Severe Storm Outlook Narrative (AC)
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ACUS03 KWNS 190703
SPC AC 190702

Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0202 AM CDT Thu Apr 19 2018

Valid 211200Z - 221200Z


Scattered strong/severe thunderstorms are possible across portions
of Texas into southern Louisiana Saturday.


Strong upper trough will migrate across the southwestern US late
this week before shifting into TX Saturday. As downstream upper
ridge shifts into the MS Valley low-level trajectories will become
more favorable for moisture to advance inland across southern into
central TX. Latest NAM guidance is the most aggressive with
continental air mass remaining wedged into portions of the southern
Plains. There is some concern this scenario may be correct given the
amount of convection that should evolve within the warm advection
zone. Most model guidance suggests one or more inches of rain may
fall from northwest TX into OK and this should suppress the boundary
into central TX. Ultimately a weak surface wave/low may develop
along the wind shift before tracking into LA during the overnight
hours. While low-level moisture is expected to increase considerably
across the warm sector (mid 60s dew points), forecast buoyancy is
not particularly high across this region. Thermodynamic environment
will be somewhat meager for robust updrafts but a strong mid-level
jet will translate across south-central TX into LA late in the
period, along with substantial height falls. Widespread convection
will evolve north of the warm front but the greatest risk for severe
will be with any storms that develop ahead of the surface wave.
Given the uncertainty in instability 5% severe probs will be issued
from central TX into coastal LA. However, strength of wind fields do
warrant consideration for a potential upgrade if instability
ultimately is greater than currently forecast.

..Darrow.. 04/19/2018

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