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863
FXUS64 KMRX 090227 AAA
AFDMRX

Area Forecast Discussion...UPDATED
National Weather Service Morristown TN
1027 PM EDT Sat Jun 8 2024

...New UPDATE...

.UPDATE...
-- Changed Discussion --
Issued at 1016 PM EDT Sat Jun 8 2024

Little changes to ongoing forecast. West to northwest flow aloft
will continue to pull a series of weak disturbances across the
Tennessee valley. A MCV over MO/AR will spread a good deal of
high-mid level clouds back into the region early Sunday morning.
Initally was expected some scattered showers by around daybreak
Sunday due to isentropic lift but MCV may limit this forcing.

A frontal boundary will move into the region Sunday afternoon
acting a focus for scattered showers and storms.
-- End Changed Discussion --

&&

.SHORT TERM...
(This evening through Sunday)
Issued at 258 PM EDT Sat Jun 8 2024

Key Messages:

1. Outside chance of a light shower through this evening, but
otherwise dry through tonight.

2. Active, thunderstorm day expected tomorrow, including a risk of
some severe storms.

Discussion:

Regional satellite and radar imagery show an MCV moving east
through central Kentucky this afternoon, with some light returns
on radar stretching southward into middle Tennessee and even the
northern plateau areas. Surface obs show that any rainfall at all
from those returns is very sparse, much less there being
measurable rain to be had. Thus, continue to think that the
mention of sprinkles that we have in the forecast for much of the
northern half of the CWA through this evening is sufficient to
cover. Further west in TN there is some more noteworthy convection
developing along the I-40 corridor, but this is moving ESE and
should clear our CWA to the south tonight. Overall, expect dry
conditions through the evening and overnight hours.

This changes tomorrow however. In a recent series of upper lows
parading eastward through the Great Lakes region, another one
strengthens to the north of Lake Huron tonight into Sunday
morning. A surface front associated with this feature will drop
south out of the Ohio valley towards our forecast area during the
morning hours tomorrow. It appears there will be multiple rounds
of convection associated with front tomorrow. The first will be
the remnants of an MCS that will develop over the Ozarks later
tonight, and arrive in our neck of the woods during the mid-
morning hours. Additional rounds of convection are expected
through the day tomorrow. SPC has an elongated marginal risk area
stretching roughly along and south of the I-40 corridor from
Arkansas eastward through Tenn and into the Carolinas. HREF CAPE
probabilities show very high odds (80-90 percent) chances of
seeing upwards of 500 J/kg surface-based CAPE values during the
day tomorrow, and even high chances (70 percent) of seeing over
1,000 J/kg as well, for areas south of I-40. When it comes to
severe weather potential, effective shear values of 30-45kt across
the CWA in concert with those instability figures will support
some organized convection capable of damaging wind gusts.
Uncertainties about the evolution of morning convection and how
that affects instability later in the day remain fairly high.
However it`s worth noting that SPC has language in their current
Day 2 outlook regarding possible upgrade to a slight risk category
for portions of the TN valley, so there is some concern that some
severe storms could develop. But again, uncertainties remain.

&&

.LONG TERM...
(Sunday night through next Saturday)
Issued at 258 PM EDT Sat Jun 8 2024

Key Messages:

1. Cooler than normal Monday and Tuesday following the cold front.
Trending warmer again mid-week onward with valley highs approaching
90 by the week`s end.

2. Tuesday looks to be mostly dry, but Wednesday onward isolated to
scattered showers and thunderstorms return each day, increasing in
probability during the afternoon and early evening hours.

Discussion:

We begin the period Sunday night with decreasing precipitation
behind the cold front. Drier air and cooler than normal temperatures
can be expected Monday and Tuesday. Out of the whole week, later
Monday into Tuesday looks to be the driest period with just an
outside chance of a shower or thunderstorm over parts of the eastern
mountainous terrain.

Following Tuesday, the trough will kick to the east and high
pressure at the surface and aloft will build in. The flow aloft is
expected to be weak for a couple of days. With increased heat mid-
week onward, chances for diurnal showers and thunderstorms
will increase.

Beyond Wednesday starts to become a bit fuzzy as a potential low
cutting off from the flow over the Midwest, locates itself over the
Gulf. This may be a source of increased moisture and chances of
seeing precipitation towards the end of the week as well as
diurnally driven convection. Within the rather weak flow, heights
will continue to rise leading to high temperatures potentially
reaching the low 90`s in the valley the end of the week.

&&

.AVIATION...
(00Z TAFS)
Issued at 656 PM EDT Sat Jun 8 2024

Main question is timing of convection for Sunday. Currently
anticipated first round of showers to move across the TAF sites
in the morning due to isentropic forcing. As the frontal boundary
moves south across east Tennessee late in the afternoon widespread
showers and storms will move across the region.

Areas of high and mid-level clouds through early Sunday morning
but increasing boundarly layer moisture/isentropic lift will
produce some marginal MVFR conditions at TRI and possibly TYS by
late morning.

Winds will be mainly west to southwest 5 to 15 mph with strong
gusts especially with convection.

&&

.PRELIMINARY POINT TEMPS/POPS...
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Chattanooga Airport, TN             68  87  64  83 /  30  50  30  10
Knoxville McGhee Tyson Airport, TN  68  82  61  79 /  20  60  30  10
Oak Ridge, TN                       67  81  59  79 /  30  60  30  10
Tri Cities Airport, TN              61  79  56  76 /  10  60  30  10
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&&

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

$$

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