SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0248 PM CDT Sun Jul 28 2024
Valid 282000Z - 291200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PARTS OF
NORTHERN/CENTRAL PLAINS AND UPPER MIDWEST...
...SUMMARY...
Scattered strong to severe thunderstorms are expected across parts
of the northern/central Plains into the Upper Midwest this afternoon
through tonight. Large hail and severe/damaging winds should be the
main threats.
...20z Update...
Several regimes and areas of thunderstorm development are expected
across the northern/central Plains into the upper Midwest this
afternoon and evening. Visible satellite shows developing cu across
the Black Hills of South Dakota and into northern Wyoming/southern
Montana. These regions may see thunderstorm development in the near
term, with potential for large hail and damaging wind. See MCD#1718
and MCD#1720 for more information.
Short term development in the next couple of hours is also possible
across western and central Nebraska and northwestern Kansas. In this
region, development is expected to remain more isolated, with a
threat of large hail and damaging wind. See MCD#1719 for more
information.
A more appreciable damaging wind threat is probable across
south-central South Dakota later this afternoon and evening. In this
region, scattered thunderstorm development is expected along a
surface cold front, with potential for large hail and damaging wind.
This activity is expected to become linear and better organized,
spreading eastward into central/eastern SD with an increasing threat
for damaging wind (isolated 75+ mph).
Overall, the current D1 Convective Outlook remains on track with no
changes needed.
..Thornton/Gleason.. 07/28/2024
.PREV DISCUSSION... /ISSUED 1128 AM CDT Sun Jul 28 2024/
...Synopsis...
Multiple low-amplitude, mid-level vorticity maxima (some
convectively augmented) will move generally east-northeastward
across the northern/central Plains and Upper Midwest through the
period. One or more of these features should aid in robust
thunderstorm development later today, although details on convective
evolution through tonight remain uncertain. At the surface, a weak
low over central SD late this morning should consolidate through
this afternoon along/near the south-central SD/north-central NE
border vicinity. A cold front will extend from northern MN into the
Dakotas, linking with this surface low. A weak lee trough/dryline
feature will extend southward from the low across parts of
western/central NE/KS.
...Northern/Central Plains into the Upper Midwest...
Scattered thunderstorms should develop across parts of
western/central SD by late afternoon along/near the cold front and
surface low. Although deep-layer shear appears marginal for
supercells, any initially more discrete thunderstorms could produce
severe hail. A fairly quick transition to a more linear mode with
greater severe/damaging wind threat is anticipated through the
evening as convection spreads eastward into central/eastern SD. With
sufficient cold pool organization, some chance for isolated 75+ mph
wind gusts may exist with this cluster. A gradual weakening trend is
expected tonight as this activity moves into a less unstable airmass
across southern MN/northern IA. A generally separate area of
convection should form along the length of the front in MN this
afternoon. Most of this area will be in a relative minimum in
mid-level flow, with modest deep-layer shear. Still, some threat for
hail and strong to severe winds may exist with any cluster that can
consolidate and spread east-southeastward through the evening.
Farther south into the central Plains (western/central NE/KS),
large-scale forcing for ascent appears more nebulous, with a broad
area of modestly enhanced mid-level westerly flow expected. Primary
forcing mechanism for convective initiation should be weak low-level
convergence along the lee surface trough. Assuming thunderstorms can
form and be sustained, a conditionally favorable environment for
severe wind gusts and hail will exist. Modest low-level flow is
forecast to veer to a westerly component and gradually strengthen
with height through mid levels, supporting sufficient deep-layer
shear for supercells. Isolated large hail will be a concern with any
persistent supercell, but a well-mixed boundary layer should also
promote severe downdraft winds. Overall coverage of severe
thunderstorms may tend to remain fairly isolated with southward
extent given the weak forcing.
...Eastern Nebraska into Iowa and Northern Missouri...
A remnant MCV is located over northeast NE late this morning per
recent visible satellite and radar imagery. This feature should
continue moving slowly eastward into western IA this afternoon. An
associated modest low-level jet and attendant warm/moist advection
may encourage additional robust thunderstorm development later today
across parts of east-central NE into western/southern IA. Sufficient
low-level shear will be present to support some tornado threat, but
the potential for supercells remains highly uncertain. A somewhat
better chance is apparent for a small cluster to develop and spread
east-southeastward through the evening along the instability axis,
while posing a threat for mainly damaging winds. Given this
potential shown in some high-resolution guidance, the Slight Risk
has been expanded east-southeastward to include more of east-central
NE into southwest IA.
...Wyoming/Southern Montana...
High-based convection is expected to develop this afternoon across
parts of WY and southern MT ahead of a mid-level shortwave trough
moving eastward from the Pacific Northwest. A couple of stronger
outflow-driven cells/clusters appear possible, with an associated
threat for isolated severe gusts.
...Tennessee Valley into the Southeast...
Numerous thunderstorms are expected to further increase across parts
of the TN Valley and Southeast this afternoon in association with a
weak mid/upper-level trough moving northeastward across the mid MS
Valley. Somewhat stronger heating and mid-level flow along the
southern periphery of this trough could support a few strong
thunderstorms, including the possibility of localized tree damage.
However, with generally modest deep-layer shear and weak mid-level
lapse rates, the potential for an organized/sustained severe threat
across this region should remain rather limited.
Read more
