Alert archive / Louisiana / Mesoscale Discussions in 2021

Mesoscale Discussion 1972

December 9, 202110 parishes in Louisiana; Hancock County, Pearl River County, Mississippi

The Storm Prediction Center issued this mesoscale discussion at Dec 9, 2021, 5:03 PM CST for 10 parishes in Louisiana; Hancock County, Pearl River County, Mississippi. It was in force for 87 min.

The area

The outline as issued.

The facts

Issued
Dec 9, 2021, 5:03 PM CST (23:03 UTC)
Expired
Dec 9, 2021, 6:30 PM CST
In force
87 min
Issued by
the Storm Prediction Center
Concerning
Severe potential...watch unlikely
Chance of a watch
5%

Counties Ascension Parish, LA, Livingston Parish, LA, Orleans Parish, LA, Saint Charles Parish, LA, Saint Helena Parish, LA, Saint James Parish, LA, Saint John the Baptist Parish, LA, Saint Tammany Parish, LA, Tangipahoa Parish, LA, Washington Parish, LA, Hancock County, MS, Pearl River County, MS

The nearest sounding before it

Slidell Radar S, LA (KSIL), launched 12:00Z, 11.1 hours before the alert went out and 57 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 2021-12-09Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 0 joules per kilogram.LCL10008507005003002001001 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 2021-12-09The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity 251 square meters per square second.19395878Sfc1 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
0 J/kg
Mixed-layer CIN
No buoyant parcel
Mixed-layer LCL
620 m above ground
0-6 km bulk shear
43 kt
0-1 km storm-relative helicity
251 m²/s²
0-3 km storm-relative helicity
272 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0

Open this sounding in Storm Lab

The text

As transmitted.

785 
ACUS11 KWNS 092303
SWOMCD
SPC MCD 092303 
MSZ000-LAZ000-100030-

Mesoscale Discussion 1972
NWS Storm Prediction Center Norman OK
0503 PM CST Thu Dec 09 2021

Areas affected...Parts of southeastern Louisiana and southern
Mississippi

Concerning...Severe potential...Watch unlikely 

Valid 092303Z - 100030Z

Probability of Watch Issuance...5 percent

SUMMARY...Loosely organized convective clusters will continue
tracking northeastward, capable of producing a localized damaging
wind gust or a brief tornado.

DISCUSSION...Recent radar trends depict some modest convective
organization over portions of southeastern LA, where a moist
boundary-layer (dewpoints in the upper 60s/lower 70s) is supporting
low-topped surface-based showers. The VWP from LIX shows veering
winds in the lowest 2 km, resulting in 0-1 km SRH of 150-200 m2/s2
north of a diffuse warm front and deep-layer shear near 50 knots.
These factors will support some potential for a strong to locally
damaging wind gust, and a brief tornado cannot be entirely ruled
out. The localized nature of the threat and low probability of
occurrence limits the need for a Watch.

..Weinman/Grams.. 12/09/2021

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

ATTN...WFO...JAN...LIX...

LAT...LON   29969081 30119099 30569102 31039093 31179067 31179028
            31038973 30808938 30458931 30068953 29878965 29779017
            29839048 29969081

Nearby

Mesoscale Discussions in Louisiana, 2021Mesoscale Discussions in Mississippi, 2021Every mesoscale discussion in 2021

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.