Alert archive / Louisiana / Mesoscale Discussions in 2018

Mesoscale Discussion 1735

December 27, 201817 parishes in Louisiana; Adams County, Wilkinson County, Mississippi; Jefferson County, Orange County, Texas

The Storm Prediction Center issued this mesoscale discussion at Dec 27, 2018, 7:12 AM CST for 17 parishes in Louisiana; Adams County, Wilkinson County, Mississippi; Jefferson County, Orange County, Texas. It was in force for 2 hr.

The area

The outline as issued.

The facts

Issued: Dec 27, 2018, 7:12 AM CST (13:12 UTC)
Expired: Dec 27, 2018, 9:15 AM CST
In force: 2 hr
Issued by: the Storm Prediction Center

All 21 counties

Acadia Parish, LA, Allen Parish, LA, Avoyelles Parish, LA, Beauregard Parish, LA, Calcasieu Parish, LA, Cameron Parish, LA, Catahoula Parish, LA, Concordia Parish, LA, Evangeline Parish, LA, Grant Parish, LA, Jefferson Davis Parish, LA, Lafayette Parish, LA, LaSalle Parish, LA, Pointe Coupee Parish, LA, Rapides Parish, LA, Saint Landry Parish, LA, Vernon Parish, LA, Adams County, MS, Wilkinson County, MS, Jefferson County, TX, Orange County, TX

The radar

The Lake Charles radar (KLCH), 35 km from the middle of the area, began a volume at 13:10 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 watches that followed

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

Tornado Watch 448Dec 27, 9:30 AM CST

The nearest sounding before it

Lake Charles Mun, LA (KLCH), launched 12:00Z, 1.2 hours before the alert went out and 35 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: 1148 J/kg
Mixed-layer CIN: -9 J/kg
Mixed-layer LCL: 508 m above ground
0-6 km bulk shear: 54 kt
0-1 km storm-relative helicity: 497 m²/s²
0-3 km storm-relative helicity: 738 m²/s²
Significant tornado parameter: 4.5
Supercell composite: 17.5

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
Dec 26, 11:40 PM CST	Mesoscale Discussion	SPC	Bossier, Caddo, De Soto	2 hr
Dec 27, 12:02 AM CST	Severe Thunderstorm Watch	SPC	Bienville, Bossier, Caddo, Claiborne, De Soto, Red River and 1 more	5 hr
Dec 27, 1:39 AM CST	Mesoscale Discussion	SPC	Bienville, Bossier, Caddo, Claiborne, De Soto, Lincoln and 2 more	2 hr
Dec 27, 3:09 AM CST	Mesoscale Discussion	SPC	Allen, Beauregard, Calcasieu, Cameron, Jefferson Davis, Vernon	2 hr
Dec 27, 3:43 AM CST	Tornado Watch	SPC	Acadia, Allen, Beauregard, Calcasieu, Caldwell, Cameron and 10 more	10 hr
Dec 27, 9:00 AM CST	Mesoscale Discussion	SPC	Avoyelles, Catahoula, Concordia, East Baton Rouge, East Feliciana, Iberville and 6 more	60 min
Dec 27, 9:29 AM CST	Tornado Watch	SPC	Ascension, Assumption, Avoyelles, Catahoula, Concordia, East Baton Rouge and 27 more	9 hr
Dec 27, 1:50 PM CST	Mesoscale Discussion	SPC	Ascension, Assumption, Catahoula, Concordia, East Baton Rouge, East Feliciana and 19 more	85 min
Dec 26, 7:13 PM CST	Mesoscale Discussion	SPC	Bell, Bosque, Collin, Cooke, Dallas, Delta and 22 more	2 hr
Dec 26, 8:51 PM CST	Mesoscale Discussion	SPC	Atascosa, Bandera, Bastrop, Bexar, Blanco, Caldwell and 18 more	114 min
Dec 26, 9:34 PM CST	Tornado Watch	SPC	Anderson, Angelina, Brazos, Burleson, Cherokee, Falls and 29 more	6 hr

Nearby

Mesoscale Discussions in Louisiana, 2018 Mesoscale Discussions in Mississippi, 2018 Mesoscale Discussions in Texas, 2018 Every mesoscale discussion in 2018

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.