Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN
Issued by NWS Knoxville/Tri Cities, TN
536 FXUS64 KMRX 111647 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 1247 PM EDT Mon Aug 11 2025 ...New DISCUSSION, AVIATION... .DISCUSSION... Issued at 1221 PM EDT Mon Aug 11 2025 Key Messages: 1. Rain showers this afternoon/evening mainly towards the mountains. Drier, with a few sprinkles/light showers, further north and west across the forecast area. 2. More widespread scattered convection, limited thunderstorm chances, on Tuesday. Tropical-like heavy rain rates possible, especially across southeast Tennessee near Chattanooga. 3. Shortwave trough and surface front continue scattered precipitation chances on Wednesday with some heavy rain rates. 4. Mostly diurnal precipitation chances through late week with weak forcing and upper-level ridge retrograding westward towards the Lower Mississippi Valley. Highest precipitation chances will be over the higher elevations each afternoon. Discussion: A low pressure system with tropical moisture near the Florida panhandle is producing widespread precipitation across the Southeast CONUS. Downslope flow across the mountains is limiting the precipitation coverage across our area. Rain is likely to continue across the far eastern mountains this evening and tonight with increasing chances late tonight into Tuesday morning near Chattanooga. This low pressure system will approach our southeastern counties on Tuesday afternoon with winds becoming more south and increasing moisture advecting across the area. PW values increase substantially. RAP forecast soundings show PW values around 2.2 inches near Chattanooga with a saturated atmosphere and deep warm cloud layer depth around 14k ft. MLCAPE is limited near 1000 J/Kg with a very skinny sounding profile supportive of weak, deep updrafts. This will support tropical warm cloud rain processes with heavy rain rates and the potential for urban and small stream flooding near the southern valley, southern plateau, southwest North Carolina, and the southern East Tennessee mountains. Similar setup on Wednesday as a shortwave quickly moves across the region with an already saturated environment. This will result in scattered showers, and a few thunderstorms, with the potential for heavy rain rates and localized flash flooding area-wide as PW values remain 2.0 to 2.2 inches across the area. Precipitation chances remain through late week and into the weekend, but uncertainty is higher during the late week time- frame. Less synoptic support is expected with primarily diurnal trend convection within an environment supportive of heavy rain rates. Most likely precipitation chances each day will be across the higher elevations. && .AVIATION... (18Z TAFS) Issued at 1221 PM EDT Mon Aug 11 2025 VFR cigs expected to prevail and TYS and TRI with downslope flow across the mountains with MVFR cigs setting up at CHA. Tempo MVFR/IFR vis is possible during rain showers at all sites, but primarily impacting CHA tonight. Upslope SSE flow near CHA will result in low cigs by late tonight and Tuesday morning with IFR conditions probable near the terminal. In addition, fog may develop late tonight with the potential for IFR cigs/vis in the vicinity of TRI. Winds remain light and from the southeast. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 73 85 72 89 / 30 80 50 80 Knoxville McGhee Tyson Airport, TN 72 86 72 87 / 30 70 50 60 Oak Ridge, TN 72 87 72 87 / 20 70 50 70 Tri Cities Airport, TN 67 85 69 84 / 20 70 50 70 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$ SHORT TERM...JB LONG TERM....JB AVIATION...JB