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
017 FXUS64 KMRX 041506 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 1106 AM EDT Thu Jul 4 2024 ...New UPDATE... .UPDATE... Issued at 1058 AM EDT Thu Jul 4 2024 Quite a bit of updates to the immediate forecast based on obs and the latest model runs. Speaking of obs, there was a delay incorporating those because of a temporary national outage. Anyhow, winds are a bit more gusty at this time and have noticed that was the case yesterday afternoon as well, so some high-res guidance was blended in to increase the sustained and gusts today. 10-20 kt low-level flow is advecting in from the SW according to SPC Meso. PoPs were also refreshed, moreso cut back/down in some areas just because of how trends are looking. Currently precip is only across the eastern middle of Kentucky. KS && .SHORT TERM... (Today and tonight) Issued at 358 AM EDT Thu Jul 4 2024 Key Messages: 1. Hot weather to continue today. Heat indices will range from the mid 90s in Virginia to the low 100s in the southern TN valley. See Heat Advisory for more information. 2. Chance of showers and thunderstorms today. Storms across northern Tennessee into southwest Virginia this afternoon may contain strong gusty winds up to low end severe criteria in the strongest cell of the day. Discussion: Upper ridge strength has technically weakened for today, with a weak shortwave ahead of the larger trough and cold front helping to flatten the ridge. However, model 850mb temperatures are warmer, and with continued weak southwesterly flow expecting today to be slightly warmer, slightly muggier across the Tennessee valley. In accordance with that, have opted for a Heat Advisory to match the worst locations, principally south of Interstate 40. With temperatures remaining elevated into the night (Chattanooga has been in the mid 80s at midnight last two nights), a reminder to remain hydrated while celebrating the nation`s birthday even after sunset. The Storm Prediction Center has a marginal risk for severe wind draped across the northern edges of Tennessee and southwest Virginia. The struggle today will be to once again convect in the face of warm air aloft. High-res guidance isn`t exactly enthused about the scenario, so overall PoPs are just chance in the north. Still, should a storm manage to intensify an updraft, can imagine it becoming strong enough for 40 to 60 mph downdraft winds in the hot and humid atmosphere. Thunderstorms should diminish or outright dissipate tonight after sunset, so nature`s fireworks are not expected to interfere with celebrations. The one thing to keep in mind tonight is a standard low level inversion will set up overnight, so don`t be surprised if firework smoke remains trapped close to the surface. && .LONG TERM... (Friday through Wednesday) Issued at 358 AM EDT Thu Jul 4 2024 Key Messages: 1. Hot Friday, with increased chances for showers and storms Friday and Friday night with a frontal passage 2. Drier weather returns during the weekend, then PoPs increase again. 3. Temperatures will continue to run a little above normal for much of the period. Discussion: We start the period with a low pressure system approaching the western Great Lakes region, with a cold front trailing into the mid Mississippi Valley region and the Southern Plains. The low pressure system will move east through the Great Lakes Friday and Friday night, pulling the cold front through our area Friday night/early Saturday. The atmosphere will be rather moist ahead of the front, with models showing PWAT values generally exceeding 2 inches Friday. HREF ensemble data indicates much of the area has a 40-70 percent chance of exceeding 2000 J/kg of SBCAPE, and MLCAPES look likely to be in the 1000-1500 J/kg range. Model soundings indicate DCAPES will likely exceed 700 J/kg as well. This suggests a potential for a few strong to marginally severe thunderstorms Friday with damaging winds the primary threat, although weak deep layer shear will be a limiting factor in this potential. Much of this activity will likely be focused along a pre-frontal trough that moves through Friday afternoon/early Friday evening time frame, with the cold frontal passage occurring later Friday night/early Saturday. The other concern for Friday will be the heat especially south, as dewpoints look likely to be high enough that with temperatures expected to top out in the lower 90s in most valley locations, there is potential for heat index values to approach or even briefly climb above 105 mainly across portions of the southern Valley. However, there are still significant uncertainties on timing of precipitation and the details of how much cloud cover will be around which may act to hold things down a bit, so no heat advisory will be issued for Friday at this time. Some convection may linger into Saturday especially eastern portions of the area depending on the speed of the front, but drier air will be filtering in behind the front Saturday. Sunday will be mainly dry as well, although there may be some isolated weak convection in the eastern mountains. By early in the week high pressure will be off to our east, and a broad upper trough will be set up over the Plains. This upper trough will gradually shift east during the remainder of the period. Moisture will begin to increase again, and chances for showers and thunderstorms will increase as well for the Monday through Wednesday time frame. Temperatures will generally run a bit above normal for the long term period, although they may tick down slightly Wednesday. && .AVIATION... (12Z TAFS) Issued at 700 AM EDT Thu Jul 4 2024 VFR should be predominant through the TAF period at all sites. There is a slight chance for scattered SHRA during the afternoon and early evening, though thunder is low probability. PROB30 still in at TRI where coverage may be enough to lend confidence to terminal impact. Winds will remain light. Dependent on rainfall, fog bringing at least MVFR visibility is most likely at TRI late in the period. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 96 78 93 75 / 20 20 70 50 Knoxville McGhee Tyson Airport, TN 95 77 91 74 / 20 20 70 70 Oak Ridge, TN 94 76 91 72 / 30 30 70 60 Tri Cities Airport, TN 91 71 91 71 / 30 20 70 70 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...Heat Advisory from 2 PM EDT /1 PM CDT/ this afternoon to 8 PM EDT /7 PM CDT/ this evening for Bradley-Hamilton-Loudon- Marion-McMinn-Meigs-Northwest Blount-Northwest Monroe-Rhea- Roane-Sequatchie-West Polk. VA...NONE. && $$ SHORT TERM...Wellington AVIATION...Wellington