Χτες το απόγευμα έπεσε χαλάζι, αλλά σήμερα έχει μόνο κρύο και παγωνιά.

Yes. Χτες and χθες both mean yesterday.

A learner should know:

• χθες is the more traditional spelling
• χτες is a very common modern spelling
• In everyday speech, many people pronounce them similarly, often closer to xtes

So in modern Greek, Χτες το απόγευμα is a perfectly normal way to say yesterday afternoon.

Greek usually uses the definite article with parts of the day and many time expressions.

So:

• το πρωί = in the morning / this morning
• το μεσημέρι = at noon / midday
• το απόγευμα = in the afternoon
• το βράδυ = in the evening / at night

This is very natural in Greek. English often omits the in these expressions, but Greek usually keeps it.

In this sentence, Χτες το απόγευμα means yesterday afternoon.

Έπεσε is the aorist (simple past) of πέφτω, which means to fall.

So literally:

• πέφτω = I fall / am falling
• έπεσε = it fell

Greek often uses πέφτω for weather phenomena, especially things that fall from the sky:

• έπεσε βροχή = rain fell
• έπεσε χιόνι = snow fell
• έπεσε χαλάζι = hail fell

This may sound a little different from standard English phrasing, but it is very natural in Greek.

Because χαλάζι here is being used in a general, indefinite way: hail as a weather event, not a specific identifiable object.

Greek often leaves out the article with weather or mass-noun expressions like this:

• έπεσε χιόνι
• έπεσε βροχή
• έπεσε χαλάζι

Using το χαλάζι would sound more specific, as if you were referring to a particular hailstorm already known in the conversation.

So the version without the article is the normal one here.

Greek commonly uses έχει or κάνει in weather expressions where English often uses it is.

Very common patterns are:

• έχει κρύο = it is cold
• κάνει κρύο = it is cold
• έχει ζέστη = it is hot
• κάνει ζέστη = it is hot

So σήμερα έχει μόνο κρύο και παγωνιά is a normal Greek way to describe the weather.

By contrast, είναι κρύο would usually mean it is cold about a thing, not about the weather in this idiomatic sense. For example:

• Το νερό είναι κρύο = The water is cold

So for weather, έχει κρύο is the expression you want.

Here κρύο is a noun, meaning cold.

That is why it works with έχει:

• έχει κρύο = there is cold / it is cold

Compare that with the adjective:

• κρύος = cold, masculine
• κρύα = cold, feminine
• κρύο = cold, neuter

Examples:

• Ο καφές είναι κρύος. = The coffee is cold.
  Here κρύος is an adjective.
• Έχει κρύο έξω. = It’s cold outside.
  Here κρύο is a noun.

So the form looks the same as the neuter adjective, but the grammar is different.

Both relate to cold weather, but they are not exactly the same.

• κρύο = cold, general coldness
• παγωνιά = frost, bitter cold, freezing conditions

So παγωνιά sounds stronger and more vivid. It suggests a harsher, more penetrating cold, often with the idea of freezing temperatures.

In the sentence, using both together emphasizes that today there is not hail, but there is still unpleasant winter weather.

Μόνο means only.

In this sentence it limits what the weather consists of today:

• σήμερα έχει μόνο κρύο και παγωνιά

The idea is: today there is only cold and frost/bitter cold.

So the contrast is:

• yesterday afternoon: hail fell
• today: not hail, just cold and freezing weather

μόνο is modifying the whole phrase κρύο και παγωνιά.

Because αλλά means but, and Greek punctuation usually separates two contrasting clauses with a comma, just as English often does.

So the sentence is divided into two parts:

• Χτες το απόγευμα έπεσε χαλάζι
• αλλά σήμερα έχει μόνο κρύο και παγωνιά

The comma marks the contrast clearly and naturally.

Yes, absolutely.

You could say:

• Χτες το απόγευμα έπεσε χαλάζι...
• Χθες το απόγευμα έπεσε χαλάζι...

Both are correct. The difference is mostly spelling style, not meaning.

A lot of learners first meet χθες in books, but χτες is extremely common in everyday language.

It is very natural, but not the only possible wording.

Greek has several weather expressions, for example:

• έπεσε χαλάζι = hail fell
• έριξε χαλάζι = it hailed
• είχε χαλάζι = there was hail

These are all possible, but they are not always identical in tone.

• έπεσε χαλάζι is vivid and common
• έριξε χαλάζι is also very common in spoken language
• είχε χαλάζι is more neutral, simply describing the condition

So the sentence you have is perfectly idiomatic.

The basic order is very natural:

• time expression: Χτες το απόγευμα
• verb: έπεσε
• subject-like weather noun: χαλάζι
• contrast: αλλά
• new time expression: σήμερα
• verb: έχει
• complement: μόνο κρύο και παγωνιά

Greek word order is more flexible than English, so some parts could move for emphasis. But the version in the sentence sounds smooth and standard.

For example, you might also hear emphasis like:

• Σήμερα έχει μόνο κρύο και παγωνιά
• Μόνο κρύο και παγωνιά έχει σήμερα

But the original order is the most neutral and learner-friendly.

A rough pronunciation guide is:

• Χτες ≈ htes or khtes
• το απόγευμα ≈ to apóyevma
• έπεσε ≈ épese
• χαλάζι ≈ halázi

A few useful notes:

• χ is not like English h exactly; it is a rougher sound, like German Bach or Scottish loch
• γ before ε in απόγευμα is pronounced like a soft y-sound
• the accented syllables are:
  • Χτες
  • α in απόγευμα
  • έ in έπεσε
  • λά in χαλάζι

So the rhythm is something like:

ΧΤΕΣ το α-ΠΟ-γευ-μα Ε-πε-σε χα-ΛΑ-ζι