The SPC is forecasting ...Severe thunderstorms expected over parts of
the Ark-La-Tex to Lower Mississippi Valley this afternoon and
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SPC AC 131228
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0728 AM CDT Fri Apr 13 2018
Valid 131300Z - 141200Z
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS
CENTRAL/SOUTHWEST AR...FAR NORTHEAST TX...FAR NORTHWEST LA...
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS SOUTHERN IA TO
NORTHEAST TX AND THE LOWER MS VALLEY...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PARTS OF THE
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS PARTS OF THE
Numerous to widespread severe storms are expected from the
Mid-Missouri Valley south into the Ark-La-Tex states and Lower
Mississippi Valley this afternoon into tonight. Several tornadoes
(some strong), very large hail, and damaging winds will be possible.
An expansive mid-level trough will amplify across the central Great
Plains today, concurrent with a 100+ kt 500-mb jet developing from
south-central OK to western MO by early Saturday. A surface cyclone
along the north-central KS/south-central NE border will slowly track
east to the southwest IA/northwest MO border by evening. A sharp
warm front will arc east across southern IA with a dryline extending
south across eastern portions of KS/OK/TX. A cold front will sweep
southeast and overtake the dryline this evening.
...East TX/OK to the Lower Mississippi Valley...
Have upgraded to a tornado-driven Moderate risk centered on the
Ark-La-Tex to central AR with the potential for several tornadoes to
occur within this region late today through tonight.
Middle 60s surface dew points are prevalent from central OK to the
Ark-La-Tex and should be diurnally maintained ahead of the dryline
across eastern OK and most of AR. A swath of 50+ kt 850-mb
southerlies will persist, yielding increasing boundary-layer
moisture through this evening beneath an elevated mixed-layer. This
should result in a broad plume of MLCAPE from 1500-2500 J/kg.
Mid-level height falls in conjunction with confluent low-level flow
should result in scattered storms developing in the mid-late
afternoon from the Ark-La-Tex through central AR. More isolated,
initially discrete storms should also develop along the dryline in
east TX/OK. Enlarged low-level hodographs, which should further
increase in size this evening, will support all hazards. While
convective mode will likely transition to predominately clusters
during the evening, the potential for a several hour window of
numerous supercells traversing the Ark-La-Tex to central AR region
yields increased confidence in the possibility of several tornadoes,
some of which should be strong.
During the overnight, a secondary strengthening of the low-level jet
towards the Lower Mississippi Valley will likely yield upscale
growth into one or more larger QLCSs that accelerate eastward. Such
an evolution will favor a potentially widespread damaging
wind/embedded tornado threat continuing east into early Saturday.
Overall intensity should be tempered to some degree by convection
outpacing surface-based instability, especially with northeast
...Mid-MO Valley to the Ozarks...
Ahead of the aforementioned dry line, the warm sector will be
strongly capped early today, owing to a robust elevated mixed layer.
However, as large-scale ascent notably increases this afternoon,
cooling/moistening around 700mb, diabatic heating, and relatively
modest boundary-layer moisture return will foster around 1000-2000
J/kg of MLCAPE. Isolated to widely scattered thunderstorms are
expected to develop during the late afternoon, from the surface low
south along the dryline. Elongated straight-line hodographs will
likely yield splitting supercells with very large hail the primary
hazard. Rather warm surface temperatures in the 80s and dry-air
aloft should tend to support outflow-dominated supercells. However,
the tornado threat may become maximized in a narrow corridor near
the warm front across southwest IA. Storm intensity will nocturnally
wane in the mid/late evening.
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