Johnson City, Tennessee 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

134
FXUS64 KMRX 211731
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
1231 PM EST Thu Nov 21 2024

...New AVIATION...

.UPDATE...
Issued at 946 AM EST Thu Nov 21 2024

The first inklings of the winter weather are moving into our
region as the low spins across the Great Lakes Region and the and
on the southern edge we`re seeing the cloud bank move out of
Kentucky along with light radar returns. Looks like some of the
lightest returns aren`t producing precipitation, which is common
during the daytime hours, but once they get closer to 30 dBZ we`re
seeing reports of light snow. Expect this to be enhanced along
the ridgetops in northeast TN/southwest VA today and we could see
some of the highest elevations start to get minor accumulations.
No major changes to the forecast for this morning update and the
previous discussion is still valid.

&&

.SHORT TERM...
(Today and tonight)
Issued at 351 AM EST Thu Nov 21 2024

.SHORT TERM...

Key Messages:

1. Breezy conditions are expected today through Friday. Widespread
gusts between 20-35mph each afternoon. Higher elevations of the
East Tennessee mountains may encroach 40mph at times.

2. With a seasonably cold air mass in place, breezy winds will lead
to wind chills in the 20s for most valley locations tonight. Wind
chills in the low teens for higher elevations of the East Tennessee
mountains.

3. Snow showers are expected to bring 1-3 inches of snow to portions
of southwest Virginia and the East Tennessee mountains, with
isolated totals between 3-6 inches in the highest peaks and
ridgetops.

Discussion:

We currently find the region under mostly clear skies as a seasonably
cold and dry air mass continues to filter in post-FROPA. A light
westerly wind has kept any widespread fog from forming and will
continue to do so into the morning hours. Though, a few spots along
sheltered valleys of waterways in southwest VA are showing fog on
GOES-16 nighttime imagery, which could very well be freezing in
isolated locations. Be cautious for a few slick spots on roads if
encountering any patchy fog.

On the synoptic scale, an anomalous upper-level low is expected to
slowly meander ESE from atop Michigan and towards the north-central
Appalachians into the evening hours. Weak impulses will drive an
area of surface low pressure along Lake Michigan and southward into
the late afternoon and overnight hours, periodically amplifying the
WNW-NW flow aloft as well. This will enhance low-level moisture in
the DGZ leading to favorable conditions for northwest snowfall in
addition to strengthen the MSLP gradient. Overall, there has been
little change since the previous forecast so lets talk impacts.

Winds/Wind Chill: The strengthening pressure gradient will lead to
wide-spread breezy winds of 20-35mph across the forecast area
starting late morning. Higher elevations of the East Tennessee
mountain may see gusts approaching 40mph when those aforementioned
impulses swing through the region. Given the northwest nature
however, HREF probabilities hold highest probabilities of 40mph or
greater(advisory criteria) to the eastern slopes of the mountains so
have continued to opt out of an advisory at this time. Breezy winds
and cold temperatures will combine for widespread wind chills in
the 20s Thursday night into Friday morning, with values into the
single digits possible across higher elevations.

Snowfall: Little change has occurred with the snowfall forecast. The
greatest moisture availability in the lowest levels, including the
DGZ, is expected to occur near or just after 00Z and through about
12Z. This is when the bulk of this wintry precipitation is expected
to occur. However, did slightly tweak the start time of the advisory
ahead by 3 hours as some flakes may begin to fly in the higher
elevations of southwest Virginia closer to the moisture source.
Again, bulk of the precipitation is expected overnight after 00Z.
Expect most the advisory area to see between 1-3 inches but favored
northwest flow locations could see isolated totals between 3-6
inches. Otherwise, portions of the Cumberland Plateau and the
northern Tennessee valley may see between a dusting to an inch.
Lesser confidence remains here due to slightly warmer temperatures
and how long it may take before some of that snow starts to stick to
surfaces. We see a lull in activity late Friday morning into the
afternoon before a secondary impulse looks to send a bit more
moisture this way. Some additional light snowfall (less than 1")
cannot be ruled out again Friday evening. Currently did not think
this warranted an extension of time into Friday for the Advisory as
it looks mostly insignificant at this time, but may need
consideration with future forecast packages.

&&

.LONG TERM...
(Friday through Wednesday)
Issued at 351 AM EST Thu Nov 21 2024

Key Messages:

1. Very minor snow accumulations continue Friday night into Saturday
morning as northwest flow continues.

2. Gusty winds continue Friday night through midday Saturday across
the higher elevations of the southern Appalachian Mountains. Gusts
from 30 to 40 mph will be common. Wind chills remain in the upper
20s to mid 30s

3. A return to normal temperatures by Sunday.

4. Rain returns to start the week.

Discussion:

Northwest flow snowfall continues across the area Friday night into
Saturday morning across the higher elevations of the east TN and
southwest VA mountains. However, only very minor snowfall
accumulations are expected through this time as the moisture is
drying up as the upper low and trough push further east. Around 0.5
inches or less of additional accumulation is expected.

Gusty winds continue across the southern Appalachian mountains
through midday Saturday. Wind gusts from 30 to 40 mph are expected.
Then, winds begin to decrease during the afternoon hours as the
pressure gradient becomes more lax. This is due to high pressure
building in from the west and the upper trough moving east. However,
keep in mind that wind chills in the higher terrain of the southern
Appalachians are still only expected to be in the upper 20s to low
30s. So please take any necessary precautions if you plan to be
outdoors.

Zonal flow is in place by Sunday and temperatures return to normal.
Another chance of precip arrives Monday night as a weak cold front
moves through the area. Temps are warm enough for precip to remain
of the liquid kind. Beyond Tuesday, the forecast is uncertain as
models are in poor agreement. Models hint at a shortwave approaching
from our west but placement, strength, and timing are poor. So will
leave NBM Pops in place, which yield slight chance to chance POPs
from Tuesday onward.

&&

.AVIATION...
(18Z TAFS)
Issued at 1226 PM EST Thu Nov 21 2024

Ceilings are beginning to lower with the incoming system. Winds
will remain breezy, and somewhat variable, although predominantly
out of the west to northwest. Light snow will move into the region
overnight, and may briefly reduce visibilities. Not expecting
much accumulations at KTYS as the ground remains warm, but could
see light accumulations at KTRI. Winds will remain breezy
throughout, and MVFR conditions are expected to prevail across
northeast TN and southwest VA for much of the back half of this
TAF cycle.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             37  50  37  58 /   0   0   0  10
Knoxville McGhee Tyson Airport, TN  35  48  38  54 /  30  10  10  10
Oak Ridge, TN                       34  48  38  54 /  20  10  10  10
Tri Cities Airport, TN              30  43  37  48 /  70  30  50  10

&&

.MRX WATCHES/WARNINGS/ADVISORIES...
NC...NONE.
TN...Winter Weather Advisory from 4 PM this afternoon to 10 AM EST
     Friday for Blount Smoky Mountains-Cocke Smoky Mountains-
     Johnson-Northwest Carter-Sevier Smoky Mountains-Southeast
     Carter-Southeast Greene-Unicoi.

VA...Winter Weather Advisory from 4 PM this afternoon to 10 AM EST
     Friday for Lee-Russell-Washington VA-Wise.

&&

$$

SHORT TERM...
AVIATION...