Nepal is close to the equator, it don't snow down in the Valleys.
Well... OK, on GoogleEarth I now see that Kahtmandu is on about the same latitude as Corpus Christi. That surprises me... but so be it.
But the altitude there has got to be a factor... I get an altitude of about 4300 feet for Kahtmandu. Seems plenty high to regularly get snow in the winter. I'm surprised that in the CIA factbook they show the altitude of Nepal goes all the way down to 70m in the southern part. Interesting. Didn't have any idea it might get that low.
Yuh lern sumpthin every day. :-)