Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0258 PM CDT Fri May 15 2026
Valid 152000Z - 161200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
OF IOWA...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE UPPER
MIDWEST AND CENTRAL/SOUTHERN PLAINS....
...SUMMARY...
Severe thunderstorms capable of producing severe/damaging winds and
large to very large hail are likely late this afternoon and evening
centered across much of Iowa. Isolated to scattered severe hail and
damaging winds are possible over a broader area from parts of the
southern High Plains to the Upper Midwest.
...20z Update Central Plains...
Several areas of thunderstorm development are expected this
afternoon and evening across the central Plains and Midwest.
Moderate instability beneath 40+ kt of mid-level flow will promote a
mixed mode of supercells and eventually linear clusters. Hail (some
2+ inches) along with damaging gusts appear likely with the more
robust supercells initially along the cold front across NE/northern
KS, and farther north along the warm front into southern MN.
Eventual upscale growth into one or more linear clusters should
favor an increase in the threat for damaging gust and a couple
tornadoes over parts of IA, IL and southern WI this evening.
...Eastern NM/CO and the TX/OK Panhandles...
Initial high-based shower and thunderstorm development is underway
coincident with very strong heating and the arrival of a weak
upper-level shortwave trough atop the well-mixed air mass west of
the dryline. With mixing depths of 4-5 km below modest buoyancy,
strong to severe gusts are possible with these showers and
thunderstorms across the southern High Plains. Wind probabilities
were shifted slightly west. See MCDs #723 and #724 for short term
information.
..Lyons.. 05/15/2026
.PREV DISCUSSION... /ISSUED 1129 AM CDT Fri May 15 2026/
...Central Plains into the Upper Midwest including Iowa...
A cyclonically influenced moderately strong belt of westerlies will
exist over the northern Plains to Upper Midwest and upper Great
Lakes. The primary surface low will remain in northern Ontario, with
a trailing cold front extending southward into the Upper Midwest and
northern/central Plains. A secondary surface low will exist across
southwest Kansas and northwest Oklahoma around peak afternoon
heating, with a dryline extending south-southwestward from this low
across much of the southern High Plains.
Continued expectations are for robust thunderstorm development along
the cold front/surface trough from eastern Nebraska into Iowa to be
delayed until late afternoon or early evening (around 22-00Z), as
large-scale ascent will remain weak until a low-amplitude shortwave
trough embedded within the westerly mid-level flow eventually
overspreads the surface warm sector. Continued low-level warm/moist
advection through the day and diurnal heating will contribute to the
development of moderate to locally strong instability (2500+ J/kg
MLCAPE) across this region by early evening. While low-level winds
are forecast to remain fairly modest, enhanced mid/upper-level flow
will support sufficient (35-50 kt) deep-layer shear for updraft
organization.
Initial supercells should pose a threat for large to isolated very
large hail (2+ inches in diameter), before likely quick upscale
growth this evening across Iowa with an increasing potential for
scattered severe/damaging winds. Some of these gusts could exceed 75
mph on a localized basis given the expectation for an organized
cluster and ample instability. A tornado or two could also occur
this evening as low-level shear gradually increases with a
strengthening low-level jet.
...Southern High Plains...
While clouds linger at midday, particularly with southward extent
across west/southwest Texas, robust daytime heating will yield a
very well-mixed/deep boundary layer near/south of the secondary
surface low over southwest Kansas/northwest Oklahoma. Mid-level
temperatures will remain cool enough to support at least weak
instability, even with modest low-level moisture/surface dewpoints.
A weak mid-level shortwave trough moving from the southern Rockies
into the southern High Plains will enhance large-scale ascent late
in the day. This should support the development of high-based
thunderstorms, with occasional strong to severe wind gusts expected.
Latest short-term guidance suggests a more probable zone of
thunderstorm-related gust potential may focus across the Texas South
Plains and Low Rolling Plains. Isolated gusts of 70+ mph may occur
given the very deeply mixed boundary layer extending up to around
500 mb. Cells that develop in west/southwest Texas may also contain
some hail, with elongated hodographs in mid/upper levels.
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