Alert archive / Louisiana / Mesoscale Discussions in 2017
Mesoscale Discussion 704
The Storm Prediction Center issued this mesoscale discussion at May 12, 2017, 9:56 AM CDT for Washington County, Alabama; 14 parishes in Louisiana; 13 counties in Mississippi. It was in force for 3 hr.
The area
The outline as issued.
The facts
- Issued
- May 12, 2017, 9:56 AM CDT (14:56 UTC)
- Expired
- May 12, 2017, 12:30 PM CDT
- In force
- 3 hr
- Issued by
- the Storm Prediction Center
- Chance of a watch
- 60%
All 28 counties
Washington County, AL, Ascension Parish, LA, Assumption Parish, LA, Jefferson Parish, LA, Lafourche Parish, LA, Livingston Parish, LA, Orleans Parish, LA, Saint Charles Parish, LA, Saint James Parish, LA, Saint John the Baptist Parish, LA, Saint Tammany Parish, LA, St. Mary Parish, LA, Tangipahoa Parish, LA, Terrebonne Parish, LA, Washington Parish, LA, Covington County, MS, Forrest County, MS, George County, MS, Greene County, MS, Hancock County, MS, Harrison County, MS, Jones County, MS, Lamar County, MS, Marion County, MS, Pearl River County, MS, Perry County, MS, Stone County, MS, Wayne 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 12:00Z, 2.9 hours before the alert went out and 39 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
- 1224 J/kg
- Mixed-layer CIN
- -6 J/kg
- Mixed-layer LCL
- 587 m above ground
- 0-6 km bulk shear
- 47 kt
- 0-1 km storm-relative helicity
- 118 m²/s²
- 0-3 km storm-relative helicity
- 136 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 2.5
The text
As transmitted.
618
ACUS11 KWNS 121457
SWOMCD
SPC MCD 121456
ALZ000-MSZ000-LAZ000-121730-
Mesoscale Discussion 0704
NWS Storm Prediction Center Norman OK
0956 AM CDT Fri May 12 2017
Areas affected...Southeast Louisiana...Southern Mississippi and
Southwest Alabama
Concerning...Severe potential...Watch possible
Valid 121456Z - 121730Z
Probability of Watch Issuance...60 percent
SUMMARY...An isolated wind damage threat along with a potential for
a brief tornado will exist across southeast Louisiana and southern
Mississippi over the next couple of hours. Weather watch issuance
may be needed across the region late this morning.
DISCUSSION...The latest surface analysis shows a corridor of
low-level moisture from southeast Louisiana extending northeastward
into southern Mississippi. A line of convection is located along the
western edge of the moist corridor with surface dewpoints ahead of
the line in the upper 60s to mid 70s F. Surface temperatures have
warmed into the upper 70s to near 80 F across southeast Louisiana
which has helped the line to become a bit more organized over the
last hour. The line is being supported by strong large-scale ascent
associated with a shortwave trough moving across the lower
Mississippi Valley evident on water vapor imagery. The line was also
located near the axis of the strongest mid-level flow which was
helping to create moderate deep-layer shear, sampled by the New
Orleans WSR-88D VWP. The VWP shows 0-6 km of 50-55 kt with veered
southwesterly flow in the lowest 1 km AGL. This wind profile could
be favorable for some damaging wind gusts with cells that obtain a
bowing structure. Although low-level shear appears relatively weak,
a brief tornado can not be ruled out along a gust front.
..Broyles/Goss.. 05/12/2017
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...MOB...JAN...LIX...LCH...
LAT...LON 31988866 31828949 30739046 30109140 29599182 29249156
29159075 29378993 30228890 31558791 31988866SPC that day
Everything else SPC issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| May 12, 10:35 AM CDT | Severe Thunderstorm Watch | SPC | Baldwin, Escambia, Mobile | 5 hr |
| May 12, 10:56 AM CDT | Mesoscale Discussion | SPC | Bibb, Blount, Calhoun, Cherokee, Chilton, Clay and 16 more | 3 hr |
| May 12, 1:06 PM CDT | Mesoscale Discussion | SPC | Blount, Calhoun, Cherokee, Clay, Cleburne, Cullman and 7 more | 2 hr |
| May 12, 1:42 PM CDT | Mesoscale Discussion | SPC | Baldwin, Barbour, Butler, Coffee, Conecuh, Covington and 8 more | 108 min |
| May 12, 4:24 AM CDT | Mesoscale Discussion | SPC | Acadia, Allen, Beauregard, Calcasieu, Cameron, Evangeline and 4 more | 3 hr |
| May 12, 10:59 AM CDT | Mesoscale Discussion | SPC | Morehouse, West Carroll | 3 hr |
| May 12, 1:43 PM CDT | Mesoscale Discussion | SPC | Ascension, Assumption, East Baton Rouge, East Feliciana, Iberville, Livingston and 12 more | 3 hr |
Nearby
Mesoscale Discussions in Louisiana, 2017Mesoscale Discussions in Mississippi, 2017Mesoscale Discussions in Alabama, 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.