Alert archive / Louisiana / Mesoscale Discussions in 2017

Mesoscale Discussion 84

January 21, 201711 parishes in Louisiana

The Storm Prediction Center issued this mesoscale discussion at Jan 21, 2017, 1:41 AM CST for 11 parishes in Louisiana. It was in force for 64 min.

The area

The outline as issued.

The facts

Issued: Jan 21, 2017, 1:41 AM CST (07:41 UTC)
Expired: Jan 21, 2017, 2:45 AM CST
In force: 64 min
Issued by: the Storm Prediction Center

Counties Acadia Parish, LA, Avoyelles Parish, LA, Cameron Parish, LA, Evangeline Parish, LA, Iberia Parish, LA, Jefferson Davis Parish, LA, Lafayette Parish, LA, Saint Landry Parish, LA, Saint Martin Parish, LA, St. Mary Parish, LA, Vermilion Parish, LA

The radar

The Lake Charles radar (KLCH), 94 km from the middle of the area, began a volume at 07:45 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 nearest sounding before it

Lake Charles Mun, LA (KLCH), launched 00:00Z, 7.7 hours before the alert went out and 92 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: 627 J/kg
Mixed-layer CIN: -37 J/kg
Mixed-layer LCL: 842 m above ground
0-6 km bulk shear: 47 kt
0-1 km storm-relative helicity: 68 m²/s²
0-3 km storm-relative helicity: 156 m²/s²
Significant tornado parameter: 0.2
Supercell composite: 0.9

Open this sounding in Storm Lab

The text

As transmitted.

077 
ACUS11 KWNS 210741
SWOMCD
SPC MCD 210741 
LAZ000-210845-

Mesoscale Discussion 0084
NWS Storm Prediction Center Norman OK
0141 AM CST Sat Jan 21 2017

Areas affected...southwest...south-central and central Louisiana

Concerning...Tornado Watch 9...

Valid 210741Z - 210845Z

The severe weather threat for Tornado Watch 9 continues.

SUMMARY...The greatest threat for additional severe storms across WW
9 is expected across eastern portions of this watch in south-central
and east-central Louisiana.  The portion of WW 9 in south-central
Louisiana may need to be extended temporally beyond the expiration
of 08Z as discrete storms continue to develop over that region and
also move inland from the Gulf of Mexico.

Meanwhile, storms tracking to the east-northeast from southeast
Texas into Louisiana should continue to diminish in intensity
allowing the rest of WW 9 to expire at 08Z.

DISCUSSION...Trends in early overnight water-vapor imagery indicated
two midlevel shortwave troughs aiding in focused thunderstorm
coverage across the northwest Gulf Coast region from southeast TX
through LA to southwest MS.

The lead impulse and associated thunderstorms from south-central LA
to southwest MS are expected to remain the primary severe-weather
threat, as this activity advances to the east-northeast into a
strongly sheared and moistening environment.  Backed (southerly)
low-level winds beneath southwesterly midlevel winds will sustain
bulk shear for organized storms.  LIX holograph also indicated 0-1
km SRH values around 200 m2/s2 favorable for low-level storm
rotation and a continued tornado threat for storms across
south-central LA.

..Peters.. 01/21/2017

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...LIX...LCH...

LAT...LON   29769362 30869254 31119226 31219175 30529168 29709114
            29429131 28989133 29099194 29419362 29769362

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Jan 20, 6:37 PM CST	Mesoscale Discussion	SPC	Acadia, Allen, Beauregard, Calcasieu, Cameron, Evangeline and 3 more	113 min
Jan 20, 7:32 PM CST	Tornado Watch	SPC	Acadia, Allen, Avoyelles, Beauregard, Calcasieu, Cameron and 9 more	6 hr
Jan 20, 10:04 PM CST	Mesoscale Discussion	SPC	Acadia, Allen, Avoyelles, Calcasieu, Cameron, Evangeline and 7 more	116 min
Jan 20, 10:44 PM CST	Mesoscale Discussion	SPC	Ascension, Assumption, East Baton Rouge, East Feliciana, Jefferson, Lafourche and 12 more	61 min
Jan 20, 11:00 PM CST	Tornado Watch	SPC	Ascension, Assumption, Concordia, East Baton Rouge, East Feliciana, Iberville and 17 more	8 hr
Jan 21, 2:55 AM CST	Mesoscale Discussion	SPC	Ascension, Assumption, East Baton Rouge, East Feliciana, Iberville, Jefferson and 16 more	2 hr
Jan 21, 6:35 AM CST	Mesoscale Discussion	SPC	Jefferson, Lafourche, Orleans, Plaquemines, Saint Bernard, Saint Charles and 1 more	55 min
Jan 21, 2:33 PM CST	Mesoscale Discussion	SPC	Bienville, Bossier, Caddo, Claiborne, De Soto, Jackson and 8 more	2 hr
Jan 21, 2:34 PM CST	Mesoscale Discussion	SPC	Allen, Ascension, Avoyelles, Catahoula, Concordia, East Baton Rouge and 16 more	2 hr
Jan 21, 3:29 PM CST	Tornado Watch	SPC	Acadia, Ascension, Avoyelles, Catahoula, Concordia, East Baton Rouge and 22 more	6 hr
Jan 21, 3:41 PM CST	Tornado Watch	SPC	Bienville, Bossier, Caddo, Caldwell, Claiborne, De Soto and 11 more	7 hr
Jan 21, 5:32 PM CST	Mesoscale Discussion	SPC	Avoyelles, Bienville, Bossier, Caddo, Caldwell, Catahoula and 23 more	118 min

Nearby

Mesoscale Discussions in Louisiana, 2017 Every mesoscale discussion 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.