Alert archive / Louisiana / Mesoscale Discussions in 2020

Mesoscale Discussion 1707

September 23, 202025 parishes in Louisiana; 6 counties in Mississippi

The Storm Prediction Center issued this mesoscale discussion at Sep 23, 2020, 1:14 PM CDT for 25 parishes in Louisiana; 6 counties in Mississippi. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued: Sep 23, 2020, 1:14 PM CDT (18:14 UTC)
Expired: Sep 23, 2020, 3:15 PM CDT
In force: 2 hr
Issued by: the Storm Prediction Center
Concerning: Severe potential...watch possible
Chance of a watch: 40%

All 31 counties

Allen Parish, LA, Ascension Parish, LA, Assumption Parish, LA, Avoyelles Parish, LA, Catahoula Parish, LA, Concordia Parish, LA, East Baton Rouge Parish, LA, East Feliciana Parish, LA, Evangeline Parish, LA, Iberville Parish, LA, Lafayette Parish, LA, LaSalle Parish, LA, Livingston Parish, LA, Pointe Coupee Parish, LA, Rapides Parish, LA, Saint Charles Parish, LA, Saint Helena Parish, LA, Saint James Parish, LA, Saint John the Baptist Parish, LA, Saint Landry Parish, LA, Saint Martin Parish, LA, Saint Tammany Parish, LA, Tangipahoa Parish, LA, West Baton Rouge Parish, LA, West Feliciana Parish, LA, Adams County, MS, Amite County, MS, Franklin County, MS, Jefferson County, MS, Pike County, MS, Wilkinson County, MS

The watches that followed

Watches SPC issued over any of the same counties within four hours of this discussion.

Tornado Watch 494Sep 23, 2:35 PM CDT

The nearest sounding before it

Slidell Radar S, LA (KSIL), launched 12:00Z, 6.2 hours before the alert went out and 182 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: 10 J/kg
Mixed-layer CIN: -271 J/kg
Mixed-layer LCL: 649 m above ground
0-6 km bulk shear: 28 kt
0-1 km storm-relative helicity: 161 m²/s²
0-3 km storm-relative helicity: 242 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.3

Open this sounding in Storm Lab

The text

As transmitted.

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SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Sep 23, 2:37 PM CDT	Tornado Watch	SPC	Avoyelles, Catahoula, Concordia, East Baton Rouge, East Feliciana, Pointe Coupee and 4 more	7 hr
Sep 23, 5:20 PM CDT	Mesoscale Discussion	SPC	Avoyelles, Concordia, East Feliciana, Pointe Coupee, Saint Landry, West Feliciana	115 min

Nearby

Mesoscale Discussions in Louisiana, 2020 Mesoscale Discussions in Mississippi, 2020 Every mesoscale discussion in 2020

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.