The monsoon normally tails off by mid-to-late September, leaving the skies clear and humidity-free in October. It can rain in October, especially earlier in the month, but not very much. Temperatures in Kathmandu remain quite hot in October, but up in the Everest region it is much cooler. The average low in Namche Bazaar (11,290 feet/3440 meters), an essential stop on the Everest Base Camp (EBC) trek, is 35°F (2°C), and the average high 53°F (12°C). Temperatures at higher altitudes will be lower.
Crowds & Costs
October is peak season for trekking in Nepal, with costs and crowds reflecting this. The EBC trek is the most popular in Nepal, and you're very unlikely to have the trails all to yourself in October. Teahouses fill up quickly, so it's important to trek with a good guide who will get you a bed at a comfortable place.
Similarly, flights from Kathmandu to Lukla fill up well in advance of October, so make your travel arrangements as early as you can. If you're planning a last-minute trip, you may have to be flexible with flight timings and the quality of accommodation you'll accept.
If you have your heart set on trekking the classic EBC route, the conditions are generally good for it in October, with clear skies and not-too-cold temperatures. However, the sheer number of people undertaking the trek in October can be off-putting for some travelers.
Travelers interested in less-beaten paths, there are many alternative routes in the Everest region that still offer spectacular views of Everest and its neighbors, but without the crowds. The Gokyo Lakes Trek, the Three Passes Trek, or even the very challenging Arun Valley to EBC trek see far fewer travelers than the standard EBC trek, yet still overlap with it in some sections, providing the best of both worlds.
What to Bring
Most good teahouses provide thick blankets, but they're not usually washed very often. It's a good idea to bring your own sleeping bag from home for the extra warmth at higher altitudes, and for comfort's sake. An easily-packable rain coat is also a good idea when trekking in October, because although the chance of rain isn't as high as in September, you wouldn't want to be caught out.
Check out the following article for more details on what you should pack for a Himalayan trek: Trekking Gear List for Nepal.
Getting There & Away
The quickest way of getting from Kathmandu to the Everest Region is to fly to Lukla. It's important to leave buffer days in your itinerary in case of delays leaving Lukla. Although conditions are generally favorable in October for flights to leave on time from either direction, don't risk missing an international flight.
Read more about getting from Kathmandu to Lukla in the following article: How to Get from Kathmandu to Lukla.
Events in October
Traditional Nepali festivals usually follow a lunar calendar. This means that some festivals that fall in October one year may be in September or November the next.
The inhabitants of the Everest region are mainly ethnic Sherpas, who follow Tibetan Buddhism. They don't celebrate all of the same festivals as Hindu Nepalis of the hill areas. So, some of the big Nepali festivals that usually fall in October aren't celebrated at all, or with much gusto, in the Everest region.
If you're traveling to Nepal in October and passing through Kathmandu, you may come across Dashain and/or Tihar. These are the two biggest festivals for most Nepalis. Dashain represents the triumph of good over evil, and is a time when most Hindu Nepalis who are able to travel back to their home towns or villages. Tihar falls shortly after Dashain; Dashain sometimes falls in September, and Tihar in October or November. If passing through Kathmandu during Dashain, it's important to make preparations. On the most important days of the festival, much of the city closes down, with fewer restaurants and shops open, and taxis being harder to come by.
One of the most important festivals for the Sherpa people is Mani Rimdu, which falls in October or November. It's worth trying to be in Tengboche for the festival if you can. Tengboche Monastery is the most important monastery in the area, and Mani Rimdu festivities focus on this small town with spectacular views of Ama Dablam. Monks dress in colorful and elaborate costumes and masks, and dance in a symbolic performances to conquer demons.