For good weather and festivals, early April
Argentina, Buenos Aires Tango Festival, with competitions, lessons, concerts and more.
Vietnam, Huong Tich/Lac Long Quan Festival (pilgrimage) Feb/Mar/early-Apr. Vietnam Pictures
Philippines, Holy week (the week to Easter), famous mostly for bloody flagellation and crucifixions. Body piercers wll love it.
Bhutan, Paro and Thimpu festival, in a stunning monastic setting monks in brilliant silks perform traditonal dances. March/April.
Nepal (Khatmandu Valley) Macchendrath Rath Jatral, 1 month. Kathmandu Pictures.
Thailand (Nationwide) Songkran Water Festival, April 12-14 every year, especially lively in Kao San Rd, Bangkok.
Chile (near Santiago) Quasimodo Processions (medieval processions, music and dancing), first Sunday after Easter. Chile Pictures
Japan (Nationwide) Cherry Blossom time, a few days of alcoholic mayhem under the trees plus Takayama Festival, Kawasaki Penis Festival. Japan Pictures
For good weather and festivals, late April
Israel (Meiron, Galilee) Lag B’Omer, Spring feast, Apr/ May, 1 day.
Nepal (Khatmandu Valley-Bhaktapur), Nepalese New Year) 4 days.
(Thimi and Bode) Bal Kumari Jatra (New Year gathering) 4 days.
Mexico (Aguascalientes) Feria de San Marcos (national fair), 2nd week of April – early May, 22 days. Mexico Pictures
Spain, Seville, La Feria de Abril, April 16-21 every year, April Fair, perhaps Seville’s best party – traditional dress, parades, dancing and wild parties. Seville Pictures.
Or go for festivals only, not the weather! i.e. this is not the best season
India (Ajmer, Raj) Islamic Fest. Feb-April, 6 days.
(Nationwide) Hindu New Year, April/May, 1 day
(Thrissur, Ker) Pooram. elephants, fireworks. April/May, 1 day
Madurai (TN) Chitra Fest. Divine marriage at wild Meenakshi temple. April/May, 10 days
(Bodhgaya and Sarnath) Budda Jayanti, full moon day in Apr/May, 1 day. India Pictures.
Burma (Myanmar), (Nationwide) Thingyan Water Festival, Mar/Apr, 3-4 days
China (Xishuangbanna) Water-Splashing Festival, 3 days. China Pictures.
Laos (Nationwide) Lao New Year, mid April.
Colombia (San Antero), National Donkey Beauty Contest , Easter, 4 days.