Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN
Issued by NWS Knoxville/Tri Cities, TN
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170 FXUS64 KMRX 161147 AAA AFDMRX Area Forecast Discussion...UPDATED National Weather Service Morristown TN 747 AM EDT Mon Sep 16 2024 ...New AVIATION... .SHORT TERM... (Today and tonight) Issued at 308 AM EDT Mon Sep 16 2024 Key Messages: 1. Dry and warm conditions expected through late this afternoon. 2. Showers associated with tropical system off SC coast will push westward across the TN/NC line this evening and overnight. Rain chances largely limited to areas north of I-40, especially in the northeast. Discussion: A developing tropical/subtropical low off the coast of South Carolina will shift northwest today and tonight. Ahead of this system we`ll have dry conditions across the forecast area for most of the day. But showers associated with this low will move across the mountains and into the northern TN valley by this evening. Initial wave of precip will likely have a difficult time as it will be moving into/attempting to displace dry air with PWATs on the order of 0.5" to 0.75". To that end, model soundings don`t show saturation descending below roughly 7k ft AGL in the Tri-Cities area until after 00z, so I`d expect a lot of the initial wave of showers to be virga or very light rain, and limited mainly to area east of the Interstate 81 corridor northeast of I-40. With time, banded precip will shift westward to more of the I-75 corridor or perhaps as far west as the northern plateau counties during the overnight hours. Some guidance shows very high PoPs tonight, upwards of 70 percent, as showers move west into our area. While I think there`s a very high likelihood of their existence, there`s some uncertainty in how widespread they`ll be and what lingering effects of downslope flow across the mountains might have on them. As such, limited PoPs to high-end chance levels outside of our northeast TN mountains and some higher terrain areas in our eastern VA counties. Otherwise, today will be another warm day with temperatures well into the 80s. Did knock the highs down a degree or two with respect to the NBM since it seems it was a tad hot yesterday. Increasing clouds, even if just high clouds, should keep highs from being quite as warm as yesterday, especially in the north. There`s also strong support for gusty northeast winds in the valley today. As the coastal low moves inland across the SC/NC border this afternoon, models show a strengthening inverted surface trough across the TN valley. After roughly 20z, high res guidance shows gusts increasing to 25 mph or so for areas northeast of the Knoxville metro area. && .LONG TERM... (Tuesday through Sunday) Issued at 308 AM EDT Mon Sep 16 2024 Key Messages: 1. Long term pattern will be dominated by tropical remnants from the Carolinas and additional development well off the Mid-Atlantic Coast. Rainfall amounts and coverage is uncertain, however, precipitation chances look best for the northeastern part of our forecast area and parts of the Appalachians. 2. Temperatures will mostly run a couple degrees above normal for middle September with the exception of areas that will be impacted by the tropical remnants. Discussion: Potential tropical cyclone 8, as labeled by the NHC, will impact some of our forecast area through part of the long term. By Tuesday morning when the long term begins, the center of the system will be close to the SC and NC state line. Before then, the 00Z GFS is notably the speedy solution taking it to where the other models eventually catch up, much faster. Easterly to northeasterly flow will mostly bring the best shower and thunderstorm chances for northeastern TN and southwest VA. Highest total QPF amounts at this time are east of I-75 north of Knoxville, into southwest VA, and along the Southern Appalachians. Due to the supposed track the system will take, the southern valley and plateau for example, may escape unscathed this coming week with dry conditions, much warmer temperatures, and more sunshine than the aforementioned regions. Once the system further weakens over land late Tuesday into Wednesday, the forecast remains and grows with uncertainty with regards to unsettled weather into the rest of the week and over the weekend. The closed upper low will eventually phase with the northern stream trough, as upper level ridging tries to move our way from the central US. At the surface, a slow moving low center well off the Mid-Atlantic coast tracking towards New England, will keep precipitation going for the east coast. We may be just far enough from the outside fringes of wrap-around flow from it to bring any good rain chances to the same areas earlier in the week. No more than a 50 percent chance in the forecast for the later week and next weekend activity. && .AVIATION... (12Z TAFS) Issued at 735 AM EDT Mon Sep 16 2024 VFR conditions will prevail through the early evening hours at all sites. However, after roughly 02z, ISOLD to SCT SHRA should be moving WNW across the TN/NC line into the vicinity of KTRI. Guidance is insistent on developing MVFR categories shortly thereafter. Tend to think that MVFR conditions may be more VSBY restrictions due to increasingly heavy shower activity, but did include a SCT025 deck. SHRA activity looks to stay north of KTYS and far removed from KCHA. Otherwise, still think some gusts of 18-20kt will occur at KTYS so kept that in there with this package. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 87 62 84 63 / 10 10 10 0 Knoxville McGhee Tyson Airport, TN 85 62 76 62 / 0 20 20 20 Oak Ridge, TN 84 62 78 63 / 0 20 20 10 Tri Cities Airport, TN 78 60 72 62 / 20 50 50 40 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$ SHORT TERM...CD LONG TERM....KS AVIATION...CD