084 
FXUS64 KMRX 210556
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
156 AM EDT Tue Jul 21 2026

...New DISCUSSION, AVIATION...

.KEY MESSAGES...
Updated at 124 AM EDT Tue Jul 21 2026

- Cold frontal passage today into tomorrow may bring several rounds 
of showers and storms, with a wide range of potential outcomes. See 
disc below.  

- There's some uncertainty, but the cold front may stall to the 
south, continuing showers and storms for parts of the forecast area 
until the latter part of the week. This could pose some flooding 
impacts.

- Below normal temperatures will follow beyond Wednesday until the 
early part of the weekend. Gradual warming to near normal early next 
week.


&&

.DISCUSSION...
Issued at 124 AM EDT Tue Jul 21 2026

The bulk of this discussion will focus on the today through 
tomorrow timeframe. There is a high level of uncertainty regarding
the timing and potential impacts during this timeframe, as there 
are various model solutions. Generally though, we are looking at 
the possibility of several rounds of showers and storms with the 
potential of strong to severe storms from later this morning 
through tomorrow morning.

Tropical Storm Bertha became officially named as of last night. Even 
though she will remain well to our south in the Gulf, her presence 
and slow movement westward may impact how things move and progress 
for today into tomorrow. From her current location off of the FL 
Peninsula coast, she will be located near New Orleans tomorrow 
morning. Part of the reason for her movement is because of weak 
flow/steering over much of the southern U.S.. The highest heights of 
the upper ridge will sink towards Texas with time, aiding Bertha to 
somewhere in the western Gulf later this week.

The pattern of high amplitude ridging to the west and troughing with 
shortwave impulses to the east continues. Multiple shortwave 
impulses will round the bottom of the trough before it's carried 
into far NE Canada later tomorrow into Thursday. At the surface, 
a cold front currently draped over IL to IA to NE/KS will 
eventually shift our direction, impacting us well before it even 
arrives. The actual front itself may not arrive until early 
tomorrow.

The potential impacts from today may come from at least three 
separate rounds of showers and thunderstorms. Each round may become 
stronger as the front gets closer and we introduce higher shear. 
Because of this possibility, it may impact the severity and 
evolution of the next round, so uncertainty is on the lower side. 
Runs of recent CAMs cannot totally grasp it or even try to align 
with one another. In the next couple of hours or so, some isolated 
to scattered showers and possible thunderstorms may develop across 
our northern tier. They will most likely mimic what we've seen the 
past couple of days with high PWATs and low overall shear. There may 
be a period of drying or there could be continuing activity until 
the next round.

Activity for the most part will be shifting down from the north and 
northwest. Later this afternoon and evening could introduce the next 
round where we will be at peak heating. Everything up until this 
point is pre-frontal. The main threats from storms will be damaging 
wind gusts and potential flooding issues. After dark, or the next 
round, will confidently be the period with the least confidence and 
certainty. Better shear rolls in as well as SRH, but surface 
instability falls off some after peak heating. CAMs disagree on 
timing of arrival as well, which Bertha may be partly to blame. 
Damaging wind gusts will continue to be the greatest threat with a
general linear storm mode. If we can generate hail, it will most 
likely be of the smaller variety. A low-end tornado threat does 
exist, mainly for the northern plateau into southwest VA. Unless 
there's some localized effects, backed surface winds may be hard 
to accomplish.

The "third" round may begin as early as 7 PM EDT, persisting through 
the overnight hours until it weakens. Movement during the overnight, 
at least according to CAMs, doesn't show much southern progression, 
so that puts flooding on the forefront of impacts. Generally, north 
of I-40 and the higher terrain can expect the higher end of QPF.

Later tomorrow into Thursday, when previously thought that it would 
dry out, may keep chances of showers and storms around with the 
potentially stalled front to our south, Bertha just off of the LA 
coast, and high pressure desperately trying to barrel in from the 
north. WPC recognizes this, keeping MRGL to SLGT ERO tomorrow into 
Thursday.

The weekend as far as precipitation goes, does become more uncertain 
with a shortwave approaching from the northwest while the front may 
still be hung up to our south. We can say with certainty though, 
that temperatures tomorrow and into the first part of the weekend 
will be noticeably below normal with low and mid 80s. Temperatures 
gradually warm to near normal values early next week.

&&

.AVIATION...
(06Z TAFS)
Issued at 124 AM EDT Tue Jul 21 2026

A few showers will be around NE TN, potentially affecting TRI
briefly with MVFR vis if one moves over the terminal. Fog may be
possible toward sunrise if this happens. During the day, winds
will become gusty from the SW at TYS and TRI. In the evening,
showers and storms are expected to move south from KY, but timing
is uncertain. TYS and TRI will have PROB30s for this at the end of
the TAF period. 

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             93  76  90  70 /   0  40  70  40 
Knoxville McGhee Tyson Airport, TN  90  74  86  68 /  10  80  80  30 
Oak Ridge, TN                       90  73  86  66 /  20  90  70  20 
Tri Cities Airport, TN              87  69  83  62 /  40  90  80  30 

&&

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

$$

DISCUSSION...KS
AVIATION...DGS


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