Alert archive / Louisiana / Tornado Watches in 2020

Tornado Watch 516

December 23, 202031 parishes in Louisiana; 8 counties in Mississippi

The Storm Prediction Center issued this tornado watch at Dec 23, 2020, 8:40 PM CST for 31 parishes in Louisiana; 8 counties in Mississippi. It was in force for 5 hr.

The area

The outline as issued.

The facts

Issued: Dec 23, 2020, 8:40 PM CST (02:40 UTC)
Expired: Dec 24, 2020, 2:00 AM CST
In force: 5 hr
Issued by: the Storm Prediction Center
Largest hail expected: 1 in
Strongest gust expected: 60 kt

All 39 counties

Acadia Parish, LA, Allen Parish, LA, Ascension Parish, LA, Assumption Parish, LA, Avoyelles Parish, LA, Beauregard Parish, LA, Calcasieu Parish, LA, Cameron Parish, LA, Catahoula Parish, LA, Concordia Parish, LA, East Baton Rouge Parish, LA, East Feliciana Parish, LA, Evangeline Parish, LA, Iberia Parish, LA, Iberville Parish, LA, Jefferson Davis Parish, LA, Lafayette Parish, LA, Livingston Parish, LA, Pointe Coupee Parish, LA, Rapides Parish, LA, Saint Helena Parish, LA, Saint James Parish, LA, Saint Landry Parish, LA, Saint Martin Parish, LA, St. Mary Parish, LA, Tangipahoa Parish, LA, Vermilion Parish, LA, Vernon Parish, LA, Washington Parish, LA, West Baton Rouge Parish, LA, West Feliciana Parish, LA, Adams County, MS, Amite County, MS, Franklin County, MS, Jefferson County, MS, Lincoln County, MS, Pike County, MS, Walthall County, MS, Wilkinson County, MS

What SPC expected

The probabilities SPC published with the watch, for the watch area over its life.

Two or more tornadoes: 40%
One or more EF2 to EF5 tornadoes: 20%
Ten or more severe wind reports: 50%
One or more gusts of 65 knots or more: 20%
Ten or more severe hail reports: 10%
One or more hailstones of 2 inches or more: 5%
Six or more combined severe hail and wind reports: 60%

Warnings issued inside it

9 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.

Issued	Product	Office	Counties	Lasted
Dec 23, 8:45 PM CST	Tornado Warning	LCH	Avoyelles, Rapides	18 min
Dec 23, 8:55 PM CST	Tornado Warning	LCH	Rapides, Vernon	35 min
Dec 23, 9:24 PM CST	Tornado Warning	LCH	Rapides	36 min
Dec 23, 9:59 PM CST	Severe Thunderstorm Warning	LCH	Avoyelles	46 min
Dec 23, 10:37 PM CST	Severe Thunderstorm Warning	JAN	Adams, Copiah, Franklin, Jefferson, Lincoln	53 min
Dec 23, 10:55 PM CST	Severe Thunderstorm Warning	LIX	East Feliciana, Pointe Coupee, West Feliciana	65 min
Dec 23, 11:07 PM CST	Tornado Warning	JAN	Copiah, Franklin, Jefferson, Lincoln	53 min
Dec 23, 11:51 PM CST	Tornado Warning	JAN	Copiah, Lawrence, Lincoln, Simpson	39 min
Dec 24, 12:15 AM CST	Tornado Warning	LIX	Saint Helena, Tangipahoa, Washington	13 min

Discussions around it

SPC mesoscale discussions over the same counties from four hours before the watch to its end.

The nearest sounding before it

Lake Charles Mun, LA (KLCH), launched 00:00Z, 2.7 hours before the alert went out and 52 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: 666 J/kg
Mixed-layer CIN: -15 J/kg
Mixed-layer LCL: 660 m above ground
0-6 km bulk shear: 57 kt
0-1 km storm-relative helicity: 227 m²/s²
0-3 km storm-relative helicity: 226 m²/s²
Significant tornado parameter: 1.0
Supercell composite: 4.5

Open this sounding in Storm Lab

The text

As transmitted.

159 
WWUS20 KWNS 240238
SEL6  
SPC WW 240238
LAZ000-MSZ000-TXZ000-CWZ000-240800-

URGENT - IMMEDIATE BROADCAST REQUESTED
Tornado Watch Number 516
NWS Storm Prediction Center Norman OK
840 PM CST Wed Dec 23 2020

The NWS Storm Prediction Center has issued a

* Tornado Watch for portions of 
  Central and Southern Louisiana
  Southwest Mississippi
  Southeast Texas
  Coastal Waters

* Effective this Wednesday night and Thursday morning from 840 PM
  until 200 AM CST.

* Primary threats include...
  A couple tornadoes possible
  Scattered damaging wind gusts to 70 mph possible

SUMMARY...A line of thunderstorms is intensifying from southeast
Texas into central Louisiana.  These storms will track across the
watch area this evening and tonight, posing a risk of locally
damaging wind gusts and perhaps a tornado or two.

The tornado watch area is approximately along and 80 statute miles
east and west of a line from 50 miles south southeast of Lake
Charles LA to 35 miles east northeast of Alexandria LA. For a
complete depiction of the watch see the associated watch outline
update (WOUS64 KWNS WOU6).

PRECAUTIONARY/PREPAREDNESS ACTIONS...

REMEMBER...A Tornado Watch means conditions are favorable for
tornadoes and severe thunderstorms in and close to the watch
area. Persons in these areas should be on the lookout for
threatening weather conditions and listen for later statements
and possible warnings.

&&

AVIATION...Tornadoes and a few severe thunderstorms with hail
surface and aloft to 1 inch. Extreme turbulence and surface wind
gusts to 60 knots. A few cumulonimbi with maximum tops to 450. Mean
storm motion vector 23030.

...Hart

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Dec 23, 10:51 PM CST	Mesoscale Discussion	SPC	Acadia, Ascension, Assumption, Cameron, East Baton Rouge, East Feliciana and 18 more	114 min
Dec 24, 1:02 AM CST	Mesoscale Discussion	SPC	Saint Tammany	58 min
Dec 24, 1:42 AM CST	Tornado Watch	SPC	Saint Tammany	7 hr

Nearby

Tornado Watches in Louisiana, 2020 Tornado Watches in Mississippi, 2020 Every tornado watch 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.