Bármennyire is rossz az előrejelzés, felkészülünk.

It is a concessive pattern meaning no matter how or however.

So Bármennyire is rossz az előrejelzés... means No matter how bad the forecast is...

A very literal breakdown would be something like:

• bármennyire = to whatever degree / however much
• is = an emphatic particle here

Yes, is often means also / too, but not here.

In this sentence, is is part of a common concessive structure with bár- words:

• bárki is = no matter who
• bárhol is = no matter where
• bármilyen is = however / no matter what kind
• bármennyire is = no matter how much / however

So here is is not translated separately as also. It helps create the sense no matter how...

Because Hungarian usually leaves out the verb van (to be) in the present tense, third person, when the predicate is a noun or adjective.

So:

• Az előrejelzés rossz. = The forecast is bad.
• not Az előrejelzés rossz van.

But in other tenses or persons, the verb appears:

• Az előrejelzés rossz volt. = The forecast was bad.
• Az előrejelzés rossz lesz. = The forecast will be bad.
• Rossz vagyok. = I am bad / unwell (depending on context)

Because bármennyire directly modifies rossz, so the adjective naturally comes right after it:

• bármennyire is rossz = no matter how bad

That makes Bármennyire is rossz az előrejelzés the natural order here.

Without bármennyire, a simple neutral statement would often be:

• Az előrejelzés rossz. = The forecast is bad.

So the word order here is largely driven by the bármennyire is + adjective pattern.

Yes, you could. It is also natural and means nearly the same thing: however bad the forecast is.

A useful nuance is:

• bármennyire emphasizes degree
• bármilyen often means whatever kind of, but with adjectives it can also work in concessive sentences like this

So:

• Bármennyire is rossz... = very clearly no matter how bad...
• Bármilyen rossz is... = also fine, slightly different in feel, but very close in meaning

Because Hungarian usually does not use subject pronouns unless they are needed for emphasis or contrast.

The ending -ünk in felkészülünk already tells you the subject is we.

So:

• felkészülünk = we prepare / we will prepare

If you added mi, it would sound more emphatic:

• Mi felkészülünk. = We will prepare. / As for us, we’ll prepare.

It is the 1st person plural form of felkészül, which means to prepare oneself, to get ready, or to prepare.

So:

• felkészülök = I prepare / get ready
• felkészülünk = we prepare / get ready

The prefix fel- is simply part of the verb here. You should not try to translate it literally as up in this sentence.

Also, this verb often takes -ra/-re to show what someone is preparing for:

• felkészülünk a viharra = we prepare for the storm

In your sentence, that part is just left unstated.

Formally, it is present tense.

But Hungarian very often uses the present tense to talk about the future when the situation makes that clear. So here felkészülünk can naturally mean:

• we prepare
• we will prepare

If someone wanted to make the future more explicit, they could say:

• fel fogunk készülni

But the simple present is very normal and idiomatic.

Az is the definite article the.

So:

• az előrejelzés = the forecast

Here it refers to a specific forecast, or the forecast already being discussed.

No. Előrejelzés means forecast or prediction in a general sense.

It is very commonly used for the weather, but it can also be used in other contexts, such as:

• economic forecasts
• sales forecasts
• technical predictions

In this sentence, it most likely means forecast in the ordinary everyday sense, probably a weather forecast if the context suggests that.