is expected somewhere along the north-central or northeastern Gulf Coast late Oct. 9. Once inland, Isaias should weaken more quickly as the remnant circulation tracks northward into the Southeast or adjacent Lower Mississippi Valley.

Sustained winds are expected to peak around 105 mph in the northern Gulf, but with weakening expected to start prior to landfall up to a couple hundred miles inland.

Daily high temperatures are expected to average at least 4 degrees Fahrenheit above normal there, with anomalies exceeding +10 degrees from north-central Texas through most of Oklahoma and adjacent parts of Kansas, Missouri and Arkansas. Farther west, most locations from the northern and western Rockies to the Pacific Coast are expecting below normal temperatures, along with most of Montana.

Daily highs are expected to average at least 3 degrees below normal from the Cascades southward and eastward, with anomalies of -8 to -12 degrees forecast in the northern Great Basin, northern Rockies, and High Plains of Montana.

Wetter than normal conditions are expected over the ensuing five days (Oct, 13 to 17) across a large part of the contiguous U.S. from the Rockies and northern High Plains eastward through New England, the Mid-Atlantic Region, the southern Appalachians, and the Florida Panhandle.

The best odds for unusually heavy precipitation extend from the central and lower Four Corners region eastward through Texas, the Red River (South) Valley, and the western Lower Mississippi Valley.  Above-normal temperatures are favored across much of the central and southern Great Plains, and southern High Plains.

Richard Tinker is with CPC/NOAA/NWS/NCEP.