321
FXUS64 KMRX 101137
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
637 AM EST Fri Jan 10 2025

...New AVIATION...

.SHORT TERM...
(Today and tonight)
Issued at 254 AM EST Fri Jan 10 2025

1. A winter storm will impact the area today into Saturday morning
with widespread accumulating snow. Snow may be mixed with sleet
and freezing across southeast Tennessee, southwest North Carolina
and far east Tennessee. Winter Storm Warning in effect for the
entire area.

2. Confidence is high for moderate to heavy snow accumulations
for areas west of interstate 81 and 75, and low to moderate east.

3. A mountain wave high wind event for the far east Tennessee
mountains and foothills for this afternoon and evening. Southerly
winds of 15 to 30 mph with gusts to 45 mph.

4. The downslope mountain wave winds will limit the snow
accumulations across the eastern side of the valley and foothills.

Discussion:

A complex and significant winter storm will move across the area
today through Saturday morning. Snow showers and flurries will
continue across the mountains and foothills of far east Tennessee
and southwest Virginia much of Saturday.

Bottom Line:

Lower confidence on snowfall amounts across the eastern Tennessee
valley, southeast Tennessee, and southwest Virginia due to
greatest potential of mixed precipitation of snow, sleet, and
freezing rain. Downslope winds off the far east Tennessee
mountains will produce compression warming over the east side of
the valley limiting snowfall there.

However, MOST IMPORTANTLY is to get the message out a significant
winter storm will effect the area today through Saturday morning.
A period of moderate to heavy snow is expected which will reduce
visibilities, cause Extremely difficut travel. The afternoon
commute across much of the area will be difficult.

Deterministic and Ensemble trends:

The deterministic and ensemble models are in pretty good agreement
with bringing a Miller-A type snowstorm will move across the area
today through Saturday morning. The main difference is that the
deterministic NAM, and higher resolution HREF and HRRR show
pressure falls on the lee of the far east Tennessee mountains due
to the strength of the 300mb jet. These pressure falls induce a
mountain wave across the mountains and foothills. The
compressional warming from the downslope winds will tend to warm
the east side of the valley/foothills and limit snowfall there.

Otherwise, a abnormally strong upper jet of 185 knots+ will move
across the Tennessee valley today. NAEFS tables shows the upper
jet about 2-3 standard deviations above normal. NAEFS also shows
fairly strong 850mb moisture transport into the southern
Appalachians.

The upper jet will produce good fronto-genetic forcing along with
isentropic lift into the region. Good dendritic snow growth is
noted as well along with several hours of CSI for snow banding
especially across southeast Tennessee, northern Plateau, western
half of the Tennessee valley and southwest Virginia.

Precipitation Types and Snow Amounts:

Confidence is high for mainly snow across the northern Plateau,
western half of the central and northern sections of the Great
Tennessee Valley into much of southwest Virginia. These is where 5
to 6 inches are expected with locally heavier amounts are
possible. The lowest confidence portion of this forecast is the
east side of the valley and southwest North Carolina. Enough warm
air advection may change the initial snow over the a wintry
mixture of snow, sleet, and possibly freezing rain. This wintry
mix may limit snow accumulations there.

Timing:

This is the highest confidence part of the forecast as models have
been fairly consistent for multiple days now with snow moving into
southeast TN around 12-15z and spreading east/northeastward
throughout the day, making it into southwest VA by 18z. Winter
precipitation will continue at a steady rate the rest of Friday and
into Saturday morning. The northwest flow Saturday will keep snow
showes and flurries going across the far east Tennessee mountains
and foothills, and southwest Virginia. Elsewhere Saturday, a
chance of flurries remains for Saturday.

Mountain Wave High Winds:

Due to a lee trough developing across the foothills this afternoon
in association with strong upper jet dynamics, pressure gradients
will tighten across the mountains producing a mountain wave event.
Southerly winds will increase to 15 to 30 mph with gusts to 45
mph.

&&

.LONG TERM...
(Saturday night through Thursday)
Issued at 254 AM EST Fri Jan 10 2025

Key Message:

1. A cold pattern will continue with flurries and/or light showers
possible early in the week.

Saturday Night through Monday

At the start of the period, the recent storm system will have pushed
off to our east with high pressure setting into the area.
Significantly cold temperatures can be expected due to subsidence
and assumed snow cover across much of the area. On Sunday, weak
ridging will be moving over the area with additional troughing off
to our northwest. This will keep a cold and dry pattern with daytime
heating likely sufficient to get most of the area to near or above
freezing. By Monday, upper troughing will flatten out slightly and
gradually move over the area with a very impressive 180+ kt jet set
up just to our north. Westerly to northwesterly flow and increasing
moisture will give another chance for flurries and light snow
showers across the region ahead of additional CAA.

Tuesday through Thursday

A similar overall pattern can be expected into Tuesday with 850mb
flow increasing to 25 kts or more. However, models differ on how
much moisture will be in place because of strong high pressure just
to our west. Additional troughing and northwest flow is indicated on
Wednesday with very strong (near 1040mb) high pressure arriving from
the west by Thursday. Moisture may be sufficient for lingering light
snow showers or flurries on Wednesday, but the bigger impact will be
a continuation of impressively cold temperatures. Many places will
likely stay at or below freezing all of these days with lows by
Thursday morning possibly reaching the single digits in some areas.
Essentially, snow that lingers and/or falls will likely remain in
shady places through these days.

&&

.AVIATION...
(12Z TAFS)
Issued at 618 AM EST Fri Jan 10 2025

Deteoriating flight conditions during the forecast period with an
area of snow developing (possibly mixed with sleet and freezing
rain across CHA) today. IFR/LIFR conditions are expected at CHA
and TYS today, eventually at TRI late today and this evening.
Winds will be light. Conditions will begin to improve to marginal
IFR/MVFR conditions toward daybreak Saturday.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             34  28  37  17 / 100  80   0   0
Knoxville McGhee Tyson Airport, TN  33  27  35  14 /  90  90   0   0
Oak Ridge, TN                       32  26  35  14 /  90  90   0   0
Tri Cities Airport, TN              34  27  32  14 /  90 100  20   0

&&

.MRX WATCHES/WARNINGS/ADVISORIES...
NC...Winter Storm Warning until 7 AM EST Saturday for Cherokee-Clay.

TN...Winter Storm Warning until 7 AM EST /6 AM CST/ Saturday for
     Bradley-East Polk-Hamilton-Marion-Sequatchie-West Polk.

     Winter Storm Warning from 10 AM EST /9 AM CST/ this morning to 7
     AM EST /6 AM CST/ Saturday for Anderson-Bledsoe-Blount
     Smoky Mountains-Campbell-Claiborne-Cocke Smoky Mountains-
     Grainger-Hamblen-Hancock-Hawkins-Jefferson-Johnson-Knox-
     Loudon-McMinn-Meigs-Morgan-North Sevier-Northwest Blount-
     Northwest Carter-Northwest Cocke-Northwest Greene-Northwest
     Monroe-Rhea-Roane-Scott TN-Sevier Smoky Mountains-Southeast
     Carter-Southeast Greene-Southeast Monroe-Sullivan-Unicoi-
     Union-Washington TN.

     Wind Advisory from 1 PM this afternoon to 9 PM EST this evening
     for Blount Smoky Mountains-Cocke Smoky Mountains-Sevier
     Smoky Mountains-Southeast Carter-Southeast Greene-Southeast
     Monroe-Unicoi.

VA...Winter Storm Warning from 10 AM this morning to 7 AM EST
     Saturday for Lee-Russell-Scott VA-Washington VA-Wise.

&&

$$

SHORT TERM...DH
AVIATION...DH