Mesoscale Discussion 394

Issued

Apr 17, 2021, 10:17 AM CDT (15:17 UTC)

Expired

Apr 17, 2021, 12:15 PM CDT

In force

118 min

Issued by

the Storm Prediction Center

Concerning

Severe potential...watch unlikely

Chance of a watch

20%

Counties Jefferson Parish, LA, Lafourche Parish, LA, Plaquemines Parish, LA, Saint Bernard Parish, LA, Terrebonne Parish, LA

663 
ACUS11 KWNS 171518
SWOMCD
SPC MCD 171517 
LAZ000-171715-

Mesoscale Discussion 0394
NWS Storm Prediction Center Norman OK
1017 AM CDT Sat Apr 17 2021

Areas affected...Parts of southeastern Louisiana coastal areas

Concerning...Severe potential...Watch unlikely 

Valid 171517Z - 171715Z

Probability of Watch Issuance...20 percent

SUMMARY...Increasing, organizing thunderstorm development is
possible offshore and near southern Louisiana coastal areas through
1-2 PM CDT, which could pose increasing risk for strong surface
gusts.  While the need for a severe weather watch is still not
anticipated, trends will continue to be monitored.

DISCUSSION...Recent new thunderstorm  development appears in the
process of increasing over the northwestern Gulf of Mexico, roughly
70-90 miles offshore of the upper Texas/southwestern Louisiana
coast.  This may be initially rooted within a zone of weak
lower/mid-tropospheric warm advection, to the north of more strongly
capping warm layers aloft associated with broad mid/upper
subtropical ridging.  However, model output is suggestive that
forcing for ascent, within the right entrance region of an
intensifying westerly upper jet (in excess of 120-130 kt around 300
mb) around the crest of this ridging, could enhance this development
through early afternoon.

Ongoing storms appear to be forming above at least a shallow
near-surface stable layer, to the immediate north of a stalled
frontal zone which extends east-northeastward, mostly offshore, but
as far north as southeasterly Louisiana coastal parishes.  Based on
latest objective instability analyses, there may be increasing
inflow of air emanating from the moist boundary-layer (with surface
dew points near 70F, supportive of CAPE in excess of 1000 J/kg) to
the south of the front within the next few hours.  Coinciding with
the strengthening upper forcing, there appears potential for
substantive further thunderstorm intensification, upscale growth and
organization, in the presence of strong deep-layer shear.

Low-level ambient wind fields are generally weak, but, gradually,
convective-scale processes could support increasing potential for
strong surface gusts, impacting coastal waters and perhaps immediate
coastal parishes.

..Kerr/Dial.. 04/17/2021

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

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

LAT...LON   29589241 29599111 30028965 30058908 30138841 29188812
            28608967 28589144 28689227 29199289 29589241

Mesoscale Discussions in Louisiana, 2021Every mesoscale discussion in 2021

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.