Severe Storm Outlook Narrative (AC)
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ACUS01 KWNS 240553
SWODY1
SPC AC 240551

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1251 AM CDT Thu May 24 2018

Valid 241200Z - 251200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER A PORTION OF
THE NORTHERN AND CENTRAL PLAINS...

...SUMMARY...
Isolated to scattered strong to severe thunderstorms are expected
across portions of the northern and central Plains and upper
Mississippi Valley this afternoon and evening.

...Synopsis...

Upper trough currently over the northern High Plains will continue
east northeast through North Dakota and the upper MS Valley region
today. Associated cold front will move east through the Dakotas,
while a warm front advances through MN. A lee trough/dryline will
reside across the central through southern High Plains.

...Northern Plains and upper MS valley region...

Ascent with MCVs currently moving through the central High Plains
will contribute to the development of thunderstorms later today over
portions of MN. Areas of residual clouds will temper boundary layer
destabilization to some degree with MLCAPE to 1500 J/kg possible,
but this region will also reside east of steeper lapse rates and
stronger winds aloft. Weak vertical shear and modest instability
should limit overall severe threat with this activity, but a few
isolated strong to damaging wind gusts and marginally severe hail
are possible.

Farther west, the pre-frontal warm sector should become moderately
to strongly unstable over the central and eastern Dakotas where
eastern fringe of steeper lapse rates will overlap western portion
of moist axis. Diabatic warming should boost MLCAPE to 2000-2500
J/kg. The stronger forcing for ascent accompanying the upper trough
is expected to affect primarily North Dakota where widely scattered
to scattered storms are expected to develop along and just ahead of
the cold front, with more isolated activity with southward extent
into South Dakota. Somewhat stronger (30-40 kt between 700-400 mb)
flow aloft accompanying the upper trough will contribute to 30-35 kt
effective bulk shear supporting primarily multicell and possibly
some marginal supercell structures. Some storms may eventually
congeal into clusters as they continue east into the evening.
Damaging wind and large hail should be the main threats.

...Central High Plains region...

Upstream vorticity maximum currently over northern AZ is expected to
move into eastern CO this afternoon, and storms are expected to
develop over the higher terrain and along lee trough before moving
into a moderately unstable atmosphere where deeply mixed boundary
layers will promote strong downdrafts. Storms may eventually congeal
into an MCS as they continue east into better moisture across KS
where a strengthening low-level jet will promote a forward
propagation through at least early evening before storms begin to
weaken. Weak vertical shear will favor multicells, but the
thermodynamic environment will support a risk for damaging wind and
some hail.

..Dial/Cook.. 05/24/2018

$$



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