SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0301 PM CDT Fri Aug 22 2025
Valid 222000Z - 231200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE NORTHERN/CENTRAL HIGH PLAINS TO THE UPPER MIDWEST/GREAT
LAKES...AND PORTIONS OF SOUTHERN/CENTRAL ARIZONA...
...SUMMARY...
Strong to locally severe thunderstorms may occur today from parts of
the northern and central High Plains to the Upper Midwest/Great
Lakes, and separately across parts of Arizona. Damaging winds and
occasional hail should be the main threats.
...20z Update...
Minor adjustments were made to remove thunder chances and the
Marginal Risk behind ongoing convection from Iowa to Wisconsin.
Otherwise, the forecast remains on track. See previous discussion
below for more information.
..Thornton.. 08/22/2025
.PREV DISCUSSION... /ISSUED 1130 AM CDT Fri Aug 22 2025/
...Synopsis...
A mid/upper-level trough/low centered over Manitoba late this
morning will move east-southeastward across Ontario and the Upper
Midwest/Great Lakes through the period. At the surface, a weak cold
front is forecast to develop southeastward across the
northern/central High Plains and Upper Midwest this afternoon and
evening. This boundary should serve as a focus for additional
thunderstorm development later today, some of which could become
strong to severe. A mid/upper-level anticyclone will remain anchored
over the Four Corners region today, with modest easterly mid-level
flow persisting over parts of AZ.
...Northern/Central High Plains to the Upper Midwest/Great Lakes...
A broad zone of isolated strong to severe thunderstorm potential
remains evident today, generally along/near a convectively
reinforced cold front extending from the central High Plains
east-northeastward to the Upper Midwest/Great Lakes. Within this
broad zone, three somewhat separate regimes of severe potential are
apparent.
Thunderstorms have recently developed across parts of
central/eastern MN and far northwest WI ahead of a remnant
MCV/subtle mid-level shortwave trough. The airmass downstream from
this activity across northern WI into the U.P. of MI is only weakly
unstable, with scattered to broken mid/upper-level clouds present.
Stronger mid-level flow is also forecast to generally lag behind the
surface cold front across this region. Still, a small cluster or two
may eventually evolve from the ongoing convection in MN, and spread
eastward through the afternoon/early evening. Occasional damaging
winds should be the main threat, but some hail may also occur with
the stronger cores given cool mid-level temperatures and around
25-35 kt of deep-layer shear aiding updraft organization. Considered
adding a Slight Risk for severe/damaging winds across parts of
northern WI and vicinity, but confidence in more robust
destabilization occurring remains low. Trends will be monitored for
a possible upgrade at 20Z, if needed.
Outflow from earlier thunderstorms continues to advance southward
across parts of eastern NE and northwest IA per recent surface
observations and visible satellite imagery. The effect of this
outflow surge on additional thunderstorm development this afternoon
remains unclear, as the primary cold front lags the outflow by a
considerable extent. Some guidance suggests that a couple of
supercells or perhaps a small cluster may develop over far southeast
SD into eastern NE and western IA later today as the airmass across
these areas gradually destabilizes. At least an isolated risk for
severe hail and damaging winds will exist if this occurs. But, the
overall severe threat remains too uncertain for a categorical
upgrade with this outlook update.
Farther west, a subtle mid-level ridge-peripheral disturbance noted
in water vapor imagery across southern WY and northwest CO, along
with strong daytime heating, should aid thunderstorm development
initially across the higher terrain of the central Rockies later
this afternoon. This activity should propagate east-southeastward
toward lower elevations in the presence of moist, post-frontal
low-level upslope flow. Isolated severe hail and winds are possible
with this activity, especially within a corridor across
interior/southeast WY into northeast/east-central CO.
...Arizona...
A fair amount of convective cloud debris is present today across
parts of AZ per recent visible satellite imagery. This may tend to
delay diurnal heating and related steepening of low-level lapse
rates to some extent. But, eventual airmass recovery is still
expected by late afternoon/early evening, with seasonably moist
low-levels still noted on the 12Z observed PHX sounding.
Thunderstorms should once again form initially along the higher
terrain of the Mogollon Rim and southeastern AZ before spreading
west-southwestward across the lower elevations of central/southern
AZ through the evening. Sufficient instability, a very well-mixed
boundary layer, and modest easterly mid-level flow should all
support an isolated threat for severe/damaging winds with this
activity.
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