Southwestern storm brought needed rains to Plains

This week featured a dynamic and changeable drought environment across the country, partially thanks to the rapidly intensifying El Niño resulting in much above-average temperatures in the eastern Pacific waters.

These warm ocean temperatures have been fueling numerous hurricanes in the East Pacific; three of which indirectly impacted the Unites States. Hurricane Nolo affected parts of the Hawaiian Islands with heavy rains, although mainly impinged on the east-facing slopes that are not in any drought or unusually dry conditions. Meanwhile, moisture from Hurricanes Odalys and Polo both contributed to a near-record moist environment over the normally dry Desert Southwest.

Very heavy rains fell on much of New Mexico, and parts of Arizona, Utah, and Colorado both early in the period and again on Monday and Tuesday when Hurricane Polo curved northeast into the Baja of California and tracked into southern New Mexico. Weekly rainfall totals were very impressive across the Southwest, with totals reaching 5 to 10 inches, accounting for a large portion of the annual rainfall in some places.

The heaviest rains fell across eastern New Mexico into northwestern Texas, helping to alleviate drought conditions. Beneficial rains also extended into southern and eastern Colorado into western Kansas and Nebraska, leading to drought relaxation.

The south-central and southeast states were not so fortunate this past week, however. Continued unseasonably hot dry conditions prevailed across the rest of Texas and Oklahoma eastward into the Tennessee River Valley, leading to worsening drought conditions in many states.

The combination of persistently hot weather with virtually no rainfall during much of August and September has led to rapid onset drought in much of Texas and Oklahoma, resulting in widespread severe, extreme, and exceptional drought coverage, which again intensified this past week. Intensifying dryness and drought also prevailed across Arkansas.

Outside of the southwestern states, the remainder of the western U.S. had fairly steady-state drought conditions this past week, with only a few improvements occurring in the northern Rockies and in Oregon.

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

The southern states have taken the brunt of recent drought intensification since August, which continued across most of Oklahoma and Texas. Worsening drought also occurred across most of Arkansas. Virtually no rain fell in this region except for far western Texas and the Oklahoma Panhandle. Combined with temperatures of 6 to 12 degrees Fahrenheit above average, the lack of rainfall contributed to the rapid intensifying drought. Most of central and eastern Texas, Oklahoma, and Arkansas are under severe, extreme, or exceptional drought classifications.

Much of Texas and Oklahoma need to receive 20 to 25 inches of rainfall over a three-month span to break out of the present drought. The lone exceptions to the drought worsening were in far western Texas and the western Oklahoma Panhandle, where several inches of rain fell as eastern Pacific tropical moisture associated with Hurricanes Odalys and Polo moved across the region.

Midwest

The Midwestern states covered a broad range of conditions ranging from extreme to exceptional drought in northern Wisconsin, to excessive wetness from prolific rainfall all summer from Iowa to Ohio, where very little drought or abnormal dryness is present.

This persistent storm track has separated the southern drought from the northern drought. The long-term drought in Minnesota experienced some relief as up to 5 inches or more of rain fell over an area of severe to extreme drought near the North Dakota border, leading to relief there. Northwestern Minnesota completely relaxed out of drought this week as more beneficial rain fell there.

Drought also continued to intensify this week across southern Missouri.

High Plains

The High Plains states experienced almost exclusively drought improvements, as many areas experienced beneficial rainfall, with Colorado, Kansas and Nebraska being beneficiaries of the east-Pacific “El Niño” tropical connection. Despite temperatures being up to 6 or more degrees above average, the plentiful rainfall has contributed to drought improvement in many areas.

Northern and eastern North Dakota also experienced substantial reduction in drought coverage and intensity as heavy rain fell near the Canadian border.

West

Outside of Arizona, New Mexico and Colorado, which experienced deep and substantial drought-busting rainfall, the western states generally had unchanging drought conditions.

Drought and dryness also improved in southwest Montana and northwest Wyoming this past week.

Looking ahead

Ongoing substantial rain was falling Tuesday morning at the onset of the new U.S. Drought Monitor week, from Arizona and New Mexico into the central and High Plains. This excessive rainy system connected to Hurricane Polo is projected to continue eastward this week into the High Plains, Midwest and South regions.

The Weather Prediction Center has moderate threats for excessive rainfall from the Southwest into Texas, Oklahoma and northward into Nebraska and Iowa. Drought-busting rains may be possible across the South as this weather system evolves this week.

Looking into the next week, the Climate Prediction Center’s 6– to 10-day outlook indicates that well-above average temperatures will shift into the western states, along with below normal precipitation chances. Meanwhile, above average precipitation chances are projected from southern Texas into the southeastern states, including Florida.

Jonathan Case is with NASA/MSFC/UAH.