893 
FXUS64 KMRX 201944 AAA
AFDMRX

Area Forecast Discussion...UPDATED
National Weather Service Morristown TN
344 PM EDT Wed May 20 2026

...New DISCUSSION, AVIATION...

.KEY MESSAGES...
Updated at 343 PM EDT Wed May 20 2026

- Rain chances increase this afternoon and evening, with continued 
high rain chances through the first half of next week.

- Organized severe storms appear unlikely during this forecast
  period, but the primary threats with storms each day will be
  lightning, locally heavy rainfall, and some gusty winds.

&&

.DISCUSSION...
Issued at 343 PM EDT Wed May 20 2026

Convection has gotten off to an early start today in an
increasingly moist air mass, developing in Middle TN and the 
Plateau, which is an area of higher surface CAPE values around 
1500 J/kg and surface confluence. There is little to no shear to 
help sustain or organize these storms, so they will mainly be 
driven by outflow boundaries, terrain, and convergence zones. 
Expect that coverage will increase in the central and southern TN 
Valley over the next few hours. The main hazards will be lightning
and some locally heavy rainfall that could cause minor flooding 
issues. 

Isolated to scattered showers are expected to persist through the 
night due to the moisture rich environment, the presence of a 
midlevel shortwave trough, and some upper divergence. A front in the 
OH Valley region today will move southward and be near our northwest 
border by Thursday morning. This will act as a focus for convergence 
and convective development Thursday. PoPs will be categorical across 
the entire area, with a chance of thunderstorms. Instability and 
shear will be lacking for any organized severe threat, although some 
gusty downburts winds and locally heavy rainfall will be possible. 

A strengthening southerly flow ahead of a low over AR lifts the 
aforementioned boundary northward on Friday, putting our area into 
the warm sector in the afternoon. LREF joint probabilities of CAPE > 
1000 J/kg and shear > 25 kt are around 30% across the area, and near 
40% in our southern sections where clouds may scatter enough to 
enhance afternoon heating. A few strong to severe storms cannot be 
ruled out for Friday, but the chance remains low. 

A deep SW flow persists through the weekend and early next week, 
with broad troughing over the central US. Disturbances ejecting from 
this broad trough will bring several rounds of enhanced rain chances 
through early next week, but the timing of these disturbances 
remains higly uncertain. Overall, the pattern favors continued high 
rain chances each day. The primary impacts will be lightning and 
locally heavy rainfall. QPF through the next 7 days will vary widely 
across our area, depending on which areas see repeated showers and 
storms over numerous days. Generally speaking, 1-3" of rain is 
forecast through the period.

&&

.AVIATION...
(18Z TAFS)
Issued at 343 PM EDT Wed May 20 2026

Showers and storms will be near CHA over the next few hours, and may 
bring TS with MVFR/ vis/cigs. This activity may spread toward TYS 
later in the evening, and potentially to TRI later in the night. 
With a moist boundary layer, low clouds at MVFR levels are expected 
to form and persist into tomorrow morning, but this may be dependent 
on whether showers pass over the terminals this evening. Confidence 
of this happening is high at CHA, medium at TYS, and low at TRI.


&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             66  83  65  83 /  70  60  90  90 
Knoxville McGhee Tyson Airport, TN  66  81  64  82 /  70  90  50  90 
Oak Ridge, TN                       64  81  63  81 /  70  80  60  90 
Tri Cities Airport, TN              62  79  61  80 /  70  90  50  80 

&&

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

$$

DISCUSSION...DGS
AVIATION...DGS


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