SPC AC 131300
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0800 AM CDT Mon Apr 13 2026
Valid 131300Z - 141200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS SOUTHERN
MINNESOTA AND PARTS OF WISCONSIN...
...SUMMARY...
Severe thunderstorms are likely across the Upper Mississippi Valley
and Great Lakes region with potential for large to very large hail,
damaging wind, and tornadoes, mainly late this afternoon into
tonight. A more conditional and isolated risk for severe storms is
possible across portions of the southern Plains late this afternoon
and evening.
...Upper Mississippi Valley/Great Lakes including MN/WI...
Multiple lead mid-level disturbances over the northern High Plains
will progress northeastward today toward the Upper Midwest, with
strengthening winds aloft across this region particularly late today
and tonight. A surface low will tend to deepen/develop
east-northeastward from northeast Nebraska this morning into far
southern Minnesota and Wisconsin by tonight in vicinity of a
slow-moving/stalled frontal boundary. Low/middle 60s F surface
dewpoints will advect north-northeastward and become increasingly
prevalent along/south of the aforementioned stationary/warm front
this afternoon. MLCAPE values are forecast to reach 2000-2500 J/kg
by around 21z/4pm CDT.
Thunderstorm development will become increasingly probable through
mid/late afternoon (21-00z) as isentropic ascent strengthens ahead
of the approaching upper disturbance. Lingering inhibition coupled
with 45-50 kt effective bulk shear should promote initially discrete
supercells along or just north of the surface boundary. Hodograph
elongation appears favorable for a large hail threat, possibly as
large as 2-3 inches in diameter with the more robust cells.
Additionally, enhanced low-level SRH along the frontal zone is
expected to result in a corridor of relatively higher tornado
potential for storms that can remain rooted immediately along the
boundary.
While the overall environment appears very favorable for intense
convection/supercells, east-northeasterly storm motions along or
just north of the warm front will likely promote clustering/upscale
growth through the evening, with an increasing damaging wind
potential and a continued tornado risk via line-embedded circulation
potential.
...Northern Illinois/northern Indiana and southern Lake Michigan...
There is the potential that a somewhat separate corridor of
severe-weather potential may unfold today, potentially born out of
subtle mid-level wave and early morning convection across northeast
Missouri vicinity and/or development later today. The initially
elevated storms would be on the edge of the
east/northeastward-advecting elevated mixed layer. Steep mid-level
lapse rates and 35+ kt effective shear could support initially
isolated hail potential, but a more organized surface-based severe
risk could manifest if some of the more-aggressive early morning
short-term guidance trends materialize (HRRR/RAP/RRFS).
...Southern Plains including Oklahoma/Texas...
A moist and potentially unstable air mass will persist regionally to
the east of a dryline located around peak heating from east-central
Kansas south-southwestward into west-central Oklahoma and western
north Texas to the Texas Big Bend vicinity. Immediately east of the
dryline, warm-sector dewpoints are expected to generally be in the
middle 60s F, supporting MLCAPE values to 2500-3000 J/kg.
The extent/likelihood of sustained deep convection later today is a
key question. The primary southern-stream trough will be well
upstream over the southwest Desert, with neutral height tendencies
across the southern Plains, although early morning water vapor
imagery and derived wind data suggest that a subtle disturbance over
northern Mexico and the southern Rockies could approach the
dryline/warm sector later today.
Regardless, ample post-dryline mixing and near-dryline
confluence/weak convergence may be sufficient for deep convective
initiation after 21z/4pm CDT, at least an isolated basis. Forecast
mass fields would imply that this is most probable across
central/southwest Oklahoma into the north Texas Big Country, and
perhaps somewhat separately across the Texas Big Bend and Rio Grande
vicinity.
If/where storms develop and mature, deep-layer shear on the order of
40+ kt will support supercells, potentially capable of all hazards
including very large hail. An increased confidence in deep
convective initiation late this afternoon/early evening could
warrant focus Slight Risk delineations in subsequent Day 1 updates.
...Northern High Plains...
Generally isolated severe storms capable of hail/wind will be
possible late this afternoon into evening along/north of the surface
front where modest low-level moisture and vertical shear will be
maximized, in the presence of steep low/mid-level lapse rates.
..Guyer/Broyles.. 04/13/2026
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z
SPC AC 130604
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
0104 AM CDT Mon Apr 13 2026
Valid 141200Z - 151200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
OF IOWA INTO NORTHERN ILLINOIS AND SOUTHERN WISCONSIN...
...SUMMARY...
Isolated to scattered severe thunderstorms are expected on Tuesday
and Tuesday night from the Southern Plains to the Great Lakes. Large
to very large hail, a few tornadoes, and damaging wind gusts will be
possible, particularly across parts of eastern Iowa, northern
Illinois, and southern Wisconsin. Additional strong storms, mainly
producing strong wind gusts, will be possible across parts of the
Northeast.
...Synopsis...
A broad swath of enhanced deep-layer southwesterly flow will
overspread the southern High Plains to the Great Lakes on Tuesday.
An upper shortwave trough over the Great Basin will slowly pivot
east through the period, emerging over the central/southern High
Plains by Wednesday morning. A weak shortwave impulse is also
forecast to move across the northern Plains and Upper Midwest. At
the surface, low pressure will be centered over the Mid-MO Valley
for much of the period, with a warm front extending east/northeast
from north-central IA into southern WI and central Lower MI.
Meanwhile, a dryline will extend southwest across eastern KS into
western TX. Ahead of these boundaries, a seasonally moist airmass
will be in place, with mid-60s dewpoints common. The aforementioned
surface boundaries will become a focus severe thunderstorm
development Tuesday afternoon into the nighttime hours.
...Mid-MS Valley and Great Lakes vicinity...
A severe risk is expected to develop by late afternoon within the
warm frontal zone from Iowa into northern IL/southern WI in a
persistent warm advection regime. While height tendencies are
forecast to remain mostly neutral, low-level convergence along the
boundary and a glancing influence from a weak shortwave impulse
migrating across the northern Plains into northern MN/Upper MI
should provide focused ascent. A southwesterly 850-700 mb jet is
also forecast to increase across the region by late afternoon into
evening. Cool temperatures aloft (around -16 C at 500 mb) and steep
midlevel lapse rates atop a moist boundary layer will support MLCAPE
around 2000-3000 J/kg amid elongated/straight hodographs. As a
result, large to very large hail will be possible with initial
supercell thunderstorms. Storm motion and southwesterly deep-layer
flow may result in convection moving to the cool side of the warm
front. Even so, elevated storms will pose a risk for significant
hail. With time, and as the low-level jet increases during the
evening, convection may consolidate/grow upscale into one or most
bowing segments and progress eastward into Lower MI/IN/OH, posing a
continued risk for hail and an increasing risk for damaging wind
gusts.
Any supercells that develop and can be sustained within the warm
sector will also pose a risk for a few tornadoes (some strong), very
large hail and damaging gusts.
...Southern Plains into eastern KS/western MO...
Moderate destabilization is forecast along the surface dryline by
afternoon. Strong heating along/just west of the dryline will
promote mixing, while low-level confluence and subtle height falls
(by 21-00z) provide sufficient forcing for ascent for isolated
thunderstorm development. Supercell wind profiles will be present
amid steep midlevel lapse rates and elongated hodographs. Large to
very large hail, locally strong wind gusts and a couple of tornadoes
will be possible. Storms should develop northward during the evening
into eastern KS and western MO as the low-level jet increases.
...Northeast...
Rounds of thunderstorms are expected during the afternoon and
evening within a warm advection regime. MLCAPE should increase to
around 1000 J/kg within a moistening low-level airmass. Strong
deep-layer westerly flow and steepening low-level lapse rates will
support isolated strong wind gusts across the region.
..Leitman.. 04/13/2026
WUUS02 PTSDY2
SPC AC 130716
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0216 AM CDT Mon Apr 13 2026
Valid 151200Z - 161200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTION OF
THE SOUTHERN PLAINS INTO SOUTHERN WISCONSIN...
...SUMMARY...
Severe thunderstorms posing a risk for large hail and strong wind
gusts will be possible across portions of the southern Plains toward
the Great Lakes on Wednesday afternoon and evening.
...Southern Plains to Great Lakes...
An upper trough will move from the Plains to the MS Valley vicinity
on Wednesday. As associated corridor of enhanced southwesterly
deep-layer flow will overspread a moist/unstable airmass ahead of a
surface dryline. The southern Plains portion of the dryline will not
move too much on Wednesday. However, the northern extent of this
boundary will intersect a weak surface low moving from the Lower MO
Valley toward Lake Michigan. This portion of the boundary will
advance eastward toward the MS River during the evening/overnight
hours.
Areas of showers and thunderstorms may be ongoing across portions of
the region Wednesday morning. As a result, there is uncertainty
regarding how the boundary layer may recover/destabilize during the
afternoon. Nevertheless, at least pockets of moderate
destabilization (1000-2000 J/kg MLCAPE) are expected within a
corridor along and east of the surface boundary. Effective shear
magnitudes greater than 40 kt will be sufficient for organized
convection, with large hail and strong wind gusts being the primary
hazards.
..Leitman.. 04/13/2026
WUUS03 PTSDY3
NOTE: THE NEXT DAY 3 OUTLOOK IS SCHEDULED BY 1930Z
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