Having just endured the hottest, driest summer ever recorded in Central Texas, I admit I feel a certain reverse kinship with Lewis and Clark regarding the long, cold winter they spent at Fort Mandan. The winter of 1805-1805 was bitterly cold on the Dakota frontier. Clark started off the month of December noting in his journal that the days were “cold & windey,” “a Cloudy raw day,” and “a Cold raw morning … with some snow.” On December 6, Clark noted, “The wind blew violently hard from the N, N W. with Some Snow the air Keen and Cold. The Thermometer at 8 oClock A, M, Stood at 10 dgs. above 0—.”

"Hunting with Sheheke: 'White Coyote' And An Expedition Member Approach Ft. Mandan Winter 1804-1805," by Michael Haynes
Unfortunately, it was only the beginning. The next day, Clark wrote:
The weather so excesive Cold wolves plenty, we only saved 5 of them, I with a party turned on the 8th out and found the Buffalow at 7 ms. distant Killed 8 & a Deer, I returned with 2 Cows leaving men with remaining meat— Several men badly frost bit— The Themormeter Stood this morning at 44 d. below Breizing [freezing].
With temperatures dipping to – 44°F, frostbite became a major concern for Lewis and Clark. According to Or Perish in the Attempt by Dr. David J. Peck, frostbite occurs when the skin’s temperature drops to 24.8°F, the freezing point of pure, undiluted water. At that point, the fluids inside and outside the skin freeze, blood vessels spasm and leak fluid into the surrounding tissues, and circulation of blood slows down or even ceases altogether. In severe frostbite cases, the tissues are so oxygen-starved that major tissue damage occurs and the tissues can actually “die.” In milder cases, the skin becomes red, swollen, blistered, and extremely painful.
1804 was long before the age of Gore-Tex, silk underwear, and goose-down coats. Lewis and Clark’s men had only buckskins, flannel shirts, wool trousers and army coats to protect them from the severe cold, putting them at serious risk. Furthermore, because of the necessity of hunting, guard duty, and fatigue work, they could not always limit their exposure to the damp, blustery winds, deep snow, and sub-zero temperatures. Despite Lewis and Clark’s measures to protect them – the captains rotated Fort Mandan’s guards every half-hour at one point — many of the men suffered from frostbite on their hands, feet, and ears. At one point, poor York was even forced to contend with “a little” frostbite on his penis. It was no wonder. On December 17, Clark recorded a mind-blowing, bone-shaking 74° below zero.
Under such extreme conditions, Lewis and Clark’s men were not the only ones suffering from the colder-than-average temperatures. The Native Americans were also feeling the cold. Clark reported on January 10, 1805:
The Indians of the lower Villages turned out to hunt for a man & a boy who had not returnd from the hunt of yesterday, and borrowd a Slay to bring them in expecting to find them frosed to death about 10 oclock the boy about 13 years of age Came to the fort with his feet frosed and had layen out last night without fire with only a Buffalow Robe to Cover him, the Dress which he wore was a pr of Cabra (antelope) Legins, which is verry thin and mockersons— we had his feet put in Cold water and they are Comeing too—
Lewis was the boy’s primary care physician, and regrettably, there was not a whole lot he could do to warm the boy’s feet and restore circulation. The boy hobbled around for a couple of weeks before the tissue on his feet started to turn black and it was clear the damaged tissue on his feet would never heal. The only recourse was frontier surgery.
On January 27, Clark wrote in his journal, “Capt Lewis took of the Toes of one foot of the Boy who got frost bit Some time ago.” Four days later, he made another entry: “Sawed off the boys toes.” It seemed the unlucky patient had lost more of his metatarsals. Fortunately, the boy escaped gangrene, infection, or further surgery. Less than a month later, on February 23, Clark recorded, “The father of the Boy whose feet were frose near this place, and nearly Cured by us took him home in a Slay—.”
By that time, the Corps of Discovery was already looking westward. They had begun to hack the keelboat and pirogues out of the ice. By February 25, Clark noted in his journal that “The Day has been exceedingly pleasant.” The worst of winter was over, and the men were anxiously looking forward to proceeding on.
More interesting reading: The Little Ice Age