Weather and seasons
May and September: long or workable daylight, the high-level route alternatives normally clear, and — the trail's defining seasonal issue — midges either dormant (May) or fading fast (September).
This trail runs an even sharper climate gradient than its neighbour the West Highland Way: Fort William and the western half sit in one of the wettest parts of Britain, while Inverness at the eastern end is in a pronounced rain shadow, getting roughly a third of the rainfall in a typical winter month. Midges are the single most decisive planning fact for most walkers, present from around early June to early September and worst in the sheltered forest sections and canal towpath — which is why May and September, not high summer, are the recommended months. The trail offers high-level alternatives at two points (Fort Augustus-Invermoriston and Invermoriston-Drumnadrochit) that climb above the treeline for better views over Loch Ness; they're the better choice in good weather and the wrong choice once winter conditions set in, when the low canal-and-forest route is the sensible option. Forestry felling operations occasionally close short sections of either route with limited notice, independent of season, and are worth checking before relying on a specific stage.
Short days, the wettest time of year on the wetter, western half of the route, and the high-level route alternatives become a real winter proposition once they climb above the treeline.
6-7°C high · -0-1°C low · ~7.5 hrs (sunrise ~08:45, sunset ~16:10)Watch for: The high-level route alternatives are directly exposed to winter weather above the treeline; the low canal-and-forest route is the sensible choice in poor conditions.An hour and a half more daylight than January, but the same winter conditions on the high-level alternatives and the same wet, muddy low route.
6-8°C high · -0-1°C low · ~9.6 hrs (sunrise ~08:00, sunset ~17:30)Watch for: Same high-level exposure as January; a settled cold spell can give very good, clear views down Loch Ness.Daylight lengthens quickly, but this is unpredictable transition weather and a late storm can still put snow back on the high-level sections.
8-10°C high · 1-2°C low · ~11.9 hrs (sunrise ~06:45, sunset ~18:45, clocks change late in the month)Watch for: Don't assume winter is over on the high-level sections just because the canal towpath feels like spring.Midges are not yet active, days are long enough for full stages, and the high-level route alternatives are usually clear of snow in a normal year.
11-12°C high · 2-4°C low · ~14.6 hrs (BST from late March; sunrise ~06:15, sunset ~21:00)Watch for: Nights are still cold; a late cold snap can still affect the high-level sections.Long daylight, the high-level alternatives normally clear, and midges still largely dormant — the best combination of the year on a trail otherwise defined by midges and short winter days.
14-15°C high · 5-6°C low · ~16.9 hrs (sunrise ~05:10, sunset ~22:00)Watch for: Ticks becoming active in bracken and long grass from this point.Close to 18 hours of daylight and generally reliable weather, but midges start biting from early in the month, worst in the sheltered, still air of the forest sections and canal towpath.
16-17°C high · 8-9°C low · ~18.0 hrs (sunrise ~04:20, sunset ~22:20, among the longest days anywhere in Britain)Watch for: Midges become a real factor from early June, worst at dawn and dusk in still, damp, sheltered stretches (forest sections, canal towpath under trees); a breeze clears them almost completely.Warm and long-dayed, but peak midge season on top of the year's busiest crowds and accommodation pressure in Fort Augustus and Drumnadrochit — widely recommended against for exactly that combination.
17-19°C high · 10-11°C low · ~17.6 hrs (sunrise ~04:45, sunset ~22:00)Watch for: Midges at their worst in the sheltered forest and canal-towpath sections; ticks also active.Still midge season and still busy, with the wetter, western half of the route also picking up rain by the end of the month.
17-19°C high · 9-11°C low · ~15.5 hrs (sunrise ~05:35, sunset ~21:10)Watch for: Midges remain a real nuisance in the sheltered stretches.Midges are fading fast, the trail is much quieter than summer, and this is widely recommended alongside May as the best balance of weather, midges and crowds.
15-17°C high · 7-9°C low · ~12.7 hrs (sunrise ~06:40, sunset ~19:20, equinox late in the month)Watch for: Midges taper off through the month but a warm, still spell early on can still bring a few days of them.Midges are essentially gone and birch/rowan colour is good along the canal and lower forest sections, but daylight and weather both deteriorate through the month, especially on the wetter western half.
11-13°C high · 5-6°C low · ~10.2 hrs (BST for most of the month; clocks change late in the month)Watch for: The clock change cuts a further hour of usable light; start treating the high-level route alternatives as a genuine winter proposition again if conditions turn.Short days and heavy rain on the western half, with the high-level sections now a real winter proposition, though the low canal-and-forest route stays a reasonable, if wet, option.
8-9°C high · 2-3°C low · ~8.2 hrs (sunrise ~08:05, sunset ~16:00)Watch for: Stick to the low route in poor conditions; the high-level alternatives above the treeline are exposed to full winter weather.The shortest days and wettest month of the year on the western half of the route, with the high-level alternatives firmly a winter-hillwalking proposition.
6-7°C high · -0-1°C low · ~6.9 hrs (sunrise ~08:45, sunset ~15:40, shortest days of the year)Watch for: Under 7 hours of daylight is the binding constraint on any stage; use the low canal-and-forest route rather than the high-level alternatives.