Mesoscale Discussion 2270
NWS Storm Prediction Center Norman OK
0249 PM CDT Tue Sep 08 2026

Areas affected...portions of extreme eastern Nebraska into central
Iowa

Concerning...Severe potential...Watch possible 

Valid 081949Z - 082145Z

Probability of Watch Issuance...60 percent

SUMMARY...Thunderstorms should gradually increase in coverage and
intensity as a surface cold front approaches. The strongest storms
may be accompanied by at least a few severe gusts and perhaps a
tornado or two. Convective trends are being monitored for the need
of a WW issuance.

DISCUSSION...A relatively broad swath of precipitation is currently
overspreading central NE into the northern half of IA, ahead of a
surface cold front, which has limited insolation and boundary-layer
destabilization across much of the region thus far. However, ample
boundary-layer mixing is underway to the southern periphery of this
rain band, where surface temperatures have heated into the 90s F (to
near 100 F in some spots). Given low to mid 70s F surface dewpoints,
MLCAPE has boosted to over 2000 J/kg despite mediocre mid-level
lapse rates.

It is unclear precisely when storms will initiate since much of the
available deep-layer ascent will glance the region to the north.
Nonetheless, a pre-frontal trough is gradually drifting east across
far southeastern NE, and this boundary may serve as a potential
focusing mechanism for more robust surface based thunderstorm
development over the next few hours. Storms may initially be
semi-discrete and anafrontal in nature. As the storms mature, and
assuming they can propagate into the warm sector, then surface-based
convection will become possible. These storms would most likely
become an MCS capable of producing a few severe gusts and perhaps a
couple of QLCS tornadoes. 

A Severe Thunderstorm Watch may be needed when convective initiation
and intensification become more apparent.

..Squitieri/Hart.. 09/08/2026

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

ATTN...WFO...DVN...DMX...OAX...

LAT...LON   41149681 41829577 42539383 42569145 42379101 41649098
            41089215 40769469 40649550 40599628 41149681 

MOST PROBABLE PEAK TORNADO INTENSITY...UP TO 90 MPH
MOST PROBABLE PEAK WIND GUST...55-70 MPH
MOST PROBABLE PEAK HAIL SIZE...UP TO 1.25 IN

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1115 AM CDT Tue Sep 08 2026

Valid 081630Z - 091200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON AND
EVENING FROM SOUTHEAST NEBRASKA ACROSS PARTS OF IOWA...

...SUMMARY...
A few severe storms capable of mainly severe wind gusts appear
possible across portions of Iowa and eastern Nebraska this afternoon
and evening.

...NE/IA...
A broad upper ridge remains over much of the central/southern US,
with moderately strong westerly flow over the northern tier of
states.  A baroclinic zone extends across southern NE into central
IA.  This feature will be sharpened by differential heating through
the day, and will be the focus for afternoon and evening
thunderstorm development.  The strongest cells will be near a 20-30
knot southwesterly low-level jet where warm advection and lift will
aid in convective initiation.  Sufficient deep-layer shear will
promote supercell and eventual bowing structures, with damaging
winds be the main concern.  Most CAM solutions suggest the majority
of convection will be just north of the surface boundary, which may
limit the overall severe threat.  Also, weak mid-level lapse rates
and warm temperatures aloft will tend to diminish the hail risk.

...CO/KS...
Farther southwest, hot surface conditions will result in a deeply
mixed boundary layer.  Scattered high-based showers and
thunderstorms are expected to form from eastern CO into
western/central KS, with gusty and occasionally damaging wind gusts
possible.

..Hart/Guyer.. 09/08/2026

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0247 PM CDT Tue Sep 08 2026

Valid 082000Z - 091200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON AND
EVENING FROM SOUTHEAST NEBRASKA ACROSS PARTS OF IOWA...

...SUMMARY...
A few severe storms capable of mainly severe wind gusts appear
possible across portions of Iowa and eastern Nebraska this afternoon
and evening.

...20Z Update...
The ongoing forecast remains on track and no changes are needed.

..Wendt.. 09/08/2026

.PREV DISCUSSION... /ISSUED 1115 AM CDT Tue Sep 08 2026/

...NE/IA...
A broad upper ridge remains over much of the central/southern US,
with moderately strong westerly flow over the northern tier of
states.  A baroclinic zone extends across southern NE into central
IA.  This feature will be sharpened by differential heating through
the day, and will be the focus for afternoon and evening
thunderstorm development.  The strongest cells will be near a 20-30
knot southwesterly low-level jet where warm advection and lift will
aid in convective initiation.  Sufficient deep-layer shear will
promote supercell and eventual bowing structures, with damaging
winds be the main concern.  Most CAM solutions suggest the majority
of convection will be just north of the surface boundary, which may
limit the overall severe threat.  Also, weak mid-level lapse rates
and warm temperatures aloft will tend to diminish the hail risk.

...CO/KS...
Farther southwest, hot surface conditions will result in a deeply
mixed boundary layer.  Scattered high-based showers and
thunderstorms are expected to form from eastern CO into
western/central KS, with gusty and occasionally damaging wind gusts
possible.

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1208 PM CDT Tue Sep 08 2026

Valid 091200Z - 101200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM EASTERN OHIO
INTO WESTERN NEW YORK...

...SUMMARY...
Isolated strong to severe thunderstorms are possible across portions
of the central Plains to the Ohio Valley on Wednesday. A more
organized severe weather threat is expected from eastern Ohio to
western New York.

...Eastern Ohio into western New York...
A mid-level trough will move from the Upper Midwest to the Northeast
on Wednesday with moderate mid-level flow expanding along the
southern periphery of this trough. A strong surface low associated
with this trough will move across northern Ontario with a cold front
extending into the Midwest. Ahead of this front, low 70s dewpoints
are forecast to advect northward across Ohio, Pennsylvania, and
western New York. Mid-level lapse rates will be relatively weak, but
the moist environment will support moderate instability amid
moderate effective shear. A line of storms is forecast to develop
along the front from central Ohio into western New York. This
environment should support damaging winds. Some tornado threat may
exist as the low-level flow strengthens during the afternoon with
clockwise curved low-level hodographs. However, a mostly linear
storm mode should limit the overall tornado threat. 

...Ohio Valley to the central Plains...
Moderate instability is forecast to develop from the central Plains
to the Ohio Valley. Across the plains, instability will be driven by
a hot, deeply mixed environment while instability farther east will
be driven by 70s dewpoints. Within this entire zone, mid-level flow
is expected to remain quite weak which will limit storm
organization. Water-loaded downbursts farther east and drier
microbursts in the mixed environment farther west will be the
primary hazard within the Marginal Risk. A zone of greater
instability from eastern Missouri into western Indiana could support
an isolated hail threat, particularly if some of this greater
instability can spread beneath stronger mid-level flow. However,
morning convection/cloudcover may be present where this most
favorable environment could develop.

..Bentley.. 09/08/2026