River Flood Warning 33, NWS Jackson, MS

Area Forecast Discussion
National Weather Service Jackson MS
630 AM CDT Fri Mar 18 2022

.UPDATE...
Updated for 12Z aviation discussion

&&

.AVIATION...
12Z TAF discussion:

-RA/TSRA/VCTS will continue to affect sites over the next couple
 of hours. Vis and cigs will continue to bounce around from VFR-
 IFR however around 16z, RA is expected to be E of us and VFR will
 prevail through the rest of the period. Winds will be S/SW and
 gusty up to 25-30kts at times./JNE/

&&

.DISCUSSION...

Today and Tonight...

Late tonight hasn't been that active across the region but that
doesn't mean the threat is over. An upper level trough with an
associated closed low system moved across the ArkLaTex region and
ejected northeast towards the Great Lakes region. Simultaneously,
a cold front is currently pushing through the Lower Mississippi
Valley while a surface warm frontal boundary lifts north across
Louisiana. There are a multiple synoptic and thermodynamic factors
that supports the current severe weather across the Deep South
early this morning.

A potent MCS will moving across Arkansas and Mississippi late
tonight/early this morning has brought rain and severe weather to
the region. An influx of boundary-layer Gulf moisture and a
strengthening low level jet will help increase low-level warm
advection. Even in this strong warm advection regime, we are still
expecting more elevated convection north of the I-20 corridor where
the Marginal Risk Threat is highlighted. Damaging winds and hail up
to a quarter size are the main threats in these areas. As for
areas south of I-20 where the Slight Risk and in particular the
southeast where an Enhanced Risk is, MUCAPE has jumped from what
models were showing last night (1000-1600 j/kg) to currently 1500-
2000 j/kg. With increased instability, and 7.5-8.0 C/km mid level
lapse rates, large hail will be possible. Along with the hail,
temperatures across the south will climb to the upper 70s and
across the southeast 80-82 degrees along with dewpoints in the mid
60s. By mid morning, 0-3km SRH values show 300-400 m^2/ms^2
updraft helicity which supports robust storms(supercells). If
storms can orient with shear vectors, a strong tornado could be
possible across the southeast this morning. While we expect this
event to be mainly hail and wind, I want to be clear that the
environment is favorable across the extreme south/southeast(HWY 84
corridor) for a few tornadoes but especially across the
southeast, where more surface based convection is possible. A
Tornado Watch has been issued for parts of southeast Mississippi
from now until 10AM. As the threat moves out of areas, expect
counties to get canceled as needed.

Not only is there a tor and hail threat, the strength of the low
level jet also supports heavy rain fall and strong wind gusts. Some
storms could train resulting in some local flash flooding. Will
advertise a Limited in the HWO for heavy rain fall for a line
stretching from Natchez to Columbus and a Limited for gusty winds
mainly for areas west of I-55.

The good thing about this system/front is that it is expected to
move through pretty quickly. By the later afternoon, rain and storms
should be east of us and dry weather will prevail through the rest
of the day/night. Expect lows to drop to the mid 40s./JNE/

Saturday through next Thursday: With high pressure crossing the
forecast area, we'll see a stretch of dry weather with seasonable
temperatures this weekend. Saturday night could end up having some
frost potential over northeast portions of the area with clear
skies and light wind, but the threat for any freezing
temperatures is very low.

As we go into early next, global models are coming into better
agreement on the evolution of a strong upper level trough expected
to slowly push east toward the lower MS Valley region. There
should be a sufficient combination of deep layer shear,
instability, and ascent for getting organized severe storms, and
timing is beginning to center on the Tue/Tue night time frame.
Given increasing confidence in severe weather, have followed
SPC's upgrade to enhanced for the HWO/graphics, but will continue
to keep any details somewhat general.

It is also looking more likely that there will eventually be a
threat for heavy rainfall with most guidance showing signals for
split upper level jet dynamics and enhanced upper level divergence
helping to anchor MCS activity. The threat for more significant
heavy rainfall still hinges on how much the trough hangs up as it
approaches the southeast CONUS ridge. /EC/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       78  44  66  38 /  41   0   1   0
Meridian      81  45  67  37 /  85   0   1   0
Vicksburg     74  44  67  36 /  16   0   1   0
Hattiesburg   81  46  68  38 /  78   0   0   0
Natchez       75  44  67  39 /  19   0   1   0
Greenville    71  44  65  40 /  21   0   1   0
Greenwood     74  45  64  39 /  37   0   1   0

&&

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

&&

JNE/EC

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