Learn Hardcore Icelandic: Ég býst við að veðrið verði gott á morgun. - I expect the weather to be good tomorrow.

býst við comes from the verb phrase að búast við, which means “to expect.” The little word við here is not the pronoun “we” but a postposition that belongs to the verb:

að búast við eitthvað = “to expect something”
In the present tense for “I,” you say ég býst við. If you want, you can insert því (the neuter demonstrative pronoun “that”) before að, like ég býst við því að…, but in everyday speech því is often dropped.

Why is the verb in the clause veðrið verði gott using verði instead of verður?

Because Icelandic uses the subjunctive mood here. After verbs of expectation (like búst við) and certain conjunctions (að in this case), the subordinate clause takes the subjunctive to signal that the event is not (yet) a fact.

Indicative: Veðrið verður gott (“The weather will be good” as a plain future statement)
Subjunctive: að veðrið verði gott (“that the weather may/be expected to be good”)

When do you use the subjunctive in Icelandic?

You’ll often see the subjunctive after:
• verbs of wishing, hoping, fearing, expecting (e.g. vona að, kvíða að, búast við að)
• conjunctions like þótt (“although”), ef in some set phrases, and in skilyrðis (“conditional”) clauses with það
• certain fixed expressions (e.g. Lifi konungur!)
In practice, if you’ve got að plus a subordinate clause under a verb that expresses something non-factual or desired, you’ll usually switch to the subjunctive.

Why is there að before veðrið, and when do you need því after býst við?

The word að is the marker that introduces an infinitive/subjunctive clause in Icelandic (like the English “that” in “I hope that…”). After býst við, you have two common patterns:

ég býst við að … (omit því)
ég býst við því að … (include því for emphasis or style)
Both are correct. In formal writing you often see því, but speakers frequently drop it and go straight into að.

Why do we say veðrið with the suffix -ið? Could we just say veður?

In Icelandic, “the weather” is normally used in the definite form, veðrið (“the weather”), because you’re talking about a specific phenomenon. If you said veður, it would feel like you were naming the phenomenon in the abstract (“weather in general”). If you want to speak more loosely, you could also say gott veður (“good weather”), but in a full sentence about tomorrow you almost always use the definite:
• Veðrið verður gott = “The weather will be good.”

Why is it á morgun and not í morgun, and what case is morgun in?

• í morgun means “this morning” (earlier today).
• á morgun means “tomorrow.”
Preposition á here governs the accusative (but for time expressions you can just memorize it as a fixed phrase). So morgun stays in its unmarked form (which is also the accusative).

Can we move á morgun to the front of the sentence? How does word order work?

Yes. Á morgun is an adverbial time phrase, so you can front it for emphasis:
• Á morgun býst ég við að veðrið verði gott.
Because it’s a main clause, you must keep the verb in second position (V2 rule): first the time phrase (Á morgun), then the verb (býst), then subject (ég), etc.

Could we replace the subjunctive verði with mun verða? What’s the difference?

You could say …að veðrið mun verða gott á morgun, using the future auxiliary mun + infinitive verða (indicative). Differences:
• verði (subjunctive) focuses on expectation/uncertainty.
• mun verða (indicative future) states a firmer future fact.
In casual speech, verði is quite common after býst við að, while mun + infinitive sounds a bit more formal or emphatic.

What’s the difference between ég býst við að, ég vona að, and ég vonast til að?

• ég býst við að = “I expect that…” (neutral prediction)
• ég vona að = “I hope that…” (I wish it to happen)
• ég vonast til að + subjunctive/infinitive = “I’m hoping/aiming to…” (slightly more formal than vona)
Nuance: býst við often carries the idea that you think it’s likely, whereas vona/vonast til emphasize desire.

How do you pronounce á morgun?

• á sounds like the English diphthong in now: [au̯].
• morgun is pronounced roughly [ˈmɔr.ɡʏn] with a rolled r and a short u like the “u” in put.
Put together: [au̯ ˈmɔr.ɡʏn].