Alert archive / Louisiana / Tornado Watches in 2020
Tornado Watch 521
The Storm Prediction Center issued this tornado watch at Dec 31, 2020, 1:27 PM CST for 16 parishes in Louisiana; Newton County, Orange County, Texas. It was in force for 8 hr.
The area
The outline as issued.
The facts
- Issued
- Dec 31, 2020, 1:27 PM CST (19:27 UTC)
- Expired
- Dec 31, 2020, 9:00 PM CST
- In force
- 8 hr
- Issued by
- the Storm Prediction Center
- Largest hail expected
- 1 in
- Strongest gust expected
- 60 kt
Counties Acadia Parish, LA, Allen Parish, LA, Avoyelles Parish, LA, Beauregard Parish, LA, Calcasieu Parish, LA, Cameron Parish, LA, Evangeline Parish, LA, Iberia Parish, LA, Jefferson Davis Parish, LA, Lafayette Parish, LA, Rapides Parish, LA, Saint Landry Parish, LA, Saint Martin Parish, LA, St. Mary Parish, LA, Vermilion Parish, LA, Vernon Parish, LA, Newton County, TX, Orange County, TX
What SPC expected
The probabilities SPC published with the watch, for the watch area over its life.
- Two or more tornadoes
- 50%
- One or more EF2 to EF5 tornadoes
- 30%
- Ten or more severe wind reports
- 40%
- 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
- 10%
- Six or more combined severe hail and wind reports
- 60%
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 12:00Z, 7.5 hours before the alert went out and 37 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.
- Mixed-layer CAPE
- 238 J/kg
- Mixed-layer CIN
- -8 J/kg
- Mixed-layer LCL
- 492 m above ground
- 0-6 km bulk shear
- 58 kt
- 0-1 km storm-relative helicity
- 181 m²/s²
- 0-3 km storm-relative helicity
- 209 m²/s²
- Significant tornado parameter
- 0.2
- Supercell composite
- 1.9
The text
As transmitted.
898 WWUS20 KWNS 311919 SEL1 SPC WW 311919 LAZ000-TXZ000-CWZ000-010300- URGENT - IMMEDIATE BROADCAST REQUESTED Tornado Watch Number 521 NWS Storm Prediction Center Norman OK 120 PM CST Thu Dec 31 2020 The NWS Storm Prediction Center has issued a * Tornado Watch for portions of Southwest Louisiana Far southeast Texas Coastal Waters * Effective this Thursday afternoon and evening from 120 PM until 900 PM CST. * Primary threats include... A few tornadoes and a couple intense tornadoes possible Scattered damaging wind gusts to 70 mph possible SUMMARY...Squall line across the northwest Gulf through southeast Texas should advance north-northeast, with additional cells possible ahead of it. Low-level shear is favorable for embedded supercells capable of producing tornadoes in addition to damaging winds with the line. The tornado watch area is approximately along and 65 statute miles east and west of a line from 40 miles south southwest of Intracoastal City LA to 20 miles northeast of Fort Polk LA. For a complete depiction of the watch see the associated watch outline update (WOUS64 KWNS WOU1). 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. && OTHER WATCH INFORMATION...CONTINUE...WW 520... 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 19030. ...Grams
SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Dec 31, 7:10 AM CST | Mesoscale Discussion | SPC | Calcasieu | 95 min |
| Dec 31, 11:21 AM CST | Mesoscale Discussion | SPC | Cameron | 114 min |
| Dec 31, 2:44 PM CST | Mesoscale Discussion | SPC | Acadia, Allen, Beauregard, Calcasieu, Cameron, Evangeline and 4 more | 2 hr |
| Dec 31, 3:30 PM CST | Mesoscale Discussion | SPC | Ascension, Assumption, East Baton Rouge, East Feliciana, Iberville, Jefferson and 13 more | 2 hr |
| Dec 30, 8:15 PM CST | Mesoscale Discussion | SPC | Brewster, Crane, Pecos, Presidio, Upton | 6 hr |
| Dec 31, 2:16 AM CST | Mesoscale Discussion | SPC | Brewster, Crane, Glasscock, Pecos, Reagan, Sterling and 2 more | 6 hr |
| Dec 31, 7:40 AM CST | Tornado Watch | SPC | Brazoria, Chambers, Fort Bend, Galveston, Hardin, Harris and 7 more | 7 hr |
| Dec 31, 9:09 AM CST | Mesoscale Discussion | SPC | Archer, Baylor, Borden, Callahan, Childress, Clay and 39 more | 6 hr |
| Dec 31, 2:59 PM CST | Mesoscale Discussion | SPC | Baylor, Callahan, Coke, Cottle, Fisher, Foard and 16 more | 4 hr |
Nearby
Tornado Watches in Louisiana, 2020Tornado Watches in Texas, 2020Every 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.