Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN

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FXUS64 KMRX 290654
AFDMRX

AREA FORECAST DISCUSSION
National Weather Service Morristown TN
254 AM EDT Sun Mar 29 2020

.SHORT TERM...(Today and Tonight)...

Main focus of the period is the approaching line of showers and
storms that are moving out of middle TN. This line has shown an
overall decrease in intensity over the past several hours but there
are still a few embedded strong-to-severe storms within the line
across middle TN and stretching down into northern AL. Though there
has been an overall decrease in intensity there has been an uptick
in lighting strikes over the past hour as a strong segment within
the line has developed over southern Middle TN. Based on HI-Res
model trends, still expect a few strong embedded thunderstorms
within this broken line segment as it enters our area and a severe
thunderstorm warning or two isn`t out of the question. We have very
little instability in place at the current hour but the models
slightly increase instabilty just ahead of the front and with the
arrival of the line. Even with the increase though, instability
values will max out around 500 J/kg MLCAPE and SBCAPE at best. Due
to the deep layer sheer in place, and still impressive shear values
in the lowest levels, we will have to closely monitor these storms
as they move toward adn into the area.

It still looks like the Cumberland Plateau counties will have the
best chance at seeing any of these strong-to-severe storms.
Isolated damaging wind gusts are possible with any of the stronger
line segments as well as nickle-to-quarter sized hail. An
isolated weak tornado still can`t be ruled either. Based on radar
trends and time of arrival tools, it looks like the line will
arrive onto the plateau between 0730 and 0830Z.

Once storms move off the plateau and into the valley, the broken
line segment further weakens and becomes even more discontinuous
according to the models. During this time it`s still possible that a
few damaging wind gusts and small hail are observed but chances
decrease the further east this line moves. Once the line gets east
of I-75 it really falls apart.

Drop off POPs pretty quickly between the mid and late morning hours
with all areas but the far eastern mountains dry by late
morning/early afternoon. Clearing skies are expected behind the
front with plenty of sun by the afternoon hours. Highs will max out
in the low to mid 70s. Gusty westerly winds from 20 to 30 mph will
be observed behind the front. Winds will calm overnight to around 5
mph and clouds will slowly increase late in the night. Overnight
lows will be in the upper 40s to low 50s.

SR

.LONG TERM...(Monday through Saturday)...

Models continue to be in decent agreement overall through mid
week, but poor run to run consistency and agreement late leads to
quite a bit of uncertainty for the latter periods.

Monday will be dry with above normal temperatures as surface high
pressure will be over the region. A mid/upper level trough will move
out of the central Plains and across our area Monday night through
Tuesday night.  The associated surface low is still forecast to
track by to our south. This system will bring rain to the area, but
with the southerly track convective energy is forecast to be
lacking, so thunder chances look low. Colder air will be moving in
on the back side of this system, and there is the possibility of
some snow flakes mixing in over the highest mountains before the
precipitation ends.  This precipitation will decrease from southwest
to northeast Tuesday night, and a few showers may linger into
Wednesday morning over the northeast before the last of the
precipitation ends.

Thursday will likely be dry as models now show upper ridging moving
across and surface high pressure extending into our area.  At some
point some weak short wave energy is forecast to move across and a
weak frontal boundary is expected to push in from the west. However,
model agreement and run to run consistency is lacking, and with
these weaker features that is common this far out.  For now will
include low PoPs in the Thursday/Friday time frame.

LW

&&

.AVIATION...
06Z TAF DISCUSSION.

A line of showers and storms will move into the valley between 08
and 10Z, affecting CHA and TYS. Once the line arrives, have a
tempo for MVFR conditions in at both terminals. Left VCTS out of
TYS as there may not be any thunder by the time the line moves
that far east. Once the line passes through during the late
morning hours, CIGs will begin to lift and skies will scatter out
by afternoon. TRI should stay VFR through the period as the line
of showers will be quite weak by the time it arrives. Gusty winds
behind the front are forecast at both TYS and TRI with gusts
ranging from 20 to 30kts from out of the west.

SR


&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             76  53  71  52  58 /  40  10  10  50  90
Knoxville McGhee Tyson Airport, TN  77  51  70  49  55 /  60   0  10  20  90
Oak Ridge, TN                       76  49  70  49  54 /  60   0   0  20  90
Tri Cities Airport, TN              76  45  69  44  54 /  40   0  10  10  90

&&

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

$$


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