First of all, everyone has their magical niche, their strengths and what works best for them. So for me to make a broad generalization like "weather spells are advanced," that applies (in my opinion) to the majority of practitioners, but if you're somehow blessed to be a naturally-talented weather-worker, then it may be second nature to you.
*Any magic where you have a large force you're seeking to influence, overcome, or conquer is going to be harder than other magics that have a more minimal target.
Influencing an entire weather pattern with all the complexities involved: tides, moon, gravity, fronts, temperature, etc., is no small doing. It's quite complex, actually. Quite complex is an understatement.
That being said, my very first homework assignment given to me by my very first teacher was to lie on my back and try to mentally will clouds to change. Back then i thought it was aprofound and worthwhile exercise. I haven't done this, though, in fifteen years.
I mean i've done workings to attempt to influence weather patterns before myself - dry weather on the 4th of July (for non-US citizens, it's a big day for fireworks). I've had successes too, but it's hard to tell what was the driving force behind those successes.
With other magics, you get clear signs, omens and portents that your spell is working or it isn't. These signs leave little to mere coincidence. If you were to light a candle and do some Sun stuff, etc. to ensure a sunny day and dry up the rain, and then lo and behold you got sunshine, how would you ever know it was your spell versus just coincidence? Maybe someone can tell me.