It is amazing - three days ago we were watching snow fall and were freezing. Today we are sitting in tee-shirts in the warm sunshine at 6pm on the shore of Og Lake, enjoying a last view of the striking pyramid of Assiniboine across the water. It is incredible, but so transient.

When we set out from Assiniboine Lodge in the early afternoon to head to the Og Lake campsite, I made the mistake of checking the weather forecast. This will be the last day of blue skies and sun, so we are enjoying it here in this beautiful setting. Tomorrow brings cloud and showers and the next day a maximum of 6°C.

But I digress – it was still a perfect blue sky day when we headed off from the Lodge, following our footsteps of the previous day trip to Windy Ridge; through the spruce and firs, across a mossy stream and down through a rocky gully to reach the Og Meadows.  The snow that we had seen just two days ago on the range ahead was well and truly gone.

Here we diverged, taking a track that followed the western flank of the meadow to commence the “Og Slog”, so called because of the supposed monotony of a long walk in the meadow. For us it was not monotonous as the different textures of green and straw-yellow and the humps and hollows of the meadow passed by. Across this palette of colour and shape, the knife-edged ridge of the continental divide looked over us.

We were also keeping a sharp eye out for Mr Grizzly, who we had watched here three days ago. Perhaps he would come out to farewell us – but no, grizzly bears are not known for their etiquette. All we saw were a couple of old paw prints in the dry mud.

The track continued on, dropping off the meadow to pass the flat shrub-filled pan of a silted up lake, then entering a rocky area near an old long moraine. The pale grey rock and scree face of the fringing mountains rose above, heading off to the north. We were rapidly approaching Lake Og.

Soon there it was – spectacularly wedged between a scrub-covered rocky slope and a grey cliff-face. It was very different to the other lakes here, a much more barren setting, but with its own beauty. High above us lay Windy Ridge – it was hard to believe that we were up there three days ago. We pitched our tent on the prime campsite with lake frontage from where we could sit and watch the changing light over Assiniboine.

So here we are, the clear blue sky is being overtaken by wisps of long white cloud. We are alone at Og Lake, just the fair Nello and I in the heart of the Canadian wilderness, now watching the clouds turn a pinkish-orange over Assiniboine with the setting sun. We couldn't be more content – we have had three of the best walking days that we have experienced. It doesn't matter any more what the weather might have in store.

As predicted, it was a grey sky that greeted us – no alpenglow this morning, but nonetheless some fine reflections of a more sombre Assiniboine in the still lake water.

We ate quickly, packed up and were away by 8.30am, hoping to make as much distance as possible before the predicted showers arrived. Almost as soon as we left camp, we crossed a small rocky outcrop beneath the impressive scree slope tumbling down from Windy Ridge. Ahead lay blue sky, behind grey clouds drifting closer – a bit of carrot and stick for hikers in the wilderness.

For the next few kilometres, the path roamed through the Valley of the Rocks, a narrow valley parallelling the range of the continental divide. It meandered around outcrops of rough-edged limestone and large spruce trees, up and down through the humps and hollows of this beautiful and tranquil place, as much zen garden as wilderness, with its mosses, lichens and low herbs growing amongst the rocks, scattered with spruce and fir of all sizes, from the very large to the quasi-bonsai.

We stopped at a clearing to have a bite to eat and take in the views of Nasswald Peak, now appearing through the forest. As we did the sun broke out (pessimist that I am, I was betting on the clouds) to illuminate its orange and tan tinted walls. For the next few kilometres we walked in the warmth of the sun and it was back to just shirts.

A short but steep rocky ravine took us out of the Valley of the Rocks, after which we climbed steeply up into the forest and then down again to reach the head of Golden Valley. This marked the junction for Porcupine Campsite further down in the valley, but our road was the high one, climbing up once again towards the cliffs of Golden Mountain.

Three times we descended into one of the steep little valleys cutting in to the range and three times we climbed back up the spurs that separated them, scolded by the resident chipmunks as we passed.

Occasionally, we had glimpses through the trees out over the valley to Nestor Peak and the snow-streaked Simpson Ridge, with its tortured geological strata. Here the sun may have been shining, but the grey cloud to the west wasn't far away.

The last valley crossed, the track took a more direct route, on a long traverse across a steep and tree-free slope. The views out across the valley and to the distant mountains at its far end were spectacular.

As the traverse ended the climb began, bringing us to the entry of Citadel Pass. We stopped to load up on fruit jellies and boost our energy for the ascent of the pass – 2km pushing steadily up a gully of open fir and spruce, through a thick understorey, seasoned with the reds and yellows of approaching autumn.

It was here that the showers finally caught us. They were light, but on a long climb, such as Citadel Pass, any excuse to stop and sit under the shelter of a spruce tree is a good one. As the showers passed and the sun returned, we pushed on to eventually emerge onto a broad larch-covered plateau; in the foreground, a large almost dry tarn lying in a deep hollow, in the background the towering presence of Citadel Peak.

We wandered around the tarn and across the plateau, transfixed by the soft beauty of the larches on the cusp of turning autumn gold – a few individuals even had.

As we strolled gently upwards towards the pass itself, a look backwards gave a panoramic view over the larch-covered plateau to the now-distant Assiniboine (it just won't go away), its peak now capped with thick grey cloud. It was such a spectacular view that we decided to stop for lunch and admire it, beneath the summits of Citadel Peak to the west and aptly named Fatigue Mountain to the east.

Lunch stop below Citadel Pass - with a cloud topped Assiniboine above the larch forest

The north side of Citadel Pass

Lunch over, a short final push brought us to Citadel Pass; we crossed it, the continental divide and from British Columbia into Alberta with the same step. From the pass, we could see way down onto the meadows of the gentler eastern slopes and beyond, to more distant peaks.

The sun was shining on us, but the sky ahead was dark and menacing. It was a superb light, the meadows and larches almost glowed against a lowering sky, while the blue waters of Citadel Lake sparkled beneath the rock tower of Citadel Peak. It really was breathtaking - a symphony in blue, gold and green.

However, the warnings were clear – the good times were definitely over and bad weather was at hand. We hurried across the meadow towards the campsite at Howard Douglas Lake as the sun vanished behind the thick band of dark cloud – soon the first drops began to fall and soon after the first peal of thunder rang across the mountains.

The temperature had also plunged to single digit degrees as the cold front moved through, so we bit the bullet and hurried on, climbing quickly up the slope to reach the campsite in a grove of spruce just above the lake. It was full of puddles and the cold rain kept falling, so we rigged up a poncho as a makeshift tarp to stop the drips that made their way through the canopy and sat there for another hour, until it finally cleared and we could pitch our tent. At least we were going to sleep dry, if in somewhat muddy surrounds.

A cup of hot soup, the warm cup bringing frozen fingers back to life, and the world already seemed a better place. A watery sun was even shining again on distant peaks. For a while it looked like we would be the only campers again, but then John (who I had met in Assiniboine while admiring the dawn reflections on the lake) walked in and joined us. It was good to have a bit of company on a bleak evening.

In reality, being caught in a thunderstorm seemed a reasonable price to pay for the spectacular natural beauty of the day's walk …. and the fair Nello has just got back into the tent and told me that she had seen some stars – hopefully a good omen for the morning.

After the thunderstorm of yesterday and the forecast of single digit maximums with showers today, we were pleasantly surprised to be greeted by the sun when we got up. It gave us the chance to pack up a relatively dry tent and we headed off on the last short section of our walk in good humour. We were joined by John and it was good to have his company – although from Seattle, he loves the Canadian Rockies and is very knowledgeable about this area.

The wind was still icy, but the climb up to the Quartz Hill saddle, at 2380m the highest point on the track, soon warmed us up. Behind us, Howard Douglas Lake grew smaller and the sun beamed through gaps in the cloud cover, lighting up parts of the landscape like a powerful beacon.

Reaching the saddle, we could look out across the undulating herb-fields of the Sunshine Meadows, one of the largest areas of alpine meadow in the Rockies. We dropped down on to it and started the crossing of this open landscape, with its peeping ground squirrels and its low green vegetation already starting to take on a mix of reds and straw yellows as autumn colours began to show through. The colour we most noticed though was grey, the colour of the increasingly menacing clouds approaching from the west. We stopped to put on our wet weather gear – better prepared than sorry.

Pushing on, the infrastructure of the Sunshine Ski Field started to come into view – our hike out of Assiniboine was almost over. However, we had decided to do one last detour before finishing. Sunshine Meadows boasts the No. 1 day-walk in Canada, a challenge too good to refuse. Down to the west, we could see the beautiful setting of Rock Isle Lake, part of this walk, and, when we reached the junction we headed off towards it. Our mood was buoyed by the re-appearance of the sun to illuminate the lake and its surrounds as we arrived – little did we know!

We farewelled John at the lake as he had a shuttle to catch from the village, and the fair Nello and I pushed on, climbing over the small rise at the western end of the lake to pick up a circuit on the Meadows Walk – the sun disappeared. By the time we had descended through the spruce and larch to reach the reed-line shores of Grizzly Lake, the first rain drops had begun to fall and an icy wind was picking up.

We hurried around and on to the Simpson Valley Lookout and did not like at all what we saw – not the magnificent views promised, but a dark swirling band of cloud, driven towards us by icy gusts.

The rain was starting to get heavier, so we hurried on, reaching beautiful Larix Lake and following a track around its shore-line. Then the first clap of thunder cracked nearby and the rain turned to hail driven by a cold sleeting wind – it was time to seek at bit of shelter, which we did.

Chewing on granola bars beneath a dense spruce, we watched out as the rain and hail turned to snow, swirling through the trees and rapidly settling on ground and branch. The world was turning white and, as the fair Nello commented, today this shouldn't be called the best walk in Canada, it should be called the best walk in Narnia.

With a strange mix of thunder and driving snow, it seemed a good idea to get on “out of here”, and we headed off into the whiteness, now leaving dark footprints on the white track through what had become a surreal landscape. The photos here do not really do justice to the force of the wind and snow. However, by the time we completed the loop and returned to Rock Isle Lake, the wind had dropped and the snow fell gently – lake and meadow were completely transformed from what we had seen less than an hour ago. What was once a landscape of greens, yellows and reds was now a monochrome world - and a strangely silent monochrome world at that. What a bonus to finish the trip!

We rejoined the main trail and wandered on down to Sunshine Village, still in a state of awe at the power and precipitous nature of the mountain weather. If we had had the gear, we could have skied down. We were lucky enough to catch the shuttle bus a few minutes after walking into the warmth of the cafeteria at the village. Barely an hour later, we were back in Banff in the warm sunshine - what incredibly changeable weather they have here.

And thus we finished our amazing 6-day adventure in the Assiniboine region – not with a whimper but a bang. We really couldn't have asked for better.