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

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FXUS64 KMRX 190251
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
1051 PM EDT Mon Mar 18 2024

...New UPDATE...

.UPDATE...
Issued at 1046 PM EDT Mon Mar 18 2024

Moisture continues to move into portions of the area tonight.
Added a few hours of flurries to southwest Virginia where a few
returns are showing up on radar. Most of this is probably
evaporating but a few flurries seem possible over the next couple
of hours. Otherwise, the rest of the forecast is in good shape.

&&

.SHORT TERM...
(This evening through Tuesday)
Issued at 308 PM EDT Mon Mar 18 2024

Key Messages:

1. Hard freeze expected tonight area wide. Winds may bring overnight
and early morning wind chills into the teens in higher elevations or
northeastern TN into southwest VA.

2. Dry weather continues through Tuesday, with temperatures
rebounding slightly in the afternoon. Low relative humidities and
breezy afternoon winds present fire danger.

Discussion:

The sharp upper trough that is driving our cold weather today and
tonight will pass through the wider region overnight tonight.
Additionally northwest winds aloft will increase to 20 to 30 knots.
The advection of a significantly cold airmass will bring a strong
hard freeze for nearly all of East Tennessee, southwest Virginia,
and especially Cherokee and Clay counties in North Carolina. Best
chances to remain above 28F will be in the urban heat islands of
Chattanooga and Knoxville, and on the southeastern slopes of any
ridge or terrain feature, due to downslope warming. Tacked on some
flurries in the Smokies for tonight, HREF has been persistent in
this possibility, zero snow accumulation expected. So far Jackson
KY radar still shows possible flurries a couple hours out from the
Kentucky border, not sure how much, if any, will fall in elevated
portions of southwest Virginia thanks to the dry lower atmosphere.

Tuesday surface winds will pivot to the southwest, with daytime
high temperatures a few degrees warmer than today. The dry airmass
associated with this system will yield another day of low relative
humidities, and afternoon mixing will bring some breezy winds to
the surface in the afternoon once more. For both those reasons,
another afternoon of elevated fire danger will be present tomorrow
afternoon.

&&

.LONG TERM...
(Tuesday night through next Monday)
Issued at 308 PM EDT Mon Mar 18 2024

Key Messages:

1. Dry conditions will continue Wednesday and Thursday with
Wednesday being breezier and Thursday being drier.

2. Light rain is expected Friday into Friday night.

3. Drier and slightly cooler conditions are expected on Saturday,
followed by a warming trend.

Tuesday Night through Friday

At the start of the period, westerly to northwesterly flow will be
in place aloft with surface high pressure centered over the northern
Gulf. This pattern will continue a dry start to the period with low-
level moisture advection from the northwest expected ahead of
another weak frontal boundary. Based on the overall synoptic setup,
this will result in increased cloud cover, which will limit mixing
and drop in RH`s. However, a more persistent westerly breeze will be
in place based on the MSLP gradient and 850mb flow approaching 25
kts. By the end of the day, winds will shift to a more northerly
direction, keeping fairly cool temperatures overnight.

By Thursday, focus will turn towards a developing system over the
Southern Plains where a shortwave/closed low will be ejecting from
the main flow. Locally, Thursday will ultimately be drier due to
subsidence and passage of the recent frontal boundary. This will
likely allow for better mixing and a further drop in RH`s, but
thankfully the MSLP gradient and 850mb flow will be weaker than
Wednesday. Thursday night into Friday, the aforementioned system
will move into the area with the surface low itself tracking to our
south. This will limit instability and overall moisture to the Gulf
Coast towards Florida. The more easterly to southeasterly flow in
the lower levels will also cause downsloping, which will limit
rainfall totals even more. Nevertheless, this system will bring area-
wide PoPs to the forecast late-week. 850mb flow could exceed 30 kts,
which may lead to a low-end mountain wave event when combined with a
decent MSLP gradient. However, any impacts would likely be pretty
limited.

Saturday through Monday

By Saturday, the system will progress east of the area, which will
shift the flow to a more northerly or northwesterly direction and
increased CAA. Moisture will likely exit the area fairly quickly,
keeping PoPs focused closer to the mountains. Most places will
likely see exiting cloud cover and slightly cooler conditions.
Saturday night into Sunday morning, high pressure will be centered
to our north, promoting subsidence and a return of drier conditions.
Also during this time and towards Monday, there are indications of a
strong system developing in the central U.S. Currently, the
potential impact is increasing southerly flow, combined with dry
conditions. For now, messaging will be limited based on limited
confidence.

&&

.AVIATION...
(00Z TAFS)
Issued at 716 PM EDT Mon Mar 18 2024

Winds will remain elevated overnight between 5 to 10 knots. The
current thinking is that skies will remain SCT to BKN tonight,
with SKC at CHA. Not expecting any precipitation near the
terminals tonight. Winds turn toward the southwest on Tuesday with
gusts up to 25 knots by the afternoon. Otherwise, VFR conditions
expected to prevail.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             29  57  37  69 /   0   0   0   0
Knoxville McGhee Tyson Airport, TN  27  54  37  66 /   0   0   0   0
Oak Ridge, TN                       26  56  35  67 /   0   0   0   0
Tri Cities Airport, TN              26  51  34  61 /   0   0   0   0

&&

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

$$

SHORT TERM...Wellington
LONG TERM....BW
AVIATION...Diegan


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