-- Discussion containing changed information from previous version are highlighted. --
274
FXUS64 KMRX 031713
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
113 PM EDT Fri May 3 2024

...New AVIATION...

.UPDATE...
Issued at 947 AM EDT Fri May 3 2024

Showers continue to move through the southern Appalachians this
morning. Very little if any lightning is occurring at this time
with the showers, but expect as the day goes on we should see a
bit more electrical activity going on. No major changes were made
to the forecast outside of hourly PoP values to line up with radar
trends this morning.

&&

.SHORT TERM...
(Today and tonight)
Issued at 330 AM EDT Fri May 3 2024

Key Messages:

1. Increasing chances of showers and storms this morning through
the evening, with a potential lull in activity overnight.

2. While severe weather is not expected, a few instances of small
hail, wind gusts up to 40 mph, and locally heavy downpours are
possible this afternoon.

Discussion:

Upper level disturbances will bring increasing chances of showers
and storms to the forecast area today. Regional mosaic radar already
depicts a rain shield moving into western Kentucky, central
Tennessee, and eastern Mississippi this morning. Precipitation
chances will gradually increase across our forecast area through
the morning hours, with just general rain showers as the
predominant weather type. As we transition into the afternoon
hours, hi-resolution models suggest development of MLCAPE in the
300-800 J/kg range, which will lead to increasing chances of
thunder. A weak shear profile and mid level lapse rates struggling
to reach 6C/km should keep any storms from reaching severe
levels, although, any stronger storm could lead to locally gusty
winds up to 40mph and pea-size hail. PWAT values will generally
approach near 1.4 inches. This is around the 90th percentile based
on sounding climatology out of BNA. As such, we cannot totally
rule out some isolated flooding concerns with any slow moving or
training convection this afternoon. Thankfully, below normal
rainfall over the last month has allowed for 1 hr FFGs of 1.8-2.3"
across the forecast area, really minimizing this threat. A
marginal risk for excessive rainfall covers areas generally along
and west of I-75 - where the better chance for relatively more
effective convection exists. Temperatures will typically be near
normal. Ensemble guidance suggest we may see a window of little to
no activity during the late evening/overnight hours.

&&

.LONG TERM...
(Saturday through Thursday)
Issued at 330 AM EDT Fri May 3 2024

Key Messages:

1. An unsettled pattern is expected through the extended period with
daily scattered to numerous showers and storms. More organized
convection is possible by Wednesday/Thursday of next week.

2. Temperatures will be generally above normal, especially next week.

Saturday through Monday

At the start of the period, a fairly weak upper-level flow pattern
will be in place with a shortwave moving in from the west. With
broad moisture and surface heating, Saturday will consist of
scattered to numerous convection throughout the day. Based on the
weak flow, the convection will be thermodynamically-driven as very
minimal shear will be present. Overall, instability will be fairly
typical of the summer, i.e. near 1,000 J/kg of MLCAPE. PWATs will
also be 1.4 inches or higher, which is around the 90th percentile
for this time of year. With these conditions, some stronger storms
with gusty downburst winds are possible, in addition to locally
heavy rainfall rates. Thankfully, fairly dry conditions, including
low-end drought, will keep any flooding concerns very localized.

Heading towards Sunday, gradual height rises are expected with
embedded shortwave energy and similar thermodynamic conditions. This
will lead to slightly warmer temperatures than on Saturday with
additional showers and storms expected. A closed upper low will also
be noted to our west and will approach towards Monday. This may lead
to slightly better coverage than on Sunday, but the overall impact
will be the same.

Tuesday through Thursday

The unsettled pattern will continue into the middle of the week with
continued embedded shortwave, broad moisture, and surface heating on
Tuesday. By Wednesday to Thursday, however, a more dynamic pattern
is anticipated with the upper jet (in excess of 100 kts) dipping
further south. Upper-level divergence will help to strengthen the
850mb, possibly to in excess of 40 kts. A surface front will also
slowly drift southward. While discrepancies still exist, these
indications suggest an environment with potentially better
thermodynamics and deep-layer shear sufficient for more organized
convection than in the earlier part of the extended period. At this
time, low probability HWO wording will be kept to encompass the
multiple rounds of convection and potential locally heavy rainfall.
However, the Wednesday to Thursday timeframe will be something to
watch for more organized and/or robust convection.

&&

.AVIATION...
-- Changed Discussion --
(18Z TAFS)
Issued at 111 PM EDT Fri May 3 2024

Showers and thunderstorms can be expected in the southern
Appalachian region through the rest of the daytime hours today.
Difficult to say exactly when a storm may impact a terminal and
there could be several rounds of storms through the evening hours.
Expect mostly showers, but cannot completely rule out lightning in
the vicinity of the airports. We should see a lull in activity
overnight, with more widespread storms and lightning expected
tomorrow.
-- End Changed Discussion --

&&

.PRELIMINARY POINT TEMPS/POPS...
-- Changed Discussion --
Chattanooga Airport, TN             66  81  64  84 /  70  80  40  70
Knoxville McGhee Tyson Airport, TN  63  78  63  82 /  70  90  50  70
Oak Ridge, TN                       63  78  62  82 /  60  90  50  70
Tri Cities Airport, TN              61  76  60  80 /  50  90  60  80
-- End Changed Discussion --

&&

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

$$

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