I think my exercise book has dropped a word in translating the following sentence, but it is probably that I am just misunderstanding some concept. Please help.

Because the weather is very bad, we´re not going to go to see them.

The book: Hava çok fena olduğundan onları görmeye gitmiyeceğiz.

My try: Havanın çok fena olduğundan dolayı, onları görmeye gitmeceğiz.

Why does the book´s sentence not have "dolayı"? Doesn´t the "dan" need something to work off of?

Yine teşekkür ederim.

Isn´t that should be : gitmeyeceğiz?

Simple answer to your question is ; Because it is unnecessary to use "dolayı " as suffix " dan" already gives the same meaning [because,since] in that concept. 

Trip, again you shouldn´t put "nın" onto "hava" , since when you say "Havanın" , that means " of the weather " but you want to say just " Weather" [Hava]

Because[since] the weather..................

Thank you! Yes, I see my mistake with "hava" now, tunci. I understand. ... And I realize now that I am leaving my "y" out when I making the future form of the verb negative. I do know better! ... Aaargh. ... I think so hard about one thing that I forget another. ... Back to the lesson book!

So, I have come back to my sentences from yesterday, and I think I see the difference now. Tell me if I am understanding correctly. Here are the sentences from my book again:

Mehmet gelmediği için Ahmedin de gelmiyeceğini ümit ederim.

Hava çok fena olduğundan onları görmeye gitmiyeceğiz.

The first sentence says, "Because Mehmet didn´t come, I hope Ahmet also will not come."

The second sentence says, "The weather being very bad, we will not go to see them."

The first construction explicitly says "because" with "için." The second construction doesn´t explicitly say "because" with a separate word, such as "için" or "dolayı" (at least from the English speaker´s perspective). Am I getting at the idea here? It is confusing for me because my book expressed both sentences with "since" or "because" in English, so I assumed it wanted me to use similar constructions when I put them in Turkish.

And a final question: Does this mean that "dolayı" is more likely to be used with something that is not a clause, that does not have a verb. In other words, with a noun phrase? So: "sizden dolayı," "parasından dolayı."

Teşekkürler! 

Quoting trip  So, I have come back to my sentences from yesterday, and I think I see the difference now. Tell me if I am understanding correctly. Here are the sentences from my book again: Mehmet gelmediği için Ahmedin de gelmiyeceğini ümit ederim.  Hava çok fena olduğundan onları görmeye gitmiyeceğiz. The first sentence says, "Because Mehmet didn´t come, I hope Ahmet also will not come."  -----> CORRECT

The second sentence says, "Because the weather being very bad, we will not go to see them."   --->Hava çok fena olduğundan 

The first construction explicitly says "because" with "için." The second construction doesn´t explicitly say "because" with a separate word, such as "için" or "dolayı" (at least from the English speaker´s perspective). Am I getting at the idea here? ---> Yes, you got the idea, however, originally there was "-den dolayı" there ---> -den dolayı 

If you use " dolayı" , then it has to be used with -dan,den  whether  it is used with noun or verb.  but "dolayı"  can be dropped and we can just use  -den [dan].

  example ; Türkçe bildiğinden  dolayı .......    =    Türkçe bildiğinden....... Because[since] he/she knows Turkish...... =   Because [since]  he/she knows Turkish

 It is confusing for me because my book expressed both sentences with "since" or "because" in English, so I assumed it wanted me to use similar constructions when I put them in Turkish. And a final question: Does this mean that "dolayı" is more likely to be used with something that is not a clause, that does not have a verb. In other words, with a noun phrase? So: "sizden dolayı," "parasından dolayı."-den  dolayı can be used both with noun phrases and verb phrases.

Sizden dolayı --> Because of  you 

Sigara içtiğinizden dolayı....> Because you smoke [smoked]... Teşekkürler! 

note : with verbs, you can just use " için" .

         Türkçe çalıştığı için......  =  Because he/she study [studied] Turkish .