SPC Aug 18, 2026 1300 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 1300Z Day 1 Outlook


Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0747 AM CDT Tue Aug 18 2026

Valid 181300Z - 191200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM NORTHEAST
KANSAS INTO CENTRAL MISSOURI...

...SUMMARY...
Thunderstorms with severe wind gusts and isolated large hail will be
possible this afternoon and evening from the central Plains into the
lower Missouri Valley. Isolated severe gusts and hail will also be
possible from the Northern Rockies into the central High Plains, and
eastward into the Midwest and southern Lower Michigan. Damaging
gusts could also occur across parts of Mississippi and Alabama.

...Central Plains into Lower MO Valley...
Warm-air advection showers and thunderstorms are currently ongoing
across south-central/southeast NE. This activity is likely
reinforcing an outflow boundary from an earlier MCS that extends
from northwest KS into the NE/KS/MO border vicinity. These showers
and thunderstorms are expected to continue southeastward over the
next few hours, while gradually diminishing in coverage and
intensity. How this outflow modifies will influence the thunderstorm
potential across northern KS this afternoon. If the boundary does
not wash out, there could be a region of notable convergence that
develops across in the northwestern/north-central KS between the
outflow (reinforced by an approaching cold front) and a heat-driven
surface low that develops across western KS. Even with this
potential convergence, convective initiation is uncertain. Most
guidance maintains warm low/mid level temperatures, with the
resultant capping suppressing any thunderstorm development. Steep
lapse rates, moderate deep-layer vertical shear, and strong buoyancy
are expected north of the boundary, and there is a conditional risk
for large to very large hail and strong downdrafts if any updrafts
can mature.

A more certain scenario is expected farther east across eastern KS,
where evening thunderstorm development is anticipated as the
low-level jet increases. Steep lapse rates and moderate vertical
shear support the potential for thunderstorms capable of large hail
during the initially more cellular mode. These storms will likely
cluster quickly, with a trend towards upscale growth into a
forward-propagating MCS which then moves into MO. Damaging gusts
will become the primary risk once this occurs.

...Northern Rockies through the Central High Plains...
A shortwave trough is forecast to progress southeastward from
British Columbia/Alberta into the northern Rockies. Thunderstorm
development is anticipated across the northern Rockies as this wave
interacts with the destabilized and buoyant airmass across the
region. Moderate westerly flow will accompany this wave as well,
supporting the potential for more organized storm structures and the
development of several line segments. These widely scattered
thunderstorms are forecast to progress eastward/southeastward this
afternoon/evening, with additional development possible from WY into
the central High Plains. The moderate westerly flow aloft, high
storm bases, and steep low-level lapse rates support the potential
for strong to severe wind gusts as these storms progress
eastward/southeastward.

...Southern WI/northern IL into Lower MI...
Low-level moisture is expected to increase across the Midwest ahead
of an approaching cold front, resulting in moderate buoyancy by the
late afternoon. Convergence along the front will be weak but still
sufficient for convective initiation, with the combination of
moderate buoyancy and moderate westerly flow aloft supporting strong
to severe storms. An initially more cellular mode could yield large
hail within the strongest storms. A quick transition towards more
linear modes is anticipated, with damaging gusts becoming the
primary severe risk within any strong line segments.

...MS/AL...
Afternoon thunderstorm development is anticipated across MS and AL
as a weak vorticity maximum progresses southeastward into the warm,
moist, and unstable environment in place across the region. Vertical
shear will be weak, and an outflow-dominant, multicellular mode is
expected. Even so, some clustering into one or more line segments
appears probable, resulting in scattered thunderstorm coverage.
Steep low-level lapse rates and relatively high cloud bases support
the potential for strong downdrafts with any more robust convection.

..Mosier/Bunting.. 08/18/2026


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SPC Aug 18, 2026 0600 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 1200Z Day 1 Outlook


Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1256 AM CDT Tue Aug 18 2026

Valid 181200Z - 191200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE CENTRAL PLAINS AND LOWER MISSOURI VALLEY...

...SUMMARY...
Thunderstorms with severe wind gusts and isolated large hail will be
possible this afternoon and evening from the central Plains into the
lower Missouri Valley. Isolated severe gusts and hail will also be
possible from the Northern High Plains eastward into the Midwest and
southern Great Lakes.

...Central and Northern Plains...
At mid-levels, a broad cyclonic flow pattern will be in place over
the northern U.S. A shortwave trough will move across the central
and northern Plains. At the surface, a cold front will advance
southward into Nebraska by afternoon. To the south of the front, an
outflow boundary from morning convection will move southward into
northern Kansas. A moist airmass will exist between the two
boundaries with surface dewpoints in the upper 60s to lower 70s F.
Within the moist air, moderate to strong instability will develop by
afternoon. The outflow boundary will be a focus for convective
initiation during the day, while additional storms are expected to
develop further west across the central High Plains in the late
afternoon. Increasing convective coverage during the early evening
should result in the development of a line segment.

RAP forecast soundings at 00Z from Salina to Kansas City have MLCAPE
in the 1500 to 2500 J/kg range with 0-6 km shear around 40 knots.
700-500 mb lapse rates are forecast to be in the 7 to 8 C/km range.
This environment will support supercells with isolated large hail.
The large hail threat will extend west-northwestward into southwest
Nebraska during the late afternoon where mid-level lapse rates will
be steeper and cells will likely remain discrete. The greatest
wind-damage potential is forecast from northern and eastern Kansas
into far western Missouri, where the development of an organized
bowing line segment will be possible in the early evening. Wind
gusts above 75 mph will be possible along the path of any intense
line segment. The severe threat may impact parts of lower Missouri
Valley and Ozarks by mid to late evening.

...Midwest/Great Lakes...
A mid-level shortwave trough will move across the north-central U.S.
today, as a cold front advances southeastward across the Midwest and
Great Lakes. To the south of the front, surface dewpoints in the 60s
F will contribute to moderate instability along an
west-northwest-to-east-northeast axis from the mid Mississippi
Valley into the southern Great Lakes. Isolated to scattered
thunderstorms appear likely to form along and south of the front in
the late afternoon and early evening. MLCAPE in the 1000 to 2000
J/kg range, 0-6 km shear around 40 knots and precipitable water in
the 1.7 to 1.9 inch range will be favorable for isolated severe
storms capable of severe wet downbursts.

...Northern High Plains...
Northwesterly mid-level flow will be in place today from the
Northern Rockies into the Northern High Plains. At the surface,
dewpoints along the moist axis from northeastern Wyoming into
central Montana will be around 50 F. As surface temperatures warm
during the day, MLCAPE is expected to increase to around 1000 J/kg
in parts of the northern High Plains. Thunderstorms are expected to
form in the higher terrain in the afternoon, moving
east-southeastward into the lower elevations. Due to the instability
and steep low to mid-level lapse rates, isolated severe wind gusts
will be possible with the stronger cells.

..Broyles/Jirak.. 08/18/2026


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SPC Aug 18, 2026 0100 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 0100Z Day 1 Outlook


Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0759 PM CDT Mon Aug 17 2026

Valid 180100Z - 181200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE CENTRAL AND NORTHERN PLAINS...AND FROM NORTHEASTERN ALABAMA INTO
WESTERN NORTH CAROLINA...

...SUMMARY...
Thunderstorms with severe wind gusts and large hail are expected
this evening across parts of the central and northern Plains.
Isolated severe gusts will also be possible from parts of the
northern Gulf Coast States into the southern Appalachians and
Carolinas.

...Central and Northern Plains...
The latest water vapor imagery shows west-northwesterly flow over
much of the northern U.S., with a low-amplitude shortwave trough
moving through the flow in the northern Plains. At the surface, a
cold front is advancing southeastward through the Dakotas. Ahead of
the front, surface dewpoints are in the 60s F. The RAP has an axis
of moderate to strong instability located from central Nebraska
northeastward into eastern South Dakota, along which MLCAPE is
estimated in the 2500 to 3500 J/kg range. Isolated thunderstorms are
ongoing near the instability axis with scattered storms ongoing to
the west of the instability max in western Nebraska and southwestern
South Dakota.

These storms are located along the eastern edge of an elevated mixed
layer extending eastward from the central Rockies. Near the storms,
the RAP is estimating 700-500 mb lapse rates in the 7.5 to 8.5 C/km
range. In addition, the North Platte WSR-88D VWP has 0-6 km shear
near 50 knots with significant directional shear evident in the
lowest 3 km above ground level. This environment will support
supercells with large hail and severe wind gusts this evening. The
more intense storms could produce hailstones exceeding 2 inches in
diameter. Short-term model forecast suggest that the storms will
continue to move east-southeastward toward the instability axis this
evening, remaining relatively discrete. However, a transition to a
broken line segment should eventually occur, which would result in a
greater wind-damage threat. A few severe gusts above 75 mph will be
possible. The severe threat should persist into the mid to late
evening...See MCD 2019.

...Northern Gulf Coast States/Southern Appalachians/Carolinas...
The latest surface analysis shows a distinct outflow boundary from
northern Alabama eastward into the western Carolinas. Strong to
severe thunderstorms are ongoing near the outflow boundary. To the
south of the boundary, surface dewpoints are in the 70s F and the
RAP is estimating MLCAPE in the 2000 to 3500 J/kg range. Within the
most unstable air, RAP forecast soundings early this evening have
0-3 km lapse rate in the 7.5 to 8 C/km range, with precipitation
water above 2 inches. In addition, the WSR-88D VWP in northeast
Alabama has 0-6 km shear in the 20 to 25 knot range. This
environment will support a potential for severe wet downbursts for a
couple more hours this evening.

..Broyles.. 08/18/2026


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SPC Aug 17, 2026 1630 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 1630Z Day 1 Outlook


Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1152 AM CDT Mon Aug 17 2026

Valid 171630Z - 181200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE
NORTH-CENTRAL PLAINS/UPPER MIDWEST AND SOUTHERN APPALACHIANS...

...SUMMARY...
Thunderstorms with severe wind gusts and large hail are expected
this afternoon and evening across parts of the central and northern
Plains. Damaging gusts will also be possible in parts of the
southern Appalachians to the North Carolina Piedmont, and possibly
across portions of the Mid-South and southern Plains.

...Northern/Central Plains...
Weak height falls are expected regionally with a seasonally
prominent strengthening of northwesterly flow aloft. A surface low
will shift eastward and an attendant cold front will push
southward/southeastward across eastern Montana, North Dakota and
toward west/northwest Minnesota. The airmass preceding this front
will be moist and strongly unstable, with dewpoints in the upper 60s
and MLCAPE over 2500 J/kg. Multiple areas of initial development are
expected, including along the front from eastern Dakotas into
western Minnesota, and in the vicinity of the pre-frontal trough
and/or front over the NE Panhandle vicinity, southern South Dakota,
and southeast Montana/far eastern Wyoming.

Mid/Late-afternoon storm development in each of these areas will
progress into zones of greater buoyancy by evening. Some initial
supercells capable of large hail are expected, especially given the
strength of the deep-layer wind profiles, while steep low-level
lapse rates and high cloud bases will support strong wind gust
potential, especially with the possibility that storms may
cluster/organize this evening across Nebraska/southern South Dakota,
and possibly across Siouxland and western Minnesota.

...Central/Southern Appalachians into the Piedmont...
Within a very moist airmass, renewed thunderstorm development is
expected along the southern flank of a remnant thunderstorm cluster
and in vicinity of the higher terrain/mountains this afternoon.
Vertical shear will not be overly strong, but moderate/strong
buoyancy and steep low-level lapse rates will still support the
potential for damaging wind gusts. These strong outflows could
promote the development of several
forward-propagating/southeast-moving line segments with a persistent
potential for wind damage, at least through early evening.

...Oklahoma/Arkansas to Mid-South...
Aided by an MCV, a small cluster of storms with a morning history of
occasional severe-caliber winds continues at midday across northwest
Arkansas. For additional short-term details, see Mesoscale
Discussion 2010. While not certain or perhaps likely, a general
eastward-persistence of this cluster could occur. Additional
isolated storm development may occur regionally later this afternoon
along the remnant outflow and/or front, with steep low-level lapse
rates and ample buoyancy supportive of damaging downburst potential
through around sunset.

..Guyer/Chalmers.. 08/17/2026


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