Severe Thunderstorm Warning 54, NWS Jackson, MS

Area Forecast Discussion
National Weather Service Jackson MS
1226 AM CST Mon Feb 10 2020

.UPDATE...
Updated for 06Z aviation discussion

&&

.AVIATION...
06Z TAF discussion:

Flight conditions have begun to worsen areawide as low CIGs and
thunderstorms associated with a slow moving frontal boundary move
into the region. MVFR conditions will exist at most sites by
tomorrow morning with visbys also declining at sites in the west
due to rain and storms. RA and TSRA will continue through much of
the day tomorrow impacting visbys. Better chances for widespread
storms will exist at our northern most sites like KGLH. KGWO, and
KGTR. These storms will train, providing little to no time for
conditions to improve.

&&

.DISCUSSION...
Regional radars showed showers and a few thunderstorms to our
southwest that will spread across the CWA overnight. Widespread
rain is expected over our whole CWA prior to sunrise. None of this
activity is expected to be severe tonight but will start to wet
the ground in advance of stronger storms MOnday. Temperatures were
running a couple degrees warmer than expected but the rain will
knock temperatures down and forecast minimum temperatures still
look on track. /22/

Prior discussion below:

Tonight through early Tuesday morning:

Several rounds of heavy rainfall will lead to widespread flash
flooding, some of which could be significant, across portions of the
ArkLaMiss. Additionally, isolated severe storms with all hazards
will also be possible.

A prolonged period of moist southwest flow will become established
across the region as a closed mid/upper-level low diving through
southern California helps to amplify an upstream longwave mean
trough centered across the Desert Southwest/Four Corners region. At
the same time, a stout 592dam 500mb ridge is progged to be located
between the Yucatan Peninsula and Cuba. The main impetus for this
first round of active weather will be a Pacific shortwave trough
embedded within the southwesterly flow ejecting through northern
Mexico and into the Gulf Coast states. This morning's 12z suite of
hi-res CAM guidance is in general agreement that the associated
upstream showers and thunderstorms over the ArkLaTex will spread
into the area during the early morning hours Monday ahead of an
advancing cold frontal boundary. The forward movement of the
boundary will slow considerably as it becomes oriented parallel to
the southwesterly flow and will essentially stall over central
Mississippi through Tuesday morning, thus setting the stage for
significant flooding.

Flooding threat - Guidance has come into good agreement on a
prolonged period of training convection along the aforementioned
frontal boundary. These storms will reside within an anomalously
moist environment characteristic of 1.75" PWATs in the 99th
percentile and impressive values of deep moisture convergence. The
greatest threat for significant flooding will be along and north of
a line from northern Richland Parish to southern Noxubee County
where rainfall amounts of 4-6" are expected. Locally higher amounts
upwards of 8" will also be possible where the heaviest rain rates
and longest period of training occurs. There will be a rather sharp
southern rainfall gradient with 2-4" along the I-20 corridor and
only 1-2" into the Pine Belt. The limited threat area for flooding
has been trimmed north for this reason. The intial flooding graphic
has been split into two separate graphics as there will be a
distinct lull in the heavy rainfall during the day on Tuesday into
early Wednesday. As such, while the rainfall totals for the first
round of heavy rain are slightly lower, the anticipated impacts
remain the same.

Severe weather - the environment ahead of the frontal boundary will
be unstable with SBCAPE values around 1000 J/kg during peak heating
on Monday. Deep-layer shear of 50-60kts will also be supportive of
organized convective structures. However, the training nature of the
convection will generally preclude a greater severe weather threat.
With that being said, isolated severe weather will be possible with
any portions of the convective line that can remain surface based
and surge into the unstable air without being undercut by cold
pools. Furthermore, hi-res CAM guidance has indicated the potential
for a few storms within the open warm sector ahead of the frontal
boundary but confidence is lower in this scenario. While the threat
is isolated, the respective parameter space is supportive of all
hazards and a marginal risk will be maintained in the HWO/graphics.

Tuesday through Wednesday morning:

A relative lull in the heavy rainfall and storms is expected during
the day on Tuesday through Wednesday morning as the lead Pacific
shortwave trough lifts into the Appalachians and forcing becomes
more nebulous. At least weak isentropic ascent will continue through
the period with showers likely, however. An isolated storm or two
will also be possible across southeastern portions of the area ahead
of the stalled boundary where enough instability could support
updrafts strong enough for charge separation and lightning.
Additional rainfall during the day on Tuesday and into Tuesday night
will generally be 0.25-0.5" and not enough to exacerbate any ongoing
flooding. Will keep the HWO/graphics clear of any hazards during the
Tuesday into Wednesday morning period.

Wednesday afternoon through early Thursday morning:

The second round of heavy rainfall and storms will take place
Wednesday afternoon through early Thursday morning as the primary,
and much stronger, shortwave trough over the Desert Southwest
finally ejects into the Southern Plains and Gulf Coast states. The
GFS has trended into agreement with the ECMWF solution which depicts
surface cyclogenesis across the ArkLaTex on Wednesday morning with
the low lifting northeast into the Ohio River Valley by Thursday
morning. This will allow the stalled frontal boundary to lift back
north as a warm front with the majority of the area residing within
the open warm sector Wednesday afternoon. An early round of
convection will be possible along the warm front Wednesday morning,
but the primary focus will shift to the cold frontal passage
Wednesday afternoon into early Thursday morning.

Flooding threat - another quick 2-3" of rainfall will be possible
with a convective line pushing through the area. Locally higher
amounts will also be possible, especially if the line moves through
slower than anticipated. While 2-3" normally isn't a big problem,
this will be occurring only 24hrs after the first round of
significant rainfall and flooding issues are expected to already be
ongoing. As such, it won't take much rain in a short amount of time
to further exacerbate flooding. PWATs will also remain in the 99th
percentile and convection will reside within an impressive 330-335K
850mb ThetaE ridge, thus further supporting intense rainfall rates.
As previously mentioned, the flooding threat has been separated into
two graphics to highlight the two distinct periods of heavy
rainfall. An elevated threat area has been added for Wednesday into
Thursday for much of the area. The eventual threat level and outlook
area for this second round will be highly dependent on where and how
much rainfall occurs Monday into Tuesday. It's definitely possible
that another significant threat area will be needed for at least
some portion of the area and will be further evaluated.

Severe weather - there's a strong signal in the 12z guidance for a
QLCS to push through the area Wednesday afternoon into early
Thursday. Sufficient instability is progged to reside ahead of the
line with the ECMWF, GFS, and NAM all depicting around 1000 J/kg of
SBCAPE. The environment will also be highly sheared with 60-65kts of
0-6km deep-layer shear, 30kts of 0-1km shear and 200-300 m2/s2 0-1km
SRH. While this parameter space is impressive, further inspection of
the orientation of the shear vectors, particularly at 0-3km and 0-
6km, reveals a boundary parallel orientation. Model QPF fields also
indicate that the QLCS will reside right on or just behind the
frontal boundary itself. This setup strongly favors cold pools
undercutting the QLCS which would greatly inhibit any severe weather
threat. Confidence in severe weather potential remains fairly low at
this point, despite the advertised enhanced risk in the
HWO/graphics. Will maintain consistency and not make any adjustments
to the threat level or area at this point, but barring any major
changes in the guidance its possible that the severe weather threat
will need to be downgraded and the reader is strongly encouraged to
stay tuned to future forecast updates.

Thursday through Sunday:

The shortwave trough axis is expected to lift into the Mid-Atlantic
Thursday with drying conditions for the region. This break in the
active pattern is currently forecast to last at least through
Friday. There are subtle differences in timing, but both GFS and
ECMWF solutions bring yet another storm system into the region next
weekend as a shortwave trough ejects out of the Desert Southwest.
/TW/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       63  71  60  60 /  95  94  60  46
Meridian      59  71  65  68 /  83  78  63  35
Vicksburg     64  72  54  56 /  98 100  59  58
Hattiesburg   62  73  67  73 /  63  45  46  30
Natchez       64  73  60  62 /  80  76  58  37
Greenville    59  62  45  50 / 100 100  60  85
Greenwood     60  64  48  54 / 100 100  56  83

&&

.JAN WATCHES/WARNINGS/ADVISORIES...
MS...Flash Flood Watch from 6 AM CST this morning through Tuesday
     afternoon for MSZ018-019-025>053.

LA...Flash Flood Watch from 6 AM CST this morning through Tuesday
     afternoon for LAZ007>009-015-016-023>025.

AR...Flash Flood Watch from 6 AM CST this morning through Tuesday
     afternoon for ARZ074-075.

&&

JPM3

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Service Notice</title>
  <link rel="stylesheet" href="index.css">
</head>
<body>
  <main class="wrap">
    <section class="card" role="status" aria-live="polite">
      <div class="status" id="status">Temporary Notice</div>
      <h1 id="headline">This service is currently unavailable.</h1>
      <p id="message1">
        The site you requested is temporarily down for maintenance or an unexpected outage.
      </p>
      <p id="message2">
        Please try again in a few minutes.
      </p>
      <p class="small" id="detail">
        If you are an administrator, restore upstream service and remove the redirect/fallback rule when normal operations resume.
      </p>
    </section>
  </main>
  <script src="index.js"></script>
</body>
</html>

Special Weather Statement
National Weather Service Jackson MS
1106 PM CST Sun Feb 9 2020

LAZ016-023-025-MSZ047-053-100600-
Tensas LA-Madison LA-Franklin LA-Warren MS-Claiborne MS-
1106 PM CST Sun Feb 9 2020

...A STRONG THUNDERSTORM WILL AFFECT TENSAS...CENTRAL MADISON AND
SOUTHEASTERN FRANKLIN PARISHES...SOUTHWESTERN WARREN AND NORTHERN
CLAIBORNE COUNTIES UNTIL MIDNIGHT CST...

At 1105 PM CST, Meteorologists were tracking a strong thunderstorm
near Cooter Point, or 18 miles southeast of Winnsboro, moving
northeast at 45 mph.

Nickel size hail and wind gusts up to 50 mph will be possible with
this storm.

This strong thunderstorm will be near...
  Newlight around 1110 PM CST.
  Lake Bruin around 1120 PM CST.
  Newellton around 1125 PM CST.
  Somerset around 1130 PM CST.
  Afton around 1135 PM CST.
  Vicksburg, Le Tourneau and Yokena around 1150 PM CST.

Other locations impacted by this storm include Mound and Delta.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

High winds can bring down trees and large limbs resulting in serious
injury or property damage. Exercise extreme caution when outdoors
during such strong winds...and be especially aware of older trees.

&&

LAT...LON 3186 9144 3212 9166 3246 9100 3214 9075
TIME...MOT...LOC 0505Z 238DEG 39KT 3201 9145

JM

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Service Notice</title>
  <link rel="stylesheet" href="index.css">
</head>
<body>
  <main class="wrap">
    <section class="card" role="status" aria-live="polite">
      <div class="status" id="status">Temporary Notice</div>
      <h1 id="headline">This service is currently unavailable.</h1>
      <p id="message1">
        The site you requested is temporarily down for maintenance or an unexpected outage.
      </p>
      <p id="message2">
        Please try again in a few minutes.
      </p>
      <p class="small" id="detail">
        If you are an administrator, restore upstream service and remove the redirect/fallback rule when normal operations resume.
      </p>
    </section>
  </main>
  <script src="index.js"></script>
</body>
</html>