Learn Icelandic: Það er kalt miðsvetrar, svo kindurnar þurfa ullina. - It is cold in midwinter, so the sheep need the wool.

It acts as a genitive of time, a fixed expression used to indicate when something generally or repeatedly happens. Here, miðsvetrar translates to "in midwinter" or "during midwinter". You will often see the genitive case used this way for seasons or times of day, like kvölds (at night) or sumars (in summer).

Why is ullina in the accusative case? Doesn't the verb þurfa sometimes take the genitive?

The verb þurfa usually takes the accusative case for the thing that is needed, which is why we see the accusative definite form ullina here. It only takes the genitive case in more formal or older texts, or in specific fixed phrases. In everyday modern Icelandic, the accusative is the standard for this verb.

What is the base form of kindurnar, and why does the plural end in -ur?

The base form is the feminine noun kind (sheep). It belongs to a specific group of feminine nouns that take -ur in the plural instead of the more common -ir or -ar. So it becomes kindur, and adding the definite article gives us kindurnar (the sheep).

Why do we use the neuter form kalt in this sentence?