471 
FXUS64 KMEG 190113
AFDMEG

Area Forecast Discussion
National Weather Service Memphis TN
813 PM CDT Sun Mar 18 2018

.UPDATE...
Updated to reduce evening and overnight PoPs.

&&

.DISCUSSION...

Latest radar loop shows area of rain slowly shrinking in coverage
as it pushes northeast across the Mississippi River as it
encounters drier low level air. Most of this elevated convection 
will remain north of I-40 with some isolated thunder. Area of 
stronger convection in East Texas...if it holds together through 
the night...is progged to stay south of the CWA altogether. So 
overall have lowered rain chances for a good portion of the 
southern CWA and the far east through the night. The west should 
start to see the next round of convective development move out of 
central Arkansas in the 10-12z time frame before sunrise so left 
higher PoPs in this region.

All the other evening forecast parameters are currently on track.

JAB

&&

.PREV DISCUSSION... /issued 756 PM CDT Sun Mar 18 2018/ 

UPDATE...

Updated for the 00z Aviation Discussion.

PREV DISCUSSION... /issued 351 PM CDT Sun Mar 18 2018/ 

At 3PM...Mostly cloudy skies prevail across the Mid-South with 
temperatures mainly in the 50s. A few light showers were noted on 
RADAR over north Mississippi, otherwise it is mostly dry across 
the area. Latest GOES east water vapor loop depicts a large 
shortwave trough over the Rockies with a weak shortwave located 
near Dallas Texas. Downstream a warm front exists draped across 
Central Mississippi. 

Short term...tonight through Monday night...
The main focus over the next 24 hours will the potential for
severe thunderstorms tomorrow morning into the early afternoon 
hours. The system will just be starting to organize over our area,
so a great deal of uncertainty remains as to whether or not 
severe storms will fire up in or just east of our area due to the
small window of opportunity. 

The weather setup will feature a compact shortwave ejecting from 
the Rockies and taking on a negative tilt as it crosses the 
Southern Plains. Meanwhile, a surface low is expected to slightly 
intensify and quickly move eastward from the Oklahoma Panhandle to
Paducah, Kentucky by sundown and swing a cold front quickly 
through our area. 

The atmosphere is expected to modify quickly ahead of the system 
as a warm front lifts north through the forecast area by early 
tomorrow morning. Scattered to numerous showers and occasional 
thunderstorms will accompany the frontal passage overnight, but 
convective activity is expected to remain weak as mid-level lapse
rates are low. 

Short term HI-RES models suggest that there will be a brief lull 
in convective activity through mid morning hours on Monday as 
heights briefly build ahead of the deepening shortwave. 60s 
dewpoints are expected to push as far north as the I-40 corridor 
by 18Z tomorrow with temperatures pushing into the lower 70s.
Model soundings all suggest that a weak 850mb capping inversion
will also be in place. This will increase SBCAPE into the 1000 to
1500 J/kg range. Directional and speed shear will be plentiful as
a 90 knot mid level jets rotates through the Mid-South during the
same time period. Winds will also be backed as the low approaches
our area from the west. Any storms that can fire ahead of the
front will have the potential to be supercellular with large hail,
damaging winds, and isolated tornadoes. 

Right now, the best overlap of severe ingredients will be near 
the Tennessee River, mainly over northeast Mississippi and 
portions of west Tennessee. The NAM continues to be the bull with 
convective parameters, suggesting a highly unstable airmass over 
the eastern half of the forecast area with as much as 2500 J/kg 
SBCAPE and 0-3 km SRH values in excess of 400 m2/s2. This would 
lead to a much higher tornado threat. The likely solution will be 
a blend of the ECMWF and GFS, with a decently unstable airmass 
mainly over northeast Mississippi and portions of west Tennessee. 
Low and mid level lapse rates will be quite healthy and support 
strong updrafts. The main threat will with any storm that does pop
up ahead of the front will be large hail and an isolated tornado 
threat. Storms that form along the front will also pose a hail 
threat with a greater damaging wind threat and possible embedded 
circulations. The front is expected to quickly traverse the 
forecast area and exit northeast Mississippi around 22Z. All 
activity is expected to be east of the area around sundown. 

Temperatures will cool into the 40s by Tuesday morning. Another
shortwave will pass through the Mid-South on Tuesday, with a
decent chance of showers throughout much of the day and plentiful
clouds. Models have backed off on freezing temperatures for 
Wednesday and Thursday mornings, although frost will be possible. 
Will remove the mention of freeze from the HWO. Dry and cooler 
than normal conditions will prevail on Wednesday and Thursday as 
we remain under the influence of northwest flow. 

There is quite a bit of uncertainty beyond Thursday as models
handle the breakdown of the trof a little bit differently.
Nonetheless, a period of unsettled weather is expected through next
weekend. Went with a blend in the long term, with chance POPs 
each day for showers and thunderstorms. Temperatures are expected 
to trend much warmer through this period with highs mainly in the 
70s. 

AC3

&&

.AVIATION.../00z TAFs/

A mix of VFR and MVFR cigs will prevail through the evening at all
terminals. A shortwave lifting northeast this evening will bring a
period of showers and a few thunderstorms to KJBR, KMEM, and KMKL.
This activity should lift off to the northeast by late evening
with mainly dry weather through the remainder of the night. Cigs
will gradually lower below critical 1500ft level requiring
declared alternates by late tonight. There may also be another
weak shortwave that may bring a period of showers and
thunderstorms to KTUP after midnight. Winds will gradually shift
from east to southeast but remain light in intensity.

A stronger upper level low and associated shortwave will move
through the area on Monday. A round of showers and thunderstorms
are expected, beginning early in the day at KJBR and spreading
east across the remainder of the terminals through the day. Skies
will eventually clear later in the afternoon with winds increasing
from the west and becoming gusty at times. 

Clear skies and diminishing west winds will continue into Monday
evening.

JLH

&&

.MEG WATCHES/WARNINGS/ADVISORIES...
AR...None.
MO...None.
MS...None.
TN...None.
&&

$$