109
FXUS64 KMRX 041732
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
132 PM EDT Tue Jun 4 2024

...New AVIATION...

.UPDATE...
Issued at 1028 AM EDT Tue Jun 4 2024

The only change made to the forecast for today during the morning
update was bringing down afternoon highs by a few degrees mainly
in the Southern Tennessee Valley. Thick cloud cover is currently
over Middle and West Tennessee moving into East Tennessee. This
early onset of cloud cover is the reason for dropping the high
temps this afternoon. Showers are currently moving into Middle
Tennessee and NE Alabama. This activity will spread into our
region by this afternoon (sooner for the Southern Valley).
Scattered showers and thunderstorms are expected across the region
this afternoon and evening as an upper level trough approaches.
With low shear and low to moderate CAPE, severe potential will be
low but nonzero.

&&

.SHORT TERM...
(Today and tonight)
Issued at 309 AM EDT Tue Jun 4 2024

Key Messages:

1. Scattered to numerous showers and storms are expected to
traverse the forecast area this afternoon and through the early
evening. Cannot rule out a few strong storms with locally gusty
winds or heavy downpours but overall, general thunderstorm
activity will be predominant.

Discussion:

Recent SPC Mesoanalysis page depicts weak vort maxima`s swinging
through the region. Combined with lingering outflow boundaries, a
few weak showers continue to briefly sprout across southern
Tennessee and southwest North Carolina. This is expected to remain
light with a very low chance of a lightning strike or two through
the morning. Upper level clouds advecting ahead of a MCV over the
lower Mississippi River Valley will help limit fog this morning,
however, some patchy fog will be possible in typical sheltered
valleys and along rivers and bodies of water.

The aforementioned activity is expected to continue an eastward
track over the next 24 or so hours, with scattered to numerous
showers and thunderstorms expected to approach the Cumberland
Plateau around noon to shortly after. SPC HREF depicts MUCAPE will
generally increase to around or just slightly above 1000J/kg with
the return of afternoon heat. Thankfully, little to no synoptic
support means effective shear should remain less than 10kts and
really hinder the chances of any strong to severe organized
activity. A few stronger storms with gusty winds and locally heavy
downpours may occur but the overall severe threat is very low.
Hi-res models are in pretty decent agreement that coverage of
showers and storms will trend downward by the early evening hours,
though the overnight may not stay totally dry. Generally expect
temperatures to remain near normal for early June but the exact
timing & coverage of showers and storms could perhaps swing things
slightly cooler than forecast.

&&

.LONG TERM...
(Wednesday through Monday)
Issued at 309 AM EDT Tue Jun 4 2024

Key Message:

1) Highest POPs of the long term are on Wednesday, as widespread
showers and scattered storms move across the area. A strong storm or
two is possible, but most likely non-severe. Primary threats with
any stronger storm is damaging winds. Isolated flash flooding is
also possible, but low probability.

2) Drier and cooler Friday through Saturday.

3) Poor agreement in models from Sunday onward, but NBM has POPs
back in the forecast through the end of the extended.

Discussion:

Wednesday morning, a weak shortwave is moving across middle TN and
into our area. This means showers and a few storms will be around to
start the day. This wave is out ahead of an unphased trough (low to
our southwest and low to our northeast) moving in from the
Mississippi River Valley. The morning showers and storms should
produce enough cloud cover to limit instability through the day.
HREF probs of 1000 J/Kg SBCAPE during the afternoon hours are pretty
low and generally range from 20 to 30% chance. Because of this, I am
not too excited about any stronger storms, especially with the weak
mid to upper level flow across our area. However, if we do see some
clearing and can generate some instability, then a few strong storms
will be possible. The primary threat will be damaging winds. NAM
soundings show PWATS of 1.6 to 1.8 inches, which is around the 90
percentile based on BNA sounding climatology. So some areas may see
some heavy rainfall, which may lead to isolated flash flooding. This
corresponds with WPC`s ERO of Marginal across our area for
Wednesday.

Showers and storms continue Wednesday night into Thursday morning as
the aforementioned unphased trough swings through. LLJ increases to
around 30kts during this time, so breezy winds are expected across
our highest terrain areas (above 5000 feet) with wind gusts up to 30
mph. Drier air begins to build into the region by late Thursday
morning with sunshine for most by mid afternoon. Deep mixing is
expected during the afternoon hours with the drier air moving in and
wind gusts up to 20 mph expected for all locations. Similar wind
gusts expected on Friday afternoon for the same reason.

Northwest flow will be in place behind the trough, leading to cooler
and drier conditions through Saturday. Highs and lows will be around
5 degrees below normal. With dewpoints in the 50s, it will be quite
pleasant. Beyond Saturday, models are in poor agreement on the large
scale pattern but NBM POPs return Sunday and remain through the end
of the period.

&&

.AVIATION...
(18Z TAFS)
Issued at 120 PM EDT Tue Jun 4 2024

Scattered showers and thunderstorms are expected this afternoon
and evening. Shower and storm activity on radar is currently
increasing near all 3 terminals. Overnight and early morning,
shower and storm activity will likely be more isolated but a stray
shower or storm cannot be ruled out. By mid to late morning
tomorrow shower and storm activity will be increasing along with
southwesterly winds. MVFR CIGs are possible in the early morning
hours but confidence is fairly low.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             69  86  69  88 /  40  80  70  20
Knoxville McGhee Tyson Airport, TN  67  83  68  85 /  40  80  90  20
Oak Ridge, TN                       67  82  66  86 /  40  80  80  20
Tri Cities Airport, TN              63  81  66  81 /  40  80  90  30

&&

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

$$

SHORT TERM...McD
AVIATION...McD