MRX disco
858
FXUS64 KMRX 072021
AFDMRX
Area Forecast Discussion
National Weather Service Morristown TN
321 PM EST Tue Jan 7 2025
...New SHORT TERM, LONG TERM, AVIATION...
.SHORT TERM...
(This evening through Wednesday)
Issued at 320 PM EST Tue Jan 7 2025
Stubborn clouds are slowly eroding across the Valley but may try to
return overnight. Otherwise, cold temperatures will maintain their
grip on the area tonight and Wednesday, with Valley highs again
mainly in the 30s. Expecting any overcast morning clouds to scatter
out around midday.
A mostly zonal pattern aloft will do little to dislodge the cold
surface air, but a weak disturbance may touch off some flurries
Wednesday afternoon and evening across SW VA.
&&
.LONG TERM...
(Wednesday night through next Tuesday)
Issued at 320 PM EST Tue Jan 7 2025
.LONG TERM...
Key Messages:
1. Confidence is strongly trending in favor of a significant winter
storm across the southern Appalachian region, with widespread
accumulating snow possible over the forecast area Friday into
Saturday.
2. Some uncertainties remain though - especially with regards to
amounts. Time will bring those details into focus however.
Discussion:
The main focus for the long term is the potential for widespread
heavy snow on Friday and Saturday, so the discussion will
concentrate on that as the remainder of the period is uneventful.
Thursday and Thursday night, an upper ridge will be situated from
the Great Lakes southward through the Ohio valley and into the
central Gulf coast, with surface high pressure over the southern
Appalachian region. Thursday afternoon through Friday a southern
stream upper low/trough shifts east from New Mexico and west Texas,
while a northern stream disturbance moves into the upper midwest
from Canada, resulting in a strong Gulf Coast surface low and
a widespread winter weather event for the southeast CONUS.
Timing:
Thursday night lows will be in the teens to low 20s, with dewpoints
firmly in the teens if not single digits, so cold air will be
entrenched across the region to start the day Fri and precip should
start/continue as snow through the event. Sometime after daybreak
Friday, the precip shield with the developing system should be
spreading our direction from MS/AL, with snowfall likely arriving by
the mid morning hours in the Chattanooga area, midday towards the I-
40 corridor, and early afternoon in the north. Ending time looks to
be roughly 4-6 AM or so in the south, and something closer to 8-10
AM in the north. The end times could be a little premature as we
transition to a northwest flow regime Saturday on the backside of
the system, but as far as impactful snow accumulations in the lower
elevations go, those times are probably good estimates at this time.
Precip types:
The forecast reflects snow, or perhaps a few short-lived periods of
rain/snow mix, across the CWA at this time. Areas of possible
rain/snow mix at the beginning would be in the foothills of the TN
mountains as H85 flow comes over the Appalachians and warms on it`s
decent into the valley. That`s reflected in the H85 temps on some
models, but also worth noting that they`re still at/slightly below
freezing, so I think snow is the only ptype we`ll have to worry
with. If the track of the system changes, ptypes could as well, but
at this point it appears we will be dealing with only snow
Snowfall amounts:
The trends in ensemble guidance over the last 24 hours have been
upward with regards to amounts in general, and that`s especially so
with regards to probabilities of amounts greater than 4" or even 6".
First off, previous forecasts had favored a relative maxima of
snowfall amounts being in the southern valley, and lesser amounts in
the north. The trends have been to favor a spreading out of those
higher amounts across much of the CWA, with guidance now suggesting
that a widespread 3-5" snowfall is possible across the forecast
area. Additionally, the 24hr probabilities of seeing great than or
equal to 6" of snow by 7 AM Saturday have come up to non-dismissible
levels now, with some +40 percent odds across significant portions
of the CWA. All of that said, it`s still too early to really hone in
on a particular value/range as the track of this system will have
significant impacts on amounts. Suffice it to say that confidence in
a widespread winter weather event is definitively trending higher.
&&
.AVIATION...
(18Z TAFS)
Issued at 320 PM EST Tue Jan 7 2025
MVFR to VFR conditions expected at the sites, with best chance for
MVFR overnight, scattering out to VFR during Wednesday.
&&
.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN 23 38 19 39 / 0 0 0 0
Knoxville McGhee Tyson Airport, TN 19 34 15 34 / 0 0 0 0
Oak Ridge, TN 19 34 15 34 / 0 0 0 0
Tri Cities Airport, TN 18 29 13 28 / 0 0 0 0
&&
.MRX WATCHES/WARNINGS/ADVISORIES...
NC...NONE.
TN...NONE.
VA...NONE.
&&
$$
SHORT TERM...GC
LONG TERM....CD
AVIATION...GC
