780
ACUS01 KWNS 110621
SWODY1
SPC AC 110619

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0119 AM CDT Thu Jun 11 2026

Valid 111200Z - 121200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THURSDAY INTO
THURSDAY NIGHT ACROSS PARTS OF SOUTHERN AMD EASTERN IOWA
...NORTHEASTERN MISSOURI...NORTHERN AND CENTRAL ILLINOIS...SOUTHERN
WISCONSIN...NORTHERN INDIANA AND CENTRAL AND SOUTHERN LOWER
MICHIGAN...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THURSDAY AFTERNOON
ACROSS THE ALLEGHENY MOUNTAINS THROUGH NORTHERN MID ATLANTIC
VICINITY...

...SUMMARY...
Strong to severe thunderstorm development, including one or two
organizing clusters, will probably be accompanied by the potential
for large hail, damaging wind gusts and perhaps a couple of strong
tornadoes in a corridor across the Midwest into Great Lakes region
Thursday through Thursday night.

...Synopsis...
A potent mid-level trough will eject across the Upper Midwest into
the Great Lakes region today, with unseasonably strong 80-100 kt
southwesterly mid-level flow over spreading portions of the
upper-Midwest. An attendant surface low will deepen lift northward
out of the central Plains into the Midwest and Great Lakes, with a
trailing cold front extending into the central/southern Plains and
warm front/modifying outflow lifting northward into the upper
Midwest/Great Lakes. Elsewhere, northwest flow is expected in the
mid levels across the Mid-Atlantic, with a series of weaker
disturbances moving through that region.

A severe MCS is expected to be ongoing at the start of the D1 period
across portions of southern Iowa into western Illinois, posing a
risk for strong to potential significant wind gusts. Additional
development is expected behind the morning MCS along the cold front
and in the vicinity of remnant outflow from the morning MCS.
Supercells capable of large to very large hail, damaging wind, and
tornadoes (a few strong) will be possible before upscale growth and
eventual evolution to a damaging wind threat into the evening.

...Mid/lower Missouri Valley into the Mid Mississippi Valley and
upper Great Lakes...
The low-level jet is expected to strengthen this morning across the
central Plains, with convection developing across southeastern
Nebraska early this morning. This initial development will likely be
supercellular and initially elevated, given strong deep layer shear
and returning moisture. Large hail will be the main concern before
cells cluster and beginning to organize along outflow. Hi-res
guidance trends have been for an organized MCS to develop and spread
eastward into portions of southern/central Iowa and northern
Illinois. Given the strengthening upper level flow and increasing
moisture, this will become surface based with the potential to
produce strong to significant wind gusts (some 70-75+ mph) in the
morning to mid-afternoon possibly extending into portions of
Michigan.

Much of the afternoon severe potential remains contingent on how the
morning MCS evolves. It is likely that a modifying outflow/warm
front will lift northward and settle into northern Illinois/southern
Wisconsin by the afternoon with the cold front further west. The
continued strong low-level jet should support strong warm air
advection and quick air mass recovery into northern
Illinois/southern Wisconsin. Additional thunderstorms are expected
to develop along the front and near the modifying boundary. Strongly
sheared profiles will support initial supercells capable of large
hail and tornadoes (a few of which may be strong to intense). There
remains some uncertainty in where the placement of the boundary will
be and how long discrete supercell storm modes can be maintained. It
is possible that a corridor of higher tornado potential will become
clear with need to include higher probabilities as details become
clearer in further outlook updates.

Eventual upscale growth is anticipated as the frontal forcing shifts
eastward. Bowing segments capable of strong to significant gusts
will likely emerge. Wind probabilities were increased (with addition
of a 45% area) with this outlook to account for the morning MCS and
for potential for a secondary round of severe to significant wind
gusts. It is possible that higher probabilities may be needed with
further outlook updates.

...Eastern Kansas into the Southern Plains...
Additional thunderstorm development is expected along the trailing
cold front into portions of the central/southern Plains. Deep layer
shear will remain mostly post-frontal, however, around 20-30 kts
effective bulk shear and moderate to strong instability will support
some supercell structures capable of large hail and damaging wind.
Storm motions and boundary parallel shear will likely lead to
clustering and messy modes through time.

...Mid-Atlantic into central Appalachians...
Forcing for ascent from multiple short-wave disturbances across the
northeast and dew points in the 60s to 70s will support development
of widely scattered thunderstorm activity by the afternoon across
the Mid-Atlantic into the central Appalachians. Though shear will be
generally weak, moderate to strong instability will be in place will
support stronger updrafts capable of damaging wind. It is likely
that several clusters will emerge with potential for organizing
along cold pools and more focused corridors of damaging wind
potential. A 30% area was added with this outlook to cover this
potential.

..Thornton/Lyons.. 06/11/2026

$$