Most of the northern plateau region has been dry the past couple of days, but the reprieve from the summer thunderstorms won’t last long, as a wet pattern appears set to grip the region this weekend.
Summer heat and the terrain differential of the Cumberland Plateau and the mountains will once again serve as the trigger for scattered thunderstorms on Friday, with coverage of these storms a little better than today. But any storms that develop over us on Friday will only be a precursor for what’s to come this weekend, as rain chances go way up Saturday and Sunday.
The National Weather Service currently has a 90% chance of rain in the forecast for Saturday, and an 80% chance for Sunday. That’s quite high for this time of year, and it’s not unjustified. With atmospheric ridging pumping up to our west, we’ll see broad atmospheric troughing here in the eastern United States, which is always a major ingredient for wet weather.
A southwesterly flow will develop on Friday that will begin pulling moist air into the region, and then a cold front will approach on Saturday, likely stalling out somewhere over Tennessee as it progresses southeastward. That’s going to be the focal point for what should be numerous showers and thunderstorms through the day on Saturday, and there will be an attendant risk of severe weather.
The risk will be quite low, but it’s certainly not non-existent, with torrential downpours and damaging wind gusts being the primary threats.
The chances for strong or severe thunderstorms will diminish somewhat for Sunday, with less instability in place after most folks see rain on Saturday. But there will still be plenty of moisture around and most people will see showers and storms again on Sunday.
Likely rain chances will continue into Monday before things finally start to dry out and we see a return to typical summer weather, with daily chances of diurnal thunderstorms.
Temperatures are likely to be several degrees below average this weekend. The high on Saturday and Sunday could very well be in the 70s. Monday will probably struggle to get out of the 70s as well, before a warming trend begins on Tuesday.
It should be pointed out that no day this weekend is likely to be a complete washout, despite the heightened chances for rain. If the high-resolution NAM model is correct, Saturday will feature only widely scattered thunderstorms. Most people will see rain, but no one is likely to see rain all day long. In fact, the NAM actually shows the most widespread activity to our west and to our south, with very little rain over the northern plateau during the day on Saturday.
Keep in mind, however, that convective activity — which is what this is — isn’t depicted very well by models. It’s the broader trends that the models can highlight, not the exact details. It’s virtually impossible to tell where thunderstorms are going to set up and how strong they’ll be. More importantly, it’s impossible to tell those areas where thunderstorm training will occur, resulting in repeated rounds of heavy rain through the day.
With that said, both the GFS and the ECMWF models keep the bulk of the precipitation to our west on Saturday, as well. The ECMWF is much wetter for our area on Sunday than on Saturday, with total rainfall exceeding one inch by the end of the weekend. The GFS is wetter on Sunday, as well, but keeps the heaviest rains to our north, across Kentucky.
The bottom line, though, is that conditions will be ripe for widely scattered thunderstorms on Saturday. Most people will see rain, and there’s the potential for some people to see a lot of rain. Even the high-resolution NAM paints pockets of 2 to 3 inches of rain across parts of the central plateau. It’s just a matter of waiting to see where those thunderstorms set up.
Areas where repeated thunderstorms do set up could see a risk for isolated flash flooding by Monday, before things start to taper off.