Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN
Issued by NWS Knoxville/Tri Cities, TN
014 FXUS64 KMRX 231109 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 709 AM EDT Sat Aug 23 2025 ...New AVIATION... .DISCUSSION... Issued at 139 AM EDT Sat Aug 23 2025 Key Messages: 1. Scattered showers and storms are likely this afternoon and evening. Due to abundant moisture and recent heavy rainfall, localized flooding is possible. 2. A significant pattern change is expected Monday through the week with highs into the 70s and lows dropping well into the 50s for many. Discussion: Currently, an upper shortwave is over the area with a more prominent closed low/trough in Ontario. At the surface, a strengthening front extends from the upper Great Lakes into the central Great Plains. Abundant moisture evidenced by PWATs of 1.5 or more and surface troughing allowed for better coverage of convection than expected across the region yesterday. Today, an initial shortwave will approach from the north with the northern front slowly progressing towards the Ohio River Valley. With even better moisture in place, scattered showers and storms are likely across the region for the afternoon through the evening. Currently, instability is indicated to be less than yesterday, generally around 1,000 to 1,500 MLCAPE during the day. But with the abundant moisture and recent rainfall, the threat for localized flooding will be the main focus to be highlighted in the HWO. The front is likely to reach the area by mid- day Sunday, which will bring additional chances for convection during the morning hours. However, instability will be much more limited at this time, and CAMs generally show more limited coverage. Sunday night into Monday, the front will move southeast of the region with northern troughing deepening across the eastern U.S. This will lead to a drier and notably cooler shift in the pattern for much of the week. By mid-week, Canadian high pressure will arrive from the northwest, bringing more ideal radiational cooling conditions. 850mb temperatures will reach early October normals of 10 Celsius or lower with radiational cooling expected overnight into the morning. Based on these trends, widespread highs in the 70s and lows well into the 50s can be expected. While 850mb temperatures will increase late in the week, additional shortwaves will help to keep temperatures mild. With limited moisture, dry conditions will likely persist. && .AVIATION... (12Z TAFS) Issued at 511 AM EDT Sat Aug 23 2025 There will be showers and storms around at times especially this afternoon into early tonight, and will try to time the most likely period for storms to impact the terminals with prob30 thunder groups although the details are uncertain. In addition, there may be some fog and/or lower cigs late in the period, but the probability of occurrence at any given site does not look high enough to include in the TAFs for now. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 85 69 86 62 / 80 40 40 0 Knoxville McGhee Tyson Airport, TN 87 69 84 62 / 70 60 50 0 Oak Ridge, TN 87 69 85 59 / 80 60 40 0 Tri Cities Airport, TN 84 66 81 59 / 60 60 60 10 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$ DISCUSSION...BW AVIATION...