Alert archive / Louisiana / Mesoscale Discussions in 2017

Mesoscale Discussion 920

May 30, 2017Jefferson Parish, Lafourche Parish, Terrebonne Parish, Louisiana

The Storm Prediction Center issued this mesoscale discussion at May 30, 2017, 1:00 PM CDT for Jefferson Parish, Lafourche Parish, Terrebonne Parish, Louisiana. It was in force for 3 hr.

The area

The outline as issued.

The facts

Issued: May 30, 2017, 1:00 PM CDT (18:00 UTC)
Expired: May 30, 2017, 3:30 PM CDT
In force: 3 hr
Issued by: the Storm Prediction Center
Chance of a watch: 5%

Counties Jefferson Parish, LA, Lafourche Parish, LA, Terrebonne Parish, LA

The nearest sounding before it

Slidell Radar S, LA (KSIL), launched 12:00Z, 6.0 hours before the alert went out and 135 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: 296 J/kg
Mixed-layer CIN: -26 J/kg
Mixed-layer LCL: 630 m above ground
0-6 km bulk shear: 17 kt
0-1 km storm-relative helicity: 184 m²/s²
0-3 km storm-relative helicity: 334 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

213 
ACUS11 KWNS 301800
SWOMCD
SPC MCD 301800 
LAZ000-302030-

Mesoscale Discussion 0920
NWS Storm Prediction Center Norman OK
0100 PM CDT Tue May 30 2017

Areas affected...A small part of southeast Louisiana (near and north
of the Gulf of Mexico coast)

Concerning...Severe potential...Watch unlikely 

Valid 301800Z - 302030Z

Probability of Watch Issuance...5 percent

SUMMARY...A locally greater, though marginal coverage, tornado risk
exists this afternoon across a small part of southeast Louisiana
from Terrebonne Parish into mainly central portions of Lafourche
Parish and southern St. Mary's Parish.  Some potential for this
marginal threat to develop/spread east into portions of Plaquemines
Parish later this afternoon to early evening.

DISCUSSION...Trends in mosaic radar imagery indicated a couple of
periodic and transient low-level rotational couplets with storms
across Terrebonne Parish and central Lafourche Parish.  These storms
were located in vicinity of an east-west oriented outflow boundary,
which extended from offshore the north-central gulf coast into far
southeast Louisiana (through central Terrebonne to southern St.
Mary's Parishes).  A very moist and unstable environment combined
with vertically veering winds, especially near and north of the
surface boundary, is enhancing the potential for storm rotation and
an attendant, mainly brief, tornado threat.  Overall coverage for
the area affected should remain limited this afternoon, precluding
higher severe probabilities in the Day 1 Convective Outlook and a
watch potential.

..Peters/Hart.. 05/30/2017

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

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

LAT...LON   29459172 29719120 29759075 29749036 29698992 29598972
            29388955 29328960 29239029 29269071 29259104 29259126
            29289156 29299172 29459172

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.