498
FXUS64 KMRX 261756
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
156 PM EDT Thu Sep 26 2024

...New AVIATION...

.UPDATE...
Issued at 954 AM EDT Thu Sep 26 2024

Main purpose of the morning update was to touch up PoPs and rain
amounts. No changes were made to winds at this time. Will adjust
forecast winds and wind gusts later this morning after the
National Hurricane Center makes any necessary adjustments to their
track and intensity forecasts. Still expect to see strong winds
with this system though.

Otherwise, just some minor adjustments to PoPs and QPF through the
afternoon hours. The NAM seems to have the current banding seen on
radar modeled fairly well in terms of areal coverage and
placement, but also seems a little bullish on rainfall totals. Did
a blend of the latest WPC guidance, the NAM, and some 12z HRRR for
some minor adjustments to amounts from roughly the Sevier county
area northwards toward Hancock and Lee counties. Will save any
further adjustments for the midday or afternoon package.

&&

.SHORT TERM...
(Today through Friday) Issued at 353 AM EDT Thu Sep 26 2024

Key Messages:

1. Flooding potential remains high as heavy, tropical downpours
affect the area today into Friday.

2. Winds will be high in the mountains, which are areas that are
used to strong winds. There is also the potential for widespread
strong winds in the TN valley late Thu night through Fri morning.

Discussion:

Hurricane Helene is in focus for the period, and the impacts the
decaying tropical system brings to our are are expected to be major.
The current NHC track has it coming ashore then track north before
curving northwest across southeast TN early Friday before being
absorbed into the upper low to our west. The two main concerns with
this system for us will be heavy rain/flooding and very strong
winds.

A precursor rain event has been ongoing, and we`ve already had a lot
of rain across areas mainly along/east of the I-75 and I-81
corridors (in excess of 4 inches in spots). We will see additional
heavy rain over these areas today, with a downtrend for a period
west of the mountains for a period later today into tonight as the
downslope winds increase and the axis of the more significant rain
shifts south and west, then likely another increase area wide late
tonight into early Friday as the tropical system approaches. WPC has
rainfall from now through Friday evening of around 3 to 4+ inches
over most of our area, with even higher amounts across portions of
SW NC and the eastern mountains. The flood watch will be expanded
into our northern Cumberland Plateau counties with this issuance.
Both flash floods and river flooding is expected.

For winds, some of the higher elevations of the mountains will see
wind gusts in excess of 70 mph, but valleys are likely to see strong
wind gusts as well later tonight into Friday morning. Mean HREF wind
gusts are showing values of 50+ across much of the area outside of
the mountains. While we may not reach actual wind warning wind
speeds in most locations outside of the mountains, we will likely
see a lot of trees down and power outages especially given the soggy
ground. Given the uncertainties of exactly how strong Helene will
get before landfall and it still being second period, and in
coordination with neighboring offices, will leave the watch out for
one more cycle. Will continue the high wind warning in the
mountains. Will also continue the Tropical Storm warning for our SW
NC counties in accordance with North Carolina partners.

&&

.LONG TERM...
(Friday night through Wednesday)
Issued at 353 AM EDT Thu Sep 26 2024

(Friday Night Through next Wednesday)

Key Messages:

1. Light rain showers likely on Saturday, no additional impacts
expected.

2. Additional light rain possible primarily in the afternoon Sunday
through Tuesday. Drier thereafter with seasonable temperatures
throughout.

Discussion:

As the forecast heads to Saturday and the weekend, Helene will be
absorbed or merged into the resident upper low that`s to our west
currently. This merged pair will be significantly weaker and less
impactful than the weather in earlier periods. A couple of days of
scattered light rain showers are possible, mostly on Saturday and
Sunday as the upper low slowly moves eastward through the Ohio River
valley. Winds Saturday morning will be a tad breezy still in the
mountains but will subside through the day. Eventually as we
progress to the midweek, the low will exit to our east, heights will
build back in, and we`ll fully begin the drying out period.
Temperatures look to remain seasonably warm, as heights increase on
the backside of the low.

&&

.AVIATION...
(18Z TAFS)
Issued at 145 PM EDT Thu Sep 26 2024

VSBY and CIGS will continue to vary with showers and heavier rain
bands from Helene`s anticipated approach. The most important
thing to note aviation-wise for all terminals will be the
increase in winds. Sustained and gusts will increase as we
approach tonight. CHA may experience the lower end of gusts, but
will probably be the most variable in direction towards the end of
the TAF period when the center of Helene moves over. TYS will
exceed 30KT in the middle of the night with direction eventually
shifting from NE to ESE. TRI appears will exceed 40KT around or
after sunrise, but things will be interesting for them as far as
WX, CIGS, and VSBY are concerned because strong mountain wave like
winds in excess of 50+ KT over the mountains, will suppress
precip and keep CIGS around VFR. TRI`s wind direction shift will
be similar to TYS with NE to start to around ESE to SE by the end
of the TAF period.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             66  74  64  74 / 100 100  30  40
Knoxville McGhee Tyson Airport, TN  68  76  64  75 / 100 100  30  40
Oak Ridge, TN                       66  74  62  72 / 100 100  40  50
Tri Cities Airport, TN              67  78  60  75 / 100 100  20  20

&&

.MRX WATCHES/WARNINGS/ADVISORIES...
NC...Flood Watch through Friday afternoon for Cherokee-Clay.

     Tropical Storm Warning for Cherokee-Clay.

TN...Flood Watch through Friday afternoon for Anderson-Bledsoe-Blount
     Smoky Mountains-Bradley-Campbell-Claiborne-Cocke Smoky
     Mountains-East Polk-Grainger-Hamblen-Hamilton-Hancock-
     Hawkins-Jefferson-Johnson-Knox-Loudon-Marion-McMinn-Meigs-
     Morgan-North Sevier-Northwest Blount-Northwest Carter-
     Northwest Cocke-Northwest Greene-Northwest Monroe-Rhea-
     Roane-Scott TN-Sequatchie-Sevier Smoky Mountains-Southeast
     Carter-Southeast Greene-Southeast Monroe-Sullivan-Unicoi-
     Union-Washington TN-West Polk.

     High Wind Warning from 8 PM EDT /7 PM CDT/ this evening to 8 PM
     EDT /7 PM CDT/ Friday for Anderson-Bledsoe-Blount Smoky
     Mountains-Bradley-Campbell-Claiborne-Cocke Smoky Mountains-
     East Polk-Grainger-Hamblen-Hamilton-Hancock-Hawkins-
     Jefferson-Johnson-Knox-Loudon-Marion-McMinn-Meigs-Morgan-
     North Sevier-Northwest Blount-Northwest Carter-Northwest
     Cocke-Northwest Greene-Northwest Monroe-Rhea-Roane-Scott TN-
     Sequatchie-Sevier Smoky Mountains-Southeast Carter-
     Southeast Greene-Southeast Monroe-Sullivan-Unicoi-Union-
     Washington TN-West Polk.

VA...Flood Watch through Friday afternoon for Lee-Russell-Scott VA-
     Washington VA-Wise.

     High Wind Warning from 8 PM this evening to 8 PM EDT Friday for
     Lee-Russell-Scott VA-Washington VA-Wise.

&&

$$

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