Below are two images of the sea level pressure and the forecast 6 hour precipitation from the 12 Z run of the GFS on March 24th. As you can see, the forecast contours (yellow) are in similar locations as the actual pressure contours (red). They are not in the exact same locations, but the general picture of the weather is accurate. They show the high pressure over the Midwest very well. The Precipitation, however seems to be overestimated as shown in the weather.