Alert archive / Louisiana / Mesoscale Discussions in 2017
Mesoscale Discussion 413
The Storm Prediction Center issued this mesoscale discussion at Apr 2, 2017, 11:37 PM CDT for 24 parishes in Louisiana; 24 counties in Mississippi. It was in force for 83 min.
The area
The outline as issued.
The facts
- Issued
- Apr 2, 2017, 11:37 PM CDT (04:37 UTC)
- Expired
- Apr 3, 2017, 1:00 AM CDT
- In force
- 83 min
- Issued by
- the Storm Prediction Center
All 48 counties
Acadia Parish, LA, Ascension Parish, LA, Assumption Parish, LA, Avoyelles Parish, LA, East Baton Rouge Parish, LA, East Feliciana Parish, LA, Evangeline Parish, LA, Iberville Parish, LA, Jefferson Davis Parish, LA, Lafayette Parish, LA, Livingston Parish, LA, Pointe Coupee Parish, LA, Saint Charles Parish, LA, Saint Helena Parish, LA, Saint James Parish, LA, Saint John the Baptist Parish, LA, Saint Landry Parish, LA, Saint Martin Parish, LA, Saint Tammany Parish, LA, Tangipahoa Parish, LA, Vermilion Parish, LA, Washington Parish, LA, West Baton Rouge Parish, LA, West Feliciana Parish, LA, Adams County, MS, Amite County, MS, Copiah County, MS, Covington County, MS, Forrest County, MS, Franklin County, MS, Hancock County, MS, Jasper County, MS, Jefferson County, MS, Jefferson Davis County, MS, Jones County, MS, Lamar County, MS, Lawrence County, MS, Lincoln County, MS, Marion County, MS, Pearl River County, MS, Perry County, MS, Pike County, MS, Simpson County, MS, Smith County, MS, Stone County, MS, Walthall County, MS, Wayne County, MS, Wilkinson County, MS
The watches that followed
Watches SPC issued over any of the same counties within four hours of this discussion.
The nearest sounding before it
Slidell Radar S, LA (KSIL), launched 00:00Z, 4.6 hours before the alert went out and 115 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
- 2436 J/kg
- Mixed-layer CIN
- 0 J/kg
- Mixed-layer LCL
- 480 m above ground
- 0-6 km bulk shear
- 57 kt
- 0-1 km storm-relative helicity
- 298 m²/s²
- 0-3 km storm-relative helicity
- 333 m²/s²
- Significant tornado parameter
- 4.6
- Supercell composite
- 19.5
The text
As transmitted.
091
ACUS11 KWNS 030437
SWOMCD
SPC MCD 030437
MSZ000-LAZ000-030600-
Mesoscale Discussion 0413
NWS Storm Prediction Center Norman OK
1137 PM CDT Sun Apr 02 2017
Areas affected...Portions of southern Louisiana and southern
Mississippi
Concerning...Tornado Watch 111...113...
Valid 030437Z - 030600Z
The severe weather threat for Tornado Watch 111, 113 continues.
SUMMARY...Threat for damaging winds and perhaps a couple of
tornadoes will potentially focus over southeastern Louisiana and
parts of southern Mississippi later tonight. A replacement watch may
be considered prior to the 07Z expiration of Watches 111/113.
DISCUSSION...An expansive mesoscale convective system continues late
this evening across the lower Mississippi Valley. While a
considerable precipitation shield over northern Louisiana and
central/northern Mississippi has limited the northward progress of a
warm front, deep/moist southerly flow across the warm sector is
maintaining robust convective elements within the broader system.
There has been a relative lull in severe reports recently, but a
modest uptick in the potential for damaging winds (and perhaps a
couple line-embedded tornadoes) may occur. With increasing
large-scale ascent associated with an approaching impulse, cells
should organize into a more focused meridional line from
southeastern Louisiana northward into Mississippi. MLCAPE values
around 1500-2500 J/kg will likely support a squall line that
advances towards the central Gulf Coast through the overnight.
Line-parallel low-level shear vectors suggest primarily an
occasional damaging-wind threat with this line. However, the
amplitude of low-level shear may also favor small-scale embedded
circulations. A replacement watch could be considered prior to the
07Z expiration of Watches 111/113.
..Picca.. 04/03/2017
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...MOB...JAN...LIX...LCH...
LAT...LON 29829259 30259300 31019224 31749123 32219047 32158888
31938853 31248864 30678908 30118987 29799051 29699162
29829259SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Apr 2, 8:07 PM CDT | Mesoscale Discussion | SPC | Acadia, Allen, Avoyelles, Beauregard, Calcasieu, Cameron and 8 more | 83 min |
| Apr 2, 8:24 PM CDT | Tornado Watch | SPC | Acadia, Allen, Avoyelles, Beauregard, Calcasieu, Cameron and 10 more | 6 hr |
| Apr 2, 9:09 PM CDT | Mesoscale Discussion | SPC | Catahoula, Concordia, East Baton Rouge, East Feliciana, Livingston, Madison and 8 more | 2 hr |
| Apr 3, 1:48 AM CDT | Tornado Watch | SPC | Ascension, Assumption, East Baton Rouge, East Feliciana, Jefferson, Lafourche and 12 more | 10 hr |
| Apr 3, 3:59 AM CDT | Mesoscale Discussion | SPC | Jefferson, Lafourche, Orleans, Plaquemines, Saint Bernard, Saint Charles and 6 more | 2 hr |
| Apr 3, 6:43 AM CDT | Mesoscale Discussion | SPC | Plaquemines, Saint Bernard | 2 hr |
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.