315
FXUS64 KMRX 131903
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
303 PM EDT Sat Jul 13 2024

...New SHORT TERM, LONG TERM...

.SHORT TERM...
(This evening through Sunday)
Issued at 300 PM EDT Sat Jul 13 2024

Key Message:

1. Hot and mostly dry weather continues.

Discussion:

Upper-level ridge continues across the Southeast CONUS with weak
troughing across the Mississippi Valley. Low-level 850mb ridge
remains centered across the Midsouth with 21C to 23C temperatures
across the Tennessee Valley and Southern Appalachians. This is also
limiting northward moisture transport across the region which is
keeping RH values lower and limiting convection each afternoon. This
will produce mostly dry weather across the region with some low 10
to 20 percent chances of weak diurnal convection across the higher
terrain. This is a pretty consistent persistence pattern for the
next couple of days.

&&

.LONG TERM...
(Sunday night through next Saturday)
Issued at 300 PM EDT Sat Jul 13 2024

Key Messages:

1. Dangerous, near record heat is expected Monday and Tuesday with
temperatures near 100 degrees and heat index values reaching around
105 degrees, especially on Tuesday.

2. Rain chances are limited until late in the week, which will also
be when temperatures cool off significantly.

Sunday Night through Wednesday

At the start of the period, quasi-zonal flow will be in place aloft
with anomalously high 500mb heights around 5,920 meters. At the
surface, high pressure will be in place across much of the eastern
U.S. Very impressive warming in the lower levels is indicated by
850mb temperatures of 21 to 22 Celsius to begin the period, values
that are just below daily maximum high values. As such a dry and
mild night will begin the period with similar conditions remaining
in place for the day on Monday. Overall moisture will still be
fairly limited with efficient mixing likely dropping dew points to
around 60 degrees, which will limit how high heat index values
reach. However, the continued dryness and impressive low-level heat
strongly suggest dangerously high temperatures, possibly to the
highest that we`ve seen since the record heat wave of 2012, i.e. 100
degrees through the southern and central Valley. A stray shower or
storm can`t be ruled out, but the chances are certainly very limited.

On Tuesday, a very weak closed low is noted to our southwest that
will move towards the area with surface high pressure starting to
break down to our south, producing a more southerly shift in winds.
850mb temperatures will remain similarly near record high values
with an increase in humidity from Monday. This means temperatures
will likely stay just below Tuesday`s, but the increase in humidity
will produce equally dangerous heat with heat indexes upwards of 105
degrees. With this increase in moisture, chances for convection will
increase but still be limited outside of the higher terrain.

On Wednesday, we continue to see a breakdown of high pressure and
upper level ridging with a cold front approaching from the Ohio
River Valley. There are still timing differences, but the trajectory
and height falls certainly suggest more substantial convection
chances, especially further north. This will hopefully provide some
relief to the extreme heat, as well as much needed rainfall.

Daily Record High Maximum Temperatures

Date    Chattanooga    Knoxville      Tri-Cities     Oak Ridge
07-14   103(1954)      101(1954)      98(1954)       101(1954)
07-15   103(1977)      98(1995)       96(1995)       100(1980)
07-16   105(1980)      100(1980)      100(1988)      103(1980)
07-17   103(1980)      101(1980)      94(1980)       103(1980)

Thursday through Saturday

Late in the week, the region will remain in a troughing pattern with
the main question being how far south the aforementioned frontal
boundary reaches. It could get hung up across the area or possibly
even move further to the south. This will keep continued chances for
much needed rain, but this will certainly depend on where the
frontal boundary ends up and how much moisture remains in the area.
In any case, temperatures will certainly be a lot cooler than the
days before heading into the weekend. The worsening drought may
continue to limit development, especially after the extreme heat.

&&

.AVIATION...
(18Z TAFS)
Issued at 1216 PM EDT Sat Jul 13 2024

VFR conditions are forecast to continue through the forecast
period with light winds and a few afternoon clouds near 5k ft. Low
precip chances are present across the mountains (about 10 percent)
but this is not expected to impact terminals.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             73  99  75 100 /   0  20   0  20
Knoxville McGhee Tyson Airport, TN  72  96  73  98 /   0  10   0  20
Oak Ridge, TN                       71  96  72  98 /  10  10   0  10
Tri Cities Airport, TN              66  93  69  95 /   0  10   0  10

&&

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

$$

SHORT TERM...JB
LONG TERM....BW
AVIATION...JB