The Canadian Rockies have a short high season, a shorter shoulder season, and an unreasonable amount of scenery in both. July and August are the months every guidebook recommends and every parking lot at Moraine Lake proves difficult; September, and specifically the middle two weeks of September, is when the range delivers what most visitors were actually hoping for — the blue-green lakes still lit, the wildlife still active, the trails still open, and roughly a third of the human traffic.
The additional argument for September is the larches. The subalpine larch, unusual among conifers, drops its needles in autumn and turns a saturated gold in the process. The window is short — typically the third week of September, sometimes creeping into the last few days of the second — and the concentration in the Larch Valley above Moraine Lake is the reason serious hikers plan around this fortnight. Parks Canada now runs a shuttle system to Moraine Lake rather than allowing private vehicles; book the earliest available shuttle for the day, which puts hikers on the trail by seven.
For a base, Fairmont Chateau Lake Louise is the obvious answer and it earns the position. The lakeview rooms on the higher floors of the main wing are the ones worth booking — the mountain-view rooms face a car park, which the marketing photographs politely omit. Ask for a room ending in 25 through 40 on the sixth or seventh floor for the best angle on the lake. The hotel's own canoe rental on the lake is worth the surcharge for a morning run out to the end of the water and back, ideally before nine when the wind picks up.
A week in the range wants two bases rather than one. Three nights at Lake Louise gives access to Moraine, Larch Valley, Lake Agnes, and the Plain of Six Glaciers; three nights further north at Jasper or south at Banff opens the Icefields Parkway, which runs 232 kilometres between the two parks and is one of the honest great drives of North America. The Peyto Lake viewpoint, the Athabasca Glacier interpretive centre, and the stop at Sunwapta Falls are the three fixed points; the rest is pull-off and photograph.
Wildlife in September is more active than in the summer heat. Bears — both grizzly and black — are in hyperphagia, feeding intensively before hibernation, and often visible on the berry slopes above the road. Bear spray is not a suggestion. Elk are in rut through late September and the bulls become genuinely dangerous around the townsites; give any elk a fifty-metre berth and do not stop to photograph one at closer range than that.
On weather, September is the honest month. Daytime highs run around fifteen to eighteen degrees Celsius through the first three weeks, dropping into the low single digits by the end of the month. The first snow at elevation typically arrives around the third week and is a routine event rather than a disruption; the road access to Moraine and to the Icefields Parkway remains open through October in most years. Pack a proper shell and a warm mid-layer; the temperature at seven in the morning at the Moraine Lake trailhead is not the temperature the forecast for Banff will suggest.
One practical note: the flights into Calgary from most origins arrive late in the evening, and the drive to Lake Louise is a two-hour night drive through elk country. It is worth staying the first night in Calgary or Canmore rather than pressing through, and starting fresh in the morning.
Avoid the Columbia Icefield skywalk. The glacier itself is worth walking on with a guided group; the glass-floored viewing platform is a paid attraction that adds nothing to what the road already delivers for free.