823
FXUS64 KMRX 091109
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
709 AM EDT Wed Apr 9 2025

...New AVIATION...

.SHORT TERM...
(Today and tonight)
Issued at 318 AM EDT Wed Apr 9 2025

Key Messages:

1. Widespread frost/freeze this morning.

2. Sunny this afternoon with warmer, near normal temperatures.

3. Increasing clouds and warm tonight ahead of an approaching
system on Thursday.

Discussion:

Southwesterly low-level flow increases this afternoon after a
cold, frosty start to the day. The increasing low-level flow is in
response to a dual jet divergent structure across the Great Lakes
ahead of a storm system across the upper Mississippi Valley. This
will result in warmer temperatures today near normal.

With increasing mid to high level clouds and southerly flow,
temperatures tonight will be warmer across the region with no risk
of frost into Thursday morning.

&&

.LONG TERM...
(Thursday through Wednesday)
Issued at 318 AM EDT Wed Apr 9 2025

Key Messages:

1. Showers and thunderstorms, some severe with large hail,
possible Thursday afternoon ahead of a cold front.

2. Longwave upper trough with cold weather and showers on Friday.
Mountain higher elevation snow Friday night.

3. Cold on Saturday with clearing conditions. Warmer air returns
Sunday and Monday.

4. Cold front dives south next Tuesday with low chance of showers
and thunderstorms.

Discussion:

Primary weather impacts of the extended are slated for Thursday
afternoon as a cold front moves towards the region. A 120 kt
upper level jet will translate southeastward towards the Tennessee
Valley on Thursday afternoon with falling heights. As a shortwave
and associated surface cold front approach the region, convection
is expected during the later afternoon. Minimal moisture return is
expected which will result in high based storms with LCL heights
around 1500m. Steep mid- level lapse rates will be present across
the region and lead to more robust than normal hail CAPE across
the Tennessee Valley. With EBShear above 40 kt and MLCAPE around
1000 J/Kg, especially south of Interstate 40, high based supercell
structures will be possible. With the higher hail CAPE and dry,
steep boundary layer lapse rates, large hail and gusty winds will
be the primary risk. The overall severe weather risk will be
spotty and conditional to the magnitude of afternoon instability.

Behind the cold front on Friday, colder air will be across the
Southern Appalachians with the trough axis across the region.
Showery weather continues with off and on rain showers during the
day. Some rain showers will change to snow across the higher
elevations of the mountains, mainly above 3000 feet elevation, on
Friday evening with some orographic enhancement. Overall amounts
should be minimal, but some localized accumulation of 1 to 2
inches may be possible across the highest peaks of the mountains.

Clouds begin to clear out Saturday as the trough axis shifts east
and surface high pressure sets up across the region. Temperatures
remain colder than normal, and areas of frost will be possible on
Saturday night into Sunday morning. With ridging building in on
Sunday and surface high pressure shifting east, southwest flow
returns with warming temperatures through early next week.

Another trough slides eastward across the Great Lakes on Tuesday
with a cold front moving southeast towards the region with at
least a chance of showers and thunderstorms; although, the amounts
of moisture available and frontal location is still somewhat
uncertain.

&&

.AVIATION...
(12Z TAFS)
Issued at 707 AM EDT Wed Apr 9 2025

VFR conditions at all sites today with increasing high clouds by
this evening ahead of a low pressure system on Thursday. Winds
remain generally light and become SW by the afternoon.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             68  47  73  47 /   0  10  70  60
Knoxville McGhee Tyson Airport, TN  66  46  66  47 /   0  10  90  70
Oak Ridge, TN                       65  46  66  46 /   0  20  90  70
Tri Cities Airport, TN              63  42  61  45 /   0  10  90  80

&&

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

$$

SHORT TERM...JB
LONG TERM....JB
AVIATION...JB