Mesoscale Discussion 1919
NWS Storm Prediction Center Norman OK
0413 AM CDT Tue Aug 11 2026

Areas affected...much of northern and central Iowa

Concerning...Severe potential...Watch possible 

Valid 110913Z - 111115Z

Probability of Watch Issuance...40 percent

SUMMARY...Developing thunderstorms may continue to evolve into a
better organized cluster through 6-8 AM CDT.  Eventually, this
probably will become accompanied by increasing potential for strong
to severe surface gusts, though how soon remains uncertain.

DISCUSSION...Convection continues to increase and intensify within a
zone of stronger warm advection, along a tightening
lower/mid-tropospheric baroclinic zone where seasonably high
moisture content is supporting large CAPE, beneath the northern
periphery of a plume of elevated mixed-layer air.  Strongest storms,
now focused south of Sioux Falls SD into the Storm Lake IA vicinity,
have yet to organize or generate a notable surface pressure
perturbation.  However, this may begin to change over the next few
hours.  

While there is considerable spread within convection-allowing
guidance, of perhaps particular note, the latest Rapid Refresh
output suggests that continuing intensifying thunderstorm
development may become accompanied by the evolution of a
strengthening lower/mid-tropospheric cyclonic circulation, based on
its depiction of strengthening rear inflow to 50-60+ kt in the
700-500 mb layer through 11-13Z.  This would probably be accompanied
by increasing potential for strong to severe surface gusts at some
point, though how soon remains unclear given the initially stable
near-surface lapse rates.

..Kerr/Smith.. 08/11/2026

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...DVN...ARX...DMX...FSD...

LAT...LON   43489513 43369280 42739114 41469157 41929321 42189496
            42819608 43489513 

MOST PROBABLE PEAK WIND GUST...55-70 MPH
MOST PROBABLE PEAK HAIL SIZE...1.00-1.75 IN

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
0100 AM CDT Tue Aug 11 2026

Valid 121200Z - 131200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PARTS OF THE
CENTRAL AND NORTHERN HIGH PLAINS...AND ALSO FOR PARTS OF THE MIDWEST
AND OHIO VALLEY...

...SUMMARY...
Thunderstorms with severe gusts and hail will be possible Wednesday
afternoon and evening across parts of the central and northern High
Plains. Damaging gusts and isolated hail will also be possible
across parts of the Midwest and Ohio Valley.

...Parts of the Midwest/Ohio Valley...
Guidance continues to vary considerably regarding potential for
early-day convection across parts of the Midwest and Ohio Valley.
Any morning convection will in turn influence the position of an
effective frontal zone that will generally extend from parts of the
mid MO Valley into the lower OH Valley. Strong heating, rich
low-level moisture, and generally steep lapse rates will result in
strong to extreme buoyancy to the warm side of the front, with
substantial MUCAPE possible to the immediate cool side of the front.


Multiple scenarios are possible. There will be some potential for
any early-day storm cluster to propagate southeastward through the
day, with a damaging-wind and isolated hail threat. Diurnal
development will be possible in the vicinity of the frontal zone,
with sufficient deep-layer shear for initial supercell potential.
Hail and possibly a tornado could accompany the strongest diurnal
storms, though there may be a tendency for clustering and perhaps
organized upscale growth, with increasing wind-damage potential.
While uncertainty remains high, one or more rounds of
organized-severe potential could evolve in the vicinity of the
frontal zone, and a 15% wind area was added where guidance currently
has the greatest signal for development. 
 
...Parts of the central/northern High Plains into the lower/mid
Missouri Valley...
To the north of a surface low across southeast CO and an
eastward-extending warm front, moist low-level easterly flow will
support potential for moderate to locally strong destabilization
across parts of western SD/NE into northwest KS/far northeast CO.
Midlevel flow will be relatively modest, but veering wind profiles
will result in sufficient deep-layer shear for storm organization.

Initial isolated to widely scattered discrete development could pose
a threat of hail and localized severe gusts. Some upscale growth and
possible MCS development may occur during the late evening and
overnight across parts of central/eastern NE and vicinity. Guidance
varies regarding the organization of any nocturnal MCS, but at least
isolated damaging-wind potential could spread eastward through the
end of the period.  

...Northern SD/southern ND into parts of MN/WI/MI...
While the strongest instability will remain south of the region,
moderate buoyancy is forecast to develop along/ahead of a front
draped from near the ND/SD border into southern MN, WI, and Lower
MI. Coverage of storms is uncertain within this regime, but moderate
northwesterly mid/upper-level flow and favorable deep-layer shear
will support organized convection, with a threat for strong to
locally severe gusts and hail if any sustained storms develop. 

...Carolinas/Southern Appalachians...
The evolution of antecedent upstream convection will have a
considerable influence on the position of the primary surface front
and any organized severe threat across parts of the southern
Appalachians and Carolinas region on Wednesday. At least isolated
storm development will be possible near the front and also across
favored terrain areas, with modest west-northwesterly flow aloft
supporting potential for outflow-driven cells/clusters with a threat
of wind damage. Any features favorably timed with the diurnal cycle
(such as a persistent storm cluster or MCV) could result in a
greater coverage of wind-damage potential, but confidence in the
details is too low for more than 5% wind probabilities at this time.

..Dean.. 08/11/2026

Day 3 Convective Outlook  
NWS Storm Prediction Center Norman OK
0230 AM CDT Tue Aug 11 2026

Valid 131200Z - 141200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE CENTRAL
HIGH PLAINS INTO THE OHIO VALLEY...

...SUMMARY...
Isolated severe storms are possible on Thursday from the central
High Plains into the Ohio Valley.

...Central High Plains eastward to the Ohio Valley...
Elevated convection and possibly a remnant MCS may be ongoing at the
start of the forecast period across parts of IA/northern MO into IL,
aided by a southwesterly low-level jet. Large-scale support for this
convection is generally forecast to weaken through the day, though
any remnant storm cluster or MCV may become the focus for afternoon
intensification and wind-damage potential into parts of the Ohio
Valley, if it is well-timed with downstream diurnal destabilization.

Otherwise, moderate to strong destabilization will again be possible
from parts of the Midwest into the central Plains, in the vicinity
of a frontal zone. The position of the frontal zone is uncertain due
to the influence of antecedent Day 1-2 convection, and large-scale
ascent appears nebulous at best for much of the day within a regime
of weak midlevel height rises. Isolated storm development cannot be
ruled out near the front through early evening, with somewhat
greater coverage possible across parts of the central High Plains
and adjacent higher terrain. Low-level warm advection may allow for
an increase in storm coverage into late evening near the front,
though the later activity would likely be somewhat elevated.  

Deep-layer shear will generally be somewhat weaker than previous
days, but still sufficient for some storm organization where deep
convection can be sustained. A broad 5% area has been included in
the anticipated vicinity of the frontal zone, though confidence in
the details of storm development and evolution remains rather low. 

...Parts of the Great Lakes and Northeast...
Moderate to strong west-northwesterly mid/upper-level flow will
overspread parts of the Great Lakes and Northeast on Thursday, in
association with a seasonably deep upper trough extending from
eastern Canada into the northeast CONUS. Guidance varies
considerably regarding the extent (if any) of destabilization across
this region during the afternoon. Probabilities may eventually be
needed for parts of this region, if confidence increases regarding
sufficient destabilization in association with the strengthening
wind fields.

..Dean.. 08/11/2026

Day 4-8 Convective Outlook  
NWS Storm Prediction Center Norman OK
0313 AM CDT Tue Aug 11 2026

Valid 141200Z - 191200Z

...DISCUSSION...
...D4/Friday...
Moderate to strong destabilization will again be possible on Friday,
near and south of a front extending from the central Plains and
Midwest into parts of the southern Mid-Atlantic. Considerable
uncertainty remains regarding the exact frontal position, but strong
storms will be possible in its vicinity. Most guidance depicts
rising midlevel heights and modest deep-layer flow/shear in the
vicinity of the frontal zone, which may tend to keep the severe
threat isolated. One possible exception will be in the Carolinas and
southern VA, where the glancing influence of a seasonably deep upper
trough over the Northeast may result in a somewhat more organized
severe threat, if sufficient destabilization can occur.  

...D5/Saturday - D6/Sunday...
Some dampening of the upper ridge (potentially aided by one or more
MCVs emerging from the High Plains) may result in severe potential
emerging this weekend across parts of the Upper Midwest and Great
Lakes/Ohio Valley. However, details regarding timing of any
shortwave troughs and position of the primary frontal zone remain
quite uncertain. 

...D7/Monday - D8/Tuesday...
Extended-range guidance generally suggests potential for a
northwesterly flow regime to develop from the northern Plains into
parts of the East by early next week. Predictability remains quite
low regarding the extent to which stronger deep-layer flow impinges
upon favorable instability, but at least isolated severe potential
may eventually develop from parts of the north-central CONUS into
the Mid-Atlantic and Carolinas.