One possible version

Dear Daddy,

It’s a gift for Father’s Day when you are reading it.

I still remember the day last summer when we went mountain climbing together. We started early in the morning. But, unluckily, it began to rain the  half way. I got all wet through, feeling cold and tired. So I couldn’t help complaining and wanted to give up. However, you encouraged me not to give up and put your coat on me softly. You said,” We won’t see the fantastic scenery unless we reach the top.” You really cheered me up. We got to the top at last and enjoyed the beauty of the nature that I had never seen.

Now, I want to say: I love you, Daddy. You raise me up!

Happy Father’s Day!

                                                              Yours,

                                                                  Mike