Alert archive / Louisiana / Tornado Watches in 2017
Tornado Watch 474
The Storm Prediction Center issued this tornado watch at Aug 28, 2017, 12:16 PM CDT for 26 parishes in Louisiana; Jefferson County, Orange County, Texas. It was in force for 12 hr.
The area
The outline as issued.
The facts
- Issued
- Aug 28, 2017, 12:16 PM CDT (17:16 UTC)
- Expired
- Aug 29, 2017, 12:00 AM CDT
- In force
- 12 hr
- Issued by
- the Storm Prediction Center
- Largest hail expected
- 0.5 in
- Strongest gust expected
- 55 kt
All 28 counties
Acadia Parish, LA, Ascension Parish, LA, Assumption Parish, LA, Calcasieu Parish, LA, Cameron Parish, LA, East Baton Rouge Parish, LA, Iberia Parish, LA, Iberville Parish, LA, Jefferson Davis 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, Jefferson County, TX, Orange County, TX
The radar
The Lake Charles radar (KLCH), 85 km from the middle of the area, began a volume at 17:16 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.
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
- 20%
- One or more gusts of 65 knots or more
- 10%
- Ten or more severe hail reports
- 5%
- One or more hailstones of 2 inches or more
- 5%
- Six or more combined severe hail and wind reports
- 30%
Warnings issued inside it
12 tornado, severe thunderstorm and flash flood warnings for its counties while it was in force.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 28, 12:24 PM CDT | Tornado Warning | LCH | Saint Martin | 36 min |
| Aug 28, 12:34 PM CDT | Tornado Warning | LIX | Lafourche, Saint Charles | 56 min |
| Aug 28, 12:58 PM CDT | Tornado Warning | LCH | Saint Martin, St. Mary | 32 min |
| Aug 28, 1:02 PM CDT | Tornado Warning | LCH | Cameron | 28 min |
| Aug 28, 2:30 PM CDT | Tornado Warning | LCH | Jefferson | 30 min |
| Aug 28, 3:14 PM CDT | Tornado Warning | LCH | Jefferson | 31 min |
| Aug 28, 3:42 PM CDT | Tornado Warning | LCH | Hardin, Jefferson | 33 min |
| Aug 28, 4:20 PM CDT | Tornado Warning | LCH | Calcasieu, Cameron, Jefferson Davis | 25 min |
| Aug 28, 4:45 PM CDT | Tornado Warning | LCH | Cameron | 30 min |
| Aug 28, 5:55 PM CDT | Flash Flood Warning | LCH | Hardin, Jasper, Jefferson, Newton, Orange | 28 hr |
| Aug 28, 6:41 PM CDT | Flash Flood Warning | LCH | Calcasieu, Cameron, Jefferson Davis | 7 hr |
| Aug 28, 7:47 PM CDT | Tornado Warning | LCH | Cameron | 43 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 12:00Z, 5.3 hours before the alert went out and 83 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
- 169 J/kg
- Mixed-layer CIN
- -37 J/kg
- Mixed-layer LCL
- 610 m above ground
- 0-6 km bulk shear
- 50 kt
- 0-1 km storm-relative helicity
- 377 m²/s²
- 0-3 km storm-relative helicity
- 499 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 2.8
The text
As transmitted.
257 WWUS20 KWNS 281713 SEL4 SPC WW 281713 LAZ000-TXZ000-CWZ000-290500- URGENT - IMMEDIATE BROADCAST REQUESTED Tornado Watch Number 474 NWS Storm Prediction Center Norman OK 1215 PM CDT Mon Aug 28 2017 The NWS Storm Prediction Center has issued a * Tornado Watch for portions of Southern Louisiana Far southeast Texas Coastal Waters * Effective this Monday from 1215 PM until Midnight CDT. * Primary threats include... A couple tornadoes possible Isolated damaging wind gusts to 65 mph possible SUMMARY...A risk for brief tornadoes and locally damaging winds will persist through this evening with multiple bands of storms associated with Tropical Cyclone Harvey. The tornado watch area is approximately along and 55 statute miles north and south of a line from 30 miles south southwest of Port Arthur TX to 35 miles east southeast of New Orleans LA. For a complete depiction of the watch see the associated watch outline update (WOUS64 KWNS WOU4). 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...This tornado watch replaces tornado watch number 473. Watch number 473 will not be in effect after 1215 PM CDT. AVIATION...Tornadoes and a few severe thunderstorms with hail surface and aloft to 0.5 inches. Extreme turbulence and surface wind gusts to 55 knots. A few cumulonimbi with maximum tops to 500. Mean storm motion vector 23020. ...Grams
SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Aug 27, 9:50 PM CDT | Mesoscale Discussion | SPC | Acadia, Calcasieu, Cameron, Jefferson Davis, Vermilion | 115 min |
| Aug 28, 1:51 AM CDT | Tornado Watch | SPC | Acadia, Calcasieu, Cameron, Iberia, Jefferson Davis, Vermilion | 10 hr |
| Aug 28, 11:37 AM CDT | Mesoscale Discussion | SPC | Acadia, Ascension, Assumption, Calcasieu, Cameron, Iberia and 13 more | 83 min |
| Aug 28, 3:58 PM CDT | Mesoscale Discussion | SPC | Acadia, Calcasieu, Cameron, Iberia, Jefferson Davis, Lafayette and 3 more | 92 min |
| Aug 28, 6:49 PM CDT | Mesoscale Discussion | SPC | Acadia, Ascension, Assumption, Calcasieu, Cameron, Iberia and 16 more | 116 min |
| Aug 27, 7:45 PM CDT | Mesoscale Discussion | SPC | Carson, Dallam, Hansford, Hartley, Hutchinson, Moore and 3 more | 2 hr |
| Aug 28, 3:00 AM CDT | Mesoscale Discussion | SPC | Jefferson | 60 min |
Nearby
Tornado Watches in Louisiana, 2017Tornado Watches in Texas, 2017Every tornado watch in 2017
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.