RSS Mesoscale Discussions from Storm Prediction Center
SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0748 AM CDT Fri May 15 2026
Valid 151300Z - 161200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS MUCH OF
IOWA...
...SUMMARY...
Severe thunderstorms capable of producing severe/damaging winds and
large to very large hail are likely late this afternoon and evening
across much of Iowa and vicinity. 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.
...Central Plains into the Upper Midwest...
Generally zonal/westerly mid-level flow will persist over the
northern tier of the U.S. today, with an upper trough/low moving
slowly eastward over central Canada. At the surface, the primary 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 likely exist over southwest
KS/northwest OK by peak afternoon heating. A dryline will extend
southward from this low across much of the southern High Plains.
Current expectations are for robust thunderstorm development along
the cold front/surface trough from eastern NE into IA 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 across this
region by early evening. While low-level winds are forecast to
remain fairly modest, enhanced mid/upper-level flow will support
sufficient 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 IA supports a risk for mainly 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. Some adjustments have been made to the Slight and Enhanced Risk
areas based on latest observational trends and short-term guidance.
Namely, the Slight Risk has been extended northward into parts of
southeast MN/southwest WI, where some risk for hail-producing
supercells should exist along/ahead of the front. The Enhanced Risk
has also been expanded to include more of western IA, as multiple
supercells may form and eventually congeal into one or more bowing
clusters through the evening.
...Southern High Plains...
Robust daytime heating will yield a very well-mixed/deep boundary
layer near/south of the secondary surface low over southwest KS and
vicinity. 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. Isolated gusts of 75+ mph may occur
given the very deeply mixed boundary layer extending up to around
500 mb. Cells that develop in west/southwest TX may contain marginal
hail, with elongated hodographs in mid/upper levels.
..Gleason/Bentley.. 05/15/2026
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