Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN
Issued by NWS Knoxville/Tri Cities, TN
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498 FXUS64 KMRX 261756 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 156 PM EDT Thu Sep 26 2024 ...New AVIATION... .UPDATE... Issued at 954 AM EDT Thu Sep 26 2024 Main purpose of the morning update was to touch up PoPs and rain amounts. No changes were made to winds at this time. Will adjust forecast winds and wind gusts later this morning after the National Hurricane Center makes any necessary adjustments to their track and intensity forecasts. Still expect to see strong winds with this system though. Otherwise, just some minor adjustments to PoPs and QPF through the afternoon hours. The NAM seems to have the current banding seen on radar modeled fairly well in terms of areal coverage and placement, but also seems a little bullish on rainfall totals. Did a blend of the latest WPC guidance, the NAM, and some 12z HRRR for some minor adjustments to amounts from roughly the Sevier county area northwards toward Hancock and Lee counties. Will save any further adjustments for the midday or afternoon package. && .SHORT TERM... (Today through Friday) Issued at 353 AM EDT Thu Sep 26 2024 Key Messages: 1. Flooding potential remains high as heavy, tropical downpours affect the area today into Friday. 2. Winds will be high in the mountains, which are areas that are used to strong winds. There is also the potential for widespread strong winds in the TN valley late Thu night through Fri morning. Discussion: Hurricane Helene is in focus for the period, and the impacts the decaying tropical system brings to our are are expected to be major. The current NHC track has it coming ashore then track north before curving northwest across southeast TN early Friday before being absorbed into the upper low to our west. The two main concerns with this system for us will be heavy rain/flooding and very strong winds. A precursor rain event has been ongoing, and we`ve already had a lot of rain across areas mainly along/east of the I-75 and I-81 corridors (in excess of 4 inches in spots). We will see additional heavy rain over these areas today, with a downtrend for a period west of the mountains for a period later today into tonight as the downslope winds increase and the axis of the more significant rain shifts south and west, then likely another increase area wide late tonight into early Friday as the tropical system approaches. WPC has rainfall from now through Friday evening of around 3 to 4+ inches over most of our area, with even higher amounts across portions of SW NC and the eastern mountains. The flood watch will be expanded into our northern Cumberland Plateau counties with this issuance. Both flash floods and river flooding is expected. For winds, some of the higher elevations of the mountains will see wind gusts in excess of 70 mph, but valleys are likely to see strong wind gusts as well later tonight into Friday morning. Mean HREF wind gusts are showing values of 50+ across much of the area outside of the mountains. While we may not reach actual wind warning wind speeds in most locations outside of the mountains, we will likely see a lot of trees down and power outages especially given the soggy ground. Given the uncertainties of exactly how strong Helene will get before landfall and it still being second period, and in coordination with neighboring offices, will leave the watch out for one more cycle. Will continue the high wind warning in the mountains. Will also continue the Tropical Storm warning for our SW NC counties in accordance with North Carolina partners. && .LONG TERM... (Friday night through Wednesday) Issued at 353 AM EDT Thu Sep 26 2024 (Friday Night Through next Wednesday) Key Messages: 1. Light rain showers likely on Saturday, no additional impacts expected. 2. Additional light rain possible primarily in the afternoon Sunday through Tuesday. Drier thereafter with seasonable temperatures throughout. Discussion: As the forecast heads to Saturday and the weekend, Helene will be absorbed or merged into the resident upper low that`s to our west currently. This merged pair will be significantly weaker and less impactful than the weather in earlier periods. A couple of days of scattered light rain showers are possible, mostly on Saturday and Sunday as the upper low slowly moves eastward through the Ohio River valley. Winds Saturday morning will be a tad breezy still in the mountains but will subside through the day. Eventually as we progress to the midweek, the low will exit to our east, heights will build back in, and we`ll fully begin the drying out period. Temperatures look to remain seasonably warm, as heights increase on the backside of the low. && .AVIATION... (18Z TAFS) Issued at 145 PM EDT Thu Sep 26 2024 VSBY and CIGS will continue to vary with showers and heavier rain bands from Helene`s anticipated approach. The most important thing to note aviation-wise for all terminals will be the increase in winds. Sustained and gusts will increase as we approach tonight. CHA may experience the lower end of gusts, but will probably be the most variable in direction towards the end of the TAF period when the center of Helene moves over. TYS will exceed 30KT in the middle of the night with direction eventually shifting from NE to ESE. TRI appears will exceed 40KT around or after sunrise, but things will be interesting for them as far as WX, CIGS, and VSBY are concerned because strong mountain wave like winds in excess of 50+ KT over the mountains, will suppress precip and keep CIGS around VFR. TRI`s wind direction shift will be similar to TYS with NE to start to around ESE to SE by the end of the TAF period. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 66 74 64 74 / 100 100 30 40 Knoxville McGhee Tyson Airport, TN 68 76 64 75 / 100 100 30 40 Oak Ridge, TN 66 74 62 72 / 100 100 40 50 Tri Cities Airport, TN 67 78 60 75 / 100 100 20 20 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...Flood Watch through Friday afternoon for Cherokee-Clay. Tropical Storm Warning for Cherokee-Clay. TN...Flood Watch through Friday afternoon for Anderson-Bledsoe-Blount Smoky Mountains-Bradley-Campbell-Claiborne-Cocke Smoky Mountains-East Polk-Grainger-Hamblen-Hamilton-Hancock- Hawkins-Jefferson-Johnson-Knox-Loudon-Marion-McMinn-Meigs- Morgan-North Sevier-Northwest Blount-Northwest Carter- Northwest Cocke-Northwest Greene-Northwest Monroe-Rhea- Roane-Scott TN-Sequatchie-Sevier Smoky Mountains-Southeast Carter-Southeast Greene-Southeast Monroe-Sullivan-Unicoi- Union-Washington TN-West Polk. High Wind Warning from 8 PM EDT /7 PM CDT/ this evening to 8 PM EDT /7 PM CDT/ Friday for Anderson-Bledsoe-Blount Smoky Mountains-Bradley-Campbell-Claiborne-Cocke Smoky Mountains- East Polk-Grainger-Hamblen-Hamilton-Hancock-Hawkins- Jefferson-Johnson-Knox-Loudon-Marion-McMinn-Meigs-Morgan- North Sevier-Northwest Blount-Northwest Carter-Northwest Cocke-Northwest Greene-Northwest Monroe-Rhea-Roane-Scott TN- Sequatchie-Sevier Smoky Mountains-Southeast Carter- Southeast Greene-Southeast Monroe-Sullivan-Unicoi-Union- Washington TN-West Polk. VA...Flood Watch through Friday afternoon for Lee-Russell-Scott VA- Washington VA-Wise. High Wind Warning from 8 PM this evening to 8 PM EDT Friday for Lee-Russell-Scott VA-Washington VA-Wise. && $$ SHORT TERM...CD LONG TERM....Wellington AVIATION...KS