Five seasons prevail in Nepal, but these are based on more than just weather: whenever you choose to go, you'll have to weigh other factors, both positive (mountain visibility, festivals, wildlife) and negative (crowds, disease).

Probably half of all tourists visit Nepal in the autumn (October to November), and for good reasons. The weather is clear and dry, and temperatures aren't too cold in the high country nor too hot in the Tarai. With the air washed clean by the monsoon rains, the mountains are at their most visible, making this the most popular time for trekking. Two major festivals also fall during this season. The downside, however, is that the tourist quarters are heaving and hustley, prices are higher and it may be hard to find a decent room, you'll wait ages for food and for trekking permits, and people are short on ready smiles and chat.

Winter (December and January) weather is for the most part clear and stable. It isn't especially cold at lower elevations - it never snows in Kathmandu, and afternoon temperatures are balmy - but the "mists of Indra" can make mornings dank and chilly (especially in unheated budget lodgings). Most travellers head down into India, leaving the tourist areas fairly quiet - too quiet, sometimes, as many restaurants pare down their menus for the season, and most trekking lodges close. This is an excellent time to visit the Tarai, where temperatures are relatively mild.

Spring (February to mid-April) brings warmer temperatures, longer days, weddings and more festivals. The rhododendrons are in bloom in the hills towards the end of this period, and in the Tarai the thatch has been cut, so despite the increasing heat this is the best time for viewing wildlife. All of which creates another tourist crush, albeit not quite as bad as in the autumn. The one factor that keeps people away is a disappointing haze that obscures the mountains from lower elevations, though it's usually possible to trek above it.

The pre-monsoon (mid-April to early June) is stifling at lower elevations, and dusty wind squalls are common. People get a little edgy with the heat; this is the time for popular unrest, but also for the Kathmandu Valley's great rainmaking festival. Trek high, where the temperatures are more tolerable.

Nepalis welcome the monsoon (June to September), which breaks the enervating monotony of the previous months, and makes the fields come alive with rushing water and green shoots. The rains rinse and renew the land. This can be a fascinating time to visit, when Nepal is at its most Nepali, but there are many drawbacks: mountain views are rare, leeches come out in force along the mid-elevation trekking routes, roads become impassable, flights get cancelled, and disease runs rampant as the rising water table brings the entire contents of city sewers to the surface.