Check the 7 day:
https://forecast.weather.gov/MapClick.php?lon=-119.03794884681699&lat=37.650648004708614#.Y_ZxmXbMIaZ
Howard Sheckter also does informative writeups with generally accurate long term forecasting (2 weeks out):
https://mammothweather.com/
Wind is a major player, if it's windy all the upper mountain lifts will be on wind hold. If you are there just to ski park this shouldn't be a problem as the parks are all near the base. End of March is a coin flip, storms still can roll through but you likely will have spring like conditions. Summit is close to 12,000 feet so it stays pretty cold up there even on warm days.
Generally, when it's sunny it's nice spring like conditions. When the weather is mixed, bring an extra layer because it'll likely be windy and therefore cold (by my standard, Southern Cali resident). Snow conditions are dryer then other parts of the west coast but not quite as dry as Colorado/Utah/Idaho.
They have a ton of snow so the entire mountain will be open, you chose a great year to come to Mammoth!