Alert archive / Mississippi / Mesoscale Discussions in 2021

Mesoscale Discussion 1752

September 15, 2021Saint Bernard Parish, Louisiana; Hancock County, Harrison County, Jackson County, Mississippi

The Storm Prediction Center issued this mesoscale discussion at Sep 15, 2021, 4:49 AM CDT for Saint Bernard Parish, Louisiana; Hancock County, Harrison County, Jackson County, Mississippi. It was in force for 116 min.

The area

The outline as issued.

The facts

Issued: Sep 15, 2021, 4:49 AM CDT (09:49 UTC)
Expired: Sep 15, 2021, 6:45 AM CDT
In force: 116 min
Issued by: the Storm Prediction Center
Concerning: Severe potential...watch unlikely
Chance of a watch: 5%

Counties Saint Bernard Parish, LA, Hancock County, MS, Harrison County, MS, Jackson County, MS

The radar

The Mobile radar (KMOB), 115 km from the middle of the area, began a volume at 09:48 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

The nearest sounding before it

Slidell Radar S, LA (KSIL), launched 00:00Z, 9.8 hours before the alert went out and 49 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 136 J/kg
Mixed-layer CIN: -10 J/kg
Mixed-layer LCL: 589 m above ground
0-6 km bulk shear: 31 kt
0-1 km storm-relative helicity: 29 m²/s²
0-3 km storm-relative helicity: 181 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.1

Open this sounding in Storm Lab

The text

As transmitted.

672 
ACUS11 KWNS 150950
SWOMCD
SPC MCD 150949 
ALZ000-MSZ000-LAZ000-151145-

Mesoscale Discussion 1752
NWS Storm Prediction Center Norman OK
0449 AM CDT Wed Sep 15 2021

Areas affected...southeast LA...coastal MS

Concerning...Severe potential...Watch unlikely 

Valid 150949Z - 151145Z

Probability of Watch Issuance...5 percent

SUMMARY...Transient/weak mesocyclones embedded within a rain shield
will potentially be capable of a tornado risk for the next few
hours.

DISCUSSION...KLIX radar imagery over the past couple of hours has
shown an increase in the number and intensity of low-level
mesocyclones over southeast LA and adjacent coastal waters south of
the MS coast.  KLIX VAD data shows a supportive hodograph for
low-level rotation and surface observations and RAP forecast
soundings indicate a very moist/weakly buoyant environment.  As
such, transient supercell structure will probably continue in the
short term and potentially pose a weak/short-lived tornado threat
with any more persistent/intense circulations.  The overall
magnitude and isolated character of the tornado risk will likely
preclude a tornado watch issuance.

..Smith/Guyer.. 09/15/2021

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...MOB...LIX...

LAT...LON   29938996 30308981 30618921 30518837 30228825 29638881
            29638945 29938996

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Sep 15, 12:26 PM CDT	Mesoscale Discussion	SPC	George, Hancock, Harrison, Jackson, Pearl River, Stone	3 hr

Nearby

Mesoscale Discussions in Mississippi, 2021 Mesoscale Discussions in Louisiana, 2021 Every mesoscale discussion in 2021

Sources

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.