I find
this site to be excellent for understanding what the fronts are doing. Thank you to 2Donkeys for pointing it out in his Transatlantic Blog!
Like FFF & others have said, it's not that the Forecasts generally get it wrong, more that they can't reliably predict the time. The above site is good for looking at what is happening generally, and then seeing how it is changing as you get closer to the day your interested in.
dp