Alert archive / Louisiana / Mesoscale Discussions in 2017

Mesoscale Discussion 87

January 21, 20177 parishes in Louisiana; 4 counties in Mississippi

The Storm Prediction Center issued this mesoscale discussion at Jan 21, 2017, 6:35 AM CST for 7 parishes in Louisiana; 4 counties in Mississippi. It was in force for 55 min.

The area

The outline as issued.

The facts

Issued
Jan 21, 2017, 6:35 AM CST (12:35 UTC)
Expired
Jan 21, 2017, 7:30 AM CST
In force
55 min
Issued by
the Storm Prediction Center

Counties Jefferson Parish, LA, Lafourche Parish, LA, Orleans Parish, LA, Plaquemines Parish, LA, Saint Bernard Parish, LA, Saint Charles Parish, LA, Terrebonne Parish, LA, George County, MS, Hancock County, MS, Harrison County, MS, Jackson County, MS

The nearest sounding before it

Slidell Radar S, LA (KSIL), launched 12:00Z, 0.6 hours before the alert went out and 71 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-pSkew-T log-p diagram, Slidell Radar S, LA at 12:00Z on 2017-01-21Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 1327 joules per kilogram.LCLEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Slidell Radar S, LA at 12:00Z on 2017-01-21The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 275 square meters per square second.1939587897117136Sfc1 km3 km6 km9 kmRMLM
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
1327 J/kg
Mixed-layer CIN
0 J/kg
Mixed-layer LCL
508 m above ground
0-6 km bulk shear
51 kt
0-1 km storm-relative helicity
275 m²/s²
0-3 km storm-relative helicity
323 m²/s²
Significant tornado parameter
2.4
Supercell composite
11.2

Open this sounding in Storm Lab

The text

As transmitted.

917 
ACUS11 KWNS 211235
SWOMCD
SPC MCD 211235 
ALZ000-MSZ000-LAZ000-211330-

Mesoscale Discussion 0087
NWS Storm Prediction Center Norman OK
0635 AM CST Sat Jan 21 2017

Areas affected...Extreme southeast Mississippi and southeast
Louisiana

Concerning...Tornado Watch 10...

Valid 211235Z - 211330Z

The severe weather threat for Tornado Watch 10 continues.

SUMMARY...Locally strong wind gusts should be the primary
severe-weather threat within the remaining valid area of WW 10
(across southeast Louisiana and extreme southeast Mississippi) until
13Z.  However, given strong low-level shear, a tornado threat cannot
be ruled out.

DISCUSSION...At 12Z, mosaic radar imagery and trends in surface
mesoanalyses indicated a well-defined comma head/mesolow had moved
into west-central Alabama and was located from Marengo to Sumter
Counties.  This low is associated with a progressive shortwave
trough expected to move into Alabama through this morning with the
expected downstream northward transport of mid-upper 60s F dew
points well underway across southern Alabama into west-central
Georgia.  Meanwhile, mosaic radar imagery also indicated a trailing
band of strong to occasionally severe storms extending from the
mesolow through extreme southeast Mississippi to southeast
Louisiana.  Low-level winds per LIX 12Z sounding and WSR-88D VWP
data have begun to veer to southwesterly, becoming parallel to the
trailing band of storms.  This will continue to limit low-level
convergence into these east-southeastward-moving storms, with a
gradual diminishing trend in a severe-weather threat through 13Z
across the remaining portion of WW 10.

..Peters/Thompson.. 01/21/2017

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

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

LAT...LON   29699125 30328981 30808903 31388838 29898828 28898868
            28658936 28879010 28839089 28899124 29699125

SPC that day

Everything else SPC issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Jan 20, 6:37 PM CSTMesoscale DiscussionSPCAcadia, Allen, Beauregard, Calcasieu, Cameron, Evangeline and 3 more113 min
Jan 20, 7:32 PM CSTTornado WatchSPCAcadia, Allen, Avoyelles, Beauregard, Calcasieu, Cameron and 9 more6 hr
Jan 20, 10:04 PM CSTMesoscale DiscussionSPCAcadia, Allen, Avoyelles, Calcasieu, Cameron, Evangeline and 7 more116 min
Jan 20, 10:44 PM CSTMesoscale DiscussionSPCAscension, Assumption, East Baton Rouge, East Feliciana, Jefferson, Lafourche and 12 more61 min
Jan 20, 11:00 PM CSTTornado WatchSPCAscension, Assumption, Concordia, East Baton Rouge, East Feliciana, Iberville and 17 more8 hr
Jan 21, 1:41 AM CSTMesoscale DiscussionSPCAcadia, Avoyelles, Cameron, Evangeline, Iberia, Jefferson Davis and 5 more64 min
Jan 21, 2:55 AM CSTMesoscale DiscussionSPCAscension, Assumption, East Baton Rouge, East Feliciana, Iberville, Jefferson and 16 more2 hr
Jan 21, 2:33 PM CSTMesoscale DiscussionSPCBienville, Bossier, Caddo, Claiborne, De Soto, Jackson and 8 more2 hr
Jan 21, 2:34 PM CSTMesoscale DiscussionSPCAllen, Ascension, Avoyelles, Catahoula, Concordia, East Baton Rouge and 16 more2 hr
Jan 21, 3:29 PM CSTTornado WatchSPCAcadia, Ascension, Avoyelles, Catahoula, Concordia, East Baton Rouge and 22 more6 hr
Jan 21, 3:41 PM CSTTornado WatchSPCBienville, Bossier, Caddo, Caldwell, Claiborne, De Soto and 11 more7 hr
Jan 21, 5:32 PM CSTMesoscale DiscussionSPCAvoyelles, Bienville, Bossier, Caddo, Caldwell, Catahoula and 23 more118 min

Nearby

Mesoscale Discussions in Louisiana, 2017Mesoscale Discussions in Mississippi, 2017Every 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.