Skied that mountain for many years, to try and describe what you will have is tough. You ski from sea level to above timberline in the same run so it is really hard to pinpoint. Being coastal doesn't make it any easier either. Go, it is a medium sized ski area that skis like a whole mountain range. Water repellent and layered is the order for clothing. Remember March's that were -20 and some +40, be ready for any of it.
March will have weather and snow at Alyeska. Equinox works just the same in AK, so plenty of daylight, 21st or so there will be 12 hrs of daylight, 12 hrs dark. The locals did some great partys on the 21st.
Have skied there in March when it was: brutal cold, raining sideways, nuking snow, spectacularly sunny. (The next day was totally different.) You are starting from sea level so you can have anything for weather, but the snow conditions are assured, there will be snow and it will be varied conditions. When cloudy the lower mt is often wet snow or even rain, but the upper mt gets snow (light to heavy it all varies with temps). Expect flat light, you could get nothing but bluebird, but expect flat.
Don't know many people upper intermediate or above that did not love it, not a great beginners mountain though. It is unique to N. America, and it does have personality. Enjoy it!