589
FXUS64 KMRX 041815
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
115 PM EST Thu Dec 4 2025

...New DISCUSSION, AVIATION...

.KEY MESSAGES...
Updated at 108 PM EST Thu Dec 4 2025

- Light wintry precipitation expected tonight over our VA counties
  and areas in TN near the KY and VA state lines. Winter Weather
  Advisories have been posted to account for this.

- Confidence is fairly high for timing and accumulations in
  Virginia, with medium confidence in northeastern Tennessee.

- Some mixed precipitation types could briefly occur as far south
  as the I-40 corridor, but predominant precip type should be rain
  and no accumulations or impacts are expected that far south.

&&

.DISCUSSION...
Issued at 108 PM EST Thu Dec 4 2025

The main forecast item of concern is the next 12-24 hours and the
possibility of some light wintry precipitation set to affect our
forecast area tonight into Friday morning.

Synoptically speaking, broad west southwesterly flow is in place
across the central and eastern CONUS, anchored by a weakening closed
low off the Baja peninsula in the west. Cold temps over the midwest
and Great Lakes regions, reinforced by troughing over eastern
Canada, along with a shortwave ejecting from southern plains, are
driving a strong WSW-ENE oriented upper jet from the Ozarks into
Kentucky. This jet and shortwave interaction will produce some light
precipitation tonight and into Friday morning across the forecast
area. Forecast soundings support a mix of precipitation types,
ranging from all, or mostly, snow in our Virginia counties to a
mixed bag in TN from the northern Cumberland plateau eastward
towards Hawkins and Johnson counties. Any further south than that
(places like Morristown, Jefferson City, Dandridge, Knoxville, etc),
nearer the I-40 corridor, there may be some snow mix in shortly
after the onset of precipitation tonight but it should be primarily
rain and certainly no accumulations are expected.

As for accumulations, deterministic guidance supports about an inch
of snow in our VA counties and a dusting to half an inch in northern
Tennessee. However, probabilistic guidance paints a different
picture, with HREF showing upwards of 80 percent odds of GTE 2
inches of snow in our VA counties and even 50 percent odds of GTE
3". REFS output isn`t much different, showing 70 percent odds of GTE
2" over an albeit smaller footprint of our VA counties, and even
some 40 percent odds of GTE 3" totals. Forecast soundings support
this ptype forecast so my confidence level in VA is fairly high.

The transition zone in northern TN is where my confidence is much
lower. The area from roughly the TN/VA line, to a line from roughly
Wartburg to Morristown to Johnson city, will feature mixed
precipitation and will changeover to rain at some point tonight. The
question really is what ptype wins out the longest and what, if any,
impacts there wind up being. Current guidance depicts at least some
chance of freezing rain and resulting light glazing, along with a
dusting to half an inch of snow tonight for areas mainly within a
county or so of the TN/KY/VA state line areas. Much further south
than that and while there could be mixed ptypes, temperatures will be
just warm enough to preclude any type of accumulations or impacts.
By the I-40 corridor, it should be all rain tonight. All wintry
precip comes to an end between daybreak and mid morning tomorrow,
holding on the longest in northern Wise and Russell counties, as
warming southwesterly flow aloft moves in.

West southwesterly flow continues aloft heading into the weekend,
with surface high pressure keeping dry conditions in place Saturday.
Another disturbance moves through Sunday into Monday for more
chances of light rain. There could be some wintry precip with that
one Sun night as temperatures cool off, but confidence is low on
both occurrence and amounts/impacts at the moment due to
disagreements amongst guidance sources.

Otherwise, dry conditions last much of the remainder of the period,
along with below normal temperatures.

&&

.AVIATION...
(18Z TAFS)
Issued at 108 PM EST Thu Dec 4 2025

VFR conditions will prevail through this evening, but cloud
heights and flight categories will lower quickly after 00z this
evening as overrunning precipitation moves in from the southwest.
Expect a fairly quick transition from VFR to IFR categories
tonight. Mixed precipitation is expected at KTRI, with only a low
chance of occurrence as far south as KTYS. Did add a brief PROB30
for RASN there but expect it to be mostly rain at KTYS and KCHA.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             38  49  39  51 / 100  20  10  10
Knoxville McGhee Tyson Airport, TN  36  45  37  49 /  90  40  10  10
Oak Ridge, TN                       34  45  36  49 /  90  30  10  10
Tri Cities Airport, TN              34  42  36  46 /  90  50  10  10

&&

.MRX WATCHES/WARNINGS/ADVISORIES...
NC...NONE.
TN...Winter Weather Advisory from 7 PM this evening to 7 AM EST
     Friday for Anderson-Campbell-Claiborne-Hancock-Hawkins-
     Morgan-Northwest Carter-Scott TN-Southeast Carter-Sullivan-
     Unicoi.

     Winter Weather Advisory from 7 PM this evening to 10 AM EST
     Friday for Johnson.

VA...Winter Weather Advisory from 7 PM this evening to 10 AM EST
     Friday for Lee-Russell-Scott VA-Washington VA-Wise.

&&

$$

DISCUSSION...CD
AVIATION...CD