Learn Turkish: Su çok soğuk havada donar. - Water freezes in very cold weather.

For most single-syllable verbs ending in a consonant, the aorist (simple present) suffix is -ar or -er. Because don- (to freeze) has a hard back vowel (o), it follows 2-way vowel harmony and takes -ar, becoming donar. Multi-syllable verbs are the ones that usually take the 4-way vowel endings like -ır or -ur.

Why do we use the aorist tense (donar) here instead of the present continuous (donuyor)?

The aorist tense is used to talk about habits, general truths, and scientific facts. Since 'water freezes in cold weather' is a universal fact, donar is the perfect fit. If you used the present continuous (donuyor), it would mean a specific pool of water 'is freezing' right at this exact moment.

Why is the locative suffix -da attached to hava and not right after soğuk?

In Turkish, grammatical case endings attach to the main noun at the very end of a descriptive phrase. The whole phrase is çok soğuk hava (very cold weather). The locative 'in' suffix (-da) goes on the final noun, making it çok soğuk havada (in very cold weather).

I learned that hava means 'air'. Does it also mean 'weather' here?