SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0250 PM CDT Tue Apr 12 2022
Valid 122000Z - 131200Z
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FAR EASTERN
NEBRASKA INTO CENTRAL IOWA...
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS NORTHEAST
KANSAS INTO SOUTHERN MINNESOTA AS WELL AS PORTIONS OF CENTRAL TO
NORTHERN TEXAS...
...SUMMARY...
Scattered severe thunderstorms capable of producing very large hail,
damaging winds, and tornadoes are expected late this afternoon and
tonight across a broad portion of the southern/central Plains into
the Mississippi Valley. Some of the tornadoes could be strong across
western and northern Iowa.
...Central to southern Texas...
Deep convective initiation along the dryline is underway with one
organized storm noted in regional radar imagery and additional
attempts at deeper convection noted in GOES visible imagery.
Isolated storms in the next 1-2 hours will likely increase in
coverage through the late afternoon and evening hours. See mesoscale
discussions #454 and #456 for additional details.
...Nebraska into Iowa...
Latest surface observations and visible imagery show a consolidated
low over central NE with a warm front lifting north across IA.
Warming temperatures and increasing boundary-layer moisture
(dewpoints in the low 60s) are augmenting instability within a
somewhat narrow warm sector. Thunderstorm development remains likely
heading into the late afternoon hours in the vicinity of the surface
low and along the dryline/cold front. See MCD #457 for additional
information.
..Moore/Mosier.. 04/12/2022
.PREV DISCUSSION... /ISSUED 1129 AM CDT Tue Apr 12 2022/
...NE/IA/KS/MO later this afternoon into tonight...
In advance of a deep midlevel trough over the central/northern
Rockies, a 984 mb surface cyclone in northeast CO this morning will
move to northeast NE this evening and northwest WI by 13/12z. Rapid
low-level moisture advection will occur through the day in the
cyclone warm sector into eastern NE and IA, as boundary-layer
dewpoints in the low-mid 60s advect northward from eastern KS, and
moisture also mixes downward as the low levels warm.
Warm/moist advection beneath midlevel lapse rates greater than 8
C/km will result in MLCAPE of 2000-3000 J/kg with weakening
convective inhibition in a narrow zone near the triple point,
coincident with focused forcing for ascent. Thus, thunderstorm
development is expected by about 22z near and immediately east of
the triple point, across northeast NE into northwest IA, and storms
will subsequently develop eastward near the warm front across
northern IA. Long hodographs with substantial clockwise curvature
in the low levels (effective SRH 300-400 m2/s2 and effective bulk
shear of 50-65 kt), in combination with the strong buoyancy and
sufficient low-level moisture, will favor supercells capable of
producing strong, long-tracked tornadoes with a storm or two this
evening, along with very large hail near the size of baseballs.
Convection will likely grow upscale into a line overnight from
western/central IA into eastern KS, as a cold front overtakes the
dryline from north-to-south. The primary severe threat will
transition to damaging winds with the overnight frontal squall line.
...TX/OK/AR/LA this afternoon through tonight...
A southern stream shortwave trough near Del Rio this morning will
move northeastward toward the Ark-La-Tex by this evening. Some
elevated convection will be possible through the day across the
eastern half of TX within the midlevel moisture plume atop the
elevated mixed layer. There will be some potential for some of this
convection to eventually root into the low levels, though any
subsequent storm evolution is uncertain. Somewhat higher confidence
exists in isolated-scattered severe storm development this
afternoon/evening along the dryline in central/north TX, near the
trailing influence of the southern stream midlevel trough. Aside
from areas impacted by elevated convection, steep midlevel lapse
rates, MLCAPE near 3000 J/kg, and effective bulk shear in excess of
40 kt will all favor supercells capable of producing very large
hail, damaging winds, and a couple of tornadoes. One or more
clusters of storms could evolve from the evening convection and
persist into tonight while spreading toward LA/AR, with an attendant
threat for damaging winds and large hail.
Farther north into OK, there is substantial uncertainty regarding
storm initiation along the dryline, with the more probable area
being across southern OK in proximity to the southern stream trough
moving over TX, and possible mesoscale influences of convective
outflow. Immediately north-northwest of the TX midlevel trough,
there is the potential for weak subsidence and disrupted hodograph
structures related to a weakness in the midlevel flow. If storms do
form along the dryline this afternoon/evening, there will be a
conditional threat for isolated very large hail. Any tornado threat
will depend on diurnal storms lingering into late evening as
low-level shear increases, but convective inhibition also increases.
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