918
FXUS64 KMRX 171157
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
757 AM EDT Tue Sep 17 2024

...New AVIATION...

.SHORT TERM...
(Today and tonight)
Issued at 312 AM EDT Tue Sep 17 2024

Key Messages:

1. Rain from a tropical low pressure system will continue to
spread across the area from southwest Virginia, into northeastern
Tennessee, and southwest North Carolina. Highest rainfall amounts
will be over and in the foothills of the Appalachians.

2. Temperatures a lot cooler today mostly to do with cloud cover.

Discussion:

What was potential tropical cyclone 8, is centered over the
Carolinas this morning. Wrap-around from the back-side is what is
currently falling across our forecast area. Currently on radar,
downsloping is evident in the reflectivity hole over Lee and Wise
counties in Virginia. We expect the precipitation to push west and
southwest into the morning and later morning hours today. CAM
solutions are suggesting that it`ll turn into a more isolated to
scattered regime outside of the higher terrain. Chances for
thunder are pretty low (< 30 percent), so not expecting any
severe weather. SPC only has southwest Virginia and what looks to
be Johnson County Tennessee clipped with general thunder today.
The center of the low loses it shape later today and thus, precip
chances decline into the night, but that won`t be all when it
comes to expected accumulation this week. (See long term forecast
below)

Extreme southern plateau and valley such as Hamilton, Marion,
and Sequatchie counties will likely not see any rainfall today
and remain mostly cloudy. A combination of lowering heights aloft
and cloud cover will keep temperatures a whole lot cooler today
compared to yesterday. The aforementioned locations will also
likely be the only places that reach 80 for highs today.

A few tenths of an inch to up to three quarters of an inch rain will
be common the next 24 hours across the area. However, closer to
the foothills and over the highest terrain of the Appalachians,
is where over one inch and even possibly over an inch and a half
may be recorded. Not expecting any flooding concerns at this time
being how dry we have been, so this is very welcome to our region.
Isolated showers will hold for extreme northeastern parts of our
CWA overnight, but areas that dry out and may even briefly clear,
will pose the possibility of fog development.

&&

.LONG TERM...
(Wednesday through Monday)
Issued at 312 AM EDT Tue Sep 17 2024

Key Messages:

1. Scattered showers possible on Wednesday, mostly in the mountains
and northern half of the forecast area. Dry conditions expected
afterwards though.

2. High pressure aloft builds Thursday onward. This should result in
highs several degrees above normal.

Discussion:

An upper low will be situated over the southern Appalachian region
to begin the period, but this feature will open up and lift
northeast into a developing east coast trough by Thursday morning.
Meanwhile, upper ridging will build north northeast from Texas
through the Great Lakes Thursday into the weekend.

Scattered, largely diurnally driven, showers will be present across
much of the forecast area on Wednesday but dry conditions are
forecast thereafter once the low lifts away to the northeast and we
have increasing influence from the upper ridge to our west. There is
some support in numerical guidance for keeping some afternoon rain
chances in the mountains Friday through the weekend. But I think
we`re more likely to remain dry so kept the forecast dry for now.

Given the pattern and developing ridge, and how dry we`ve been
lately, the NBM forecast highs for the long term don`t seem
unreasonable. Highs on Sat and Sun will likely approach 90 in the
south, with upper 80s as far north as the I-40 corridor and lower
80s in the north. This isn`t going to approach any calendar
day records (those are near 100 degrees for Chattanooga, and firmly
into the lower 90s up north for example), but it will be 3-5 degrees
above normal.

&&

.AVIATION...
(12Z TAFS)
Issued at 739 AM EDT Tue Sep 17 2024

Light to moderate, possibly heavy rain at times has reached TYS
this morning. CHA should mostly remain VFR through the day with
the only impacts from the tropical system being NEly winds and
lowering CIGS throughout the day. Guidance does indicate CIGS will
drop to MVFR there tonight. TRI and TYS will mostly categorize as
MVFR for much of the day with light to moderate rain, BR, and low
CIGS at times. There will be possible drops below MVFR like there
have been already. Tonight will need close monitoring when we are
forecast to briefly clear because fog may be an issue overnight.
Low CIGS will persist after rain diminishes.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             81  65  86  64 /  10  10  10   0
Knoxville McGhee Tyson Airport, TN  75  65  82  64 /  60  20  40   0
Oak Ridge, TN                       76  63  82  63 /  50  20  30   0
Tri Cities Airport, TN              75  63  77  62 /  70  40  60  10

&&

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

$$

SHORT TERM...KS
LONG TERM....CD
AVIATION...KS