I know this topic has been discussed in great length in a recent thread. Specifically, fog or zero disability occurs suddenly when the wx is nominally clear.The above happened to me recently on one of my rare VFR (simulator) flights from San Bernadino to Camarillo, CA. (I almost always, fly IFR).As I approached CMA the wx, 10 mile vis, with scatterred, suddenly fogged in and went to zero disability, and I lost the airport.I have not tried Microsoft's suggestion of deleting the temp. internet files prior to initiating the flight,but apparently others have done this without success.I've never had the above take place on an IFR flight, only on this one VFR flight. I don't see any logical reason why flying VFR or IFR would have any connection to the weather problem. Has anyone had this happen to them while IFR?Bob

I've never had the problem you mentioned specifically, but you might look to see what the temp and dew points were. If they suddenly became very close together, or the same, then MS' new weather engine may have generated fog on its own. Is the fog right on the ground? If not, then it may be a stratus type cloud and your cloud density settings are less than the max. That will give you something that looks like fog when you get right in it, but you won't necessarily see the cloud from a distance.Glenn