SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0737 AM CDT Mon Apr 28 2025
Valid 281300Z - 291200Z
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FOR SOUTHERN
MN...NORTHERN IA...AND WESTERN WI...
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM
NORTH-CENTRAL AND WESTERN OK INTO THE TX BIG COUNTRY AND SOUTHWEST
TX...
...SUMMARY...
Multiple corridors of severe thunderstorms are expected across the
Upper Midwest later today into tonight, with a regional severe
weather outbreak possible. The most dangerous period is likely
during the late afternoon and evening when strong tornado potential
should be maximized. Scattered large to very large hail and damaging
winds are likely as well.
...Synopsis...
Recent satellite imagery shows a mature cyclone centered over UT,
with a shortwave trough progressing northeastward through the
central High Plains within the eastern periphery of this cyclone.
Farther north, overnight convection across SD has contributed to the
development of vorticity maximum, which is currently moving into
western MN.
Early morning surface analysis places a deep low over central SD,
with a dryline extending south-southwestward from this low across
central NE, western KS, the northwest TX Panhandle, southeast NM,
and far West TX. A warm front extends eastward from this low to the
ND/SD/MN border vicinity before then arcing more southeastward
across southwest MN, central IA, and eastern MO. A large warm sector
characterized largely by 60s dewpoints exists between these two
features.
Expectation for the central High Plains shortwave trough to progress
quickly northeastward throughout the period, accompanied by a strong
jet streak (i.e. 70 to 80 kt at 500 mb). The surface low will eject
northeastward as well, reaching central MN by 00Z and continuing
into northwestern Ontario by 12Z Tuesday. Coincident
northward/northeastward movement of the warm front will bring a
warm, moist, and unstable airmass into the Upper Midwest ahead of
the approaching dryline, which will likely extend from central MN
southwestward into the TX Permian Basin by mid-afternoon. Severe
thunderstorms are expected to develop along the length of this
dryline, with the greatest severe potential across the Upper
Midwest.
...Upper Midwest...
A regional severe weather outbreak still appears possible across the
Upper Midwest, with a threat of strong to intense tornadoes, very
large hail, and swaths of damaging winds.
Convective line ongoing across central MN is expected to continue
quickly northeastward through the region, leaving ample time for the
warm front to progress northward and bring a warm, moist, and
unstable airmass into the region ahead of the dryline. Thunderstorm
initiation along the dryline is forecast to begin around 18-20Z near
the SD/MN/IA border intersection vicinity, before then continuing
quickly eastward across southern MN and northern IA throughout the
late afternoon and early evening. Volatile environmental conditions
are expected south of the warm front and east of the dryline, with
strong instability (MLCAPE near/above 3000 J/kg) and deep-layer
shear, and a persistently intense low-level jet that will maintain
very favorable low-level shear/SRH.
This environment will be conditionally favorable for long-track
supercells with strong/intense tornado potential if a discrete mode
can be maintained. Quick upscale growth into a more linear or
cluster mode is possible, but the vertical shear appears strong
enough for a discrete mode to be maintained as well. A scenario
where a primary line develops with discrete storms ahead of it is
possible as well. In any case, the overall environment supports the
potential for large to very large hail, damaging gusts, and strong
to intense tornadoes with any discrete storms. Line-embedded
tornadoes and strong gusts are possible within any convective lines.
A more conditional scenario exists farther south from central IA
into northeast KS/northwest MO. Here, the kinematic environment will
remain supportive of supercells capable of all severe hazards, but
capping could prove detrimental to deep convection given the weaker
low-level convergence and large-scale ascent. Any supercell that can
initiate and be sustained could become long-tracked within the
expanding and very favorable warm sector, posing a threat for strong
to intense tornadoes and very large hail.
Farther west, a couple of supercells may develop in the region
between the prefrontal trough/dryline and cold front, and pose a
threat of large hail and locally damaging gusts as they move across
northeast NE/southeast SD into parts of MN/IA.
...Western/Central OK...Northwest/Southwest TX...
Daytime heating, and resultant airmass destabilization, coupled with
convergence along the dryline is expected to result in convective
initiation from the TX Big Country into southwest TX during the
afternoon. Steep lapse rates and strong vertical shear will support
supercells, with large to very large hail as the primary severe
risk.
Farther north in western OK, convective development will likely wait
until around 00Z when the dryline begins to retreat. The increased
low-level moisture coupled with a reduction in convective inhibition
could result in a 2-4 hour window where convective initiation is
more likely. At the same time, the low-level jet is forecast to
strengthen considerably, resulting in a kinematic environment
supportive of supercells. The tornado threat would likely maximize
between 00-04Z before nocturnal stabilization forces storms to
become more elevated. Hail potential could persist into
north-central OK as any storms that develop progress northeastward
throughout the night.
..Mosier/Broyles.. 04/28/2025
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