Weather and climate that start with n v u x k y?

Question

I need help finding a word that has to do with weather or climate that begins with n v u x k y please help me if you have a good word for all of them you will get as best answer please help me!!!

Answer 1

K - k-index

N - nor'easter

U - unsettled

V - valley exit jet

X - x-band

Y - yellow snow

Answer 2

n-Nimbostratus

v-vortex cloud

u-?

x-?

k-Katabatic winds

y-?

I am sorry I couldn't be of more help to you. Good luck!