Before the snows come the rains, which fill the trenches snaking through the shattered landscape with water: cold water that in some places laps the tops of boots and leaves soldiers' feet wet, freezing -- and without care, potentially gangrenous.
And then the ground freezes, which means it's harder to dig the trenches in the first place.
Winter has come finally to Russia's nearly 10-month-old invasion of Ukraine, with the most ferocious fighting shifting from the south to the eastern Donbas region, where Russian troops are pummeling the city of Bakhmut and Ukrainian forces are trying to consolidate their gains further to the north.
What's new at this stage in the war is cold: freezing temperatures inflict misery on troops, mechanical grief on gears and vehicles, and torpor on movement and strategy. For military observers, it's an open question whether the cold will freeze the conflict until the spring, or whether one side will be able to take advantage.
But even if the Ukrainians do manage to seize the initiative, or the Russians make additional gains, the ground war will remain a source of misery for soldiers on both sides for months.
"It does suck, it's just going to be cold and wet, and there's no doubt about it," said Ben Hodges, a retired U.S. Army general who commanded U.S. forces in Europe between 2014 and 2018. "Weather is weather, dirt is dirt. There's not much you can do with that, even with technology," he told RFE/RL.
"But it will be much worse for the Russians than the Ukrainians," he said. "I say that from a material standpoint; Russians, newly mobilized soldiers who are not properly equipped, not joining cohesive units, no leadership."
Snow is already blanketing swaths of northeastern and eastern Ukraine, where the Donbas is located, and temperatures have hovered below freezing for much of the country as well.
Repeated Russian missile fusillades have destroyed much of the country's electricity and heating infrastructure, leaving millions in cities and towns struggling to stay warm, plug in their phones, or simply flush their toilets.
It's worse in the trenches, experts say. "The basic mistake is to be in a trench at all," said Colonel Janne Makitalo, Finnish military officer and a professor at the Finnish National Defense University in Helsinki. "That's the worst place to be at all in summer or winter. You should be able to scatter your forces, in wooded areas."
"It's not really modern warfare to have trenches, especially because of the water, but also when someone is moving drones around, you don't have much cover," he said.
Western intelligence officials believe the intensity of fighting will slow with the colder temperatures. "We're seeing a kind of a reduced tempo already of the conflict," Avril Haines, the director of U.S. national intelligence, said during a presentation on December 3, "and we expect that's likely to be what we see in the coming months."
That's not an assessment shared universally.
As mud freezes and the ground firms up, tanks and heavy tracked vehicles will be able to move more easily, Serhiy Cherevatiy, a spokesman for the Ukrainian military's eastern command, said this week. "We are doing everything to be ready for the winter period of military operations," he told Armia Inform, a Defense Ministry news service. "We are preparing our equipment; we are transferring it into winter operation, we are providing the units with special clothing and ammunition and those means that provide the opportunity to warm up and rest."
"Winter is usually the best season for mechanized warfare in Ukraine whereas spring is the nightmare season for fighting in Ukraine," the Institute for the Study of War, a Washington research organization, said in its daily assessment on December 4. "The thaw swells rivers and streams and turns fields into seas of mud. Ukrainian forces likely are preparing to take advantage of frozen terrain to move more easily than they could in the muddy autumn months."
Winter conditions pose serious challenges for the troops in the field: in the trenches, in the mud, and in the snow, where tracks can be more easily spotted, or in the woods, where leafless branches mean it's easier to use drones to spot units and equipment tucked among the trees.
"Everything moves a little bit slower," Hodges said. "It drains you, the soldiers, the cold, it wears you out."
For Russian troops, anecdotal evidence suggests serious problems in terms of basic clothing and equipment for surviving and fighting in cold temperatures. Russia's logistics and supply-chain networks have been stretched by the sudden mobilization, ordered on September 21 by President Vladimir Putin, of hundreds of thousands of men.
Some newly mobilized Russian units have taken to social media like Telegram to complain about having to buy their own equipment: things like heating stoves, for example. And Russia has reportedly turned to North Korean garment factories to make winter uniforms and underwear for its troops.
"The new 'mobiki' don't have the newest equipment," Makitalo said, using a colloquial shorthand to describe mobilized soldiers. "If you only have jogging shoes in wintertime in a combat zone, you are very quickly becoming not a soldier; you are becoming cannon fodder."
"Russia is increasingly fielding a late Soviet army, a 20th-century army maybe, with kit from the 1960s and 1970s," Mark Galeotti, a longtime expert on Russain security forces, told The Daily Telegraph last month. "In those circumstances I really don't see how Russia can make major breakthroughs on the battlefield."
Russian forces have also been plagued by a lack of discipline and unit cohesion; reports of insubordination, even desertion, have been rampant for months, even back into the spring. Some Russian media have reported the appearance of "barrier troops" who are charged with blocking Russians units from retreating in defiance of commanders' orders.
"You have to make soldiers drink water in the winter, stay hydrated," Hodges said. "And then of course disease will move quickly through an undisciplined formation when they go to relieve themselves, in the trenches."
Still, Russia may be seeking to merely hold its lines until the spring, as it continues to bolster troop strength with more of the estimated 300,000 mobilized men who are being trained and equipped.
"It may be Russia's tactic to force a stalemate through the winter from more entrenched positions with the intent to begin rotating newly trained and equipped mobilization forces to the front as spring approaches," the Atlantic Council, another Washington-based think tank, said in a report last month.
"One shouldn't underestimate the stoicism of the Russian soldier," Lawrence Freedman, a former professor of war studies at King's College London, said in a recent podcast. "There's been large numbers of wars in which they've been defeated and gone through misery, and yet they've still sort of hung in there."
Stoves, Tents, Boots, Gloves
The Ukrainians, meanwhile, have benefited from Western supporters shipping not just artillery and ammunition, but also modern winter gear: The British Defense Ministry said recently it had shipped 195,000 winter clothing items, and Canada said it has sent about 500,000 winter uniforms.
The Pentagon last month said it was shipping more than 200 power generators, and previously sent tents, heaters, and thousands of pieces of cold-weather gear.
Still, Makitalo said, "The Russian side has endless supplies; the Russians have so much ammunition, so many vehicles, and so many explosives, and missiles, the situation is that Ukraine is an underdog."
"The Ukrainians don't have enough winter clothing; winter combat boots, rubber boots with lining, winter gloves," he said.
"It's also important to donate stoves to heat bunkers, heated tents, sleeping bags. Sleeping mats are very important, so you don't sleep on cold ground," he added. "You need to have power generators, to charge batteries, laptops, management systems, drones, cell phones."
And for larger machinery -- howitzers, armed personnel carriers, tanks, trucks -- soldiers struggle with basic maintenance: oil turns viscous in sub-freezing temperatures; poor-quality rubber gaskets can crack.
"Maintenance is harder, to do the things you're supposed to do on your vehicles," Hodges said. "You have to have different types of lubricants for artillery. You have to keep proper tire pressure. You have to have a good logistics system backing you up. "
Simple field techniques change in the winter too, Makitalo says: When the Finnish military trains its soldiers in cold-weather fighting, they learn to clean all the oil from warm rifle barrels before they leave their tents to go out into the cold. Otherwise, condensation will appear on the metal, and then freeze, potentially jamming the rifle.
"Given the ground conditions, I'm not sure I would be an effective commander in Ukraine right now," he said.