Based on the level of respect or formality, you can say "It's going to freeze tonight" in Korean in 3 ways:

• Informal: bam-e eol-ggeoya (밤에 얼꺼야)
• Formal: bam-e eol-ggeoyeyo (밤에 얼꺼예요)
• Very formal: bam-e eol-ggeomnida (밤에 얼껍니다)