SPC AC 070555
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1255 AM CDT Mon Sep 07 2026
Valid 071200Z - 081200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER NORTHWEST
INTO CENTRAL NORTH DAKOTA AND SOUTHEAST SOUTH DAKOTA INTO NORTHEAST
NEBRASKA...
...SUMMARY...
Widely scattered severe storms capable of mainly large hail are
expected over portions of northwest and central North Dakota and
southeast South Dakota into northeast Nebraska Monday afternoon into
evening. A tornado or two is possible in southeast South Dakota. A
broader area of isolated large hail and damaging wind potential
exists over the northern and central Plains into upper Mississippi
Valley. Locally damaging wind gusts appear possible over the central
Gulf Coast states Monday afternoon and evening.
...Synopsis...
A vigorous short-wave trough will pivot from the northern Rockies
through the northern High Plains with an associated strengthening of
the mid/upper-level wind field forecast across the northern Plains
into the upper MS Valley. A low-level jet (LLJ) will also be
sustained over the northern and central Plains into upper MS Valley
ahead of a surface cold front advancing through the northern Plains
and central High Plains.
...Northern and central Plains into the upper Mississippi Valley...
Clusters of mainly elevated thunderstorms may be ongoing at 12Z
Monday from eastern MT into the Dakotas within a zone of forcing for
ascent preceding a lead, mid-level disturbance and coincident with
the exit region of the LLJ. The presence of steep mid-level lapse
rates, MUCAPE of 1000-1500 J/kg, and 35-45 kt of effective bulk
shear will be supportive of some storm organization with an
associated risk for isolated large hail occurrences through the
morning hours as that convective regime shifts east across the
Dakotas.
On the periphery of more persistent cloudiness associated with the
morning storms, stronger insolation coupled with dewpoints in the
upper 60s to low 70s F and modestly steep mid-level lapse rates are
expected to yield a moderately unstable air mass by mid to late
afternoon with MLCAPE up to 1500-2500+ J/kg and a weakening cap.
Surface-based thunderstorm development will become increasingly
likely at that time, aided by increasing height falls attending the
primary short-wave trough.
The 00Z models indicate one potentially favored location for storm
development over portions of south-central and southeast SD into
northeast CO, from the vicinity of a secondary surface low southwest
along a pre-frontal trough. RAP-based hodographs over southeast SD
indicate considerable veering through the lowest 1-2 km AGL with
effective SRH of 200-300 m2/s2 and effective bulk shear magnitudes
of 40-45 kt, owing to the proximity of the LLJ. Accompanying
thermodynamic profiles suggest modest low-level lapse rates with
some residual capping. However, given surface-based storm initiation
and sustenance, supercells would be likely with an associated large
hail and tornado threat.
A hotter and more well-mixed boundary layer is expected with
southwestward extent ahead of the pre-frontal trough where
high-based storms capable of severe wind gusts and hail appear
possible.
Surface-based storms also appear possible ahead of an occluding
surface low and trailing cold front from northwest into central ND.
While the boundary layer may remain relatively cool from the
early-day storms, cooling mid-level temperatures will effectively
steepen lapse rates, yielding sufficient instability amidst 40-50 kt
of deep-layer layer. As such, supercells appear possible with an
attendant risk for large hail.
...Central Gulf Coast...
A hot and very moist air mass is forecast Monday afternoon ahead of
a weak front pushing into the region from the north with MLCAPE
increasing to 2500-3500 J/kg. Forcing for ascent will remain weak as
will vertical shear; however, the degree of instability and high
moisture content will be supportive of intense pulse storms capable
of damaging wet microbursts from mid-afternoon into evening.
..Mead/Chalmers.. 09/07/2026
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z
SPC AC 070513
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1213 AM CDT Mon Sep 07 2026
Valid 081200Z - 091200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE CENTRAL PLAINS TO THE UPPER MIDWEST...
...SUMMARY...
Strong to severe storms are possible on Tuesday from the central
Plains into the Upper Midwest.
...Central Plains to Upper Midwest...
An upper shortwave trough will move across the northern Plains and
Upper Midwest on Tuesday. Enhanced mid/upper southwesterly flow will
overspread the Mid-MO to Upper MS Valley as this occurs. Meanwhile,
a surface low over Manitoba will lift northeast through the early
Wednesday. A trailing cold front will sweep eastward across the
Upper Midwest, with the southern extent of the boundary stalling
over southern NE. Ahead of the front, a very moist airmass will be
in place, supporting pockets of weak to moderate instability.
Most forecast guidance depicts ongoing thunderstorms Tuesday morning
across parts of MN/WI within a warm advection regime. This activity
could pose a risk for hail and strong wind gusts. Early day
thunderstorms could impact airmass recovery and destabilization for
afternoon/evening severe potential ahead of the advancing cold
front. If sufficient recovery occurs, another round of severe
potential could develop from southeast MN into WI and the MI Upper
Peninsula. Otherwise, severe potential will increase during the
evening with southward extent ahead of the front across IA/eastern
NE and perhaps northern KS. While vertical shear will lessen with
southward extent, initial cells will likely develop into line
segments along the front. An initial risk of hail and strong gusts
will transition to mainly a damaging wind risk as storm mode becomes
more linear.
..Leitman.. 09/07/2026
WUUS02 PTSDY2
SPC AC 070635
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0135 AM CDT Mon Sep 07 2026
Valid 091200Z - 101200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
OF THE MIDWEST...
...SUMMARY...
Isolated strong to severe thunderstorms are possible across portions
of the Midwest on Wednesday.
...Midwest...
An upper trough will progress eastward across the Great Lakes on
Wednesday, bringing enhanced westerly flow over the region. At the
surface, a cold front will shift southeast through the period,
becoming positioned from the Upper Ohio Valley to the TX Panhandle
by Thursday morning. Ahead of the front, a moist airmass will be in
place. Midlevel lapse rates are not forecast to be particularly
steep, but pockets of weak to moderate instability are forecast,
particularly across the Lower MO Valley into OH. Morning showers and
thunderstorms will likely be ongoing near and north of the cold
front from Iowa into Lower MI. As the front progresses southeast
through the afternoon and evening, additional thunderstorm
development is expected across the destabilizing warm sector.
Deep-layer flow is expected to largely remain parallel to the
surface boundary. This environment should largely favor a more
linear storm mode and convection could become undercut by the front.
Nevertheless, vertical shear will be sufficient for organized
convection and damaging winds appear possible within corridors of
greater instability into Wednesday evening/early Thursday.
..Leitman.. 09/07/2026
WUUS03 PTSDY3
NOTE: THE NEXT DAY 3 OUTLOOK IS SCHEDULED BY 1930Z
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