Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0741 AM CDT Thu Apr 17 2025
Valid 171300Z - 181200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS LATE THIS
AFTERNOON INTO EARLY TONIGHT FROM EASTERN NEBRASKA INTO WESTERN AND
CENTRAL IOWA...
...SUMMARY...
Isolated to scattered severe thunderstorms are expected, mainly from
late afternoon into early tonight from eastern Nebraska into western
and central Iowa. Very large hail to 3 inches in diameter or
greater, isolated severe gusts of 60-70 mph, and a couple of
tornadoes will all be possible.
...NE/IA/MN/MO through early tonight...
Southwest mid-upper flow will persist through the period from the
southern High Plains to the central Plains and upper MS Valley,
downstream from a large-scale, positive-tilt trough from MB to the
Great Basin. A weak surface wave is expected to move along an
associated baroclinic from the mid MO Valley to the upper MS Valley,
while a lee cyclone develops south-southeastward across the central
High Plains. A modifying Gulf air mass (boundary-layer dewpoints in
the mid 50s to low 60s) will continue to spread northward in the
warm sector from the southern Plains to eastern KS, IA and southern
MN, beneath the eastern extent of a relatively warm EML.
A cluster of elevated storms, with embedded supercell structures, is
ongoing over southwest MO. These storms are expected to weaken this
morning as the low-level jet and associated warm advection diminish,
coincident with the eastward expansion of the EML. In the interim,
isolated large hail (around 1 inch diameter) and strong gusts (50-60
mph) will be possible for a couple of hours this morning across
southwest MO. In the wake of the morning convection, surface
heating and continued moisture advection will result in steady
destabilization from eastern KS to eastern NE/western IA and
southern MN. Thunderstorm development is expected near 20z into
southern MN where the cap will be a little weaker, and after about
22z in eastern NE (near and just east of the cold front/dryline
triple point).
The storm environment into southern MN will favor a mix of
supercells and storm clusters capable of producing large hail
(generally 1-1.75 inch diameter) and isolated strong-severe gusts
(50-60 mph). The environment farther south will favor a long-track
supercell or two from eastern NE this evening into western/central
IA through early tonight, potentially affecting Omaha and Des
Moines. Steep midlevel lapse rates, MLCAPE of 2000-2500 J/kg and
long hodographs through a deep layer will favor swaths of very large
hail (up to 3 inch diameter or greater) and occasional severe gusts
of 60-70 mph. There will be a narrow window of opportunity for a
couple of tornadoes this evening with sufficient moisture
(boundary-layer dewpoints near 60 F) as low-level shear increases.
..Thompson/Grams.. 04/17/2025
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