763
FXUS64 KMRX 192322
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
722 PM EDT Fri Jul 19 2024

...New AVIATION...

.SHORT TERM...
(This evening through Saturday)
Issued at 312 PM EDT Fri Jul 19 2024

Key Messages:

1. Some places will likely remain rain free, but rain chances
continue to improve through the short term as multiple rounds of
showers and thunderstorms are expected.

2. Continue below normal temperatures will continue.

Discussion:

Main concern for the short term period is timing of shower and
thunderstorm activity. Overall, we`ll remain situated on the eastern
side of a trough positioned over the lower and mid-Mississippi river
valley region. Embedded in that trough will be shortwave activity
lifting northeast out of the central Gulf states and moving through
the Tennessee valley. This is expected to drive multiple rounds of
convection over the next 24 hours or so. Currently have one of these
impulses moving into the TN valley from the southwest, another is
expected around or shortly before daybreak tomorrow, and finally we
should see more diurnally driven convection tomorrow afternoon.

Nothing looks terribly concerning in terms of severe weather or
flash flooding. Forecast soundings do show deep layer shear,
instability, or downdraft CAPE values that are supportive of severe
type convection, with surface based CAPE values forecast to be only
around 1000 J/kg, and DCAPE less than 500 J/kg. PWATs will be
increasing tonight and tomorrow and storm motions are weak. Thus
storm propagation will likely be focused on outflow boundary
interactions. As such, if a storm maintains itself for a prolonged
period of time it`s conceivable there could be a very isolated flash
flooding threat this afternoon or tomorrow. But all in all that
threat even appears low given the ongoing drought conditions.

Otherwise, we`ll continue to get a break from the oppressive heat,
with forecast highs remaining below seasonal norms tomorrow.
Considered undercutting NBM guidance by a degree or two for
tomorrow`s highs as upstream readings this afternoon have been stuck
in the 70s. Given the expected cloud cover tomorrow as shortwave
activity shifts north to the TN valley, I wouldn`t be surprised to
see some valley highs nearer to 80 degrees versus norms of mid to
upper 80s. Hard to say where that would be though, and any prolonged
sunbreaks would allow for temps to climb quickly so the NBM
guidance, which is already 4-6 degrees below normal, was fine.

&&

.LONG TERM...
(Saturday night through next Friday)
Issued at 312 PM EDT Fri Jul 19 2024

Key Messages:

1. An unsettled weather pattern will persist through the long term
with daily chances for showers and thunderstorms.

2. Slightly below normal temperatures expected through the extended
forecast.

Discussion:

A pretty pronounced closed upper low will encompass eastern Canada
much of the long term with troughing over our area of the country,
while ridges dominate the desert SW and the western Atlantic. With
this pattern, low level SWly flow will be the persistent/dominate
direction. In other words, SWly flow and lower heights will mean
increased humidity, lower than normal temperatures, and
afternoon/evening convective instability. A stationary front draped
to our southeast and another developing to our northwest next week,
will also contribute to daily chances of showers and thunderstorms.
This will also keep cloud cover around, limiting our daytime highs
to the 80s. Even with decreased temperatures, dew points in the 60s
and 70s will make it feel much hotter.

Any rainfall will be welcome of course with the drought conditions
we have in place. Precipitation totals for the entire long term show
many locations receiving 1.5 to 2.5 inch range with the Appalachians
possibly reaching 3 to 4 inches of accumulated rainfall. MRGL ERO`s
are in place the next couple of days, but it would take a short-
lived storm with heavy rain rates to reach any sort of flooding
potential. PWATs will range between 1.5 to 2.0 inches, portraying
how water loaded the atmosphere is and will support prolific rain
makers.

&&

.AVIATION...
(00Z TAFS)
Issued at 715 PM EDT Fri Jul 19 2024

There will be some showers around at times, and there will be some
thunderstorms as well especially during the heating of the day.
Timing continues to be problematic, but there does appear to be a
period overnight when probability is lowest before it picks up
again later tonight into the day. The highest chance of lower
cigs/vsby with showers and/or fog looks to be late tonight into
early Saturday, and will include MVFR conditions all sites in a
prob30 group for several hours. Just vague VCTS all sites for
the latter part of the period for now, but hopefully timing will
become clearer as we get closer.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             70  86  70  86 /  50  70  40  80
Knoxville McGhee Tyson Airport, TN  69  85  70  86 /  50  70  40  80
Oak Ridge, TN                       69  84  68  86 /  50  70  30  80
Tri Cities Airport, TN              67  82  66  86 /  50  70  30  70

&&

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

$$

SHORT TERM...CD
LONG TERM....KS
AVIATION...