Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN
Issued by NWS Knoxville/Tri Cities, TN
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712 FXUS64 KMRX 171801 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 201 PM EDT Tue Sep 17 2024 ...New AVIATION... .UPDATE... Issued at 1100 AM EDT Tue Sep 17 2024 Light showers are spreading out as they move west and southwest through east Tennessee. The tropical low pressure system will gradually open up as it rotates over the western Carolinas. The more steady rain is much more spotty now. Cloud cover and rain is keeping temperatures down 10 to 15 degrees below yesterdays. Current temperatures this morning in the 60s have only a warmed a few degrees from this mornings lows. Have updated the forecast to reflect current trends with lower rain chances this afternoon except in the higher elevations closer to the low pressure area to the east. Expect showers to decrease gradually during the afternoon into the evening. && .SHORT TERM... (Today and tonight) Issued at 312 AM EDT Tue Sep 17 2024 Key Messages: 1. Rain from a tropical low pressure system will continue to spread across the area from southwest Virginia, into northeastern Tennessee, and southwest North Carolina. Highest rainfall amounts will be over and in the foothills of the Appalachians. 2. Temperatures a lot cooler today mostly to do with cloud cover. Discussion: What was potential tropical cyclone 8, is centered over the Carolinas this morning. Wrap-around from the back-side is what is currently falling across our forecast area. Currently on radar, downsloping is evident in the reflectivity hole over Lee and Wise counties in Virginia. We expect the precipitation to push west and southwest into the morning and later morning hours today. CAM solutions are suggesting that it`ll turn into a more isolated to scattered regime outside of the higher terrain. Chances for thunder are pretty low (< 30 percent), so not expecting any severe weather. SPC only has southwest Virginia and what looks to be Johnson County Tennessee clipped with general thunder today. The center of the low loses it shape later today and thus, precip chances decline into the night, but that won`t be all when it comes to expected accumulation this week. (See long term forecast below) Extreme southern plateau and valley such as Hamilton, Marion, and Sequatchie counties will likely not see any rainfall today and remain mostly cloudy. A combination of lowering heights aloft and cloud cover will keep temperatures a whole lot cooler today compared to yesterday. The aforementioned locations will also likely be the only places that reach 80 for highs today. A few tenths of an inch to up to three quarters of an inch rain will be common the next 24 hours across the area. However, closer to the foothills and over the highest terrain of the Appalachians, is where over one inch and even possibly over an inch and a half may be recorded. Not expecting any flooding concerns at this time being how dry we have been, so this is very welcome to our region. Isolated showers will hold for extreme northeastern parts of our CWA overnight, but areas that dry out and may even briefly clear, will pose the possibility of fog development. && .LONG TERM... (Wednesday through Monday) Issued at 312 AM EDT Tue Sep 17 2024 Key Messages: 1. Scattered showers possible on Wednesday, mostly in the mountains and northern half of the forecast area. Dry conditions expected afterwards though. 2. High pressure aloft builds Thursday onward. This should result in highs several degrees above normal. Discussion: An upper low will be situated over the southern Appalachian region to begin the period, but this feature will open up and lift northeast into a developing east coast trough by Thursday morning. Meanwhile, upper ridging will build north northeast from Texas through the Great Lakes Thursday into the weekend. Scattered, largely diurnally driven, showers will be present across much of the forecast area on Wednesday but dry conditions are forecast thereafter once the low lifts away to the northeast and we have increasing influence from the upper ridge to our west. There is some support in numerical guidance for keeping some afternoon rain chances in the mountains Friday through the weekend. But I think we`re more likely to remain dry so kept the forecast dry for now. Given the pattern and developing ridge, and how dry we`ve been lately, the NBM forecast highs for the long term don`t seem unreasonable. Highs on Sat and Sun will likely approach 90 in the south, with upper 80s as far north as the I-40 corridor and lower 80s in the north. This isn`t going to approach any calendar day records (those are near 100 degrees for Chattanooga, and firmly into the lower 90s up north for example), but it will be 3-5 degrees above normal. && .AVIATION... (18Z TAFS) Issued at 155 PM EDT Tue Sep 17 2024 With the westward movement of the remains of the tropical low and moisture MVFR conditions affecting all 3 sites with ceilings from 1 to 2 thousand feet this afternoon. Tonight the rain chances should decrease but ceilings and visibilities will lower at TYS, TRI and CHA. Ceilings below 1000 feet probable at TYS and TRI with low visibilities about 2 miles or less at TYS and TRI. Guidance for TRI is for below 1 mile visibility but if ceiling holds a low ceiling below 500 feet would be more of a restriction. Forecasting 1 mile as minimum at this time for TRI. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 65 86 64 90 / 10 10 0 0 Knoxville McGhee Tyson Airport, TN 65 82 64 86 / 20 40 0 20 Oak Ridge, TN 63 82 63 85 / 20 30 0 10 Tri Cities Airport, TN 63 77 62 80 / 40 60 10 40 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$ SHORT TERM...TD LONG TERM....CD AVIATION...TD