RSS Mesoscale Discussions from Storm Prediction Center
SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0732 AM CDT Sun Jul 12 2026
Valid 121300Z - 131200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
EASTERN GEORGIA INTO THE CAROLINAS...SOUTHERN/CENTRAL ARIZONA...AND
THE UPPER PENINSULA OF MICHIGAN...
...SUMMARY...
Thunderstorms capable of producing isolated to scattered
severe/damaging winds may occur this afternoon/evening across parts
of the Carolinas/Southeast into the southern Plains, and separately
over southern/central Arizona. Large hail and severe winds also
appear possible over portions of the Upper Peninsula of Michigan.
...Carolinas/Southeast into the Southern Plains...
Multiple rounds of thunderstorms over the past couple of days have
convectively overturned the moist airmass across the Carolinas.
Cloud cover is also a bit more prevalent this morning across this
region per recent visible satellite imagery, with a weak surface
front extending generally east-west across NC. This cloudiness may
tend to delay/hinder daytime heating and related steepening of
low-level lapse rates to some extent. But, filtered heating through
cloud breaks and the presence of low to mid 70s surface dewpoints
should still aid in at least weak to moderate instability developing
south of the front by mid afternoon. Current expectations are for
scattered thunderstorms to once again develop this afternoon over
the higher terrain of the Appalachians and vicinity as a weak
mid-level trough/shear zone spreads slowly eastward from the TN
Valley to the Carolinas by this evening. While deep-layer shear will
remain modest, this convection should spread generally eastward,
with some potential for loosely organized clusters capable of
producing isolated to scattered damaging winds. Severe wind
probabilities have been generally adjusted southward based on latest
observational and guidance trends. Thunderstorms developing this
afternoon along/near the Atlantic Coast sea breeze across the FL
Peninsula may also pose an isolated severe/damaging wind threat.
Farther west into the lower MS Valley and southern Plains,
deep-layer flow/shear is expected to remain rather weak. While
thunderstorms will occur along/south of a convectively reinforced
boundary, they should generally remain quite limited in
organization. Still, a risk for locally severe/damaging winds may
exist this afternoon as temperatures warm and the moist low-level
airmass south of the boundary destabilizes with daytime heating.
...Upper Midwest/Great Lakes...
Upper ridging is expected to build northward through the period
across the northern Plains/Upper Midwest, with an EML and associated
steep mid-level lapse rates advecting eastward across the upper
Great Lakes. Diurnal heating of a moist low-level airmass and the
presence of the EML will support moderate to locally strong
instability across this region by early afternoon. Modest
west-southwesterly low-level flow will veer strongly with height
through mid/upper levels to north-northwesterly, aiding 30-40+ kt of
deep-layer shear.
The potential for southward-moving supercells capable of producing
both large hail and severe/damaging winds remains apparent,
especially across the U.P of MI with multiple supercells already
ongoing across northern Lake Superior/Isle Royale this morning.
There is still some uncertainty whether these supercells can be
sustained with southward extent, as temperatures are forecast to
gradually warm through the day in the 850-700 mb layer in tandem
with the EML. Regardless, the ongoing severe thunderstorms this
morning, coupled with potential for additional robust convection
spreading southeastward from western Ontario later today, justify
greater severe hail/wind probabilities across parts of the U.P of
MI. Isolated 2+ inch diameter hail appears possible given the strong
deep-layer shear, steepening mid-level lapse rates, and expected
supercell mode.
...Arizona...
Mid/upper-level ridging will remain prominent today over the Rockies
and Plains, with around 20-30 kt of easterly mid-level flow
persisting over AZ/NM. Ongoing showers and thunderstorms this
morning will shift westward through the day, with ample daytime
heating still anticipated for much of southern/central AZ. The
boundary layer will become very well mixed by mid afternoon as
surface temperatures reach into the 90s/low 100s. Orographic lift
should aid parcels in reaching their LFCs over the higher terrain
along the Mogollon Rim and in southeast AZ. The modestly enhanced
easterly mid-level flow should aid this activity in spreading
generally westward into the lower elevations of southern/central AZ
through the remainder of the afternoon and continuing into the
evening. Scattered severe/damaging winds will likely be the main
threat given steepened low-level lapse rates and efficient momentum
transfer in convective downdrafts. Some potential for clustering may
exist, and the severe wind probabilities have been expanded westward
across more of southern/central AZ with this update.
...Montana...
The potential for locally strong/gusty winds may exist this
afternoon with high-based convection that could spread from
southwest into northern MT on the northwestern periphery of the
amplified upper ridge over the Rockies/Plains. Confidence in
sustained thunderstorms developing along/ahead of a weak front
across this region remains rather low due to limited low-level
moisture and capping concerns, so severe wind probabilities have not
been introduced at this time.
..Gleason/Thornton.. 07/12/2026
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