Two rivers in southeast Colorado carried flood warnings into Friday morning, and neither of them was fed by the mountains. The Purgatoire River near Las Animas crested at 10.46 feet about 2 p.m. Thursday, a foot and a half over minor flood stage, after rising from a trickle in a few hours before dawn. The Arkansas River at Lamar passed bankfull at 10.14 feet just after midnight Friday, with Prowers County emergency management reporting water in low ground along the river Thursday afternoon. The cause was a single night of rain, Wednesday into Thursday, that fell on ground still soaked from the wettest October the lower Arkansas Valley has recorded.

The rain

A compact low-pressure system crossed from Utah into southern Colorado Wednesday afternoon and moved out to the southeast Thursday morning. It put 9 inches of snow on Leadville. On the plains it produced rain, and more of it than the forecasts had suggested. The National Weather Service office in Pueblo wrote shortly after midnight Thursday that scattered showers would dissipate by late morning. By the time observers read their gauges Thursday morning, the totals for the previous 24 hours were, by the service's cooperative and CoCoRaHS networks:

• Timpas, 1.88 inches
• La Junta, 1.61
• Rocky Ford, 1.49
• Las Animas, 1.32
• Cheraw, 1.19
• John Martin Dam, 1.12
• Holly, 1.00 to 1.10, on top of 0.75 the day before
• Wiley, 0.87
• Lamar, 0.55 to 0.71
• Kim, 0.55
• Southwest Kiowa County, 0.33

A normal entire November brings La Junta half an inch and Las Animas four tenths. Thursday's rain alone was three times a full month's worth at both. It came on top of the Sunday and Monday storm, which left 0.45 at Las Animas, 0.78 at Holly and 0.93 at John Martin Dam on Tuesday morning's readings. And it came on top of October. Las Animas recorded 6.13 inches in October, the most for any October since its records began in 1893 and more than five times normal. The previous mark was 4.27 inches in 2008. La Junta had 3.79 inches in October, nearly three times normal, Holly 4.33, and Eads 3.06.

On ground that wet, rain does not soak in. It runs.

The Purgatoire

The Purgatoire had been carrying about 11 cubic feet per second at the state's gauge at Ninemile Dam near Higbee, in the canyon country southwest of Las Animas. By 5 a.m. Thursday it was carrying 5,660. The rise came out of the canyons of the Comanche National Grassland between Rock Crossing and Higbee, where the overnight rain measured about an inch at the few gauges there. The river at Rock Crossing, upstream, never rose above 323. An hour later the gauge below Highland Dam, just above Las Animas, read 2,780 cubic feet per second.

The Pueblo office issued its flood warning for the Purgatoire near Las Animas at 9:02 a.m. Thursday, when the river was at 8.8 feet and expected to reach 9.1. By 9:15 it was at 9.6. The crest, 10.46 feet about 2 p.m., is above the July 2023 crest of 10.35 feet on the service's list and just under the 10.52 of August 2004. Minor flood stage there is 9 feet, and the service describes flooding at that level as agricultural, into low-lying ground along the river. The river was back to 7.2 feet, below bankfull, by 10:15 p.m., and the service said no further flooding was forecast, though it left the warning in place until late Friday night. The state's gauge read 339 cubic feet per second at dawn Friday.

A second pulse is still in the river. The Purgatoire below Trinidad, far upstream, rose from 60 cubic feet per second to 2,190 at 2 p.m. Thursday on rain near Trinidad, and was down to 510 by Friday morning. The weather service's forecast for Las Animas does not show it causing more flooding there.

Smaller creeks all over Bent and Otero counties did the same thing Thursday morning. Timpas Creek at Highway 10 near Swink rose nearly 11 feet between midnight and noon. Crooked Arroyo near Swink went from 37 cubic feet per second to 143. Mud Creek below the dam near Toonerville went from 10 to 169, and Rule Creek, which had been dry, ran 40.

The Arkansas

The Arkansas River at La Junta rose from 29 cubic feet per second to 1,650 by 2 a.m. Thursday, the first river to respond, as Timpas Creek and the Rocky Ford country drained into it. The service's statement Thursday evening had the river at 9.6 feet at La Junta, expected to peak just over 10 feet overnight, below the 11-foot flood stage, and fall through Friday. At Las Animas, above John Martin Reservoir, the Arkansas rose from 55 to 593 by 5:15 p.m. Thursday.

John Martin Reservoir caught all of that and the Purgatoire too. The dam's release stayed at 2 to 5 cubic feet per second throughout, and the reservoir gained about 2,500 acre-feet between Wednesday and Friday morning, to 39,900.

So the water at Lamar did not come through the dam. It came from the creeks between the dam and the town. The state's gauge on the Arkansas above the Amity Canal, a few miles below John Martin, went from 9 cubic feet per second Wednesday to 1,350 at 6 p.m. Thursday. At Lamar, the river rose from 97 cubic feet per second to 1,330, and the stage from 6.3 feet to 10.14 at 12:30 a.m. Friday. Bankfull at Lamar is 10 feet and flood stage is 11. The Pueblo office issued the Lamar warning at 6 p.m. Thursday, when the river was at 8.9 feet, on a report of flooding from emergency management, and at 4:33 a.m. Friday extended it until late morning, saying the river would stay near bankfull with localized flooding of lowlands near Lamar, including the meadows near County Road 13. The service compared the crest with one of 9.3 feet on August 29, 2002. The river was at 9.2 feet at 5 a.m. Friday and is expected near 8 feet by late evening. At Granada it was still rising at dawn.

Elsewhere

The Rio Grande at Alamosa fell below flood stage Thursday and the service cancelled its warning at 10:34 p.m. A separate warning for the low ground where the Conejos River meets the Rio Grande, including Alamosa East and Lasauses, runs until 4 p.m. Friday. That water is the last of the Sunday and Monday storm draining out of the San Juan Mountains, not Thursday's rain.

What comes next

Dry. The Pueblo office expects no measurable rain through at least Thursday of next week, with highs in the 60s on the plains, 5 to 10 degrees above normal. The rivers will drop through the weekend. All river readings here are provisional and come from the National Weather Service, the Colorado Division of Water Resources and the U.S. Geological Survey, and the rainfall totals from the CoCoRaHS and cooperative observer networks.