RSS Mesoscale Discussions from Storm Prediction Center
SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1253 AM CDT Wed Sep 16 2026
Valid 161200Z - 171200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER NORTHERN
UTAH AND EASTERN PARTS OF THE OHIO VALLEY...
...SUMMARY...
A couple of strong to severe thunderstorms appear possible across
northern Utah and eastern parts of the Ohio Valley today.
...Synopsis...
A mid-level anticyclone will prevail over the southern Plains to the
TN Valley as a stationary upper trough morphs into a cut-off upper
low along the West Coast today. Multiple mid-level impulses will
pivot around the anticyclone and overspread the Midwest to OH
Valley, supporting occasional rounds of showers and thunderstorms.
Given rich low-level moisture along the northern periphery of the
mid-level anticyclone, a couple of strong to severe storms may
occur. A few strong to severe storms may also occur over portions of
northern UT as a pronounced mid-level impulse rotates around the
developing West Coast upper low, resulting in overlapping cooler
temperatures and stronger flow aloft.
...Northern UT...
As the aforementioned impulse pivots around the evolving upper low,
a 50+ kt 500 mb jet streak and corresponding 7 C/km mid-level lapse
rates will overspread northern UT during the day. Surface heating
will be limited given widespread cloud cover. Nonetheless, forecast
soundings suggest that surface temperatures near 70 F may yield
MLCAPE as high as 1500 J/kg given steep tropospheric lapse rates.
Furthermore, stronger winds aloft that gradually veer with height
will yield around 50 kts of effective bulk shear and elongated
hodographs with some low-level curvature. Multicells and perhaps
embedded supercells should be the primary storm mode, capable of
isolated instances of severe wind and/or hail.
...Midwest into the OH Valley...
Multiple rounds of showers and thunderstorms will be ongoing at the
start of the period (12Z Wednesday) and will continue through the
period (to 12Z Thursday). Some intensification of storms may occur
over OH and immediate surrounding areas with one weak impulse by
afternoon peak heating. Assuming some appreciable insolation can
occur, surface temperatures may rise through the 80s F, amid 70s F
dewpoints, contributing to 1500-2500 J/kg MLCAPE. Given meager
vertical wind shear, mainly pulse cellular and multicellular storms
are expected. The stronger storm cores may produce wet downbursts,
accompanied by an isolated damaging gust threat.
Another mid-level impulse will traverse the Midwest overnight, with
several CAM guidance members supporting nocturnal convective
initiation over IA in the 03-12Z period. At the moment, the
evolution of this convection is uncertain, so no severe
probabilities have been added. However, should more established
convection develop overnight, an instance of marginally severe hail
cannot be completely ruled out.
..Squitieri/Supinie.. 09/16/2026
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SPC 0600Z Day 2 Outlook
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1227 AM CDT Wed Sep 16 2026
Valid 171200Z - 181200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
...SUMMARY...
The risk for severe thunderstorms appears low across the U.S.
Thursday through Thursday night.
...Discussion...
Within the westerlies, which remain confined to the northern
mid-latitudes, models continue to indicate that consolidating
large-scale mid-level troughing will dig through northern Ontario,
Quebec and adjacent portions of the Northeast through this period.
It appears that this may contribute to some southwestward
suppression of the persistent prominent mid-level ridging initially
centered near or southwest of the Mid South vicinity early Thursday.
In lower levels, it appears that this will be accompanied by a
developing area of surface low pressure, trailed by a reinforcing
cool intrusion across the St. Lawrence Valley, upper Great Lakes and
adjacent Upper Midwest. A preceding front, advancing to the
south/southeast of the lower Great Lakes, may continue to overtake
the Ohio Valley segment of an initial quasi-stationary frontal zone
and advance through much of the Mid Atlantic and lower Ohio Valley
by 12Z Friday. The quasi-stationary boundary may remain so across
the lower Missouri Valley, but perhaps shift slowly northward across
the central Great Plains in response to a weak short wave
perturbation migrating around the northwestern periphery of the
mid-level ridging.
It appears that this impulse will precede a cut-off low, initially
inland of the northern California coast, before redeveloping
north-northeastward and elongating across the northern Intermountain
region and Great Basin later Thursday through Thursday night.
Along the southeastern periphery of the mid-level ridge, another
perturbation is still forecast to slowly overspread portions of
south Atlantic coastal areas.
...Great Plains through Ohio Valley...
Guidance continues to indicate that seasonably high boundary-layer
moisture content, focused along and south of the initial
quasi-stationary frontal zone, and generally beneath the mid-level
ridging, will again contribute to sizable mixed-layer CAPE with
insolation Thursday. However, generally warm thermodynamic profiles
and weak deep-layer mean flow/shear probably will continue to
inhibit the risk for organized severe thunderstorm activity.
In association with a low amplitude mid-level wave emerging from the
Four Corners, an increase in thunderstorm development is forecast
overnight, aided by lower/mid-tropospheric warm advection on a
strengthening southerly 850-700 mb jet. Focused mostly across the
middle Missouri Valley, well to the north of the surface frontal
zone where elevated instability is likely to remain limited, this
activity is expected to remain weak with little risk for severe
weather.
..Kerr.. 09/16/2026
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SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0230 AM CDT Wed Sep 16 2026
Valid 181200Z - 191200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS LATE FRIDAY
AFTERNOON AND EVENING ACROSS PARTS OF NORTHWESTERN KANSAS...SOUTH
CENTRAL AND EASTERN NEBRASKA...ADJACENT SOUTHEASTERN SOUTH DAKOTA
...WESTERN AND CENTRAL IOWA...
...SUMMARY...
Strong thunderstorms may impact portions of the central Great Plains
through southern portions of the middle Missouri Valley late Friday
afternoon and evening, accompanied by at least some risk for severe
weather.
...Discussion...
A vigorous short wave trough in the westerlies is forecast to dig
across the northern Atlantic Seaboard accompanied by significant
surface cyclogenesis near and east of the Canadian Maritimes. In
the wake of the cyclone, it appears that a cold front will continue
advancing offshore and through the southern Mid Atlantic Seaboard.
A trailing low-level baroclinic zone may remain more or less
quasi-stationary across the lower Ohio and lower/mid Missouri
Valleys into northern high plains, beneath a weaker belt of
westerlies in the southern mid-latitudes.
Within this regime, a mid-level trough and embedded low are forecast
to slowly progress across the Intermountain West through Rockies
vicinity, preceded by a more subtle perturbation crossing the middle
Missouri Valley. The latter impulse, and another westward migrating
wave across the Florida Peninsula vicinity may contribute to further
suppression of persistent mid-level ridging, which may otherwise
maintain a considerable influence across a shrinking corridor
centered across the southern Great Plains through Tennessee Valley.
...Central Great Plains through southern Mid Missouri Valley...
Convective potential remains uncertain for Friday through Friday
night. However, latest model output suggests that the mid-level
perturbation overspreading the middle Missouri Valley will be
accompanied by a moderate jet including 30-40 kt southwesterly flow
in the 850-700 mb layer overspreading the central Great Plains
through upper Mississippi Valley.
As insolation contributes to a more strongly heated and deeply mixed
boundary layer along modestly deepening surface troughing
coincident with the low-level jet axis, there may be sufficient
moisture to support scattered thunderstorm development capable of
producing a few strong downbursts across parts of northwestern
Kansas through south central Nebraska late Friday afternoon and
evening.
Closer to a weak developing frontal wave near the Missouri River,
roughly between Omaha and Sioux City, seasonably high boundary-layer
moisture content along a warm frontal zone to its south may support
a corridor of sizable CAPE and potential for much more vigorous
thunderstorm development. Lower/mid-tropospheric inhibition might
remain an issue concerning boundary-layer based thunderstorm
development, but a late afternoon/early evening supercell and small
upscale growing cluster do not appear out of the question, before
storms become elevated while spreading southeastward through
portions of central Iowa during the evening.
..Kerr.. 09/16/2026
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