Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN
Issued by NWS Knoxville/Tri Cities, TN
702 FXUS64 KMRX 172330 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 730 PM EDT Sun Aug 17 2025 ...New UPDATE, AVIATION... .UPDATE... Issued at 725 PM EDT Sun Aug 17 2025 Showers and storms are starting to come to an end this evening across the area with the setting sun. A few more storms could develop before sunset, but they would be few and far between, and the chances for even a rumble of thunder are quickly diminishing. Overnight hours should be fairly quiet with overnight lows dropping within a few degrees of what we experienced this morning as the clouds from afternoon convection should clear out of the region. No major changes have been made to the forecast for this update and the previous discussion is still valid. && .DISCUSSION... Issued at 151 PM EDT Sun Aug 17 2025 Key Messages: 1. Isolated damaging wind threat exists this afternoon and evening. PoPs may be underestimating rain chances so we`ll monitor and amend the forecast as necessary. 2. Developing northwest flow ahead of, and behind Hurricane Erin, will push a weak front through the region Wed - Fri. Rain chances increase and temperatures return to near normal. 3. Next weekend could be the first true cold front passage, and resulting air mass change, that we`ve seen in a while. Possibility of lower than normal temps and much drier air? We`ll see! Discussion: There are three main topics to discuss in the forecast period. The chances for storms this afternoon and evening...an active mid-week period...and the possibility of a legitimate frontal passage at the end of the forecast period next weekend. For this afternoon and evening, a thermodynamic environment featuring roughly 700-800 J/kg of downdraft CAPE and 1,500 J/kg of mixed layer CAPE will be in place. This along with a remnant outflow boundary from an overnight MCS moving from Kentucky into middle and eastern TN, will allow for scattered shower and thunderstorm development. While not a slam dunk severe storms environment by any means, I wouldn`t be surprised if some significant weather advisories or even a severe thunderstorm warning or two were required later today. In this environment, a report or two of damaging winds certainly seems plausible. The NBM was too low regarding rain chances and coverage so I blended in some ARW CAM guidance to bring PoPs up. If current trends continue, they may still be underdone, so will monitor and amend the forecast as necessary through the afternoon and evening hours. For Monday through Wed/Thu, upper ridging over the Arklatex begins to flatten out and shift west as a trough tops the ridge along the central US/Canadian border tonight into Monday and begins to descend into the Great Lakes and Ohio valley region. Mon and Tue look mostly dry outside of the east TN mountains, but fairly warm across the forecast area. As we get to the Wed/Thu timeframe, the ridge has relocated to the Four Corners region, while Hurricane Erin marches north well off of the Carolina coast. A weak surface low associated with the aforementioned Great Lakes shortwave will have drug a front southward into the Ohio valley to lower Mississippi valley region by Wednesday, increasing rain chances across much of Kentucky and Tennessee, our forecast area included. Erin finally pulls north of the latitude of the Outer Banks by Thu morning, allowing an eastern CONUS trough to fully take shape and northwest flow aloft locally to drive that front south of the area by Thu/Fri. While the front will be south of us, there`s not a true air mass change. As such, I`d expect rain chances to be remain high through the end of the week, leading to temperatures being closer to seasonal norms. Looking to next weekend...I don`t want to get your hopes up too much...but there`s signs that point to the the western ridge/eastern trough pattern continuing and perhaps the first true cold front passage for a long while. We`re talking about dewpoints down into the upper 50s or low 60s, and highs in the lower 80s here folks. We`ll see - that`s a long ways off, and there is plenty that could change. Don`t break out the fall decorations just yet, we`ve still got plenty of warm season left. But it`s a reminder that we`re getting closer to that time of year for sure. && .AVIATION... (00Z TAFS) Issued at 725 PM EDT Sun Aug 17 2025 VFR conditions are expected at TYS/CHA for the next 24 hours. At TRI we could get a brief window of IFR to MVFR fog, but with conditions overnight expected to be similar to last night and only brief light fog developed this morning have went with a persistence forecast keeping dense fog at bay. Outside of early morning fog TRI should also remain VFR for the next 24 hours. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 73 94 73 94 / 10 10 0 20 Knoxville McGhee Tyson Airport, TN 72 93 71 93 / 10 10 0 20 Oak Ridge, TN 71 93 71 93 / 10 0 0 10 Tri Cities Airport, TN 68 89 68 89 / 10 10 10 30 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$ DISCUSSION... AVIATION...