SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1130 AM CDT Fri Aug 15 2025
Valid 151630Z - 161200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON AND
TONIGHT FROM PARTS OF SOUTH DAKOTA INTO THE UPPER MIDWEST...
...SUMMARY...
Scattered strong to severe storms are likely today and tonight over
parts of the northern Plains and Upper Mississippi Valley.
...MN/IA/WI...
Recent satellite imagery shows a pair of convectively generated
vorticity maxima moving across the northern/central Plains, with the
northernmost vorticity max over the eastern ND/SD border and the
southernmost vorticity max over north-central NE. Showers and
thunderstorms have persisted near these features over the last
several hours, but the strongest cells in both of these clusters
have recently shown a weakening trend. A moist and buoyant airmass,
characterized by dewpoints in the upper 60s/low 70s, exists
downstream and redevelopment is possible ahead of both of these
vorticity maxima. How that redevelopment evolves is uncertain, with
recent guidance offering varied solutions regarding overall coverage
and evolution.
Redevelopment appears most probable with the southern vorticity
maxima, given the ample moist and buoyancy that exists downstream.
This development should grow upscale quickly, with the resulting
convective cluster then tracking southeastward. Recent guidance
continues to trend farther south, so the wind probabilities were
extended southward to cover this potential. Damaging gusts appear
like the most likely threat through the evening. Current progression
of the northern vorticity maximum takes it into a less buoyant
airmass across central MN and northern WI, and redevelopment
along/ahead of this disturbance appears less likely.
Depending on the strength of the IA cluster, additional development
is possible in its wake amid a strengthening low-level jet and
associated warm-air advection over its outflow. Steep mid-level
lapse rates should still be in place, supporting strong updrafts and
large hail with these elevated storms.
Lastly, a decaying convective line may reach the southwestern
MN/northwestern IA vicinity late in the period. Given the potential
for preceding storms, the amount of buoyancy that will still be in
place remains is uncertain. However, if thunderstorm coverage is low
or most storms develop farther east, enough buoyancy could remain to
support strong updrafts capable of damaging gusts and/or hail within
the convective line or any preceding more cellular storms.
..NE/SD this afternoon through tonight...
Strong heating and ample mid-level moisture will result in scattered
high-based thunderstorm development across eastern WY and western
NE/SD by late afternoon. Isolated hail and strong gusts are possible
with this initial activity. This activity will then track
east-northeastward through the early evening into a progressively
more moist and unstable air mass across NE and SD. The combination
of improving thermodynamic environment and an intensifying nocturnal
low-level jet will likely aid in thunderstorm intensification and
upscale growth through the evening across northern NE and central
SD. Guidance continues to vary significantly with the strength of
this MCS, but general consensus would suggest the threat for strong
to severe gusts will persist across SD tonight. There is at least a
low probability for the development of a well-organized MCS that
could produce significant severe gusts. However, that probability is
currently too low to introduce an unconditional sig wind area.
...TX Coastal Plain into the Hill Country and Southeast TX...
A maturing tropical disturbance is near south TX, with associated
outflow currently spreading northward across the TX Coastal Plain.
Limited lightning has been noted with in the short-lived cores that
have been developing along this outflow. This process of brief
intensification along this outflow is expected throughout the day,
with an overall increase in thunderstorm coverage anticipated. A
modest increase in low to mid-level flow is expected along the
eastern periphery of this system, spreading northward into central
and southeast TX. Even so, shear will remain weak, with a
disorganized multicellular pulse storm mode anticipated. Given the
very moist profiles (i.e. PW values over 2"), a few water-loaded
downbursts are possible, but should be isolated enough to preclude
the need for severe probabilities.
..Mosier/Wendt.. 08/15/2025
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