Wetter fall raises flood concerns in Southern New Mexico

A summer that began with parched ground and wildfire warnings is ending with a much different set of concerns for Southern New Mexico, as forecasters turn their attention to an active start to fall. 

Chad Merrill, a senior meteorologist with AccuWeather’s long-range forecast team, said conditions have already improved since he spoke with the Bulletin in May. Las Cruces has received about 3.86 inches of rain this summer, compared with an average of 4.15 inches. 

Much of Doña Ana County entered summer abnormally dry, while its northern fringe was experiencing moderate drought. Merrill said the southern portion of the county is no longer considered abnormally dry, and moderate drought has been reduced to the far northern edge. 

“That’s what we were expecting,” Merrill said. “We were expecting the summer to start out with the high wildfire risk and then transition to a flash flooding risk.” 

AccuWeather expects rainfall to trend above average across Southern New Mexico through September and October, with November closer to or slightly above normal. Merrill said a strengthening El Niño, lingering moisture and possible tropical systems in the eastern Pacific could contribute to more frequent bursts of heavy rain. 

“Our team actually has a moderate risk for flash flooding,” Merrill said. “A good bit of that would be the first part of the fall season.” 

Merrill cautioned that remaining drought conditions do not eliminate that threat. 

“You can still be in a drought and have flash flooding,” he said. “There could be some heavy doses of rain over a short period of time.” 

Warm Pacific waters could further influence the pattern. Merrill pointed to a positive phase of the Pacific Meridional Mode, a climate pattern associated with warmer-than-average waters between Southern California and Hawaii. Combined with El Niño, he said those conditions could provide additional moisture for storms reaching the Southwest. 

Las Cruces averages about 2.65 inches of rain during the fall, according to Merrill. Several previous El Niño years were considerably wetter, including 4.83 inches in 1972, 4.5 inches in 2015 and 3.96 inches in 1986. 

“There’s a possibility of at least an inch of rain more than average going through the fall season,” Merrill said. “Unfortunately, that all doesn’t usually distribute very nicely over a three-month time span. You usually get that in spurts.” 

While additional rainfall could further improve conditions in Doña Ana County, Merrill said one wet season would not solve the Southwest’s larger water problems. 

Reservoirs across the Colorado River Basin, including Lake Mead and Lake Powell, would need multiple productive seasons to recover from long-term shortages. A strong winter snowpack in the higher elevations of the Rockies would provide a greater benefit than individual heavy-rain events because snowmelt releases water more gradually, Merrill said. 

“For your specific county, the drought’s definitely going to improve, for sure,” he said. 

For residents, Merrill said preparedness will be important when storms develop. People should take watches and warnings seriously, know where to go if water threatens their property and avoid driving across flooded roads because the depth can be difficult to judge. 

Thunderstorms can also bring dangerous lightning, even after several consecutive dry days. 

“When thunder roars, people should go indoors,” Merrill said. 

Temperatures are expected to finish near average overall, although periods of warmer weather remain possible. Merrill said rain and cloud cover could produce noticeable temperature swings without bringing unusually cold air into the region. 

AccuWeather forecasts, maps and additional weather information are available at AccuWeather.com.