I’ve switched to Carrot weather instead and it offers Apple Weather as a source which gives similar results as the main weather app. Seems to be something wrong with the weather API. I use Foreca as a source primarily now.
My understanding is the pandemic actually caused some serious gaps in weather forecasts. Some commercial flights transmit weather conditions to central authorities , which are extremely useful for building granular forecasts.
During the pandemic, commercial air traffic plummeted. While it has returned to normal levels, it seems the models are still missing some historical data.