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000
FXUS64 KMRX 191508
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
1108 AM EDT Fri Apr 19 2024

...New UPDATE...

.UPDATE...
Issued at 1058 AM EDT Fri Apr 19 2024

Morning shower/thunderstorm activity and cloud cover have both
cleared out quicker than expected. This has lead to increased
heating and an increase in temperatures and decrease in cloud
cover compared to the previous forecast. Based on the latest
high-res model guidance, development is expected by the afternoon,
especially in the northern half of the area. This should help to
balance out high temperatures close to the previously forecast
highs. The overall severe threat is still similar with effective
shear (40+ kts) and MLCAPE (>1,000 J/kg) both expected to be
slightly better in northern portions of the area. However, places
further south will see better mixing and overall DCAPE values. A
lot of the recent CAM runs have shown more development in the
south than in earlier runs, but those storms may take on a
slightly less organized structure driven more by thermodynamics.
In any case, there remains no tornado potential due to very
minimal low-level shear and a focus on damaging winds and hail
with notable (600+ J/kg) of instability in the hail growth region.
The overall impacts and threats are about the same, but
instability may end up being slightly higher than expected with
the clearing.

&&

.SHORT TERM...
(Today and tonight)
Issued at 307 AM EDT Fri Apr 19 2024

Key Messages:

1. Scattered showers and a few thunderstorms move in through this
morning. A few strong storms are possible.

2. A second round of scattered strong thunderstorms this afternoon
across the Tennessee valley. Gusty winds and large hail possible
with the afternoon thunderstorms.

Discussion:

A few showers and storms will move through the area this morning.
CAMS show isolated to scattered activity moving onto the Cumberland
Plateau between 07 and 08Z, then spreading eastward into the east TN
Valley through sunrise. This is in response to 500mb vorticity
moving through the area ahead of a cold front located back across
west TN. Current meso-analysis shows a few hundred joules of CAPE
west of I-75, which is where a few storms are expected through
sunrise. Given the weak insatiability field, don`t expect any severe
weather during this timeframe but an isolated strong storm can`t be
ruled out.

After sunrise, isolated showers and a few storms will remain
possible through late morning across the whole forecast area.
Instability begins to increase from late morning and into the
afternoon hours with daytime heating. HREF mean ensemble SBCAPE
values for this afternoon range between 1000 and 1500 J/kg. This
coincides with when the cold front will be moving through the area.
This results in showers and storms increasing in coverage as the
front passes through. Isolated damaging wind gusts up to 60 mph and
hail from 1 to 1.25" will be the primary threats this afternoon with
any stronger storms. The larger hail sizes are due to steep mid
level lapse rates along with moderate 0-6km shear of 30 to 40kts.
The 0-6km shear will increase the residence time of hail in the
updrafts of any stronger storms. The shear in the lowest levels is
very weak today, thus removing the threat of tornadoes. SPC
currently has most of our area under a marginal risk for severe
storms.

&&

.LONG TERM...
(Saturday through Thursday)
Issued at 307 AM EDT Fri Apr 19 2024

Key Messages:

1. Outside of rain chances Sunday, drier and cooler conditions are
expected into early next week, especially Monday.

2. Rain chances and more seasonal temperatures will return by
Wednesday and Thursday.

Discussion:

By Saturday a surface front will have exited the area to the
southeast as the upper level pattern becomes quasi-zonal. Northerly
surface winds will bring drier and cooler air to the region. A weak
shortwave disturbance translating through the mean flow will bring a
return to precipitation chances Sunday, however, this will generally
remain restricted to areas along and south of Interstate-40. Mean
ensemble guidance probability of 24 hour precipitation GTE to a
tenth of an inch is 50-70%. Probability for GTE half an inch is 20%
or less. Some patchy frost will be possible Sunday night, with
temperatures falling into the mid to upper 30s. The question will be
if winds lighten enough with the shortwave traversing the area.

Dry conditions with a warming trend will kick off the new work week.
The next chance for some additional light rain showers will come
Wednesday as a trough digs into the Ohio Valley. Better forcing
remains well to our north, leading to only light precipitation. For
Wednesday, mean ensemble guidance probability of 24 hour
precipitation GTE to a tenth of an inch is only 30-60%. High
pressure builds in behind the front Wednesday, with returning dry
conditions.

&&

.AVIATION...
(12Z TAFS)
Issued at 742 AM EDT Fri Apr 19 2024

Mostly VFR conditions this morning at all sites, except for a few
hours of TEMPO MVFR through late morning. Additional scattered
showers and storms develop this afternoon and PROB30 MVFR
conditions are in at all sites. MVFR conditions are likely later
tonight and will last through the end of the period.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             80  56  72  50 /  50  10  10  20
Knoxville McGhee Tyson Airport, TN  77  53  68  48 /  80  20  10  10
Oak Ridge, TN                       77  52  69  47 /  70  10  10  10
Tri Cities Airport, TN              74  50  66  44 /  80  20  10  10

&&

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

$$

SHORT TERM...
LONG TERM....KRS
AVIATION...