Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1139 AM CDT Sun Sep 13 2026

Valid 131630Z - 141200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE
NORTHEAST...

...SUMMARY...
Isolated to widely scattered severe thunderstorms will be possible
across parts of the upper Ohio Valley into the Northeast this
afternoon and evening. Isolated strong to severe thunderstorms may
also occur across parts of the central and northern High Plains.

...Northeast and upper/middle Ohio Valley...
Have upgraded portions of the region to a categorical Slight Risk
with expectations of a semi-focused regional corridor of wind damage
later this afternoon through early evening. Within large-scale upper
troughing over eastern Canada, a strong west-southwesterly mid-level
jet will overspread the Great Lakes into the Ohio Valley and
Northeast later today into tonight. A surface cold front will
likewise track eastward across these regions through tonight. A
seasonably moist low-level airmass will be in place ahead of the
cold front, but poor lapse rates aloft (around 6-6.5 C/km) and cloud
cover should limit the degree of destabilization that can occur this
afternoon, although cloud cover has tended to thin/abate since early
this morning across the upper Ohio Valley. While the main influence
of the upstream upper-level trough will not arrive until this
evening, strengthening mid-level flow through the day will support
35-45 kt of deep-layer shear and the potential for organized bands
of convection.

At least widely scattered thunderstorms are expected to develop
along/ahead of the front by mid afternoon (around 19-22Z) from parts
of Ohio into western New York, and then spread quickly eastward
across the upper Ohio Valley into the Northeast. The deep-layer
shear will be strong enough for some supercells initially, with
perhaps a marginal/isolated hail threat even with the poor lapse
rates present aloft. But, clusters/bowing segments with an isolated
damaging wind threat should quickly develop given the linear forcing
of the front. This convection is forecast to weaken with eastward
extent this evening with the onset of nocturnal cooling, and as it
encounters a less unstable airmass.

...Wyoming and central/northern High Plains to Missouri Valley...
A closed mid/upper-level low over the Pacific Northwest this morning
will move eastward to the northern Rockies/High Plains through the
period. Diurnal destabilization will generally be limited ahead of
this low, though a narrow zone of weak instability may develop by
late afternoon across southern Wyoming, and across northeast
Colorado into the Nebraska Panhandle in a modest low-level upslope
flow regime. Isolated thunderstorm development is expected with
sufficient wind profiles for isolated severe hail/wind potential.

Elevated thunderstorms should again increase in coverage across
western/central South Dakota towards the mid Missouri Valley late
tonight into early Monday morning. Moderate MUCAPE and sufficient
cloud-layer shear could support an isolated hail threat with the
initial development across western/southern South Dakota, though
mergers/interactions and weakening buoyancy will likely limit the
longevity and eastward extent of this threat into the mid Missouri
Valley.

..Guyer/Weinman.. 09/13/2026

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1229 PM CDT Sun Sep 13 2026

Valid 141200Z - 151200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM SOUTHEAST
NEBRASKA INTO WESTERN IOWA...

...SUMMARY...
Scattered strong to severe thunderstorms may impact parts of eastern
Nebraska into western Iowa late Monday afternoon into early evening.

...Discussion...
A mid-level trough will move across the northern Plains on Monday
with a strengthening 60-70 knot mid-level jet streak. The surface
pattern will feature a surface low across the Canadian Prairies and
a secondary weaker surface low across the central Plains. A moist
airmass will advect northward to the east of the surface trough with
mid to upper 60s dewpoints advecting into Nebraska and Iowa.  

Thunderstorms will likely be ongoing at the beginning of the period
across eastern South Dakota and Minnesota into Iowa amid moderate
isentropic ascent. In the wake of this morning activity, northward
recovery will occur across northeast Kansas into southeast Nebraska
and southwest Iowa. Within this zone, a narrow period of favorable
conditions is forecast to develop ahead of front from southeast
Nebraska northward. Most guidance shows storms developing within an
environment featuring 2500+ J/kg MLCAPE and 30 to 35 knots of
effective shear during the afternoon. This would support a supercell
storm mode. If this discrete storm mode can be maintained, a EF2+
tornado threat will exist given the nearly purely streamwise
vorticity in the lowest 2km from RAP forecast soundings in the
region. Limiting factors to this scenario are multiple storms
developing along the front and quickly growing upscale and a lack of
strong venting flow aloft which may result in disruptive downbursts
before a more organized, strong low-level mesocyclone can develop. 

Farther southwest, moderate instability and strong heating/lapse
rates may support isolated damaging wind gusts. Some guidance shows
~30 knots of effective shear which could support some marginally
rotating storms. If this occurs, some isolated large hail may be
possible. The 5% hail probability has been extended southwestward to
account for this threat. 

Elevated thunderstorms will persist into the overnight period across
southern Wisconsin and northern Illinois within a strong low-level
jet and isentropic ascent. However, only modest elevated instability
and limited cloud-bearing shear should preclude much severe threat
farther east into southern Wisconsin and northern Illinois.

..Bentley.. 09/13/2026

Day 1 Fire Weather Outlook  
NWS Storm Prediction Center Norman OK
1142 AM CDT Sun Sep 13 2026

Valid 131700Z - 141200Z

...Central Wyoming...
A robust upper-level low continues to make eastward progress into
the Pacific Northwest while an accompanying 65-70 knot mid-level jet
maxima moves into the Northern Rockies. Surface pressure falls 
observed across the northern WY/northern high plains of MT will
persist as a surface low evolves across this region. Resultant
stronger deep-layer southwest flow within a well-mixed and dry
boundary layer is expected for a few hours this afternoon across
central WY. Sustained southwest winds of 15-20 mph and RH as low as
15% will align with dry fuels (ERCs in the 80-90th percentile range)
where Elevated highlights have been introduced. These dry and breezy
conditions will occur prior to potential showers and thunderstorms
late this afternoon and evening.

No changes were made to the existing Elevated highlights across the
Great Basin into portions of the Snake River Valley and southwestern
Montana as forecast remains on track.

..Williams.. 09/13/2026

.PREV DISCUSSION... /ISSUED 0159 AM CDT Sun Sep 13 2026/

...Synopsis...
A strong upper-level low with a 65-70 kt jet streak is expected to
progress eastward across the Pacific Northwest today, resulting in
widespread dry and windy conditions across portions of the Great
Basin into the Snake River Valley and far southwestern Montana. 

...Great Basin into portions of Idaho and Montana...
Dry and windy conditions owing to deep boundary layer mixing beneath
the strong upper low and associated jet streak will result in
widespread 15-20 MPH winds across much of the Great Basin during the
afternoon. From southern Nevada into far western Utah, relative
humidity could reach as low as 10-15% with southwesterly winds,
while the post-frontal airmass across northern Nevada will possess
westerly winds with 15-20% relative humidity. With ERCs approaching
the 80th annual percentiles, at least Elevated fire-weather
conditions are expected, and locally Critical conditions are
possible where terrain induced wind gusts are favored. Further north
into the Snake River Valley and portions of southwest Montana,
southwest winds of 20 MPH (with locally higher gusts) are
anticipated to overlap with relative humidity of around 15%. While
there appears to be a potential corridor for Critical fire-weather
concerns, they overlap with more modest fuels and a lower density
fuelscape.

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