All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His Slave and Messenger.
It is recommended to invoke Allaah, The Exalted, during rainfall as there are reported authentic Ahaadeeth relevant to this. The Prophet said in one of those Ahaadeeth: “Seek an answer to your supplication at the time when the armies meet (in the battlefield), when the Athaan (call to prayer) is announced, and when the rain falls.” [Al-Albaani graded it Hasan (good) in As-Silsilah As-Saheehah] Another narration reads, “Two will not be rejected, supplication when the Athaan (call to prayer) is being called and under the rain.” [Al-Albaani graded it Hasan in Saheeh Al-Jaami‘ As-Sagheer]
Hail and snow are considered rain but in a frozen form. Therefore, it is permissible to use melting snow or hail for ritual purification. The Shaafi‘i scholar Ash-Sheeraazi wrote about the types of pure water that can be used in ritual purification: “Whatever comes down from the sky: rain, water of melting snow or hail. The evidence in this regard is the verse that reads (what means): {…and sent down upon you from the sky, rain by which to purify you ...}[Quran 8:11]”[Al-Muhaththab]
Perhaps you mean by 'losing reward' that your supplication will be rejected. If this is what you meant, then you should know that when a Muslim appeals to his Lord while observing all the conditions needed for the acceptance of his supplication, and all the impediments to having one’s supplications answered are avoided, his supplications will very likely be accepted. It should be noted that disliking rainy weather is not considered an impediment to having one's supplications answered, Allaah willing.
It is known that people often rejoice when rain falls; that is why Allaah, The Exalted, says (what means): {It is Allaah who sends the winds, and they stir the clouds and spread them in the sky however He wills, and He makes them fragments so you see the rain emerge from within them. And when He causes it to fall upon whom He wills of His servants, immediately they rejoice.}[Quran 30:48]
If someone dislikes rain out of fear of potential harm such as drowning or the collapse of buildings or the like, then there is nothing wrong with that. Anas ibn Maalik narrated: Once, in the lifetime of the Prophet the people were afflicted with drought. While the Prophet was delivering the Khutbah on a Friday, a Bedouin stood up and said, "O Messenger of Allaah! The livestock are dying and the families (offspring) are hungry; so pray to Allaah to bless us with rain." The Prophet raised his hands towards the sky and at that time there was not a trace of cloud in the sky. By Him in Whose Hands my soul is, as soon as he lowered his hands, the clouds started gathering like mountains. Before he got down from the pulpit, I saw rainwater trickling down his beard. It rained that day, the next day, the third day, the fourth day, and till the next Friday. The same Bedouin - or another man - stood up (during the Friday Khutbah) and said, "O Messenger of Allaah! The houses have collapsed and our possessions and livestock have drowned; so invoke Allaah (to protect us)." The Prophet raised both his hands and said, "O Allaah! Around us and not over us." Whichever side the Prophet directed his hand, the clouds dispersed from there till a hole (in the clouds) was formed over Madeenah. The valley remained flowing (with water) for one month, and no one came from outside who did not talk about the abundant rain." [Al-Bukhari and Muslim]
Allaah knows best.