regex for html parsing (in c#)

Parsing HTML reliably using regexp is known to be notoriously difficult.

I think I would be looking for a HTML parsing library, or a "screen scraping" library ;)

If the HTML comes from an unreliable source, you have to be extra careful to handle malicious HTML syntax well. Bad HTML handling is a major source of security attacks.

When you write <td[^<]+?> I guess you really mean <td[^>]*>

That is "opening brace, td, maybe stuff other than closing brace..."

<tr>[\s]<td[^<]+?>Max Temperature[\w\s]*</td>[\s]

Not looked at it all yet, but that [^<] probably needs to be [^>] as you're trying to match all non-> until the > that's before Max temperature.

The " (ºC)" before the closing td was matched against:

<tr>[\s]<td[^<]+?>Max Temperature[^<]*</td>[\s]

Is that \w a word-boundary? I think that it gets a little tricky there, I'd use a more general approach.

And on the third line, there is one whitespace after the td tag, is that accounted for?

<td[^<]+?>[\s]?(?<time>([\d\:]+))</td>[\s]</tr>

I use https://www.regexbuddy.com/ for such controls. So far I tested @sgehrig's suggestion is correct

Use the Html Agility Pack or a similar library instead, as @Bjarke Ebert suggests. It's the right tool for the task.