434 
FXUS64 KMRX 201052
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
652 AM EDT Sun Sep 20 2026

...New AVIATION...

.KEY MESSAGES...
Updated at 648 AM EDT Sun Sep 20 2026

- Well above normal temperatures to persist into early this week. But
  relief is on the way, with a pattern change expected mid-week 
  and much cooler temperatures to follow.

- Expect isolated to scattered showers today, with increasing 
  coverage Monday through Wednesday. 

- A few strong to severe storm with damaging winds could occur
  today and Monday, with damaging winds being the primary threat.
  Localized flooding will be possible each day through Wednesday 
  as well. 

&&

.DISCUSSION...
Issued at 112 AM EDT Sun Sep 20 2026

An upper ridge, still centered over the Arklatex, will continue to 
weaken on Sunday. Despite lowering heights, I would expect there to 
be less shower and thunderstorm coverage today versus the last 
couple of days thanks to a lack of forcing mechanism and slightly 
lower low level moisture and PWATs. There will be convection, just 
not as much. An isolated strong to severe storm and damaging wind 
threat, or some localized heavy rains, can't be ruled out. But, the 
threat is quite low and I would expect that we will remain in the 
general thunder area in SPC's Day 1 convective outlook. For Monday, 
expect a marked increase in convective activity as a weak upper low 
shifts east from the plains into the Ohio valley. Forecast soundings 
suggest afternoon MLCAPE values will range from around 1,500 J/kg to 
over 2,000 J/kg area wide Monday afternoon. PWATs will increase a 
bit too, all of which will support some isolated damaging wind gusts 
from collapsing storms. Storm motions will be slow too, so localized 
heavy rains and flooding could be an issue too. Tuesday should 
feature fairly widespread showers too, but instability looks far 
less so the severe potential looks negligible.

Lastly, despite the waning influence of the ridge, there's no air 
mass change until the mid-week time frame. So temperatures will 
remain well above normal Sunday through Tuesday. Highs in the upper 
80s to mid 90s are on tap for Sun and Mon, with low 80s to low 90s 
for Tuesday. Barring any unforeseen circumstances, Chattanooga looks 
to continue it's record setting streak of 90 degree days and should 
top out at 50. Wednesday is the first day of sub-90 forecast highs.

Speaking of Wednesday, and a break in the heat...late Tuesday into 
Wednesday a rex block pattern sets up, with the upper ridge building 
on the Canadian side of the Great Lakes, and the upper low 
re-intensifying south of the ridge over the Ohio valley. This will 
result in surface high pressure well to our north, and northerly low 
level flow pushing a cold front through the region sometime on 
Wednesday. We'll still be warm...maybe 1-3 degrees above normal as 
opposed to +12-15 degrees...but rain and cloudy conditions will be a 
welcome change. We'll wrap the week with temperatures around or 
slightly below normal with highs in the 70s to 80s, and lows in the 
50s may even make an appearance by week's end.

&&

.AVIATION...
(12Z TAFS)
Issued at 648 AM EDT Sun Sep 20 2026

Dense fog at TRI will burn off shortly after TAF issuance and
return to VFR. For TYS and CHA, VFR conditions are forecast 
throughout the period. The signal for thunderstorms and showers 
this afternoon isn't too impressive. Hi-res models indicate 
isolated storm coverage at best, with the greatest chance at TRI. 
I have maintained the PROB30 there and kept the other two sites 
VFR and dry. Winds remain generally light and variable. Pattern 
would likely support the redevelopment of fog Sunday night/early 
Monday morning at TRI, but I've left it out for now to focus on 
the earlier time frame. 

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             95  72  95  70 /  20  10  40  50 
Knoxville McGhee Tyson Airport, TN  93  70  93  69 /  10  10  40  60 
Oak Ridge, TN                       92  70  92  68 /  10  10  40  50 
Tri Cities Airport, TN              87  66  88  65 /  20  10  30  60 

&&

.MRX WATCHES/WARNINGS/ADVISORIES...
NC...NONE.
TN...NONE.
VA...NONE.
&&

$$

DISCUSSION...CD
AVIATION...BH


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