716
FXUS64 KMRX 151407 AAA
AFDMRX

Area Forecast Discussion...UPDATED
National Weather Service Morristown TN
1007 AM EDT Wed May 15 2024

...New UPDATE...

.UPDATE...
Issued at 950 AM EDT Wed May 15 2024

An upper trough axis will move across the southern Appalachians
today producing marginal instability with MLCAPE near 1000 J/kg.
Model soundings show a fairly saturated profile with mid-level
lapse rates are only around 6 degrees. WBZ heights are fairly low
ranging from 8500-9500 feet.

Effective shear is limited at best with only 20-25 knots. Enough
Hail CAPE to produce small hail with the stronger storms today.

Coverage of storms remains uncertain but do expect scattered
showers and thunderstorms.

Convection coverage will be greatest between 3 and 6 pm
diminishing toward sunset due to loss of daytime insolation.

Otherwise, mostly cloudy/partly sunny this afternoon.

For Tonight, we will re-evaluate the potential of fog development.
Plenty of low-level moisture so fog and low-clouds anticipated.
Some dense fog is possible.

&&

.SHORT TERM...
(Today and tonight)
Issued at 338 AM EDT Wed May 15 2024

Key Message:

1. Scattered to numerous showers and thunderstorms this afternoon
and evening. Although MRGL does clip small parts of eastern Tennessee,
not expecting any severe weather; a strong storm or two may be
possible with gusty winds and small hail.

2. Gradual clearing tonight will allow a window overnight of
possible fog development.

Discussion:

The upper low axis will be centered over us this morning as it
continues to move eastward. Two areas of low pressure exist; one
over the VA coast and the other over KY. The one in KY with an
additional front will be what provides today`s weather. Flow is
expected to become westerly to northwesterly with the passage of
the upper low, so upslope enhancement will be an additional
forcing mechanism across the terrain.

This doesn`t scream severe weather with this kind of set-up. The
HRRR and a couple other CAMS show precip being no more than
scattered. With CAPE values generally less than 900 J/kg and
effective shear struggling to reach 30 kt, feel pretty confident
that nothing more than a strong storm will occur today. Not to
mention, shear will be fairly unidirectional as well.

Tonight, precipitation will end for much of the area except
upslope areas of the Appalachians, plateau, and Cumberland
Mountains. Any clearing tonight, does increase the risk of fog
development with increasing subsidence.

&&

.LONG TERM...
(Thursday through Tuesday)
Issued at 338 AM EDT Wed May 15 2024

 Key Messages:

1. Showers and thunderstorms likely Friday and Saturday, possibly
lingering into Sunday.

2. Chances for severe storms exist on Friday and Friday night, but
there`s a good amount of uncertainty there.

3. Ridging builds in next week leading to temperatures climbing
above 80 across most of the Valley.

Discussion:

The period begins with upper ridging extending northward from
the central Gulf coast northward to the Tennessee valley on
Thursday. Expect dry conditions across much of the area beneath this
ridging. However some showers and thunderstorms may linger in our
Virginia counties and maybe down into the northern parts of the east
Tennessee mountains as a weakness in the ridge is noted over eastern
Kentucky thanks to a weak wave moving through the Midwest into the
Ohio valley during the day Thursday.

Friday into the weekend remains fairly uncertain, mainly with
respect to any severe weather chances we might have locally. There`s
good agreement that it will be an unsettled, and wet stretch. But
there is significant disagreement from deterministic guidance in how
this system will be handled. The previous long term forecaster had
this to say and I think it`s still a reasonable description of the
forecast. Some of the longer range models have come into slightly
better agreement on the positioning of the low, with the greatest
storm coverage across the Tennessee Valley down to the Gulf Coast,
but the severe parameters in forecast soundings are still a bit all
over the place. Things are currently trending towards the boundary
with strongest storms staying closer to the Gulf, but hopefully we
see multiple model runs confirm this as to help increase confidence
in storm strength over the weekend.

Depending on how Friday and Saturday unfold, it may arrive Sunday or
it may be Monday, but most guidance is in agreement with building
another ridge in from the west for some dry conditions and warming

&&

.AVIATION...
(12Z TAFS)
Issued at 741 AM EDT Wed May 15 2024

Out of all stations, CHA experienced the worst VSBY and CIGS
overnight down to LIFR. They should improve within the next hour
or two. The rest of the day, CIGS will avg MVFR heights. The chance for
showers and maybe a couple thunderstorms returns late this morning
and early afternoon as an additional front is expected to cross
the area. Not expecting anything severe. Winds no more than 10 KT
from a westerly direction, but could very well gust with a
thunderstorm. Models already ping at fog developing overnight once
precipitation exits to the east and we begin to clear out under
increasing subsidence. Have introduced it in this set of TAFs to
indicate the possibility. TRI hints at possibly the worst CIGS and
VSBY.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             78  61  85  63 /  60  20   0  10
Knoxville McGhee Tyson Airport, TN  74  61  80  60 /  80  30   0  10
Oak Ridge, TN                       75  60  82  60 /  80  30   0  10
Tri Cities Airport, TN              71  58  77  57 /  80  50  20  10

&&

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

$$

SHORT TERM...DH
LONG TERM....CD
AVIATION...KS