The atmospheric conditions were just right. This morning's Flagstaff NWS discussion mentions a slightly moist layer at 500mb, right where the jets are. There was also a bit of a upper-level disturbance passing through last night. Tom P noted that nothing was conspicuous on the water-vapor images, and indeed nothing obvious on the more sensitive fog-reflectivity images---the stuff was just too small to show much temperature contrast with the ground. \Brian -- See message header for info on list archives or unsubscribing, and please send personal replies to the author, not the list.