Mesoscale Discussion 1861
NWS Storm Prediction Center Norman OK
0439 AM CDT Sat Aug 08 2026

Areas affected...parts of west central Nebraska int
southwestern/south central South Dakota

Concerning...Severe potential...Watch unlikely 

Valid 080939Z - 081215Z

Probability of Watch Issuance...20 percent

SUMMARY...A period of rapidly intensifying thunderstorm development
posing a risk for large hail appears possible by 5-7 AM CDT.  Due to
the relatively isolated, and perhaps short-lived, nature of the
threat, it is not clear that this will require a severe weather
watch, but trends are being monitored.

DISCUSSION...Downstream of a subtle perturbation migrating around
the northern periphery of prominent mid-level ridging centered over
the southern Great Basin, large-scale ascent appears to be in the
process of increasing across the South Dakotas Badlands vicinity
through Nebraska Sandhills.  This is being aided by
lower/mid-tropospheric warm advection, as veering and strengthening
flow in lower-levels (including to 30-40 kt around 850 mb) begins to
support a rapid return of low-level moisture above a relatively
cool/stable surface-based layer.

Forecast soundings, including latest Rapid Refresh guidance,
indicate that moistening near the initially dry base of the elevated
mixed-layer air is contributing to strong destabilization, including
CAPE increasing in excess of 2000 J/kg.  With pronounced veering of
winds with height contributing to strong deep-layer shear, the
environment is becoming increasingly conducive to the development of
supercells capable of producing large hail.  Based on
convection-allowing and related output, and trends in latest
infrared satellite imagery, it appears that at least a few storms
may rapidly initiate during the 10-12Z time frame.

It is not clear how long this threat will continue after daybreak,
due to some combination of upscale convective growth, continued
warming (and increasing inhibition) aloft, and weakening of the
nocturnal low-level jet.

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

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

ATTN...WFO...LBF...UNR...

LAT...LON   43940163 43129981 41670016 41620135 43300220 43940163 

MOST PROBABLE PEAK HAIL SIZE...1.50-2.50 IN

Day 2 Convective Outlook CORR 1
NWS Storm Prediction Center Norman OK
0130 AM CDT Sat Aug 08 2026

Valid 091200Z - 101200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE MIDWEST...

CORRECTED FOR THUNDERLINE

...SUMMARY...
Thunderstorms with severe wind gusts will be possible Sunday
afternoon and evening from parts of the northern Plains
east-southeastward into the southern Great Lakes. Severe gusts will
also be possible in parts of the southern Appalachians, Maine and
southeast Arizona.

...Northern Plains/Mid To Upper Mississippi Valley/Southern Great
Lakes...
Mid-level flow will be west-northwesterly on Sunday from the
northern Plains into the Great Lakes. At the surface, a moist and
unstable airmass will be in place from South Dakota eastward into
the southern Great Lakes. Although moderate instability is forecast
to develop over much of this corridor by afternoon, large-scale
ascent will remain relatively weak. For that reason, thunderstorm
development will confined to areas where low-level convergence
becomes maximized. Some solutions show an east-to-west axis of
strong low-level convergence from Iowa into northern Indiana,
suggesting this could be a favored area for thunderstorm development
in the afternoon and evening. 

Forecast soundings near this axis in the late afternoon have surface
dewpoints in the 70s with moderate to strong instability. 0-6 km
shear is forecast to be in the 35 to 45 knot range with a
substantial amount of low-level directional shear. This should
support a severe threat with supercells and short intense line
segments. Severe wind gusts will be the primary threat.

Further west into parts of the northern Plains, a subtle shortwave
trough is forecast to move into South Dakota during the day. A
post-frontal airmass will be in place ahead of the shortwave with
surface dewpoints in the 60s to near 70 F. This will contribute to
moderate instability by afternoon. Thunderstorms that develop near
the axis of instability will have potential for isolated severe
gusts during the late afternoon and early evening.

...Maine...
A mid-level shortwave trough is forecast to move across the Great
Lakes on Sunday, with west-southwesterly flow located over the
Northeast. Ahead of the system, a cold front is forecast to move
eastward across New England. As surface temperatures warm during the
day, thunderstorm development is expected to take place near the
front in the higher terrain across parts of western Maine. These
storms are forecast to move quickly eastward across central and
eastern Maine during the afternoon. Moderate instability, steep low
lapse rates and sufficient deep-layer shear will likely support an
isolated wind-damage threat.

...Southern Appalachians...
Moderate instability will develop on Sunday across much of the
southern Appalachians, where surface dewpoints will be in the upper
60s to mid 70s F. As surface temperatures warm during the day,
scattered thunderstorms will develop in the higher terrain. The
moderate instability, along with precipitable water values in the
1.70 to 1.85 inch range, will support a potential for isolated
severe wet downbursts as instability becomes maximized in the late
afternoon.

...Southeast Arizona...
Surface dewpoints across southern Arizona will be in the upper 50s
to near 60 F on Sunday. As surface temperatures warm during the day,
moderate instability will develop over much of southern Arizona.
Thunderstorms are expected to form in the higher terrain of eastern
Arizona, with the storms moving west-southwestward into the unstable
air during the late afternoon and early evening. Steep low-level
lapse rates and large surface temperature-dewpoint spreads will
support an isolated wind-damage threat.

..Broyles.. 08/08/2026

Day 3 Convective Outlook  
NWS Storm Prediction Center Norman OK
0220 AM CDT Sat Aug 08 2026

Valid 101200Z - 111200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM PARTS OF
NORTHERN ILLINOIS EAST-SOUTHEASTWARD INTO WESTERN PENNSYLVANIA...

...SUMMARY...
Thunderstorms with severe wind gusts will be possible on Monday from
parts of northern Illinois eastward into western Pennsylvania.
Isolated severe gusts will also be possible from parts of the
central and northern Plains into the Midwest.

...Southern Great Lakes...
A mid-level shortwave trough will move into the Great Lakes region
on Monday. At the surface, a quasi-stationary front is forecast to
be located from northern Illinois eastward into northwestern
Pennsylvania. Surface dewpoints to the south of the front are
forecast to be in the 70s F, which will contribute to moderate
destabilization by midday. Scattered thunderstorms appear likely to
develop near the front by early afternoon, with the storms moving
southeastward into the unstable air. To the south of the front,
MLCAPE is forecast to peak in the 2000 to 3000 J/kg range. In
addition, the models show moderate deep-layer shear in place which
will most likely support a mixed mode, with supercells and short
intense line segments capable of severe wind gusts. The severe
threat could continue into the mid to late evening if a cold pool
can become established and persist.

...Central and Northern Plains/Midwest...
West-northwesterly mid-level flow will be in place over much of the
north-central U.S. on Monday. At the surface, a low is forecast to
deepen over South Dakota as a cold front moves through the northern
Plains. To the south of the front, an axis of strong instability
appears likely to develop by afternoon from northern Nebraska
eastward into Iowa, where model forecasts suggest that MLCAPE could
peak in the in the 3500 to 4500 J/kg range. In addition, forecast
soundings show directional shear in the low to mid-levels, which
will contribute to moderate deep-layer shear over much of the moist
sector. This environment should support an isolated severe threat
during the late afternoon and early evening. Due to relatively weak
large-scale ascent, convective coverage is expected to be isolated,
with any severe threat remaining localized.

..Broyles.. 08/08/2026

Day 4-8 Convective Outlook  
NWS Storm Prediction Center Norman OK
0355 AM CDT Sat Aug 08 2026

Valid 111200Z - 161200Z

...DISCUSSION...
...Tuesday/Day 4 and Wednesday/Day 5...
A broad cyclonic mid-level flow pattern is forecast from the upper
Mississippi Valley into the Northeast on Tuesday and Wednesday. At
the surface, a moist airmass is forecast to be in place over most of
the eastern half of the nation with a quasi-stationary front located
from the northern Plains east-southeastward into the southern Great
Lakes. To the south of the front, surface dewpoints in the 70s F
will likely result in the development of moderate to strong
instability. Isolated to scattered thunderstorms appear likely to
develop each afternoon in areas where low-level convergence becomes
maximized. Outflow boundaries will be important in determining where
the greatest convective coverage ends up being. In addition to the
instability, moderate deep-layer shear is forecast over much of this
moist airmass suggesting that an isolated wind-damage threat will be
possible. However, the lack of any appreciable mid-level shortwave
trough introduces considerable uncertainty.

...Thursday/Day 6 and Saturday/Day 8...
From Thursday to Saturday, mid-level flow is forecast to become
westerly over much of the northern U.S, with a front located from
the central Plains eastward into the southern Great Lakes and Ohio
Valley. Thunderstorm development will be possible each afternoon and
evening near this front. Surface dewpoints in the 70s F to the south
of the front, along with moderate to strong instability will make
isolated severe thunderstorms possible each afternoon and evening.
However, spatial uncertainty concerning any potential severe threat
is considerable at this range.