Alert archive / Louisiana / Mesoscale Discussions in 2021

Mesoscale Discussion 1743

September 14, 2021Orleans Parish, Saint Bernard Parish, Saint Tammany Parish, Louisiana; Hancock County, Mississippi

The Storm Prediction Center issued this mesoscale discussion at Sep 14, 2021, 12:32 PM CDT for Orleans Parish, Saint Bernard Parish, Saint Tammany Parish, Louisiana; Hancock County, Mississippi. It was in force for 88 min.

The area

The outline as issued.

The facts

Issued
Sep 14, 2021, 12:32 PM CDT (17:32 UTC)
Expired
Sep 14, 2021, 2:00 PM CDT
In force
88 min
Issued by
the Storm Prediction Center
Concerning
Severe potential...watch unlikely
Chance of a watch
20%

Counties Orleans Parish, LA, Saint Bernard Parish, LA, Saint Tammany Parish, LA, Hancock County, MS

The nearest sounding before it

Slidell Radar S, LA (KSIL), launched 12:00Z, 5.5 hours before the alert went out and 51 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-pSkew-T log-p diagram, Slidell Radar S, LA at 12:00Z on 2021-09-14Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 428 joules per kilogram.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Slidell Radar S, LA at 12:00Z on 2021-09-14The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 24 square meters per square second.1939Sfc1 km3 km6 km9 kmRMLM
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
428 J/kg
Mixed-layer CIN
-19 J/kg
Mixed-layer LCL
736 m above ground
0-6 km bulk shear
28 kt
0-1 km storm-relative helicity
24 m²/s²
0-3 km storm-relative helicity
136 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.3

Open this sounding in Storm Lab

The text

As transmitted.

577 
ACUS11 KWNS 141732
SWOMCD
SPC MCD 141732 
MSZ000-LAZ000-141900-

Mesoscale Discussion 1743
NWS Storm Prediction Center Norman OK
1232 PM CDT Tue Sep 14 2021

Areas affected...Southeast LA and vicinity

Concerning...Severe potential...Watch unlikely 

Valid 141732Z - 141900Z

Probability of Watch Issuance...20 percent

SUMMARY...The threat for a couple of supercells and an isolated
tornado will persist through the afternoon, but a watch does not
appear necessary at this time.

DISCUSSION...On the far eastern fringes of weakening Tropical Storm
Nicholas, there has been a recent uptick in supercell structures
within a broken southeast-northwest oriented band.  This convection
is just east of the more persistent clouds/rain that are reducing
buoyancy, and close to the east edge of the somewhat stronger
flow/hodograph curvature noted in the LIX VWP.  The environment is
sufficient for occasional rotating storms in the eastern convective
bands of Nicolas, though the threat for more than an isolated/brief
tornado is still in question given only slow expected changes to the
environment.  Thus, this area will continue to be monitored, but a
tornado watch does not appear necessary at this time.

..Thompson.. 09/14/2021

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

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

LAT...LON   29078937 29708983 30099040 30439046 30649028 30648987
            30328930 29688865 29248860 28998900 29078937

SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Sep 14, 12:41 AM CDTMesoscale DiscussionSPCCameron3 hr

Nearby

Mesoscale Discussions in Louisiana, 2021Mesoscale Discussions in Mississippi, 2021Every 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.