-- Discussion containing changed information from previous version are highlighted. --
405
FXUS64 KMRX 160718
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
318 AM EDT Mon Sep 16 2024

...New SHORT TERM, LONG TERM...

.SHORT TERM...
-- Changed Discussion --
(Today and tonight)
Issued at 308 AM EDT Mon Sep 16 2024

Key Messages:

1. Dry and warm conditions expected through late this afternoon.

2. Showers associated with tropical system off SC coast will push
westward across the TN/NC line this evening and overnight. Rain
chances largely limited to areas north of I-40, especially in the
northeast.


Discussion:

A developing tropical/subtropical low off the coast of South
Carolina will shift northwest today and tonight. Ahead of this
system we`ll have dry conditions across the forecast area for most
of the day. But showers associated with this low will move across
the mountains and into the northern TN valley by this evening.
Initial wave of precip will likely have a difficult time as it will
be moving into/attempting to displace dry air with PWATs on the
order of 0.5" to 0.75". To that end, model soundings don`t show
saturation descending below roughly 7k ft AGL in the Tri-Cities area
until after 00z, so I`d expect a lot of the initial wave of showers
to be virga or very light rain, and limited mainly to area east of
the Interstate 81 corridor northeast of I-40. With time, banded
precip will shift westward to more of the I-75 corridor or perhaps
as far west as the northern plateau counties during the overnight
hours. Some guidance shows very high PoPs tonight, upwards of 70
percent, as showers move west into our area. While I think there`s a
very high likelihood of their existence, there`s some uncertainty in
how widespread they`ll be and what lingering effects of downslope
flow across the mountains might have on them. As such, limited PoPs
to high-end chance levels outside of our northeast TN mountains and
some higher terrain areas in our eastern VA counties.

Otherwise, today will be another warm day with temperatures well
into the 80s. Did knock the highs down a degree or two with respect
to the NBM since it seems it was a tad hot yesterday. Increasing
clouds, even if just high clouds, should keep highs from being quite
as warm as yesterday, especially in the north. There`s also strong
support for gusty northeast winds in the valley today. As the
coastal low moves inland across the SC/NC border this afternoon,
models show a strengthening inverted surface trough across the TN
valley. After roughly 20z, high res guidance shows gusts increasing
to 25 mph or so for areas northeast of the Knoxville metro area.
-- End Changed Discussion --

&&

.LONG TERM...
-- Changed Discussion --
(Tuesday through Sunday)
Issued at 308 AM EDT Mon Sep 16 2024

Key Messages:

1. Long term pattern will be dominated by tropical remnants from the
Carolinas and additional development well off the Mid-Atlantic
Coast. Rainfall amounts and coverage is uncertain, however,
precipitation chances look best for the northeastern part of our
forecast area and parts of the Appalachians.

2. Temperatures will mostly run a couple degrees above normal for
middle September with the exception of areas that will be impacted
by the tropical remnants.

Discussion:

Potential tropical cyclone 8, as labeled by the NHC, will impact
some of our forecast area through part of the long term. By Tuesday
morning when the long term begins, the center of the system will be
close to the SC and NC state line. Before then, the 00Z GFS is
notably the speedy solution taking it to where the other models
eventually catch up, much faster.

Easterly to northeasterly flow will mostly bring the best shower and
thunderstorm chances for northeastern TN and southwest VA. Highest
total QPF amounts at this time are east of I-75 north of Knoxville,
into southwest VA, and along the Southern Appalachians. Due to the
supposed track the system will take, the southern valley and plateau
for example, may escape unscathed this coming week with dry
conditions, much warmer temperatures, and more sunshine than the
aforementioned regions.

Once the system further weakens over land late Tuesday into
Wednesday, the forecast remains and grows with uncertainty with
regards to unsettled weather into the rest of the week and over the
weekend. The closed upper low will eventually phase with the
northern stream trough, as upper level ridging tries to move our way
from the central US. At the surface, a slow moving low center well
off the Mid-Atlantic coast tracking towards New England, will keep
precipitation going for the east coast. We may be just far enough
from the outside fringes of wrap-around flow from it to bring any
good rain chances to the same areas earlier in the week. No more
than a 50 percent chance in the forecast for the later week and next
weekend activity.
-- End Changed Discussion --

&&

.AVIATION...
(06Z TAFS)
Issued at 140 AM EDT Mon Sep 16 2024

Generally speaking, expect VFR categories to prevail through the
period at most sites. The caveat may be KTRI. Low pressure moving
inland (northwest) from the South Carolina coast will spread
SHRA across the Appalachians and into the northern TN valley this
evening. Guidance is mixed as to whether VSBY or CIGS will drop in
response to these showers encroaching on KTRI late in the period.
Tend to think it would be mainly VSBY reduction given the dry air
in place ahead of it. However, given the uncertainty, decided to
just go with a VCSH and show CIGS lowering into the lower VFR
ranges after 21z.

&&

.PRELIMINARY POINT TEMPS/POPS...
-- Changed Discussion --
Chattanooga Airport, TN             87  62  84  63 /  10  10  10   0
Knoxville McGhee Tyson Airport, TN  85  62  76  62 /   0  20  20  20
Oak Ridge, TN                       84  62  78  63 /   0  20  20  10
Tri Cities Airport, TN              78  60  72  62 /  20  50  50  40
-- End Changed Discussion --

&&

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

$$

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