13w36a saw the addition of biome categories, but there is a problem, the biomes at the center of the 4 categories (cold and medium) spawn way to frequently, whereas the biomes at the edge (hot and snow-covered) have not been balanced out and therefore spawn way too far from each other, making them a lot too rare.
However, there seem to be other details, Deserts and Savannas are actually fairly common, whereas Canyons are rarer, and Jungles are VERY rare. However the snow-covered biomes are unbelievably rare, significantly rarer than the hot biomes, in a very long biome search i did not find a single snow-covered biome (extreme hills is a cold biome).

Here is a tally count proving what I mean, i went in a single direction and did a count for every biome I bumped into, this does not include technical biomes (e.g. river, beach...), and doesn't include Ocean/Deep Ocean biomes:
Plains: 68
Desert: 25
Desert Hills: 13
Savanna: 26
Savanna M: 7
Sunflower Plains: 14
Forest: 65
Mesa F (no such biome, just applies to a Mesa with Mesa Plateau F): 2
Mesa: 2
Forest Hills: 24
Extreme Hills: 41
Extreme Hills+: 32
Swampland: 14
Roofed Forest: 12
Birch Forest Hills: 9
Birch Forest: 18
Taiga: 29
Taiga Hills: 9
Swampland M: 1
Flower Forest: 7
Jungle: 3
Desert M: 3
Extreme Hills+ M: 3
Extreme Hills M: 3
Mega Taiga Hills: 1
Mega Taiga: 3
Birch Forest M: 3
Birch Forest Hills M: 1
Ice Plains: 8
Ice Mountains: 8
Cold taiga: 7
Mesa (Bryce): 1
Jungle Hills: 1