Increase float and when increase decrease

[ItArth]

I have this script i whant that when the SkyType enum is in cloudy the cloudMaterial float “CutOff” increase exponentially to 1 and when the enum its in sunny the CutOff decrease to 0

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class RainSystem : MonoBehaviour
{
    public enum SkyType { Sunny,Cloudy};
    public SkyType skyType;

    public Material cloudMaterial;

    private void Start()
    {
    }

    void Update()
    {
        switch (skyType) 
        {
            case SkyType.Cloudy:
                Cloudy();
                break;

            case SkyType.Sunny:
                Sunny();
                break;
        }
    }

    void Cloudy()
    {
        cloudMaterial.SetFloat("_CutOff", 1);
    }

    void Sunny()
    {
        cloudMaterial.SetFloat("_CutOff", 0);
    }
}

[Hellium]

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class RainSystem : MonoBehaviour
{
    public enum SkyType { Sunny,Cloudy};
    public SkyType skyType;
    public float changeSpeed = 1;
    private float sunny;

    public Material cloudMaterial;

    private void Start()
    {
        sunny = cloudMaterial.GetFloat("_CutOff");
    }

    void Update()
    {
        switch (skyType) 
        {
            case SkyType.Cloudy:
                Cloudy();
                break;

            case SkyType.Sunny:
                Sunny();
                break;
        }
    }

    void Cloudy()
    {
        sunny = Mathf.MoveTowards(sunny, 1, changeSpeed * Time.deltaTime);
        cloudMaterial.SetFloat("_CutOff", sunny);
    }

    void Sunny()
    {
        sunny = Mathf.MoveTowards(sunny, 0, changeSpeed * Time.deltaTime);
        cloudMaterial.SetFloat("_CutOff", sunny);
    }
}