SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0756 AM CDT Mon Aug 04 2025
Valid 041300Z - 051200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
THE NORTHERN AND CENTRAL HIGH PLAINS...
...SUMMARY...
Thunderstorms with severe gusts and hail will be possible today and
tonight from parts of the northern Rockies into the Dakotas and
central/southern High Plains.
...Central High Plains...
Early morning surface analysis shows upper 50s dewpoints in place
across eastern CO, western KS, and western NE, with slightly lower
dewpoints across the NE Panhandle. Moist, southerly low-level flow
will help increase dewpoints across the region throughout the day,
likely resulting in upper 50s to low 60s dewpoints during the
afternoon despite strong heating and boundary-layer mixing. This
should result in a strongly buoyant but minimally capped airmass
across the region by the late afternoon. Additionally, low-level
southeasterly flow will veer to northwesterly in the mid levels,
resulting in moderate to strong deep-layer vertical shear and an
overall wind profile that favors supercells. As such, there is
conditional risk for severe thunderstorms. However, the forcing
mechanism for convective initiation is uncertain.
Upper ridging that currently extends from the Southwest into the
northern High Plains is expected to persist throughout the day, with
heights likely rising across the central High Plains. A shortwave
trough currently moving through the Great Basin is expected to move
within the northern periphery of this ridging, reaching the central
Rockies by this afternoon. Even so, given that heights are forecast
to rise across the central High Plains, the downstream influence of
this wave into the central High Plains will likely be minimal. This
overall lack of larger scale ascent leads to uncertainty regarding
storm coverage since more mesoscale factors, such as low-level
convergence along the lee troughing and weak low-level upslope flow,
will be the mechanisms for convective initiation. High-resolution
guidance offers varied storm coverage, with more recent HRRR runs
(i.e. 06-08Z) keeping the area largely free of storms versus earlier
runs (i.e. 00Z) which show scattered coverage. However, these drier
and less convective HRRR runs appear to be outliers compared to all
the other available guidance, and the general expectation is that
low-level convergence and upslope flow across the Black Hill
vicinity should be enough for scattered convective initiation.
As mentioned previously, the overall environment supports supercells
capable of large to very large hail and strong gusts. Any supercells
that develop could last for a few hours, but should eventually trend
towards a more linear mode with one or more clusters evolving across
western/central NE and northeast CO this evening. Aided by a 40+ kt
low-level jet, continued upscale growth should support these
clusters of strong to severe storms into the overnight hours where
damaging winds will be possible.
...Northern Rockies into eastern Montana...
Shortwave trough currently moving through southern OR is forecast to
continue northeastward through the northern Rockies today and
tonight, while becoming increasingly negatively tilted. Ascent
attendant to this wave will interact with a modest buoyant airmass
from central ID into central MT, resulting in scattered to numerous
thunderstorms across the region. Initially more cellular storms are
expected across the higher terrain of central ID and western MT with
eventual cold pool amalgamation resulting in one or two
eastward/northeastward progressing clusters across central and
eastern MT. Some hail is possible with the more cellular storms, but
damaging gusts appear to be the greater severe risk. Sufficient
severe storm coverage is anticipated across central and eastern MT
to merit introducing 15% wind probabilities.
...Southern High Plains...
Strong heating along a lee trough could support isolated
thunderstorm development from the Raton Mesa into southeast
CO/northeast NM. The thermodynamic environment here will be similar
to areas farther north, with large buoyancy (3000+ J/kg MLCAPE) and
40-50 kt of effective shear anticipated. A supercell mode is
expected initially with any storms that mature, with large hail,
damaging gusts, and a brief tornado possible. Storm maintenance into
the OK/TX Panhandles is possible, particularly given the
strengthening low-level jet.
...Central/Southeast Texas...
A decaying MCS continues to push southward/southeastward across
central TX at 35 kt. Isolated damaging gusts will remain possible
with this system over the next hour or two, but warming cloud tops
and lowering echo tops suggest this system will continue to weaken.
Additional storm development is possible along the western portion
of the outflow, but low-level stability should mitigate updraft
strength.
..Mosier/Bentley.. 08/04/2025
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