Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN
Issued by NWS Knoxville/Tri Cities, TN
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
348 FXUS64 KMRX 250743 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 343 AM EDT Wed Sep 25 2024 ...New SHORT TERM, LONG TERM... .SHORT TERM... (Today through Thursday) Issued at 335 AM EDT Wed Sep 25 2024 Key Messages: 1. Scattered to numerous rain showers and thunderstorms to continue. Torrential rainfall is possible, with flash flooding an increasing risk with time. 2. A low end risk for severe weather this morning to around noon, before more widespread shower development ends severe risk. While a strong to severe wind gust is the more probable threat, cannot rule out a potential tornado. Discussion: The upper trough that is dominating the southeast`s weather pattern will pinch off as an upper level low today and begin its pivoting in Missouri and Arkansas through Thursday. This is the main timeframe of what the research literature calls a predecessor rainfall event. Rich moisture and broad but strong ascent will allow for rain showers and some thunderstorms to develop and move northwards through the southern Appalachian region. Additionally, the cold front associated with the upper low will stall out just to our west, adding a focal point ahead of the front for showers to move parallel to. Hard to say what, if any, severe threat we have today. HRRR and NAM indicate the best timeframe for a possible severe storm is in the morning hours after sunrise to around noon, before rain showers become too numerous and cut down on available convective instability. But during that few hour period, effective shear is of course still strong, and we might be just able to squeak a surface based storm out paired with strong 3CAPE. The SPC has our eastern half in a marginal risk for a low end tornado and wind threat, which aligns with the potential seen in model soundings. High res CAMs indicate by around noon we should see a blossoming of showers and elevated thunderstorms begin moving south to north across the region. This will eventually evolve into two periods of widespread rain, one Wednesday afternoon into evening, and the second more notable period likely much of Thursday. The Weather Prediction Center has given us a moderate risk of excessive rain along the mountains both today and Thursday, with a high risk in North Carolina on Thursday. It is rare to have such elevated risk for successive days and points to the high end potential for numerous flash flooding events as the event progresses this week. && .LONG TERM... (Thursday Night through Tuesday) Issued at 335 AM EDT Wed Sep 25 2024 Key Messages: 1. Remnants from Tropical Storm Helene expected to impact the region Thursday night and Friday. Flooding possible as well as strong gusty winds. 2. Unsettled weather will continue throughout the long term period with temperatures near seasonal norms. Discussion: The latest official NHC forecast has the center of the remnants of Helene approaching Thursday night and moving across southeast TN and off to our NW during the day Friday. With this track, we will see strong wind gusts and some additional very heavy rain. The strongest winds are expected to be over the higher elevations of the mountains, with gusts in excess of 60 mph likely. Some valley areas will likely see gusts in excess of 40 mph as well. Still enough uncertainty of the exact track of the system to hold off a bit longer on any high wind watch for the mountains, but one may be needed soon. Heavy rainfall can be expected as well Thursday night into Friday. The highest amounts are expected to be across the eastern mountains as well as southeast Tennessee, with current QPF values in excess of 3 inches for the 24 hour period. Downslope flow should help to hold precip values a bit lower for the central and northern areas west of the mountains, but even there amounts are expected to exceed an additional inch. Depending on how much rain and flooding occurs with the earlier rainfall, the flood watch may end up needing to be extended in these northern and central areas. And flooding continues to be a major concern for southeast TN and the eastern mountain areas including SW NC, and the flood watch there will be continued as is. Flash flooding, and significant river flooding are both a concern. Once the tropical system exits, the upper low that will be hanging over the region will continue to keep us with chances for showers and a few thunderstorms over the remainder of the period. Temperatures will generally not be too far from seasonal normals. && .AVIATION... (06Z TAFS) Issued at 1258 AM EDT Wed Sep 25 2024 Scattered showers and thunderstorms to continue overnight, primarily north of KCHA. VFR conditions will deteriorate to MVFR VIS for much of the area after 18z tomorrow as a more widespread round of showers and storms spreads across the area. Low confidence on when CIGs deteriorate to MVFR, but will be more likely during moderate to heavier rainfall. Outside of thunderstorms, winds should remain light and somewhat variable. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 77 65 73 67 / 80 60 80 90 Knoxville McGhee Tyson Airport, TN 75 65 73 67 / 90 90 80 90 Oak Ridge, TN 74 63 72 65 / 80 80 80 90 Tri Cities Airport, TN 76 64 73 66 / 90 90 80 80 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...Flood Watch from 11 AM EDT this morning through Friday afternoon for Cherokee-Clay. TN...Flood Watch from 11 AM EDT /10 AM CDT/ this morning through Friday afternoon for Bledsoe-Blount Smoky Mountains-Bradley- Cocke Smoky Mountains-East Polk-Hamilton-Johnson-Marion- McMinn-Meigs-Northwest Monroe-Rhea-Sequatchie-Sevier Smoky Mountains-Southeast Carter-Southeast Greene-Southeast Monroe-Unicoi-West Polk. Flood Watch from 11 AM EDT this morning through Thursday morning for Anderson-Claiborne-Grainger-Hamblen-Hancock-Hawkins- Jefferson-Knox-Loudon-North Sevier-Northwest Blount- Northwest Carter-Northwest Cocke-Northwest Greene-Roane- Sullivan-Union-Washington TN. VA...Flood Watch from 11 AM EDT this morning through Thursday morning for Lee-Russell-Scott VA-Washington VA-Wise. && $$ SHORT TERM...Wellington AVIATION...Wellington