They can only work with so much information. For instance where i am based, we have the higher grounds of sheffield etc which takes the battering of bad weather whikst doncaster is in a valley in comparison and we miss alot of the bad bad weather. For instance on snowy days, you can see cars driving through with maybe 3 or 4 inch of snow still on top of car, whilst we get a light dusting of the stuff. Not sure if the forecasts take local geographical elements into account.
But either way ive not checked the forecast for quite some yrs now. Not even when i was trad because i lost too many days in the past when i did.
Now i have a magic stone outside my house. If its a dark shiny grey, its raining whereas if its a dull grey, its not raining