Why is it "cold weather" not "the cold weather", even though it says "اَلْطَّقْس"?
There are bits of translations between Arabic in English which do not coincide in terms of definitions. Meaning, it is just used in that manner. Here are some examples:
1. You say in English (I love nature) meaning you love to be in natural grounds and probably everything green. In Arabic, you would say أحب الطبيعة - The word "nature" has to be defined in Arabic because it is the nature that we know (and since we know it, it has to be defined by AL). In English though since it is a term meaning the whole nature or the concept of nature it seems definition is not required.
2. In English, "News" in naturally a plural noun and to make it singular you might need to add to it, like "an item of news." In Arabic though, there is a singular خبر and a plural أخبار .
So, these are just two examples of many incidents where English and Arabic do not coincide completely in terms of defining a word or making a word plural, and many other things as well. I think this exists between every two languages even if they are of the same family (check German and English for example).