How is it possible a forecast min 0 / max 6 and an actual temperature of -3?!

Current temperature and conditions CAN be outside forecasted ranges. Forecast is BEFORE the fact, current observation is AFTER the fact. I don't think Garmin can do anything about this. The watch just displays…
I believe one is a forecast , one is actual. Weather forecast is often wrong and sometimes the actual is outside the range in the forecast.
Note that in my case the photo was taken inside my house, so "-5°" is from weather provider too, not from the sensor. I think a good weather service should adjust their data with the ongoing…
Many weather apps reflect data like that. It depends what period they reflect as the day , often times I notice a max or a min not in line with the expectation. remember one is an expectation , the other is a reality. So the expectation was a 0 but i reality it is lower. Often temp are higher or lower than forecast.
Current temperature and conditions CAN be outside forecasted ranges. Forecast is BEFORE the fact, current observation is AFTER the fact. I don't think Garmin can do anything about this. The watch just displays the data as it is from weather provider.