-- Discussion containing changed information from previous version are highlighted. --
000
FXUS64 KMRX 040532
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
132 AM EDT Sat May 4 2024

...New AVIATION...

.UPDATE...
Issued at 819 PM EDT Fri May 3 2024

Showers will continue to linger this evening. A few storms
possible in the Southern Valley and Cumberland Plateau. A lull in
activity is likely overnight. Although, some showers will still be
possible. Some patchy fog is possible in the early morning hours
due to ground moisture but development will be somewhat limited
due to cloud cover overnight. I went with Consshort guidance for
POPs in the overnight period. NBM seems a bit overdone. CAMs are
closer to Consshort with sporadic weak showers overnight.

&&

.SHORT TERM...
(This evening through Saturday)
Issued at 240 PM EDT Fri May 3 2024

Key Message:

A few instances of small hail, gusty winds, and locally heavy
downpours are possible this afternoon with showers and thunderstorms.

Discussion:

Currently showers and thunderstorms are traversing across much of
the southeastern United States being aided by a shortwave moving
through the Tennessee Valley this afternoon. As of this writing
there is predominantly just rain showers, but increasing
instability means we`ll likely see more thunderstorms moving
through the southern Appalachians through the rest of the evening.
Soundings and CAMs are still showing a few hundred (maybe up to
near 1000) J/kg of MLCAPE the rest of this afternoon. Combine this
with a fairly week lapse rate and very little shear, and the
chances for widespread sever weather continue to look low. With
that being said an individual thunderstorm could bring brief heavy
rain, small hail, and gusty winds in areas that have destabilized
this afternoon. With how slow these storms are currently moving
and the possibilty of multiple storms over a small area, the
biggest threat the rest of the afternoon/evening is likely to be
flooding of low lying or poor drainage areas.

As we head into the overnight hours we should see a lull in
activity, and although the threat of rain does not go away, but the
risk of lightning and strong storms really decreases as the
shortwave exits the area and the atmosphere becomes more stable
overnight.

On Saturday we will likely see a similar story as today, with
morning showers transitioning into afternoon thunderstorms with
heavy rain, small hail, and gusty winds as the primary hazards in
the strongest storms. Forecast soundings show a similar
environment with weak to moderate CAPE and weak shear, so once
again widespread severe weather looks unlikely.

&&

.LONG TERM...
(Saturday night through next Friday)
Issued at 240 PM 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.

Discussion:

We start the period with a fairly weak upper level flow pattern over
the region and a short wave moving through. Most model guidance
suggest the short wave will exit by early Sunday, with short wave
ridging building in.  This may allow for less coverage of showers
and thunderstorms Sunday afternoon, but it still looks like there
will be enough moisture and instability for at least scattered
convection. The upper level ridging looks to be short lived as
another short wave aloft moves in Sunday night/Monday, along with
more numerous showers and thunderstorms. Models suggest modest
instability with MLCAPES likely around 100J/kg or less for both
Sunday and Monday and shear will be on the weak side given the
weaker flow.  However some stronger storms with gusty downburst
winds will be possible as well as locally heavy rainfall rates given
the near 90th percentile PWATs (around 1.4 inches both days).

The unsettled pattern will continue for the Tuesday through Friday
time frame, although timing of individual short waves in the flow is
uncertain.  Ensembles do suggest a more dynamic pattern developing
with the upper jet nosing in from the west/northwest then dipping
south, and mean 850 mb flow will likely increase to 30+ kts and may
exceed 40 kts at some point during the period.  In addition, a cold
front is forecast to be moving in from the northwest by the end of
the period.  There are still model differences and timing questions,
but the data does indicate that by Wednesday we will see an
environment with potentially better thermodynamics and deep-layer
shear sufficient for more organized convection than in the earlier
part of the extended period. This will bear watching going forward.

The long term period will generally feature temperatures above
seasonal normals, although precipitation timing/coverage may help to
hold high temperatures down on some wetter days, and the cold front
moving in Friday is expected to help hold temperatures Friday down
closer to normal although timing that far out is of course still very
uncertain.

&&

.AVIATION...
-- Changed Discussion --
(06Z TAFS)
Issued at 129 AM EDT Sat May 4 2024

Scattered showers and thunderstorms continue through the forecast
period which will impact aviation at all sites. CHA will see some
impacts early this morning with convection being more isolated
during the morning and mid-morning hours. This afternoon,
thunderstorm activity will become more widespread with more
impacts expected in the vicinity of all terminals. Some areas of
low clouds and fog are possible this morning, mainly in the
vicinity of TYS and TRI. Winds remain generally light.
-- End Changed Discussion --

&&

.PRELIMINARY POINT TEMPS/POPS...
-- Changed Discussion --
Chattanooga Airport, TN             81  64  84  65 /  70  20  50  50
Knoxville McGhee Tyson Airport, TN  78  63  82  63 /  60  40  50  50
Oak Ridge, TN                       78  62  82  63 /  70  40  50  50
Tri Cities Airport, TN              76  59  79  60 /  90  40  60  40
-- End Changed Discussion --

&&

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

$$

SHORT TERM...
AVIATION...JB