Unsettled weather spreads into parts of the Midwest, Mid-Atlantic, andSoutheast today......Hazardous heat possible across South Florida and South Texas this week......Significant flash flooding possible across portions of East Texas andLouisiana on Thursday...A fairly weak frontal system centered over the Missouri Bootheel continuesto drive wet and unsettled weather east of the Mississippi River today,with several areas of shower and thunderstorm activity noted across theeastern half of the Lower 48. Through tomorrow morning, the StormPrediction Center maintains a Slight Risk of severe weather across theTennessee Valley and over North-Central Florida as thunderstorms organizeand intensify this afternoon. Severe hail and wind remain the primaryconcerns, although a tornado or two is also possible. Isolated flashflooding also can not be ruled out with some of these storms along theslow moving front, with localized rainfall of 1-3" possible.Across South Florida, persistent southwesterly winds ahead of anapproaching mid-level ridge axis will set the stage for very warm weatherbeginning tomorrow, with heat indices exceeding 100 degrees possible.Localized Major heat-related impacts are possible with this round of hotweather through the work week according to experimental NWS HeatRiskguidance. Hazardous heat also will build into South Texas tomorrow andThursday as a warm front returns northward from the Gulf of Mexico,ushering in a very warm and moist airmass into the region.Heat aside, this returning warm front will also set the stage forpotentially significant heavy rainfall across East Texas and Louisiana onThursday as training thunderstorms focus along the frontal boundary. Thecurrent forecast calls for areal rainfall totals of 3-4" (locally higher)in this region, which has seen a near continuous stream of heavy rainfallover the last two weeks and is particularly sensitive to any additionalrain. Accordingly, a Moderate Risk (level 3/4) is in effect on the Day 3Excessive Rainfall Outlook, which suggests numerous instances of flashflooding are likely Thursday into Friday.