204 FXUS64 KMRX 241507 AAA AFDMRX Area Forecast Discussion...UPDATED National Weather Service Morristown TN 1107 AM EDT Tue Jun 24 2025 ...New UPDATE... .UPDATE... Issued at 1059 AM EDT Tue Jun 24 2025 Main forecast concern remains the heat with expected heat indices of 100 to 105 degrees today with extreme HeatRisk expected across parts of Knoxville and Chattanooga areas. Major HeatRisk for the Tri-Cities. Heat advisory remains in effect. Satellite is already showing a good deal of Cu and possible TCU development across the far east Tennessee mountains and mountains of southwest Virginia. SPC Meso analysis shows MLCAPE increasing to 2500 to possibly 3000 J/Kg later today. No shear so storm mode will be pulse type. Due to DCAPES well over 1000 J/Kg and Theta-E differences in excess of 30K, Isolated strong/damaging downbursts are possible with the stronger storms. Due to strong ridging remaining over the southern Appalachians coverage will be isolated/scattered in nature and mainly across the terrain features. Due to slow nature of the storms, localized heavy rain and runoff issues are possible. Little change to ongoing forecast. && .SHORT TERM AND LONG TERM... (Today through next Monday) Issued at 229 AM EDT Tue Jun 24 2025 Key messages: 1. Hot temperatures continue through Wednesday. A slight reprieve from the heat is expected thereafter, though still warm. 2. Isolated to scattered storms over the higher terrain outside of the TN valley will each afternoon and evening through Friday. 3. Rain chances increase this weekend into early next week as the pattern becomes more active. Discussion: A strong upper ridge will be centered directly over our forecast area and the southern Appalachians through Wednesday before weakening significantly by week's end as an active northern stream jet impinges from the north and some sort of tropical wave works westward across Florida's great bend area. Though weakened, we'll keep broad ridging in place through the weekend before what appears like a pattern change takes place next week with the ridge flipping to the western CONUS and a trough developing in the east. In terms of impacts, the heat is the main forecast item of note really. Today will be warm no doubt, but Tuesday and Wednesday will be the warmest with widespread mid and upper 90s expected. Resulting afternoon heat index values will push into the 103 to 108 degree range for much of the TN valley. A heat advisory has been issued to account for this. It seems unlikely the higher terrain of the Cumberland Plateau, east TN mountains, and our western NC and southwest VA counties will reach that 103-108 heat index range so they were left out of the heat advisory for the time being. One other caveat, I would be willing to bet the Sequatchie river valley will see those heat index values but there's also a significant portion of those counties at elevation. For now we've got the most populated areas accounted for so I will let future shifts further refine the extent of the advisory. Otherwise, rainfall through late this week will be hard to come by but not non-existent. Today through Wednesday afternoon and evening convection is expected over the mountains and plateau areas. Some of this may push out into the lower elevations via outflow boundaries but most areas should be dry. An increase in shower/thunderstorm coverage is expected Thu and Fri as the ridge weakens. Then this weekend into early next week could be fairly active as the ridge further weakens and shortwave activity and resulting boundaries approach the area from the north. && .LONG TERM... && .AVIATION... (12Z TAFS) Issued at 710 AM EDT Tue Jun 24 2025 Suppressive ridge of high pressure keeping hot, dry weather in place over the region with light winds. An isolated shower or two possible over the higher elevations, but no impacts are expected near the terminals. A handful of clouds around today near 5k feet meanwhile VFR conditions will continue. Low probability of patchy fog near KTRI between 06z tonight and the end of this TAF period. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 98 75 98 73 / 0 0 20 20 Knoxville McGhee Tyson Airport, TN 96 74 96 73 / 10 10 20 20 Oak Ridge, TN 96 74 97 73 / 10 10 20 20 Tri Cities Airport, TN 95 70 94 70 / 10 10 30 20 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...Heat Advisory until 7 PM EDT /6 PM CDT/ Wednesday for Anderson- Bledsoe-Bradley-Grainger-Hamblen-Hamilton-Hawkins-Jefferson- Knox-Loudon-Marion-McMinn-Meigs-North Sevier-Northwest Blount-Northwest Cocke-Northwest Greene-Northwest Monroe- Rhea-Roane-Sequatchie-Sullivan-Union-Washington TN-West Polk. VA...NONE. && $$ SHORT TERM...DH LONG TERM....DH AVIATION...DH