-- Discussion containing changed information from previous version are highlighted. --
618
FXUS64 KMRX 070509
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
109 AM EDT Tue May 7 2024

...New AVIATION...

.UPDATE...
Issued at 1120 PM EDT Mon May 6 2024

The threat for strong or severe storms has pretty much
deteriorated for the night. Some light to moderate showers
currently exist over far NE TN, SW VA, and parts of the valley.
Lightning activity is east of the Appalachians into the Piedmont
of Virginia and lower elevations of North Carolina. The southern
valley and plateau will likely continue to remain dry for the rest
of the night.

Immediate forecast was changed to reflect current and future
radar trends the next 8 hours. PoPs were either removed or
downgraded for the western part of the CWA. Hourly forecast
updated to reflect the same current and future trends.

There may also be a chance for fog development overnight,
especially areas that saw precipitation today. Patchy dense fog is
possible, so be cautious if you have to drive overnight or very
early tomorrow morning.

KS

&&

.SHORT TERM...
(This evening through Tuesday)
Issued at 244 PM EDT Mon May 6 2024

Key Messages:

1. Scattered to numerous showers/storms this afternoon/evening will
diminish later tonight. A few storms mainly southern half may be
strong to severe this afternoon/evening.

2. Scattered showers and storms expected again Tuesday, with a few
strong to severe storms possible again mainly in the afternoon.

Discussion:

We will start the period with an MCV moving in from the west. We
will see additional showers and thunderstorms this afternoon into at
least the early part of tonight, with the greatest coverage likely
to be across the central and north with the better forcing. However,
the best instability and bulk shear will overlap across the south
into central areas late this afternoon and evening, so a few storms
especially south/central may become strong to severe with strong
gusty winds and hail the main threats. Isolated supercellular
structures also look possible in this environment, so there also is
a very low risk of a brief tornado this afternoon/early evening
again mainly southern half. Some isolated to scattered convection
may linger for much of the night mostly north although this should
be weaker as convective energy lessens.

Tuesday will see short wave ridging over the area although the axis
will shift to our east during the day. Convective energy will build
with heating and most sources indicate MLCAPES are likely to peak in
excess of 1,500 J/kg with deep-layer shear reaching at least 30 to
35 kts.  Overall model guidance including the CAMS suggests more
isolated to scattered coverage, but given the thermodynamic and
shear profiles there is a threat that some storms will become severe
with damaging winds and large hail again the primary threats.

&&

.LONG TERM...
(Tuesday night through next Monday)
Issued at 244 PM EDT Mon May 6 2024

Key Messages:

1. Unsettled weather with potential for strong to severe
thunderstorms most likely late Wednesday. Increasing potential for
isolated flooding in saturated locations.

2. Cold front to pass through Friday morning, with a cooler airmass
settling in through the weekend.

Discussion:

Unsettled atmosphere continues, with not much changes from the
overall thinking the last couple of days. Weak shortwave ridge will
be headed out Tuesday night from the region, and a dual jet streak
setup will be hanging over the central US, with a stronger polar jet
to the north and a weaker subtropical jet nosing in across Texas
into northern Mississippi. The largest question Tuesday night
through Thursday is when do storms form and move into East Tennessee
and surrounding areas. Long range CAM guidance is just moving into
range for Tuesday night. There`s some questions given the expected
ridge in the short term period, but convection may redevelop in the
evening across portions of the area, most likely Virginia and to our
north and northeast. If convection does fire and then move in,
there`s enough shear by this time to support a severe storm, but the
biggest question will be if a storm can translate that to the
surface, given nighttime loss of instability and low level stability
questions.

Wednesday is a big unknown daytime. The shear and instability should
be present, but the last ingredient is lift and that seems to be
lacking. The high res NAM is just within range and it doesn`t show
much activity aside from an errant left splitter. The larger global
guidance does have some thunderstorm activity during the day on
Wednesday, with the GFS and its ensemble being particularly
aggressive, and the Euro ensemble more conservative. Should those
more conditional storms fire, environment would be conducive to
severe wind and hail. On a wider view, thunderstorms are expected to
fire out over the Ohio River to Mississippi River intersection, and
should grow upscale with time. These storms are higher confidence in
origination and formation, and will move our direction heading into
Wednesday night. Still, plenty of questions on when exactly they
reach our area and how much instability will be present then. The
most likely risk would be with damaging straight line winds in these
storms. Assuming an overnight arrival (based off current guidance),
low level instability could be hard to come by if an inversion sets
up before the line arrives.

Timing arrival of the potential MCS or linear system will then
influence how much recovery can take place into Thursday to allow
for a final round of showers and thunderstorms. Stronger storms look
to remain to the southeast of Tennessee outside our area on
Thursday. Last thing of note to mention is high PWATs combined with
the several days of thunderstorms and an expected MCS Wednesday
night is still consistent with the potential for isolated flooding.
Thus far storm coverage has been intermittent enough to allow for
efficient runoff, but flash flood guidance has dipped a bit,
especially in northeastern Tennessee where 3 hour guidance has
dipped to 2 inches. Locations that receive repeated rounds of
thunderstorms may see minor or urban flooding issues.

Finally we get to the high confidence portion of the forecast. The
GFS and Euro are in agreement (and their ensembles seem to match
closely as well) with a cold front passing through the region on
Friday morning. In association with the frontal passage, a longwave
trough will settle in over the Eastern United States on through the
weekend, 850mb temperatures are in the single digits in both sets of
guidance. Checking Nashville sounding climatology, this is good for
the 10th to 25th percentiles for this time of year. End result is
this airmass will result in rather pleasant afternoons for the wider
region! Shower chances are fairly low (20 to 30%) at this range over
the weekend, and will come down to how much lift the rotating
shortwaves in the overall trough can help generate showers. Apart
from the potential for scattered showers, the weekend will be
pleasant and calm.

&&

.AVIATION...
-- Changed Discussion --
(06Z TAFS)
Issued at 1259 AM EDT Tue May 7 2024

Currently late this evening, showers and a few isolated
thunderstorms continue to shift off to the east with most of the
area expected to stay dry overnight. Fog and/or low clouds will be
a focus for TYS and TRI with impacts not expected at CHA.
Currently, mention of MVFR was included for TYS and TRI, but lower
reductions are possible. By the sunrise, improvements will be
slower at TRI as a few additional showers may develop across the
area. Otherwise, the sites should all reach VFR conditions by
mid-day with the main uncertainty being where and when additional
storms develop in the afternoon and early evening hours. CHA`s
chances for this look to be more towards the evening hours as
earlier activity is indicated to be further north.
-- End Changed Discussion --

&&

.PRELIMINARY POINT TEMPS/POPS...
-- Changed Discussion --
Chattanooga Airport, TN             69  87  68  85 /  60  60  80  70
Knoxville McGhee Tyson Airport, TN  67  83  67  80 /  60  50  80  70
Oak Ridge, TN                       66  83  66  82 /  60  60  80  70
Tri Cities Airport, TN              64  81  63  77 /  60  50  70  70
-- End Changed Discussion --

&&

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

$$

SHORT TERM...
LONG TERM....Wellington
AVIATION...BW