216
FXUS64 KMRX 161718
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
118 PM EDT Tue Jul 16 2024

...New AVIATION...

.UPDATE...
Issued at 1109 AM EDT Tue Jul 16 2024

Low-level deformation zone across the region has resulted in a few
areas of showers and thunderstorms developing along this axis.
This scattered activity will continue into the afternoon, and we
may also begin to see some additional isolated diurnal convection
across the higher terrain. In areas that are receiving rainfall
mid-day, this will likely result in slightly cooler afternoon max
temperatures, but with added humidity, heat index values will
still be into the 90s and lower 100s.

JB

&&

.SHORT TERM...
(Today and tonight)
Issued at 323 AM EDT Tue Jul 16 2024

Key Messages:

1. Isolated to weakly scattered showers and storms this afternoon.

2. Continued hot temperatures with heat indices in the upper 90s
to lower 100s.

Discussion:

Currently, an upper disturbance is owing to increased troughing
across portions of the mid-west, with on going convection across
Indiana and Illinois well ahead of a surface boundary. We will
remain displaced enough from primary forcing that just the typical
diurnally driven isolated to scattered convection is expected this
afternoon. HREF ensemble members generally depict around 1500-2000
J/kg MLCAPE for the afternoon hours among almost no shear. Latest
RAP soundings suggest DCAPE will reach around 1000-1200 J/kg
during peak mixing hours. Given the above, a few stronger storms
with locally gusty winds cannot be ruled out but the overall
threat for any severe storms is quite minimal at this time.

We continue to expect another afternoon with unseasonably hot
temperatures, with heat indices in the upper 90s to lower 100s
across much of the area. There is a tad bit of uncertainty with
this however, as a handful of models such as the HRRR, GFS, and RAP
suggest we mix out quite well and dewpoints may even struggle to
reach 70 degrees(The current forecast weighted with NBM10th
percentile has Td generally in the low 70s). It is possible that a
few isolated areas approach 105 degree Heat Index like the past
few days but don`t believe it is widespread enough to justify a
heat advisory at this time, especially given the aforementioned
uncertainty.

We see a lull in activity during the late evening/early overnight
hours before a frontal boundary approaching from the northwest
brings increased forcing and a return of some showers and storms
early Wednesday morning. However, the bulk of the activity will
occur throughout Wednesday and more information on this can be
found in the long term discussion below.

&&

.LONG TERM...
(Wednesday through Monday)
Issued at 323 AM EDT Tue Jul 16 2024

Key Messages:

1. A frontal passage will bring widespread showers and storms across
the area Wednesday into Thursday.

2. A break from the heat is expected behind the frontal passage,
with slightly below normal temperatures from Thursday through
Tuesday.

Discussion:

Wednesday, a deep upper level trough and associated cold front
approach from the northwest. A few showers and storms are expected
to be ongoing Wednesday morning ahead of the front. Then, coverage
increases around mid day as surface heating increases and forcing
becomes stronger as the front draws closer. With good moisture and
forcing, this will be the best chance of widespread rain we have
seen in quite some time. As far as storm potential, not seeing
anything too concerning at the moment. However, a few strong storms
are possible due to an increase in shear, around 20kts, with the
approaching trough. The main threat will be isolated damaging
straight line winds. Overall though, severe weather is not expected
at this time.

The big forecast question is how far south does the frontal boundary
push by Thursday. If it is still in the vicinity expect another day
of widespread showers and storms. However, if it pushes too far
south then the bulk of the precip will be to our south and we will
be much drier. NBM POPs suggest the front is still in the vicinity
Thursday so will continue with that trend for now. Storm total QPF
between Wednesday and Thursday has most locations around 1 inch of
rainfall.

Beyond Thursday, precip chances remain elevated but with no distinct
features moving through the flow. The elevated precip chances are
due to higher than normal moisture values across the area due to a
strong area of high pressure across Bermuda. This high placement is
conducive for Gulf moisture streaming into the southeastern U.S.
Precip during this timeframe will be diurnally driven. The other
good news is that temperatures will be slightly below normal during
this time as well. High temps will generally be in the mid 80s. The
coolest day is Friday, with temps in the lower 80s.

&&

.AVIATION...
(18Z TAFS)
Issued at 116 PM EDT Tue Jul 16 2024

Scattered showers and thunderstorms continue in the vicinity of
terminals this afternoon. With residual outflow boundaries across
the region and increasing boundary layer convergence this evening
into the overnight hours, there remains 20 to 30 percent or
greater probabilities for convection in the vicinity of terminals
overnight. However, outside of convection VFR conditions will
prevail with light SW/WSW winds.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             75  95  73  89 /  20  80  70  90
Knoxville McGhee Tyson Airport, TN  75  93  72  85 /  50  80  80  80
Oak Ridge, TN                       74  92  71  84 /  40  80  80  80
Tri Cities Airport, TN              71  91  69  81 /  70  90  80  80

&&

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

$$

SHORT TERM...KRS
AVIATION...JB