As far as I know Garmin uses a quite limited set of weather stations for their weather information on various devices and in Garmin connect, mainly airports (https://support.garmin.com/en-US/?faq=iSaDaYsypP3QYBVRveLXAA). That means that your nearest station may actually be quite far away (even 50 km or more) and at a completely different altitude.
Unfortunately, Garmin doesn't show which station they use for the weather widget on the scale, there is also no information for which period the forecast is. I often see the "actual temperature" (or whatever it is) to be quite a bit outside the range of the forecast. This erratic behaviour and lack of information makes the whole thing quite confusing and useless for me.
How to deal with it? Deactivate it (via GCM) - or take it with humor.
