Alert archive / Louisiana / Mesoscale Discussions in 2024

Mesoscale Discussion 821

May 17, 202422 parishes in Louisiana; 5 counties in Mississippi

The Storm Prediction Center issued this mesoscale discussion at May 17, 2024, 9:17 PM CDT for 22 parishes in Louisiana; 5 counties in Mississippi. It was in force for 58 min.

The area

The outline as issued.

The facts

Issued: May 17, 2024, 9:17 PM CDT (02:17 UTC)
Expired: May 17, 2024, 10:15 PM CDT
In force: 58 min
Issued by: the Storm Prediction Center
Concerning: Severe potential...severe thunderstorm watch likely
Chance of a watch: 80%

All 27 counties

Ascension Parish, LA, Assumption Parish, LA, East Baton Rouge Parish, LA, Iberia Parish, LA, Iberville Parish, LA, Jefferson Parish, LA, Lafayette Parish, LA, Lafourche Parish, LA, Livingston Parish, LA, Orleans Parish, LA, Plaquemines Parish, LA, Saint Bernard Parish, LA, Saint Charles Parish, LA, Saint James Parish, LA, Saint John the Baptist Parish, LA, Saint Martin Parish, LA, Saint Tammany Parish, LA, St. Mary Parish, LA, Tangipahoa Parish, LA, Terrebonne Parish, LA, Vermilion Parish, LA, West Baton Rouge Parish, LA, Hancock County, MS, Harrison County, MS, Jackson County, MS, Pearl River County, MS, Stone County, MS

The radar

The Hammond radar (KHDC), 100 km from the middle of the area, began a volume at 02:18 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, 2.3 hours before the alert went out and 120 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: 3589 J/kg
Mixed-layer CIN: -2 J/kg
Mixed-layer LCL: 700 m above ground
0-6 km bulk shear: 58 kt
0-1 km storm-relative helicity: -40 m²/s²
0-3 km storm-relative helicity: 21 m²/s²
Significant tornado parameter: -1.2
Supercell composite: -4.6

Open this sounding in Storm Lab

The text

As transmitted.

142 
ACUS11 KWNS 180217
SWOMCD
SPC MCD 180217 
MSZ000-LAZ000-180315-

Mesoscale Discussion 0821
NWS Storm Prediction Center Norman OK
0917 PM CDT Fri May 17 2024

Areas affected...southern Louisiana and far southern Mississippi

Concerning...Severe potential...Severe Thunderstorm Watch likely 

Valid 180217Z - 180315Z

Probability of Watch Issuance...80 percent

SUMMARY...The severe weather threat will increase into the overnight
hours across southern Louisiana and far southern Mississippi.

DISCUSSION...A very moist Gulf airmass is in place across southern
Louisiana this evening with a 18.5 mean mixing ratio on the 00Z LIX
RAOB and mid to upper 70s dewpoints across most of the Delta. This
deep moisture is supporting 2500 to 4000 J/kg MUCAPE (per SPC
mesoanalysis) which should be maintained for much of the overnight
period across the region. Strong shear (60 to 70 knots) will support
supercells with a primary threat of large hail and damaging wind
gusts. Weak low-level flow, per LIX 00Z RAOB and HDC VWP, combined
with weak low-level lapse rates and at least partially elevated
inflow bases, should limit the tornado threat during the overnight
period. 

A severe thunderstorm watch is likely by 03Z to cover the overnight
supercell threat.

..Bentley/Smith.. 05/18/2024

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

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

LAT...LON   29339361 29999288 30539157 30878975 30868887 30708861
            30508843 30198841 29518871 29028896 28778959 28979075
            29079140 29009212 28919270 28879291 29339361

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
May 18, 11:44 AM CDT	Mesoscale Discussion	SPC	Attala, Carroll, Choctaw, Clay, Kemper, Lowndes and 7 more	2 hr

Nearby

Mesoscale Discussions in Louisiana, 2024 Mesoscale Discussions in Mississippi, 2024 Every mesoscale discussion in 2024

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.