度: degrees are Celsius
十八度 is eighteen degrees Celsius. Chinese never states the scale because it uses only one, and 摄氏 (Celsius) is said only in a scientific text. A temperature below zero is said with 零下, "below zero": 零下五度 is minus five degrees.
Auntie Wang and Xiaoyu are enjoying a fine morning in the courtyard. Rain is forecast for tomorrow.
Auntie Wang
今天天气真好,不冷也不热。
Jīntiān tiānqì zhēn hǎo, bù lěng yě bù rè.
The weather really is lovely today, neither cold nor hot.
Xiaoyu
是啊。可是天气预报说明天下雨。
Shì a. Kěshì tiānqìyùbào shuō míngtiān xiàyǔ.
It is. But the forecast says rain tomorrow.
Auntie Wang
是吗?那我明天不出去了。
Shì ma ? Nà wǒ míngtiān bù chūqù le.
Does it? Then I shall not go out tomorrow.
Xiaoyu
明天多少度?
Míngtiān duōshao dù ?
How warm will it be tomorrow?
Auntie Wang
早上十度,中午十八度。
Zǎoshang shí dù, zhōngwǔ shíbā dù.
Ten degrees in the morning, eighteen at midday.
Xiaoyu
早上有点儿冷,我要多穿一件衣服。
Zǎoshang yǒudiǎnr lěng, wǒ yào duō chuān yī jiàn yīfu.
It is a bit cold in the morning, I will put on an extra layer.
Chen Hao
我喜欢下雨,下雨不热。
Wǒ xǐhuan xiàyǔ, xiàyǔ bù rè.
I like the rain, it is not hot when it rains.
Auntie Wang
下雨的时候别忘了带伞。
Xiàyǔ de shíhou bié wàng le dài sǎn.
When it rains, do not forget to take an umbrella.
Chen Hao
我的伞在家里,回去就拿。
Wǒ de sǎn zài jiā lǐ, huíqu jiù ná.
My umbrella is at home, I will pick it up when I get back.
Xiaoyu
我也要带一把伞。
Wǒ yě yào dài yī bǎ sǎn.
I will take one too.
十八度 is eighteen degrees Celsius. Chinese never states the scale because it uses only one, and 摄氏 (Celsius) is said only in a scientific text. A temperature below zero is said with 零下, "below zero": 零下五度 is minus five degrees.
天气真好 is an exclamation: the weather really is fine, and I am glad of it. 天气很好 is a neutral statement, and the 很 in it is almost empty of meaning, a mere prop in front of the adjective. A bare Chinese adjective, 天气好, sounds like an unfinished comparison.
别忘了 means "do not forget". 别 forbids something that has not yet happened, and 不要 says the same thing more firmly. The final 了 that often goes with it is not the 了 of the past: it presses, as in 别走了, do not go just yet.