The Indian Himalaya can be flyable all year round, except during the monsoon months of July to early September. The busiest flying season is post-monsoon during the autumn, although as more people come to fly, either in helicopters or planes or some other flying aircraft, in the mountains, spring is becoming more popular. From early October to December it is usually flyable every day. This makes it an excellent place to come when the weather in Europe has deteriorated and the Southern Hemisphere season has not yet started.
The monsoon usually finishes during the second half of September. There can be flyable days immediately afterwards, but the air is usually very moist and it often overdevelops. Over the next few weeks the land and air dry out and over-development is less of a problem. Usually the rice is harvested around the middle of October, which further reduces the amount of water vapour in the air. This not only improves the quality of the thermals, but also means that there are many more places to land out when flying XC. From mid-October to Mid-November conditions are at their best, although in October the midday thermals are often too strong for inexperienced pilots to enjoy.
Things start calming down during November and are fairly dead by the beginning of December, when there are usually strong multiple inversions and very stable conditions. Unfortunately the strongest inversion is usually around take-off height. Often it seems to be about 10m below take-off, so you can't even top land! Occasionally weather systems break up the inversions and provide excellent flying, even during the winter months. I have been told of one pilot who got well above '3122' on Christmas Day a few years ago.
Unfortunately (for information purposes) all fliers, birds included, fly south to Goa and Maharashtra for winter, so none of us know what conditions are like during January/February! As spring progresses the weather warms up again and there can be excellent flying conditions, although nothing like as reliable as the autumn. Conditions are probably at their best during March & April. Bob Drury has described the conditions during May well enough to put off all but the most experienced pilots and June is for loonies only!
Manali and the Kullu Valley
Manali is one of the most popular tourist destinations in India, for both foreigners and Indians alike. This makes getting there very easy, if somewhat arduous. The quickest and most comfortable (and by far the most expensive) method is to fly into Bhuntar Airport at Kullu. The one or two daily flights from Delhi usually go via Shimla and in clear weather give a spectacular introduction to the beauties of the Himalaya. The next most comfortable method will be in a taxi or other tourist car. A private taxi from Delhi will take at least 15 hours and will probably cost around $150 depending on your skills at bargaining.
By far the most common method of transport is via 'deluxe' tourist bus. These are run by Himachal Tourism, Himachal Transport & a great many tourist operators. The Himachal Tourism bus leaves from the HPTDC office in Janpath, Delhi at around 6am and arrives in Manali approximately 18 hours later. The Himachal Transport buses depart from the ISBT in North Delhi. Two common private bus operators are Hari and Harisons - tickets for both are sold everywhere in Paharganj and other backpackers areas of Delhi. Nominally the private tourist buses leave from close to Paharganj, but in reality they then drive all over Delhi picking up further passengers before departing. This process can take over two hours. Government buses are preferable as they tend to be less prone to theft and have a better safety record - the private operators usually drive the whole way, whereas the government buses will change drivers at the half-way point.
Billing and the Kangra Valley
Due to its position halfway between two of the most popular tourist destinations in Himachal Pradesh - Manali & Dharamsala - Billing is very well served for transport. The most convenient and comfortable way to travel is by deluxe bus. There are regular private and state deluxe buses from Delhi to Dharamsala and Mandi (all Kulu/Manali buses go via Mandi), both about 70km away, and also two state buses per day from Delhi to Palampur about 35km away. These all take around 12hrs, plus a further 2 hours 'connection' to Bir or Chaugan. The choice varies between ordinary (bumpy, slow), semi-deluxe (bumpy, not quite so slow) and deluxe (2x2 seating and fewer stops but still bumpy).
Another option is to take an overnight train from Delhi to Pathankot and continue onwards by bus or taxi. There are also ordinary buses from Delhi to Baijnath and Jogindernagar. The best of these is the DTC Indraprastha Service from Delhi to Baijnath. It leaves ISBT, Delhi around 6pm and arrives in Baijnath 12 hours later. All buses travelling between Baijnath and Jogindernagar pass the turn-off for Bir, Chaugan and Billing - ask for 'Bir Road'. There are taxis and rickshaws available at the junction for around Rs30.