Flash Flood Warning 54, NWS Jackson, MS

Area Forecast Discussion
National Weather Service Jackson MS
123 PM CST Mon Nov 20 2023

...New DISCUSSION...

.DISCUSSION...
Issued at 108 PM CST Mon Nov 20 2023

This Afternoon Through Tonight ...

A substantial severe weather threat remains likely, initially
beginning across southeast Arkansas and into eastern Louisiana this
afternoon. This activity spreads across the rest of the area into
the evening and overnight with the threat for tornadoes, some
strong, damaging winds, and hail possible. Flash flooding will not
be widespread as storm motions will be quite rapid with heavy rains
relatively brief. In isolated urban corridors where runoff is
maximized with poor drainage, some ponding along roads will however
be possible.

Regarding the meteorological synopsis, a narrow ridge aloft and the
associated surface high that came into our area over the weekend
behind a cold front has now shifted east of our area. This is in
response to a large longwave upper trough moving across the central
portion of the country. With the stronger trough now impinging on
the area, the backside moisture return behind the departing surface
high in combination with lowering surface pressures and enhanced
southerlies ahead of the incoming surface cyclone is resulting in
rapid boundary layer recovery. With only a few hours of deep
southerlies, this is resulting in a narrow, pinched warm sector.
Overtop this narrow zone of deep moisture, lapse rates aloft are not
particularly impressive either and thus the net result on a
thermodynamic level is weak instability overall. Most unstable cape
values (MUCAPE) will likely remain constrained beneath 1500 J/KG for
the area with most areas struggling to reach 1000 J/KG.

In spite of this, strong to extreme wind shear (0-6 km bulk shear at
or above 90 kts) and substantial forcing for ascent associated with
the nose of a very powerful jet advancing into the
downstream/divergent area of the approaching trough will likely be
sufficient to take advantage of the well above seasonal moisture
content and warmth at least within that narrow corridor in the
vicinity of the approaching front. This front will likely be
somewhat convectively modified with storm outflows, but in general
will extend from a surface low that will likely move from southern
Arkansas into northern Mississippi through tonight.

Within the boundary layer, shear will likely begin to further
increase into the early evening as the low level jet begins to
strengthen. Winds at 850 mb will likely increase from 40- 45 kt
to 55-60 kt during the time period. Surface winds will remain
generally backed, southerly to south-southeasterly, until impacted
by storm outflows. This will likely result in 0-1 km SRH values
moving from around 200 m^2/s^2 this afternoon to upwards of 400
m^2/s^2 by evening. Traditional severe weather indices sig tor
parameter (STP) and 0-1 km energy-helicity index (0-1 km EHI)
could end up the 1-2 range. Readers are cautioned to recall that
these numbers may under-represent the risk when the event is known
to be heavily driven by wind shear.

Mesoscale guidance remains insistent that, as might be expected, the
strongest individual storms are likely those that deviate to the
right of the mean flow. The HRRR, for example, suggests the
strongest 0-3 km updraft helicity is likely to occur with such
storms. These storms will likely have transient supercell
characteristics in close proximity to or embedded within the
advancing broken squall. These right-movers, however, will find that
any rightward motion will quickly push the storms into areas of
decreasing low level moisture content and for that reason the
strongest storms may struggle to maintain longevity. Further,
forecast soundings indicate that storms may be relatively low-
topped. The implication could be that storms will rapidly develop
within a narrow but very supportive corridor, becoming mature and
producing severe weather in a rapid fashion, before weakening as
they move northeast. With storm motions quite rapid, this potential
scenario could allow for cell maturity, including tornado
production, to occur rapidly with strong tornadoes possible as well.
These factors, coupled with a potentially messy storm mode yielding
rain wrapping around updrafts and the overnight timing, poses an
increased risk to life and property.

North of the "enhanced" risk, centered approximately along and south
of the I-20 corridor, storms will likely be most intense in
proximity to the warm front. The warm sector will be increasingly
narrow with northward extent within this "slight" risk delineation,
but proximity to the surface low, the warm front and advancing cold
front, and maximized deep layer shear could allow for bowing
structures and wind damage in the more northern areas should one of
these bowing features advance in the vicinity of the diffuse warm
front could be of somewhat greater coverage/longevity than may
otherwise be expected with the meager . The strong tornado threat,
however, will likely be substantially lower in these areas than
within the "enhanced" risk areas to the south.

The hail and flash flood risks do appear to be secondary hazards.
Regarding flash flooding, quickly moving storms and the overall
storm system not lingering, along with antecedent drought
conditions, should help limit the risk except in the more flood
prone, urban areas. For hail, storms that may be somewhat low-
topped, a messy, quasi-linear storm mode, and limited instability
both within the hail growth region aloft and overall will likely
make severe hail reports somewhat uncommon. A hail stone or two as
large as golfball can't be totally ruled out with the best
chances for that being with the earlier storms west of I-55 while
storm mode may be slightly more cellular/discrete and instability
may reach a relative maximum.

It's also worth noting that in the hour or two ahead of the band of
thunderstorms, gusty southerly winds could reach 30-35 mph. Given
the relative proximity to the approaching squall, a wind graphic was
not generated. These winds could down weak limbs sporadically,
potentially causing isolated power interruptions. This could
potentially affect the ability to receive severe weather warnings as
storms approach and is another reminder to have multiple ways to
receive warnings.

Storms finally end from west to east overnight with a cool northwest
wind moving in behind the cold front. /86/

Tomorrow through Monday...

For Tuesday, the cold front will pass through our region with some
lingering showers remaining behind before decreasing in coverage by
the afternoon and evening hours. Drier and colder air will filter
into the area in the wake of the aforementioned cold front.
Temperatures will be slightly below seasonal as highs will be in the
middle to upper 50s and lows will be in the upper 30s to lower 40s.
Patchy frost will be possible for northern Mississippi and near the
Delta region for Wednesday night into Thursday morning. Thursday
will bring the next chance for additional rainfall to our area. A
shortwave trough, located near northern Mexico/South Texas will push
eastward; as a result, rainfall chances will increase across the
CWA. Lack of instability will keep severe weather chances very low
to non-existent for this system. Precipitation chances will range
between 40-50% before decreasing by Friday morning and accumulating
total will range under a quarter inch, which will help alleviate
some of the ongoing drought. Friday through the weekend, quiet
conditions and near seasonal high and low temperatures are
expected. /SW/

&&

.AVIATION...
(18Z TAFS)
Issued at 1138 AM CST Mon Nov 20 2023

Cloud cover will increase through this evening with showers and
thunderstorms likely for western sites after 21Z and until 06Z. For
central and eastern sites, similar conditions are expected from 00z
until 09z. Southerly wind gusts as high as 20-30 knots are possible
ahead of the band of strong to severe storms. Ceilings remain low
through the remainder of the TAF period with lighter northwesterly
winds following the cold front passage. /86/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       80  57  63  43 /  90 100  40  20
Meridian      72  60  69  44 /  70 100  70  20
Vicksburg     79  54  61  42 /  90 100  20  10
Hattiesburg   76  63  70  47 /  60  90  80  20
Natchez       79  55  62  43 /  80 100  20  20
Greenville    71  53  57  40 / 100  90  20  10
Greenwood     72  54  59  42 /  90 100  30  10

&&

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

LP/SW/LP

Preliminary Local Storm Report
National Weather Service Jackson MS
418 PM CST Mon Nov 20 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0411 PM     Tstm Wnd Gst     2 E Tallulah            32.41N 91.15W
11/20/2023  M52 MPH          Madison            LA   Mesonet

            Measured by private weather station at
            Tallulah Airport.

&&

DL

Preliminary Local Storm Report
National Weather Service Jackson MS
439 PM CST Mon Nov 20 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0430 PM     Hail             Ferriday                31.63N 91.56W
11/20/2023  M1.25 inch       Concordia          LA   Storm Chaser

&&

DL

Preliminary Local Storm Report
National Weather Service Jackson MS
514 PM CST Mon Nov 20 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0426 PM     Hail             2 S Clayton             31.69N 91.54W
11/20/2023  E1.75 inch       Concordia          LA   Law Enforcement

&&

CE

Preliminary Local Storm Report
National Weather Service Jackson MS
515 PM CST Mon Nov 20 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0433 PM     Tstm Wnd Dmg     3 NE Ferriday           31.67N 91.52W
11/20/2023                   Concordia          LA   Law Enforcement

            Trees down and lines down NE of Ferriday.

&&

CE

Preliminary Local Storm Report
National Weather Service Jackson MS
534 PM CST Mon Nov 20 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0451 PM     Hail             3 NE Pine Ridge         31.66N 91.32W
11/20/2023  E0.70 inch       Adams              MS   Emergency Mngr

            Dime sized hail was reported on Gaylor Rd.

&&

DL

Preliminary Local Storm Report
National Weather Service Jackson MS
555 PM CST Mon Nov 20 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0538 PM     Tstm Wnd Gst     1 NNW Gluckstadt        32.53N 90.10W
11/20/2023  E60 MPH          Madison            MS   Amateur Radio

&&

CE