A possible tornado Sunday afternoon caused some damage to a home southwest of Mount Vernon, Jefferson County Emergency Management Agency Director Steve Lueker said.  The National Weather Service will investigate whether a small tornado did touch down or if straight-line winds caused the damage, he said.  No one was hurt in the afternoon storm that brought heavy rain and small hail to much of Southern Illinois, with more storms forecast overnight and through the early part of the week, according to the National Weather Service in Paducah.  Lueker said he received unconfirmed reports of wind gusts of 45 miles per hour.  The home off Illinois 148 had some roof and siding damage but that it was livable.  A garage at a nearby location also was damaged and several trees were uprooted.