ACUS02 KWNS 211728
SWODY2
SPC AC 211726
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1226 PM CDT Fri Aug 21 2026
Valid 221200Z - 231200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SATURDAY INTO
SATURDAY EVENING ACROSS PARTS OF THE NORTHERN INTERMOUNTAIN REGION
INTO NORTHERN ROCKIES...THE FRONT RANGE INTO CENTRAL GREAT
PLAINS...THE SOUTHEASTERN GREAT PLAINS...MIDDLE/UPPER OHIO VALLEY
AND ADJACENT LOWER GREAT LAKES REGION...
...SUMMARY...
Scattered strong storms may impact a corridor from near the northern
Rockies into the southeastern Great Plains, as well as the middle
and upper Ohio Valley vicinity, Saturday. These may pose at least
some potential to produce severe wind and hail.
...Discussion...
Models indicate that the increasingly deformed remnants of a
mid-level low will be forced inland across the northern U.S. Pacific
coast during this period, with a still vigorous remnant perturbation approaching the Canadian/northern U.S. Rockies by late Saturday
night. Downstream, the center of a prominent mid-level ridge is
forecast to slowly shift across and east of the southern Rockies,
with amplified ridging within the westerlies to the north
overspreading much the Canadian Prairies and northern U.S. Great
Plains.
To the east of this ridging, it appears that large-scale troughing
will undergo further amplification across areas east of the
Mississippi Valley through the Atlantic Seaboard. Within this
regime, guidance indicates that one vigorous short wave impulse will
dig southeast of the Upper Midwest/adjacent Great Lakes through the
upper Ohio Valley by late Saturday night, trailed by a similar
strength impulse across northwestern Ontario toward the northern
Great Lakes vicinity. These are likely to be preceded by at least a
couple of increasingly sheared perturbations, including one
generally forecast to accelerate northeastward offshore of the
southern Mid Atlantic coast early in the period.
Near the southwestern flank of the larger-scale troughing, a
convectively generated or augmented perturbation might maintain
strength within modest north-northwesterly flow, around the eastern
periphery of the stronger mid-level ridging, across the southeastern
Great Plains toward northwestern Gulf coast.
In lower-levels, it appears that the leading edge of a series of
surges of cooler air, probably reinforced by convective outflow
across at least portions of the Great Plains, may reach central
Texas and northern portions of the remainder of the Gulf Coast into
southern Mid Atlantic Seaboard by 12Z Sunday. This is expected in
the wake of a modestly deepening surface low to the north of the
lower Great Lakes, and a weaker secondary low developing
near/offshore of the Mid Atlantic.
...Ohio Valley into lower Great Lakes region...
In advance of the vigorous lead digging short wave trough, and an
associated influx of surface cooling, a corridor of low-level
moistening may contribute to potential for moderate boundary-layer destabilization by late afternoon. It appears that this will have
to occur in the wake of early period warm advection driven
convective cloud cover and precipitation likely to overspread the
region. However, breaks in the cloud cover and the onset of cooling
aloft may become sufficient to support scattered vigorous
thunderstorm development. Despite generally modest to weak vertical
shear, modest steepening of lower into mid-level lapse rates of
temperature and potential wet-bulb temperature may be sufficient to
contribute to profiles conducive to localized downbursts, in
addition to marginally severe hail.
...Front Range into southeastern Great Plains...
Latest convection-allowing guidance and other model output remains
rather varied concerning the potential evolution of storms and the
associated risk for severe weather through this period. However,
there do appear at least a couple of corridors with a somewhat
higher likelihood for thunderstorm initiation and organization
Saturday through Saturday night.
One may develop on the eastern periphery of the mid-level high
across the southeastern Great Plains, where stronger
lower/mid-tropospheric warm advection may focus near the nose of an increasingly suppressed plume of elevated mixed-layer air. Wind fields/vertical shear may be modest to weak, but a corridor of
higher low-level moisture content may support storm inflow with
large CAPE ahead of a remnant convective perturbation, supporting
potential for the evolution of an intensifying and organizing south/southwestward propagating storm cluster with risk for severe
hail and wind.
Another may focus in moistening upslope flow along/east of the
Laramie mountains through Colorado Front Range by late Saturday
afternoon. Perhaps aided by a weak short wave impulse slowly
pivoting across this region, around the periphery of the mid-level
high, convection may consolidate into an intensifying and organizing
cluster propagating into the adjacent Great Plains by Saturday
evening, aided by updraft inflow of air characterized by moderately
large CAPE.
...Eastern Idaho into western Montana...
Multiple waves of scattered thunderstorm development appear possible
across the region Saturday into Saturday night, ahead of the inland
advancing short wave trough. In the wake of an initial round of overnight/early period convection, models suggest that boundary
layer moistening will be sufficient to support increasing, though
still rather modest to weak, CAPE with heating and deep mixing by
late Saturday afternoon. Still, thermodynamic profiles may become
conducive to a few localized downbursts into Saturday evening.
..Kerr.. 08/21/2026
$$
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