Johnson City, Tennessee 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

651
FXUS64 KMRX 180555 AAC
AFDMRX

Area Forecast Discussion...UPDATED
National Weather Service Morristown TN
1255 AM EST Sat Jan 18 2025

...New AVIATION...

.UPDATE...
Issued at 901 PM EST Fri Jan 17 2025

Forecast mostly on track, only a few minor updates. Dewpoints
running several degrees lower than previously forecast. Still
expect the surface to begin to moisten up over the next several
hours as moisture streams in from the southwest. However, the dry
air currently in place may delay the onset of precip by a few
hours. TRI hourly temp already at their forecast low of 33, so
lowered the min temp down to 31. Otherwise, all else on track.

&&

.SHORT TERM...
(This evening through Saturday)
Issued at 227 PM EST Fri Jan 17 2025

1. Last sunny day with temps around normal for a long time.

2. Rain moves in tomorrow with some wintry precipitation mixed in at
the highest elevations tomorrow.

Discussion:

Currently light winds, clear skies, and temperatures right around
seasonal normals are ongoing across the region. Enjoy em while you
got em as mother nature changes her tune starting later tonight.
Overnight southern stream jet in the mid/lower levels really ramps
up over our region out of the southwest ahead of the digging trough
to our west. Clouds will increase in coverage later this evening
which will help keep temperatures warm, and likely above freezing
for everywhere outside of the higher elevations of the Appalachians
and ridgetops.

Rain will be heaviest and most widespread overnight right as the
trough/shortwave moves overhead. There could be some embedded
heavier downpours, but overall expect light rain for much of the
overnight and into the morning hours. Once daybreak begins we`ll
continue to see rain chances, but rain will become more showery and
isolated in nature. By the end of Saturday expect to see generally
less than a half an inch of liquid across the area, with some of the
orographically enhanced areas possibly seeing amounts up to 1 inch
of liquid.

During the overnight hours temperatures in the highest elevations
could drop low enough to see precipitation fall in the form of snow.
Sounding profiles are generally hovering around 4000 feet or higher,
so we could see some wintry weather mixed in around 3500 feet of
elevation and higher in the southern Appalachian region. In addition
winds will be gusty with the strengthening jet, but with a southwest
orientation mountain wave enhanced winds are typically not present.
However anyone driving over the mountains should take extra
precaution with possibly slick roads and gusty winds overnight.

&&

.LONG TERM...
(Saturday night through next Friday)
Issued at 227 PM EST Fri Jan 17 2025

Key Messages:

1. A system will move through Saturday night and Sunday, bringing
light snow even to lower elevations of northeast Tennessee and the
Central Tennessee Valley. Highest amounts look confined to the
Southern Appalachians and southwest Virginia.

2. VERY COLD Sunday through Thursday morning. Coldest temperatures
of the season for many. Monday morning through Wednesday morning
will be the coldest with lows ranging in the teens for most of the
TN Valley to single digits elsewhere. Wind chill could make it feel
as cold as 15 below zero across the highest terrain.

3. Trend warmer end of the week with great uncertainty over the next
system.

Discussion:

A cold front will move through the region Saturday evening bringing
widespread rain chances overnight Saturday. By early Sunday morning,
a changeover to light snow is expected across the region. Sunday
morning light snow will continue with accumulating snow expected
even in the Central Tennessee Valley as a strong trough moves into
the region. By Sunday afternoon, light snow will start to taper off
in the Central Valley. Meanwhile, snow rates will increase in the
higher elevations of East Tennessee and Southwest Virginia as 850 mb
northwest flow increases to 20 to 30 knots. Mountain snow will start
to decrease around or after midnight going into Monday as 850 winds
decrease.

The best window for accumulating snow in the Valley will be Sunday
morning through early or mid afternoon. Expected snow totals are
generally around one inch near Knoxville. One to two inches will be
possible north and east of Knoxville extending into Northeast
Tennessee and the lower elevations of Southwest Virginia. In the
higher elevations of Southwest Virginia and the East Tennessee
mountains, snow totals will be much higher due to terrain forcing
from the northwest flow on the backside of this system, 2-4 inches
in most mountain locations and 3-5 inches possible on the tallest
peaks (above 4500-5000 ft). Snow will come to an end Sunday evening
for the lower elevations and early Monday morning for the higher
elevations.

Temps will remain cold on Sunday with CAA in place behind the cold
front. A very cold air mass will remain in place through Thursday
morning. The coldest day will be Monday with highs not getting out
of the 20s even in the Valley! Wind chills as low as -15 will be
possible in the higher terrain overnight Sunday night. Otherwise,
winds will be light enough to not have a significant wind chill
factor. It will still be dangerously cold though with calm winds
allowing lows in the single digits and teens in the Valley, even
colder elsewhere.

POPs are low for the rest of the forecast period. It looks like a
mid week system will stay south of our region and a system late in
the week looks pretty moisture starved. We will still have to keep
an eye on it with such cold temps in place.

&&

.AVIATION...
(06Z TAFS)
Issued at 1248 AM EST Sat Jan 18 2025

First wave of rainfall has already arrived at KCHA, but is having
difficulties moving further north due to entrenched dry air so
have delayed onset of SHRA at KTYS and KTRI a tad. Guidance is
universally insistent on bringing flight categories down to MVFR
and even IFR at all terminals later today. Hard to go against that
kind of consistency, but I`m also not seeing those CIGS anywhere
upstream where guidance says they should exist now. As such, kept
the trend but delayed the onset of those categories by a bit.
Lastly, showers should persist for a 6-9hr window. Afterwards the
low levels will remain saturated so some -DZ could occur, but will
leave that out of the TAFs for now.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             55  33  38  13 /  80  40  10  10
Knoxville McGhee Tyson Airport, TN  53  31  36  10 /  80  70  40  10
Oak Ridge, TN                       50  30  35  10 /  80  60  40  10
Tri Cities Airport, TN              48  32  36  10 /  80  70  80  10

&&

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

$$

SHORT TERM...
LONG TERM....McD
AVIATION...CD