RSS Mesoscale Discussions from Storm Prediction Center
SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0257 PM CDT Tue Jun 30 2026
Valid 302000Z - 011200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
OF WESTERN KANSAS...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE SOUTHERN
HIGH PLAINS TO THE GREAT LAKES AND PARTS OF NEW ENGLAND...
...SUMMARY...
Scattered severe thunderstorms are still expected across parts of
the central High Plains, with severe wind gusts (60 to 85 mph) being
the primary hazard during the late afternoon and evening. Other
severe thunderstorms are still expected across the Great Lakes and
Northeast, as well as broader parts of the central Plains to middle
Missouri Valley.
...20Z Update...
The most noteworthy change made to the Day 1 Outlook for the 20Z
update was to join the two Slight Risk areas, driven by wind
probabilities, across the Plains to the Great Lakes. Furthermore,
the CIG1 area was expanded northeast into the Upper MS Valley.
Guidance consensus has consistently depicted a persistent region of
likely cold-pool-driven convection propagating around the upper
ridge periphery, from the central Plains this evening, toward the
Great Lakes through 12Z tomorrow morning. Uncertainty remains
regarding the overall morphology and evolution of this convection,
hence the constraining of severe wind probabilities to Category
2/Slight risk. However, overnight storms will traverse an elongated
axis of strong buoyancy, characterized by 8-9 C/km 700-500 mb lapse
rates atop 70+ F surface dewpoints (per 18Z OAX and GRB observed
soundings), along with forecast 30-40 kts of effective bulk shear.
As such, if more organized storm modes (particularly bow echoes) can
develop tonight, a couple of 75+ mph gusts could occur.
Otherwise, the previous forecast remains on track, with mainly minor
changes made to thunder and severe probabilities to reflect the
consensus among the latest observations and numerical guidance.
..Squitieri.. 06/30/2026
.PREV DISCUSSION... /ISSUED 1150 AM CDT Tue Jun 30 2026/
...Southern/Central Plains...
Scattered thunderstorms are forecast later this afternoon over the
High Plains on the western rim of richer low-level moisture and
strong insolation. Model guidance shows considerable erosion of the
capping layer by mid-afternoon with MLCAPE ranging from 1500 J/kg
over the Texas South Plains to 3500 J/kg over western Kansas.
Initially higher-based convection will gradually move east into
richer moisture and promote larger thunderstorm cores and increased
potential for storm clusters to develop. Large hail will be possible
with any initial supercell activity (i.e., most probable from the
northern Texas Panhandle into Kansas; 25-40 kt effective shear).
However, very steep surface to 300-mb lapse rates will favor strong
evaporative cooling with the more intense cores. Ample deep-layer
shear will exist for organized storms, but veering/backing of flow
with height will aid in storm outflow aggregating as linear clusters
become the primary storm mode with time. These organized but linear
clusters will likely be efficient in promoting severe wind gusts
(60-85 mph) during the early evening, coincident with a
strengthening LLJ and WAA before this threat wanes by late evening.
Weaker deep-layer shear farther south in the southern High Plains
will likely limit both storm organization and overall coverage of
the wind risk.
Later into this evening, confidence has increased in mainly
nocturnal development in a post-frontal environment, that will
probably have its genesis by early evening in the vicinity of
northeast Colorado/southwest Nebraska. These storms will likely
increase/expand northeastward tonight with large hail and damaging
wind potential, which could actually increase and become somewhat
more prominent overnight across northern Nebraska/southeast South
Dakota and neighboring Siouxland as storms cluster and as the warm
front quickly shifts northward regionally.
...Upper Midwest/Great Lakes...
A few strong storms could occur early this afternoon across northern
Michigan, but primary concern is the potential for redevelopment
later today, potentially focused along a zone of modifying
outflow/differential heating, with robust instability to the south.
Although the degree of mid-level capping is a key uncertainty, where
storms do redevelop, ample tropospheric flow will support organized
storms, including supercells capable primarily of a hail/wind risk
and perhaps a tornado. Storms will likely become more probable and
increase this evening with at least some hail and wind potential
continuing tonight.
...Northeast States...
A cluster of storms over southeast Ontario at midday will likely
continue to progress southeastward over Lake Ontario toward northern
New York today. See Mesoscale Discussion 1396 for additional
details. These storms coincide with a 30-40 kt belt of northwesterly
mid-level flow that resides on the immediate periphery of a
gradually building upper-level ridge and associated elevated mixed
layer. Residual cloud cover, via overnight/pre-dawn decayed
convection, casts a bit of uncertainty regarding boundary layer
destabilization over portions of this region, especially with
northeastward extent. Nonetheless, increasing storm
coverage/intensity is expected this afternoon including
clusters/bowing segments and possibly a few supercells.
...Southeast...
Located to the south of an upper high centered over the Tennessee
Valley, a very moist air mass is present across much of the region.
Strong heating will yield moderate buoyancy by early afternoon.
Forecast soundings depict around 20-kt effective shear which will
aid in minor multicellular organization. Localized 50-60 mph gusts
capable of isolated wind damage will accompany the stronger storms.
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