Hey ngakai78,
"A 10-day weather forecast is available for most countries and regions. The data is provided by Apple Weather. If you use iOS 15.2 or earlier, you'll see a 10-day forecast that's provided by The Weather Channel." You can review more information here: Feature availability and data sources in the Weather app. This article may have information that could help.
If not, make sure the iOS software is up-to-date. The latest version is iOS 16.3 and can be checked in Settings > General > About. If you need information on backing up your data to ensure it's safe and/or updating the software, follow the steps below or in this article: Update your iPhone or iPad.
1. Back up your device using iCloud or your computer.
2. Plug your device into power and connect to the internet with Wi-Fi.
3. Go to Settings > General, then tap Software Update.
4. If you see more than one software update option available, choose the one that you want to install.
5. Tap Install Now. If you see Download and Install instead, tap it to download the update, enter your passcode, then tap Install Now. If you don't know your passcode, learn what to do.
The article also includes steps on updating using a computer.
If you continue to have the issue, make sure the date, time and time zone is correct. If it isn't correct, update it to the correct time zone and also make sure "Set Automatically" is enabled in Settings > General > Date & Time. Incorrect information can cause issues.
If there is a VPN installed/enabled, it could cause issues, so disable it and try again:Check VPN (Virtual Private Network) and third-party software to help resolve network connectivity issues.
Hope this helps. Take care.