As a plot this is pretty sketchy, but is hopefully an antidote to the "wandering monster" syndrome. Ie. "You meet monster x." "We beat the stuffing out of it, then proceed." The idea is use weather and fatigue rules plus the wolves to provide a night of high tension and brainstorming but perhaps surprisingly little combat.
The idea is to get a trading mule-train over a broad mountain pass to the plain's people beyond as early in the season as possible. High profit is assured by being the first trader of the season through, ahead of any big caravans. The mountain pass is fast way through which a mule train of light, high-value goods (ie spices, salt, liquors, specialised textiles) can exploit, returning later in safety with first choice of furs and winter craft-goods in exchange. The players may be doing it this on their own account if sufficient organised, or may be paid as escorts. Either way, their return should be proportional to the number of mules brought safely through the mountains. The hazards are cold and wolves, though some rarer nasties might come into play. Instead of a single encounter, the wolves will dog the party all the way, avoiding a fight but occasionally making rushes in hope of panicking a horse or mule loose. They also will worry the party at night, calling fatigue rules into play. Wind, rain and cold will also take there toll, hampering defence efforts. I find turns of 3 hours from 6am to 6pm, and 4 hours from 6pm to 6am to be good for this type adventure. Also, I wouldnt bother with the tedium of mule/horse v. wolves fights. Assume that the wolves are opportunist and 4-8 will rush an opening. If it goes well, then more will join in. Give the wolves a 1/6 say (better if mobility reduced etc) per combat round of bringing down a mule if not interfered with. Will retire immediately if resisted. If defenders say all go to protect say the tail of train, then good chance that another group of wolves will seize chance to attack elsewhere. The very first attack can be full-scale (all the wolves) but wont last more than 4 rounds (probably less - as long as it takes to realise that mules are defended). It will with luck :-) though panic your magic users into wasting a lot of power that they will have trouble regaining.
The wolves should perhaps be in inverted commas - because I don't know or care whether the behaviour I'm describing is "realistic" (not being part of the New Zealand ecology!). Call them something else appropriate to your world if need be. The party will pick up a wolf pack early in the piece. The pack is very hungry though certainly not suicidally so, having unsuccessfully chased their normal prey (deer or something else suitable) over the pass. They are NOT interested in the humans, being too prickly for the amount of meat to warrant the trouble unless conditions are very favourable. They are however very attracted by the mules which they can easily outrun especially when laden with about 200lb of goods. Any horses are also very good game in heavy snow, though they will outrun wolves on hard ground. Attacking animals they will attempt to hamstring or take out the jugular. Faced with humans, they will generally withdraw, out of missile range if necessary. A human isolated even temporarily from others will be game however provided odds of at least 4 to 1 can be brought to bear. Wolves to the front will "face off" keeping out of weapon reach but feinting lunges to help the attackers from behind. These will attempt hamstringing, or a knock-down followed by worrying to the neck. At any concerted attack on them, they will fade, especially if one their no. is hurt or killed. They will eat their own dead quite happily when safe to do so. The pack animals will be frightened and likely to bolt with each attack. Some kind of beast- mastery/horsemanship should be tested on each occurrence unless the party have devised foolproof tethering. If the wolves successfully get an animal, then the party will have a respite of several hours. The attack will end when either the wolves have eaten about one animal between two/three; they have lost a quarter of their number; or easier game presents itself. (GM could be dicing for this or just pretending - bring on the other animals when the party has had enough).
Weather can be manipulated gloriously in this scenario: Wind should make all missile-fire difficult. Rain should affect bowstrings and visibility. Cold should affect all manual skills at very least. Snow should affect mobility.
Here is an example crossing: A successful weather-forecasting will tell bad weather on way, but they should clear the pass if hurried. Snow is encountered in patches as the party climb through sparse timber - and suddenly they have a wolf pack about them making good use of the cover to avoid missiles etc. while making occasional lunges. (1 per turn at most). The sparse timber gives way to thorn scrub as evening comes and party will take severe cold effects if they do not camp here. Fire is possible but the timber disappears as thorn-scrub gives way to snow-covered grasses and rock higher up. It gets very cold during the night and the wolves make lunging attacks 1-2 per turns. The idea here is the party becomes fatigued, spell-users cant replenish power etc. As each attack is met, the wolves will melt back into the night, gathering in again an hour or so later.
The next day bodes bad weather as the wind rises and the sky darkens. As the party trudge through heavy snow they should take further cold and fatigue minuses while the rising wind will play havoc with missile fire. If they turn back, then a heavy snowstorm will block the pass for nearly two weeks, while a forecasting will still indicate they can cross before the storm hits. The wolves are unencumbered and will tread quickly over the icy surface on the snow. They will only attack 2-3 times today, but will aim at the horses. The broad pass, fortunately relatively safe from avalanches, will be crossed in the late afternoon and the storm gathers fury. The snow is not so deep on the southern side and large rock formations and boulders make numerous sheltering points not far down the southern side. GM might like some other nasties living in these cave-like shelters though. It will be 4 freezing hours in pelting snow though down to firewood. At least the shelters and weather will mean little attention from wolves this night.
Next morning is somewhat warmer and the snow-showers give way to rain. By the time the party gets down to the tree line it is pouring, making fire (which they are probably reliant on) impossible without magical means. Hopefully their magic- users will have had a night's sleep by now :-). The wolf attacks will get very intense in the timber (they are now really hungry), before perhaps other easier game takes them away.