165
ACUS01 KWNS 300559
SWODY1
SPC AC 300557

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1257 AM CDT Tue Apr 30 2024

Valid 301200Z - 011200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE MID MISSOURI VALLEY INTO THE CENTRAL PLAINS...

...SUMMARY...
Severe thunderstorms will be possible this afternoon and evening
from parts of the upper Mississippi Valley southwestward into the
mid Missouri Valley, and central to southern Plains. The greatest
threat is expected from western and central Iowa southwestward
across far southeast Nebraska, far northwest Missouri into northeast
Kansas, where very large hail, severe wind gusts (possibly above 70
mph) and a few tornadoes are expected.

...Upper Midwest/Mid Missouri Valley/Central Plains...
An upper-level trough will move into the central and northern Plains
today, as an associated 60 to 70 knot mid-level jet moves through
the trough. At the surface, a deepening low will move into
southeastern South Dakota, resulting in strong moisture advection
across the mid Missouri Valley and central Plains. A north-northeast
to south-southwest corridor of maximized low-level moisture will
setup from eastern Kansas into western Iowa, where surface dewpoints
will be in the lower to mid 60s F. Surface heating along this
corridor will result in moderate instability by afternoon, with
MLCAPE peaking in the 2000 to 3000 J/kg range. Ahead of the upper
trough, large-scale ascent will likely support scattered
thunderstorm development during the mid afternoon from eastern South
Dakota into eastern Nebraska. This convection is expected to
increase in intensity and coverage, moving eastward across Iowa, and
developing south-southwestward into northeast Kansas during the late
afternoon. A broken line of strong to severe storms will move
east-southeastward toward the Mississippi River Valley in the early
to mid evening.

Along and near the instability axis, RAP forecast soundings at 21Z
from near Omaha to Kansas City have supercell wind profiles, with
strong speed shear in the low to midlevels and 0-6 km shear
generally from 40 to 55 knots. Lapse rates are forecast to be very
steep in the low to midlevels. 700-500 mb lapse rates around 8 C/km
will be very favorable for supercells with large hail. The more
dominant supercells should be capable of hailstones greater than 2
inches in diameter. 0-3 km lapse rates are forecast to be
exceptionally steep, with some forecast soundings having 0-3 km
lapse rates near 9 C/km. This should support a wind damage threat
with supercells and the more intense short line segments. Wind gusts
above 70 mph will be possible. Low-level shear should also be strong
enough to support tornado development with the more intense
supercells. The severe threat is expected to continue from late
afternoon into the early to mid evening. The severe threat should
become marginal by late evening, as the convective system moves
through the lower Missouri Valley and southern sections of the
central Plains.

...Southern Plains...
West-southwesterly mid-level flow will be in place across the
southern Plains today. At the surface, a corridor of maximized
low-level moisture will be in place to the east of a dryline from
western Oklahoma into west Texas. Surface dewpoints in the 60s F
will contribute to the development of moderate instability by
afternoon. MLCAPE is forecast to peak in the 2500 to 3500 J/kg
range. Although large-scale ascent will likely be limited, low-level
convergence near the dryline should result in isolated convective
initiation during the mid to late afternoon. With any cell that can
initiate and move away from the dryline, an isolated severe threat
will be possible.

RAP forecast soundings to the east of the dryline at 00Z/Wednesday
generally have 0-6 km shear in the 30 to 40 knot range, with very
steep lapse rates in the low to mid-levels. Some forecast soundings
in western Oklahoma and northwest Texas have 0-3 km lapse rates near
9 C/km. This environment will likely be sufficient for organized
cells with isolated large hail and strong  gusts. The severe threat
will be marginal from southwest Oklahoma into west Texas, where
convective coverage is expected to be very isolated.

..Broyles/Thornton.. 04/30/2024

$$