ST. LOUIS — Whether it was the bone-chilling rain or the pitch-black darkness while lost in a forest, circumstances that doomed an Air Force veteran and two young sons on a Missouri hike illustrate the need for simple precautions that could avert similar tragedies, experts said Tuesday.

Authorities have said experienced hiker David Decareaux and two of his boys, ages 10 and 8, weren’t equipped for the elements when they set out Saturday on the Mark Twain National Forest’s Ozark Trail in light clothing, only to succumb to temperatures that plunged to freezing and a downpour that made that worse. Their bodies were found the next day on the trail, their surviving dog beside them.

Such deaths are rare, marking the first among hikers in the 1.5 million-acre Mark Twain forest in at least two decades. Experts say other hikers should take note: Don’t take any foray into a forest for granted, particularly during the winter when daylight is shorter and weather can be unforgiving.

“It’s not Disneyland,” said Charlotte Wiggins, a spokeswoman for the forest. “There are different conditions than you’ll find in a park area.”

Forecasters had warned for days that the weather would turn ugly Saturday, but it’s not clear whether Decareaux, 36, knew that when he ventured out with sons Dominic and Grant with a flashlight, cellphone and some food. They had no compass or supplies for cold weather. In such a remote area, officials say, the cellphone wouldn’t be of much use, given the lack of signal there.

With the temperature unseasonably near 60, Decareaux was wearing only a light jacket. One of his sons was clad in a fleece pullover, the other a sweater.

Hours into the hike, Reynolds County Sheriff Tom Volner said, a couple who drove by the Decareauxes offered them the five-mile ride back to the lodge, where Decareaux’s wife and their three other children awaited. Decareaux declined and pressed on, by the sheriff’s estimation still with enough time to return to the lodge by sundown if hiking at a brisk pace.

But the weather worsened. The temperature by evening sank into the 40s, and a storm drenched the area with 2 inches of rain. Overcast skies, combined with the abundance of trees and lack of ambient light, likely limited visibility even before sunset.

Somehow in the darkening, wet and cold conditions, the hikers made a crucial mistake. Instead of veering onto the Blue Trail to get back to the lodge, they continued on the Ozark trail, Volner said. He said the turn is noted by “little-bitty 2-inch markers” — the kind of thing that could be overlooked in darkness, rain or simply due to stress.

After sunset, staff at the lodge became worried and began driving around looking for the missing trio, then called for help. But after midnight, heavy rain was causing flash flooding and washing out roads, and the search was called off for the night.

By morning, with temperatures below freezing, the bodies were found on the trail just a mile from the lodge, on the other side of a large, rocky hill. They’ll be buried Friday in a veterans’ cemetery, near St. Louis.

The fact that someone got lost wasn’t unusual in the Mark Twain, where Wiggins said search crews are sent out a couple of times a year.

But despite his military training and years of hiking, including previously in the area where he ultimately died, Decareaux failed to account for changeable weather and the prospect of things going so awry, the sheriff said.

“When you’re hiking in the winter, prepare for the worst,” Volner said. “I know it was 60 degrees when they left, but the weather changes quickly in the wintertime down here. Even a solar blanket would have helped.”

Pete Olsen, the American Hiking Society’s vice president of programs, said it is important to tell someone where you’re going and when you expect to return, giving an idea of where searchers should look if you’re late.

“Nobody ever plans on getting lost,” Olsen said.

He urged adventurers to take rain gear and extra food and dress in layers, especially in mountainous areas where temperatures at the bottom may be much warmer than the temperature at elevation. Taking a whistle to help alert searchers also wouldn’t be a bad idea.

“The more well-prepared you are, the better you’ll fare,” said Dr. Mark Levine, an emergency physician at St. Louis’ Barnes-Jewish Hospital. In Decareaux’s case, “everything worked against him.”