Not much love for the BOM here. The fact is, we don't manufacture the weather. We can control much of the our flying environment, but we can't predict the weather, only offer estimates of what may happen.
The fact is that weather forecasting is far more accurate now than it has been in the past, now that the bom has more powerful supercomputers to model the weather. They can't get it it perfectly right, though, weather is chaotic. What is amazing is how accurate their forecasts are compared to just 20 years ago.
In other words, make sure you have enough fuel on board to cope with the unpredictable.