426
ACUS01 KWNS 130559
SWODY1
SPC AC 130558

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1258 AM CDT Thu Aug 13 2026

Valid 131200Z - 141200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
IOWA INTO ILLINOIS...

...SUMMARY...
Isolated to scattered severe thunderstorms appear possible today
from parts of the southern/central High Plains to the mid
Mississippi and lower Ohio Valleys. Damaging winds should be the
main threat, but occasional hail may also occur.

...Iowa into Illinois/Indiana...
An MCV has developed early this morning with an ongoing cluster of
thunderstorms across central NE. This activity is expected to spread
eastward through the morning, and should be in the vicinity of
western/central IA by the start of the period. There is still
uncertainty regarding how intense this cluster will be due to the
presence of fairly substantial MLCIN downstream into IA. Even so,
warm/moist advection associated with a low-level jet over the
southern/central Plains and the presence of a rather moist/unstable
airmass into IA suggest some potential for an organized cluster to
pose a risk for scattered severe/damaging winds as it moves eastward
through the morning. A brief embedded tornado may also occur if
convection can remain surface based.

Even greater uncertainty exists this afternoon regarding potential
convective evolution, with most guidance showing the cluster
weakening as it moves into IN. Regardless, the airmass downstream
and to the south of outflow associated with the morning cluster will
destabilize through the day, and any additional thunderstorms that
form could pose at least an isolated threat for damaging winds and
perhaps some hail given the strong buoyancy forecast.

...Southern/Central High Plains...
High-based thunderstorms are forecast to initially develop over the
higher terrain of the central Rockies/Front Range this afternoon,
with post-frontal low-level upslope flow persisting across the
central High Plains. As this activity spreads east-northeastward and
encounters greater instability, consolidating outflows should
support some increase for isolated severe gusts given steepened
low-level lapse rates. Occasional hail may also occur with the
stronger cores that develop. Consideration was given to including
greater severe wind probabilities across eastern CO into parts of
KS, but modest deep-layer shear casts some doubt on overall
thunderstorm organization/intensity. A somewhat separate area of
thunderstorms may also develop farther south across the southern
High Plains in a very hot and well-mixed boundary layer. This
activity should also pose a threat for isolated severe gusts through
the afternoon.

...Great Basin...
Modestly enhanced southwesterly mid-level flow will persist today
across the Great Basin downstream of a weak mid-level trough over
CA. Weak to locally moderate instability is forecast to develop
through the afternoon as filtered diurnal heating occurs. Scattered
to numerous thunderstorms are expected to form and spread
northeastward across this destabilizing airmass, with strong to
severe gusts possible. Based on latest guidance trends (00Z HREF),
have expanded the Marginal Risk for severe/damaging winds to include
more of the Great Basin.

...Northeast...
Seasonably cool mid-level temperatures are forecast today across
parts of the Northeast, with a mid-level trough expected to move
east-southeastward from Quebec into New England. While instability
is forecast to remain fairly limited, strong west-northwesterly flow
aloft may support a risk for isolated damaging winds with
thunderstorms that develop and spread southeastward through the
afternoon. Isolated hail may also occur with the stronger cells.

..Gleason/Moore.. 08/13/2026

$$