Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN

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FXUS64 KMRX 281515
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
1015 AM EST Wed Feb 28 2024

...New UPDATE...

.UPDATE...
Issued at 1014 AM EST Wed Feb 28 2024

Overall, the forecast is largely on track with fairly minimal
changes made so far. Currently, the cold front has just passed
through the Nashville area with the line of showers and storms right
along the boundary. Just ahead of the line, instability continues to
be surface-based and about 250 J/kg or greater. Isolated damaging
winds continue to be the main concern as this line moves into the
area, especially with the 850mb jet in excess of 50 kts area-wide.
The tornado concern continues to be non-zero based on low-level
instability and very favorable wind profiles, but radar trends have
so far only revealed fairly isolated and weak areas of rotation.
There is limited clearing ahead of the line, but the timing may
allow for further destabilization. Regarding changes to the actual
forecast, temperatures were increased slightly over the next couple
of hours as they have been warmer than expected. PoPs were also
adjusted to account for the timing and track of the line. The timing
of the Wind Advisory was extended to 4 PM EST to account for the
strong flow behind the front. A decrease to an advisory in the
mountains will be considered with the afternoon package, but the
extension for remaining areas was the main update.

&&

.SHORT TERM...
(Today and tonight)
Issued at 253 AM EST Wed Feb 28 2024

Key Messages:

1. Widespread windy conditions will continue until frontal passage
occurs today. Also, weak thunderstorms along the front may be
able to mix down some stronger winds aloft, for an outside chance
of damaging winds today.

2. Temperatures will fall through the day behind the front; highs
for most areas today will occur before Noon to 1 PM eastern.

Discussion:

Currently have a strong cold front situated from the northern OH/IN
border, southwest through the Ozarks and into Arklatex region
this morning. This front will push eastward at a fairly rapid pace
today, pushing into the plateau region around 10am, and exiting
the forecast area to the east by 1-2pm eastern. Calendar day high
temperatures will largely occur before noon today, with
readings falling through the day, even during peak heating hours
this afternoon. This is all being driven by a strong jet streak
(+170kt) and upper trough that will be moving eastward from the
plains and into the Ohio valley region today.

In terms of forecast concerns, it`s mainly just the winds.
Strong pressure gradient along with a truly expansive +50kt 850 mb
wind field (covering most of the Ohio valley, Kentucky, Tennessee,
and even the northern halves of Georgia, Alabama, and Mississippi
early this morning) is leading to widespread wind advisory
criteria across the deep south and points north. This will
continue to be the case through FROPA, which should occur roughly
around 10am in the plateau, and closer to 2pm eastern along the
eastern extent of our CWA. Current wind advisories and high wind
warning look to be in good shape both in terms of the wind gusts
they`re advertising, and timing. The other aspect of the winds
will be the possibility of a stray damaging wind gust along the
front. This is an ana front setup with most of the precip
occurring behind the front. However, the combination of strong
vertical forcing along the front and some meager instability
aloft, will yield a minor damaging wind threat. If any convective
elements along the front can mix down stronger winds from aloft,
there could easily be some wind damage. Along those lines, did
manually add in some slight chance of thunder along the frontal
passage today. I don`t think we`ll see widespread thunderstorms as
forecast instability isn`t great, but felt the NBM`s lack of
thunder wasn`t reasonable.

The strongest forcing is just now taking shape, so the current
upstream regional radar mosaic probably isn`t too representative
of what the precip shield will look like as the front rolls
through. However, do expect it to be fairly narrow precip band
when it moves through so have PoPs tailing off pretty quickly this
afternoon and evening. Temps will fall pretty rapidly behind it so
I expect there to be a changeover to snow in the mountains. Doubt
we`ll see any snow outside of that due mainly to how quickly
precip moves out. Don`t have any notable accumulation in the
mountains but wouldn`t be surprised to see a few tenths in the
higher terrain. Lows tonight will fall into the 20s area wide.

&&

.LONG TERM...
(Thursday through Tuesday)
Issued at 253 AM EST Wed Feb 28 2024

Key Messages:

1. Cooler temperatures to stick around Thursday and Friday.

2. Next chance for rain Friday, temperatures begin to rebound back
to warm weather for the weekend.

3. Rain potential still highly uncertain next week.

Discussion:

Extended period starts with surface high pressure located directly
overhead and a chilly airmass that will briefly linger for the last
two days of the workweek. A weak shortwave will cross the center of
the US on Friday, and isentropic ascent will bring light rain
showers to the wider region Friday afternoon and evening. Since
soundings show a sharp inversion aloft owing to the isentropic lift
and cold surface layer, took thunder out. DESI NBM was likewise
pessimistic. With the impulse continuing onwards, persistent
southwesterly flow will gradually bring a warmer airmass into
Tennessee and northwards, bringing the next bout of pleasant weather
just in time for the weekend. Can`t rule out an isolated shower over
the weekend, but most places should be dry.

Heading into next week, the global guidance is coming into better
agreement on a sharp trough ejection over the Northern Rockies
exiting into Canada somewhere around Minnesota. Seems like a low
chance any weather attached to the associated frontal boundary will
make it down here before petering out and being rebuffed by the next
round of return flow. Instead likely will have to watch for southern
stream shortwaves that may bring rain chances back next week. Still
a lot of uncertainty regarding the track and timing of all of the
systems, both the front approaching from the north and any potential
southern shortwaves.

&&

.AVIATION...
(12Z TAFS)
Issued at 648 AM EST Wed Feb 28 2024

The latest high resolution guidance suggests rainfall today will
be within a tight window as the front moves through. Have confined
mention of SHRA/TSRA to a roughly 2hr TEMPO group at all
terminals. Also appears that MVFR or IFR conditions will follow
suite. Regarding winds, KTRI has yet to see the gusts other sites
have seen, but that should change in the next 2-3 hrs. Expect
FROPA to bring a stark wind shift, with WNW gusts of 20-25kt
expected behind the front.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             71  31  53  40 /  90  10   0  20
Knoxville McGhee Tyson Airport, TN  70  28  50  35 / 100   0   0  10
Oak Ridge, TN                       69  28  50  35 /  90   0   0  10
Tri Cities Airport, TN              69  25  48  32 /  90  10   0   0

&&

.MRX WATCHES/WARNINGS/ADVISORIES...
NC...Wind Advisory until 4 PM EST this afternoon for Cherokee-Clay.

TN...Wind Advisory until 4 PM EST /3 PM CST/ this afternoon for
     Anderson-Bledsoe-Bradley-Campbell-Claiborne-East Polk-
     Grainger-Hamblen-Hamilton-Hancock-Hawkins-Jefferson-Knox-
     Loudon-Marion-McMinn-Meigs-Morgan-North Sevier-Northwest
     Blount-Northwest Carter-Northwest Cocke-Northwest Greene-
     Northwest Monroe-Rhea-Roane-Scott TN-Sequatchie-Sullivan-
     Union-Washington TN-West Polk.

     Wind Advisory until 7 PM EST this evening for Johnson-Southeast
     Carter-Southeast Greene-Southeast Monroe-Unicoi.

     High Wind Warning until 7 PM EST this evening for Blount Smoky
     Mountains-Cocke Smoky Mountains-Sevier Smoky Mountains.

VA...Wind Advisory until 4 PM EST this afternoon for Lee-Russell-
     Scott VA-Washington VA-Wise.

&&

$$

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


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