U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 181704 
Storm Prediction Center ac 181703 

Day 1 convective outlook corr 2 
National Weather Service Storm Prediction Center Norman OK 
1203 PM CDT Thu Apr 18 2019 

Valid 181630z - 191200z 

..there is an enhanced risk of severe thunderstorms parts of 
la/MS/al/western Florida Panhandle... 

Corrected again for old categorical graphic 

Several tornadoes (a few significant) and scattered to widespread 
damaging winds are possible through tonight across the lower 
Mississippi Valley and central Gulf Coast states. 

..lower MS valley/central Gulf Coast states... 
Considered an upgrade to a tornado-driven moderate risk but have 
deferred mainly due to uncertainties regarding convective Mode and 
lack of intense/long-track updraft helicity signal from the href. 

Two separated clusters/lines are ongoing, one across north-central 
to southwest la and the other just off the mouth of the Sabine River 
in the Gulf. This activity should merge into a broader qlcs that 
moves east-northeast across the lower MS valley into Alabama through 
tonight. Rich boundary-layer moisture sampled by the 12z Lake 
Charles sounding and characterized by upper 60s to lower 70s dew 
points will spread north ahead of this activity in conjunction with 
an amplifying low-level jet. Surface cyclone near Lake Charles will 
deepen as it ejects into the Tennessee Valley through tonight. Moderate 
insolation/boundary-layer heating is underway downstream of the rich 
moisture plume. The combination of these will contribute to a swath 
of 750-1500 j/kg MLCAPE amid weak mid-level lapse rates, likely 
extending as far north as central MS to central Alabama during the late 
afternoon and evening. Strong low/deep-layer shear will be favorable 
for embedded bowing and supercell structures, however generally 
line-parallel flow may be a limiting factor. Nevertheless, potential 
exists for scattered to widespread damaging winds along with 
short-track tornadoes (a few of which may be significant). The most 
likely region for these hazards to occur is across MS this afternoon 
and Alabama this evening. Whether or not more discrete convection can 
become sustained ahead of the qlcs is uncertain. Most cams suggest 
ahead of the line convection should struggle to intensify along the 
leading edge of forcing for ascent. The overall severe risk should 
subside some overnight, but at least an isolated wind/tornado threat 
should persist into western Georgia and the eastern Florida Panhandle through 
early morning. 

.Grams/Wendt.. 04/18/2019 


Mesoscale Discussion

acus11 kwns 181451 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 181450 

Mesoscale discussion 0387 
National Weather Service Storm Prediction Center Norman OK 
0950 am CDT Thu Apr 18 2019 

Areas affected...lower MS valley 

Concerning...severe potential...Tornado Watch likely 

Valid 181450z - 181615z 

Probability of watch issuance...95 percent 

Summary...Tornado Watch will likely be issued by 16z across portions 
of the lower MS valley. 

Discussion...mid-morning water-vapor imagery depicts a well-defined 
short-wave trough over Texas shifting east toward the lower MS valley. 
In response to this feature, an expansive corridor of convection has 
evolved across the Sabine River valley into the northwestern Gulf of 
Mexico. Over the last hour or so, warm advection-induced convection 
has evolved just off the la coast ahead of a remnant mesoscale convective vortex along the 
Upper Texas coast. It appears this warm advection-convection will 
advance north across southern la into southwestern MS into the early 
afternoon hours. Gradual intensification is expected with 
pre-frontal supercells possible. Otherwise, primary storm Mode 
should be more linear in nature focused along the advancing wind 
shift. Tornado threat will be highest with the pre-frontal 
supercells and damaging winds should be focused with the linear 

.Darrow/grams.. 04/18/2019 

..please see www.Spc.NOAA.Gov for graphic product... 


Latitude...Lon 29549345 31729258 32849118 32179002 29289120 29549345