Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0100 AM CDT Fri Apr 17 2026
Valid 171200Z - 181200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
INTO TONIGHT ACROSS PARTS CENTRAL AND SOUTHWESTERN WISCONSIN...FAR
SOUTHEASTERN MINNESOTA...EASTERN IOWA...MUCH OF NORTHERN AND CENTRAL
ILLINOIS...NORTHERN AND CENTRAL MISSOURI...EASTERN AND SOUTHERN
KANSAS...AND NORTHERN OKLAHOMA...
...SUMMARY...
Widespread strong to severe thunderstorm development appears
possible today into tonight across parts of the Upper Midwest
southward across the lower Missouri Valley into central Great
Plains. Initially this may be accompanied by a risk for large hail
and a few strong tornadoes, before damaging wind gusts become the
most prominent hazard by this evening.
...Discussion...
A couple of notable short wave perturbations have emerged from
splitting larger-scale mid-level troughing now overspreading the
northern Rockies and Great Basin. One, including a remnant embedded
cyclonic circulation, is beginning to accelerate east-northeastward
into and across the central Canadian/U.S. border vicinity. The
other is still digging into the eastern Great Basin, but forecast to
turn across the Wyoming/Colorado Rockies during the day, before
shearing northeastward toward the Upper Midwest. It appears that
this will be preceded by several lower amplitude impulses already
emanating from the subtropical eastern Pacific.
In lower-levels, a significant cold front is already surging
southward to the lee of the northern Rockies and forecast to advance
across much of the remainder of the northern Great Plains by 12Z
this morning. Models indicate that significant cyclogenesis may
subsequently ensue northwest/north of Lake Superior toward James Bay
later today through tonight. At the same time, it appears that a
secondary frontal wave will migrate northeast of the mid Missouri
Valley through the Upper Midwest/Great Lakes vicinity. Another lee
cyclone may attempt to form near/north of the Texas/Oklahoma
Panhandle vicinity, but probably will be overtaken by the southward
surging cold front before migrating out of the high plains.
The northward advection of relatively moist low-level air is ongoing
from the southern into central Great Plains and lower Missouri
Valley, and forecast to continue spreading northward within a
pre-cold frontal plume through portions of the Upper Midwest/Great
Lakes region by this afternoon. Beneath steep lapse rates, this may
contribute to sizable mixed-layer CAPE within a corridor from the
east central Great Plains through the mid/upper Mississippi Valley
by this afternoon.
There is notable spread among the various model output concerning
most of these developments, which may have a significant impact on
the convective evolution and associated severe weather potential
today through tonight. However, potential exists for widespread
convective development capable of producing damaging surface gusts,
large hail and a couple of strong tornadoes.
...Upper Mississippi Valley/Midwest vicinity...
It appears that a corridor of stronger surface pressure falls may
shift from western Iowa north-northeastward through western
Wisconsin by early this afternoon, accompanied by substantive
boundary-layer destabilization and strengthening southerly low-level
wind fields with enlarging hodographs. Based on the latest model
output, including convection allowing guidance, it appears that this
may contribute to a window of opportunity for discrete supercell
development within an environment potentially conducive to strong
tornadoes, before activity grows upscale and eventually outpaces the
northeastward boundary-layer destabilization.
...Central Great Plains through middle Mississippi Valley/Midwest...
Uncertainty lingers concerning how quickly the surface cold front
will tend to undercut a developing corridor of stronger pre-frontal
surface heating and destabilization, particularly across the central
into southern Great Plains. However, by early this afternoon, this
corridor appears likely to develop along an axis from south central
Kansas toward northwestern Missouri, providing a focus for rapidly
developing storms including supercells. Initially this may include
hail exceeding 2 inches in diameter, and potential for a few
tornadoes before convection grows upscale, spreads east of the axis
of maximum instability and also become undercut by the front.
Perhaps aided by forcing associated with one of the perturbations
emerging from lower latitudes, there appears a signal in model
output that the upscale growing convection may eventually become
better organized with one or two notable mesoscale convective
vortices evolving while spreading ahead of the front across and
northeast of the lower Missouri Valley late this afternoon and
evening. Downward mixing of strengthening rear-inflow, within a
sheared ambient southwesterly deep-layer mean flow already on the
order of 35-40 kt, widespread strong to severe wind gusts appear
possible, with strongest gusts and/or perhaps brief tornadoes
accompanying evolving mesovortices along the gust front.
The cold front/dryline intersection may become another focus for
discrete supercell development across parts of south central Kansas
into adjacent northwestern Oklahoma by late afternoon. However, the
extent of the associated severe weather potential will depend on how
quickly this activity is overtaken by the cold front.
..Kerr/Lyons.. 04/17/2026
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