Severe Thunderstorm Warning 417, NWS Jackson, MS

Area Forecast Discussion
National Weather Service Jackson MS
455 AM CDT Sun Jun 18 2023

...New DISCUSSION...

.DISCUSSION...
Issued at 450 AM CDT Sun Jun 18 2023

Today and Tonight...Quite a challenging forecast exists across the
forecast area today into tonight.  Currently, several perturbations
embedded in west northwest flow aloft are lined up from southeast
Arkansas back into east Oklahoma ahead of a closed low pressure
system over south central Kansas. These have sparked several
complexes of showers and storms across those areas overnight.  As
this low tracks east into the Mid-Mississippi River Valley through
the course of the day and into the Ohio River Valley tonight, these
perturbations/disturbances and any subsequent or associated east
southeast advancing outflow boundaries will all aid in the
development of showers and storm across the region, with multiple
rounds of storms possible from early this morning into late tonight.

While the overall synoptic pattern hasn't changed, high-res models
are currently struggling with the placement and propagation of these
boundaries and such. Therefore, it's making exact timing of these
multiple rounds of storms very difficult to nail down during the
period.  That said, because it's now moving into the far northwest
portions of the Delta region, the first round of severe storms is
now moving through the northern half of the CWA as I type. As the
comnplex exist the CWA here in a few hours, the question is will
it leave a boundary in it's wake, and if, so where will it reside
for possible storm development later today. Therefore, attention
will need to strongly be paid locally as well as upstream to real
time satellite, observations, of course radar, and other mesoanalysis
to better depict the timing of these rounds of storms as well as
the areas affected.

With the airmass over the region becoming strongly unstable through
the day with at least 3500-4500 J/kg of SBCAPE forecast, coupled
with very steep mid-level lapse rates on the order of 7.5-8.5 C/km
and 29-32 vertical totals, and strong deep layer wind shear around
60 knots, severe storms are expected across the forecast area.  This
includes the potential for super cells as well as fast-moving
organized bowing lines of storms.  Damaging winds of 70 mph and
large hail up to tennis ball size are possible, with the largest
hail threat expected this afternoon and evening.  Also, a tornado
cannot be ruled out. In addition, near constant lightning strikes
are expected with storms, along with very heavy downpours.  With
several rounds of storms forecast, and thus the training of storms
possible, up to 3 inches of rain in a short amount of time is
possible and could result in flash flooding.  The severe threat will
continue into late tonight, with activity currently forecast to exit
the forecast area by day break Monday morning.

Lastly, if widespread cirrus debris from convection to the north is
able to vacate the area this afternoon, highs will warm into the
middle 90s across mainly east central Louisiana and southwest
Mississippi.  These hot temperatures combined with the humid
conditions, could result in dangerous heat stress conditions across
mainly the southwest half of the CWA. /19/

Monday into Saturday...Synoptic pattern will consist of building
subtropical ridge from Mexico through the Southern Plains up into
the Mid West to Great Lakes. This will help drive the upper low to
cutoff & become closed off over the southeast states & gradually
build southward & retrograde by mid- late week. This will help
drier profiles closer to an inch & a quarter PWs will build in
Monday into Tuesday. There will be some residual shear &
instability for isolated but more diurnal severe convection to
start the week on Monday & another round into Tuesday. Kept
mention of "Marginal" for areas southeast of the Natchez Trace
corridor for Monday & south of Interstate 20 into Tuesday. Main
concerns are wind & hail, with bulk shear slightly relaxing (i.e.
30-35kts) & profiles becoming more unidirectional, favoring single
& multicell. Highest rain & storm chances will be east of
Interstate 55, with less coverage in the Mississippi River
corridor. Some lingering jet dynamics help some redevelopment
before midday Tuesday.

Heat will build south of Interstate 20 & kept same areal
configuration of heat stress concerns into Monday & "Limited"
potential into Tuesday for extreme southwest Mississippi & northeast
Louisiana. With scattered rain coverage but likely less cloud cover
than Sunday, an advisory may be needed in future updates. With the
retrograding closed low, moisture build from east to west & best
convergence & diurnal rain/storm chances to be southeast of the
Natchez Trace corridor & especially east of Interstate 55. Thermo
profiles become slightly less oppressive & highs peak below normal
in the mid-upper 80s, with heat stress concerns much less as heat
indices only peak into the mid-upper 90s. Highs gradually moderate
back near normal in the low 90s into next weekend. Rain & storm
chances will unfortunately persist into next weekend as closed low
becomes more open trough & sits over the southeast states &
convergence persists. /DC/

&&

.AVIATION...
(06Z TAFS)
Issued at 1225 AM CDT Sun Jun 18 2023

Flight categories are forecast to fall to a mix of mainly
MVFR/IFR categories due to developing low stratus, as well as some
patchy fog. Chances for convection will also increase during the
overnight hours, and remain high through much of Sunday as several
rounds of storms are forecast to track to the east across the
region. Some of the storms will be severe and capable of producing
wind gusts of 61 knots and large hail up to the size of tennis
balls, especially late Sunday. Near continuous lightning strikes
and heavy downpours are expected to accompany all of today's
convection as well. Winds overnight will be light with a southerly
component to calm. Away from convection, winds will be southerly
between 5-10 knots. /19/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       90  72  90  71 /  80  70  40  20
Meridian      87  71  90  69 /  70  60  60  30
Vicksburg     92  72  92  73 /  70  60  20  20
Hattiesburg   91  74  92  73 /  70  40  70  40
Natchez       94  74  94  73 /  40  50  30  30
Greenville    86  71  89  70 /  90  60  10  10
Greenwood     88  71  90  70 /  90  80  20  10

&&

.JAN WATCHES/WARNINGS/ADVISORIES...
MS...None.
LA...None.
AR...None.
&&

19/DC

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