Ukraine wants to push forward. Black, soupy mud is making that difficult.

The troops of Ukraine’s 43rd Separate Artillery Brigade have just about everything they need to begin the expected spring counteroffensive. They are well rested, have plenty of ammunition and are now in possession of several advanced German-made self-propelled howitzers, which have replaced their old Soviet artillery pieces.

But for the moment, they are barely moving forward, stalled not by ferocious Russian attacks, but by an enemy no less tenacious: the viscous central Ukrainian mud.

“Until the weather improves, there will be no counteroffensive,” said a lieutenant with the brigade named Serhii. “The vehicles will get stuck and then what will we do if the shooting starts?”

Deep and black, with a consistency similar to a mixture of cookie dough and wet cement, the spring mud is one obstacle that the Ukrainian military, for all of its ingenuity, finds difficult to overcome. It jams weapons and steals the boots from soldiers’ feet. Wheels and treads spin and spin, only digging military vehicles deeper into the mire.

Serhii made the decision to pull all of the new Panzerhaubitze 2000s from the field, for fear that the 60-ton howitzers would be unable to escape should they come under fire. Last week, one had to be towed when it became stuck in the mud. Over the weekend, at the unit’s rear position in southeastern Ukraine’s Zaporizhzhia region, troops were busy scraping off a heavily caked layer of sludge from treads and armored plating.

Ukraine is under pressure to launch a counteroffensive and avoid a stalemate that could last through 2023 or longer. Failure to make some progress in the war, by recouping stolen land or inflicting serious damage on Russian forces, could harm morale and test the patience of Ukraine’s western backers.

The Zaporizhzhia region, half-occupied by Russian forces, and with vast farm fields leading down to the Azov Sea, is considered a likely area for Ukraine’s big push. But among all of the variables commanders must consider before launching the attack, the weather may be the most unpredictable.