The short answer
For the widest choice of tours, visit from late spring through the middle of the season, roughly May to September. That is when ships arrive, shops open and boats, planes and bear tours run on full schedules. For bears and salmon, late summer is best. For lower prices and quiet streets, the shoulder months have their own appeal, as long as you accept fewer options.
Rain, always
Ketchikan is one of the wettest towns in North America, and rain can fall in any month. Summer is usually drier than autumn, and early summer often has the best chance of clear days, but nothing is guaranteed. The upside is the lush green forest and the mist on the mountains, which many visitors find part of the beauty. Pack waterproof layers, and plan activities that work in drizzle.
Late spring
In May and early June the town wakes up. Days are long, shops open and the first ships arrive. Wildflowers and fresh green growth are at their best, and crowds are lighter than in midsummer. Some seasonal tours may not yet be running, so check dates. Whales are present, and eagles are active, but the salmon run has not yet begun in force.
Midsummer
June and July bring the longest days and the largest crowds. Tours run on full schedules, so you have the most choice and the most competition for popular times. The weather is mild, with daytime temperatures that feel cool by southern standards. Book key tours and rooms well in advance. Creek Street and the docks are busiest at midday, so go early or late.
Late summer and early autumn
The salmon run peaks from about July into early autumn, with fish crowding the creeks and bears coming down to feed. This is the best time for bear viewing and for fishing charters. Rain tends to increase as autumn approaches, and the first signs of fall color appear. Many tours still run through September, then wind down as the cruise season ends.
Winter
From late autumn into early spring, Ketchikan is quiet. Many shops and seasonal tours close, ferry and flight schedules can be affected by weather, and temperatures hover near freezing, with rain more common than deep snow at sea level. For travelers who want solitude, local life and low prices, winter has charm, but you must plan carefully and confirm that what you want to do is open.
Daylight
Summer days are long, with light late into the evening, which gives you time for dinner after a tour. Winter days are short and dark, so plan indoor activities and bring a flashlight for evening walks. Photographers should note that the soft, overcast light of a rainy day can make excellent forest and fjord images.
Planning by goal
Choose May for green and fewer crowds, July for full services, late August and September for bears and salmon, and the quiet months for a different kind of trip. Whatever you choose, leave slack in your schedule for weather, especially around flights and boat trips, and read cancellation terms before you pay.
Temperatures and clothing
Summer days are mild, often in the fifties and sixties Fahrenheit, and winter days hover around freezing, with cold wind and damp air that feels colder than the number suggests. Layers beat a single heavy coat: a waterproof shell, a warm mid-layer and quick-drying base layers. Waterproof footwear with good grip matters year-round, because wet boardwalks and trails are slippery.
Costs and crowds
Prices for rooms and tours rise with demand, and the cruise calendar sets the rhythm of the town. On days when several ships are in port, popular tours sell out and streets fill. Midweek and shoulder dates are calmer. If you are flexible, ask operators which days are quietest and book those, and consider staying a night or two after the ships have gone, when the town returns to its own pace.
A balanced recommendation
If you can choose freely, aim for early summer for the best mix of services, long days and good odds of clearer weather, or late summer if bears and salmon are your priority. Accept that rain will visit either way, pick activities that work in it, and book the weather-sensitive ones early in your stay so you have time to reschedule.