Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN
Issued by NWS Knoxville/Tri Cities, TN
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006 FXUS64 KMRX 221906 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 306 PM EDT Sun Sep 22 2024 ...New SHORT TERM, LONG TERM... .SHORT TERM... (This evening through Monday) Issued at 303 PM EDT Sun Sep 22 2024 Key Messages: 1. Isolated showers and storms continue overnight. Fog expected for any area that receives rain. 2. Isolated to scattered showers and storms tomorrow. 3. Hot again tomorrow, temps around 5 to 10 deg above normal. Discussion: A few isolated showers and storms will continue through the night as weak short wave energy passes through the region. Any area that receives rainfall will likely see fog thereafter. Tomorrow, the flow becomes more zonal as high pressure shifts to our southeast. This zonal flow, combined with additional shortwave energy moving through, will increase chances of showers and storms across the area. Though there will be increased coverage, not all areas will see showers or storms. There is a marginal risk for severe storms tomorrow but I am not that excited about it. The reason for the marginal is increased shear in the mid to upper levels with 0-6km shear around 30kts. Shear in the lower levels is weak to non-existent. With the increased mid to upper shear, storms will be able to be longer lived than summer-time pulse variety. However, mid level lapse rates of 4 to 5 C/km are unimpressive. The main threat with any stronger storm will be gusty winds due to some drier air at the surface. Again though, not that excited about the severe potential. && .LONG TERM... (Monday night through next Sunday) Issued at 303 PM EDT Sun Sep 22 2024 Key Messages: 1. A significant pattern change is in the offing during the extended period with ridging aloft being replaced by a trough over the mid- section of the nation. End result, increasing chances of much needed rainfall across the region. 2. Ensemble Prediction System along with the latest deterministic models are beginning to align with a significant tropical cyclone developing in the Caribbean and Gulf of Mexico then moving north. 3. Depending on how this tropical cyclone interacts with the upper trough over the mid-section of the nation and upper ridge over Florida, this low may move into the Tennessee valley and southern Appalachians late week. Discussion: For Monday night and Tuesday, first in series of short-waves lift out of the developing mid-nation upper trough. Best dynamics will be over the northern half of the region. MLCAPES will be in the 750- 1500 range with very limited mid-level lapse rates and shear. Main concern will be lightning and gusty winds up to 30-40 mph Tuesday afternoon. For Tuesday night and Wednesday, the upper trough continues to deepen over the mid-section of the nation with a frontal boundary becoming quasi-stationary over the Tennessee valley. MLCAPES of 500- 100 with PWS around 1 standard deviation above normal per NAEFS. Main concern will be locally heavy rainfall. Storm motion will be nearly parallel with the boundary so can not rule out localized runoff issues. For Thursday into next weekend, a significant tropical system will likely (40-60 percent probabilities of development in the Caribbean and Gulf of Mexico) be affecting the Gulf coast states. Latest Ensemble Forecast System (EPS) and deterministic models showing this low moving north into the Tennessee valley and southern Appalachians. Here are the potential concerns: 1. Heavy rainfall and flash flooding, especially the Plateau, southeast Tennessee, and southwest North Carolina. 2. Windy conditions, especially for the favored mountain wave high wind areas of far east Tennessee Mountains, and the Plateau. As this system eventually develops, models will likely form more of a consensus of track and timing, and potential impacts. && .AVIATION... (18Z TAFS) Issued at 133 PM EDT Sun Sep 22 2024 VFR conditions forecast through the period. However, brief MVFR conditions possible if any storm moves over a terminal this afternoon and evening. Not enough confidence at the moment though to include mention. Also, leaving out fog at TRI overnight based on lack of occurrence the last two nights but it`s not out of the question. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 70 92 69 91 / 10 30 10 40 Knoxville McGhee Tyson Airport, TN 69 90 67 89 / 20 50 20 60 Oak Ridge, TN 68 89 66 86 / 20 50 20 70 Tri Cities Airport, TN 65 85 64 83 / 30 70 40 70 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$ SHORT TERM... LONG TERM....DH AVIATION...