Alert archive / Louisiana / Mesoscale Discussions in 2021

Mesoscale Discussion 472

May 2, 202114 parishes in Louisiana; Newton County, Sabine County, Texas

The Storm Prediction Center issued this mesoscale discussion at May 2, 2021, 1:47 PM CDT for 14 parishes in Louisiana; Newton County, Sabine County, Texas. It was in force for 88 min.

The area

The outline as issued.

The facts

Issued: May 2, 2021, 1:47 PM CDT (18:47 UTC)
Expired: May 2, 2021, 3:15 PM CDT
In force: 88 min
Issued by: the Storm Prediction Center
Concerning: Severe potential...watch unlikely
Chance of a watch: 20%

Counties Allen Parish, LA, Beauregard Parish, LA, Bienville Parish, LA, Caldwell Parish, LA, Catahoula Parish, LA, Grant Parish, LA, Jackson Parish, LA, LaSalle Parish, LA, Natchitoches Parish, LA, Rapides Parish, LA, Red River Parish, LA, Sabine Parish, LA, Vernon Parish, LA, Winn Parish, LA, Newton County, TX, Sabine County, TX

The radar

The Ft Polk radar (KPOE), 36 km from the middle of the area, began a volume at 18:49 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

The nearest sounding before it

Shreveport, LA (KSHV), launched 12:00Z, 6.8 hours before the alert went out and 136 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: 410 J/kg
Mixed-layer CIN: -56 J/kg
Mixed-layer LCL: 760 m above ground
0-6 km bulk shear: 37 kt
0-1 km storm-relative helicity: 144 m²/s²
0-3 km storm-relative helicity: 120 m²/s²
Significant tornado parameter: 0.2
Supercell composite: 1.6

Open this sounding in Storm Lab

The text

As transmitted.

319 
ACUS11 KWNS 021847
SWOMCD
SPC MCD 021847 
LAZ000-TXZ000-022015-

Mesoscale Discussion 0472
NWS Storm Prediction Center Norman OK
0147 PM CDT Sun May 02 2021

Areas affected...Central Louisiana and far east Texas

Concerning...Severe potential...Watch unlikely 

Valid 021847Z - 022015Z

Probability of Watch Issuance...20 percent

SUMMARY...A gradual increase in storm intensity is expected through
the afternoon. Isolated large hail and damaging wind gusts along
with a tornado or two will be the primary threats.

DISCUSSION...An area of showers has shown gradually cooling cloud
tops over the past hour. The environment is currently not overly
favorable for severe weather with MLCAPE around 500 to 1000 J/kg and
a mostly unidirectional wind profile. However, additional heating
and low-level moisture advection is expected to yield greater
instability by later this afternoon in the 1000-1500 J/kg range.
This may be sufficient for a few stronger updrafts and supercell
structures given 35 to 40 knots of effective shear. Weak rotation in
most of the ongoing showers further supports the potential for
supercell structures, at least initially. Veered low-level flow
should limit the overall tornado threat, but moderate speed shear
(0-1 km shear around 25 kts per KPOE VWP) and more backed low-level
flow across northeast Louisiana may support a tornado or two by
later this afternoon/evening. 

A watch is possible, but the limited area and duration of the threat
may preclude the need for a watch.

..Bentley/Dial.. 05/02/2021

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

ATTN...WFO...JAN...LCH...SHV...

LAT...LON   32209366 32399313 32289234 31929187 31459165 31269173
            30989219 30599286 30479339 30689369 31089390 31649394
            32209366

SPC that day

Everything else SPC issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
May 2, 3:33 PM CDT	Mesoscale Discussion	SPC	Avoyelles, Caldwell, Catahoula, Concordia, East Carroll, Franklin and 5 more	117 min
May 2, 4:46 PM CDT	Tornado Watch	SPC	East Carroll, Madison, Tensas, West Carroll	5 hr

Nearby

Mesoscale Discussions in Louisiana, 2021 Mesoscale Discussions in Texas, 2021 Every 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; radar from the NEXRAD Level II archive.