Alert archive / Louisiana / Mesoscale Discussions in 2021

Mesoscale Discussion 378

April 13, 20217 parishes in Louisiana

The Storm Prediction Center issued this mesoscale discussion at Apr 13, 2021, 2:44 PM CDT for 7 parishes in Louisiana. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued: Apr 13, 2021, 2:44 PM CDT (19:44 UTC)
Expired: Apr 13, 2021, 4:45 PM CDT
In force: 2 hr
Issued by: the Storm Prediction Center
Concerning: Severe thunderstorm watch 94

Counties Iberia Parish, LA, Jefferson Parish, LA, Lafourche Parish, LA, Plaquemines Parish, LA, St. Mary Parish, LA, Terrebonne Parish, LA, Vermilion Parish, LA

The nearest sounding before it

Slidell Radar S, LA (KSIL), launched 12:00Z, 7.7 hours before the alert went out and 138 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: 0 J/kg
Mixed-layer CIN: No buoyant parcel
Mixed-layer LCL: 1989 m above ground
0-6 km bulk shear: 41 kt
0-1 km storm-relative helicity: 70 m²/s²
0-3 km storm-relative helicity: 88 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

768 
ACUS11 KWNS 131944
SWOMCD
SPC MCD 131944 
LAZ000-132145-

Mesoscale Discussion 0378
NWS Storm Prediction Center Norman OK
0244 PM CDT Tue Apr 13 2021

Areas affected...southern Louisiana

Concerning...Severe Thunderstorm Watch 94...

Valid 131944Z - 132145Z

The severe weather threat for Severe Thunderstorm Watch 94
continues.

SUMMARY...Severe risk continues -- mainly over coastal areas of
southern Louisiana.

DISCUSSION...Latest radar loop shows outflow from widespread inland
convection now moving southward toward/off the southern Louisiana
Coast, and is expected to clear all Parishes west of the river in
the next 1 to 2 hours.  Greatest ongoing severe risk remains with
the more surface-based storms near this outflow -- across
Terrebonne/Lafourche/Jefferson/Plaquemines Parishes, where large
hail and locally strong/possibly damaging gusts may occur.

Elsewhere, weaker storms in a warm-advection regime north of the
outflow are increasing across south central Louisiana.  While some
hail cannot be ruled out, the greater risk should taper off as
outflow advances into the northern Gulf of Mexico.

..Goss.. 04/13/2021

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

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

LAT...LON   29789242 29899211 29839161 29719098 29749058 29998996
            29858932 29468905 28808883 28729130 29289212 29789242

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Apr 13, 8:28 AM CDT	Mesoscale Discussion	SPC	Acadia, Allen, Ascension, Assumption, Avoyelles, East Baton Rouge and 11 more	2 hr
Apr 13, 11:43 AM CDT	Mesoscale Discussion	SPC	Ascension, Assumption, East Baton Rouge, Iberia, Iberville, Jefferson and 16 more	2 hr
Apr 13, 12:06 PM CDT	Severe Thunderstorm Watch	SPC	Ascension, Assumption, Iberia, Iberville, Jefferson, Lafourche and 10 more	6 hr
Apr 13, 3:43 PM CDT	Mesoscale Discussion	SPC	De Soto	2 hr

Nearby

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.