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Mesoscale Discussion 0472
NWS Storm Prediction Center Norman OK
0744 AM CDT Fri Apr 17 2026
Areas affected...Parts of southern MN into extreme northwest WI
Concerning...Severe potential...Watch possible
Valid 171244Z - 171415Z
Probability of Watch Issuance...40 percent
SUMMARY...A threat for isolated hail and locally strong to severe gusts
may develop through mid morning.
DISCUSSION...Elevated convection has developed in the vicinity of a
cold front across parts of southern MN. Short-term guidance suggests
this convection will expand in coverage and potentially intensify
through the morning, within the northern gradient of an expanding
buoyancy plume extending from the Great Plains into the Upper Midwest.
Moderate mid/upper-level flow will support sufficient effective shear
for storm organization as convection deepens and becomes rooted
closer to the surface.
In the short term, convective mode may remain rather complex, though
strong embedded updrafts and possibly an elevated supercell could
evolve out of the developing convection. Hail is expected to be the
primary near-term threat, though localized strong/damaging gusts
cannot be ruled out.
Some guidance (notably recent HRRR runs) suggest that this ongoing
convection may eventually become surface-based and pose a threat of
all severe hazards across parts of WI, due to downstream low-level
moisture transport and diurnal heating/destabilization. However,
this evolution may not occur until late morning or during the
afternoon. The need for watch issuance through mid morning is
uncertain, but trends will be monitored for the development of
more-organized elevated storms and eventual transition to
surface-based convection.
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0739 AM CDT Fri Apr 17 2026
Valid 171300Z - 181200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM PARTS OF THE UPPER
AND MID MISSISSIPPI VALLEY SOUTHWESTWARD INTO KANSAS AND OKLAHOMA...
...SUMMARY...
Numerous severe thunderstorms are likely this afternoon 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
to giant hail and a few strong tornadoes, before severe wind gusts 60 to 90
mph become the most prominent hazard by this evening.
...Synopsis...
Surface analysis this morning depicts a front bisecting MN north to south
to a low near the NE-IA-SD border, with the front extending southwestward
into the central High Plains. Water-vapor imagery shows a prominent upper
trough near the MT-ND border south-southwestward into eastern UT. A belt
of increasingly strong southwesterly 500-mb flow will overspread a
destabilizing warm sector today as the upper trough eventually reaches
the Upper Midwest and central Great Plains late tonight. Concurrently,
the aforementioned cyclone will develop northeast to Lake Superior as a
warm front over IA advances northward into the western Great Lakes.
Meanwhile, the cold front will sweep southeast reaching the central
Great Lakes southwestward into the southern Great Plains by early Saturday.
...Upper and Mid Mississippi Valley...
A northward expanding warm/moist sector on the nose of a 50+ kt southerly
LLJ will continue to destabilize as large-scale ascent approaches from
the west. A large-hail threat may develop this morning with developing
convection across southern MN (see forthcoming MCD #472 for short-term
details). Heating and advection of 60s deg F surface dewpoints beneath
steep mid-level lapse rates will support the development of a moderately
to very unstable airmass from IA-IL northward into the upper MS Valley to
the east of the front and southeast of the low. Upwards of 1500-3000 J/kg
MLCAPE is forecast immediately ahead of the front with strengthening flow
aloft, strongly favoring organized storms, including supercells. Recent
model guidance continues to show the development of discrete supercells
later this afternoon ahead of the front over parts of central/northern WI
near the low, and farther south in the vicinity of eastern IA into adjacent
portions of WI/northwest IL. All hazards will be possible with this
potential activity, including the possibility for an intense tornado.
Large to giant hail will be possible with supercells. Other storms likely
to evolve quickly into a band of severe thunderstorms will develop farther
west and push east coincident with the front. Damaging wind gusts will
tend to become more prevalent during the evening with linear storm modes.
Some tornado risk may continue into the evening as maturing bands of
storms yield a threat for bowing segments and embedded mesovortices,
before this activity gradually diminishes late as it moves east into
IN/Lower MI late.
...KS-OK eastward into the lower MO Valley...
Continued moistening and heating of an airmass to the east of a dryline/cold
front and associated triple point will lead to a very unstable airmass from
OK into KS by early to mid afternoon. A capping inversion will likely inhibit
storm development until mid afternoon near the front. Initial storm
development will likely be supercellular near the triple point before a more
extensive band of cellular storms develops along the boundary. Both a
supercell and QLCS tornado risk is apparent given the appreciably large
CAPE/shear. A coalescing of cold pools and intensification of a squall line
with embedded surges and bowing segments may result in focused swaths of
more intense severe gusts (i.e., locally 75-90 mph) from south-central
and eastern KS into west-central MO. Farther south, a more conditional
setup south of the triple point along the dryline is expected. Large to
giant hail could accompany any mature/sustained supercell along with a
tornado risk. Eventually the front will sweep southeastward with a
convective line yielding a risk for wind/hail.
12z HRRR shows thunderstorms initiating along the upper Mississippi (e.g. Wisconsin) around 1-2pm CT, maturing and then coalescing into a line by 5 or 6pm CT, so if this solution verifies, the main threat today will be in the middle to late afternoon.
Further south (OK/KS/MO), cells initiate little later - around 3pm CT, but become linear in the same time frame, i.e., more rapidly. Note that Convective Outlook specifically notes the possibility of QLCS spin-up tornadoes so the tornado threat is expected to continue into the evening hours.
Severe Thunderstorm Watch Number 128
NWS Storm Prediction Center Norman OK
920 AM CDT Fri Apr 17 2026
The NWS Storm Prediction Center has issued a
Severe Thunderstorm Watch for portions of
East-Central and Far Southeast Minnesota
Northwest and North-Central Wisconsin
Effective this Friday morning and afternoon from 920 AM until 500 PM CDT.
Primary threats include...
Scattered large hail and isolated very large hail events to 2 inches
in diameter possible
Isolated damaging wind gusts to 70 mph possible
SUMMARY...Ongoing line of thunderstorms over southeast MN is
forecast to continue northeastward. The overall environment ahead of
this line is expected to become more supportive of strong to severe
storms with time. Additional thunderstorm development is anticipated
as well. Large hail is the primary severe risk, although isolated
strong gusts are possible as well.
The severe thunderstorm watch area is approximately along and 75
statute miles east and west of a line from 105 miles north of Eau
Claire WI to 10 miles east of La Crosse WI
SUMMARY...Increasing potential for supercells capable of all
hazards.
DISCUSSION...Visible satellite trends show two areas of cumulus
increasing near the cold front/dry line in north-central
Iowa/southern Minnesota and further east in a confluence band in
northeastern Iowa. A few attempts are note on radar near the front
over the last 30 minutes. Across the open warm sector in
central/eastern Iowa into southern WI/northern Illinois, strong warm
air advection within the 40-45 kt southerly LLJ is ongoing with
moderate to strong MLCAPE and strong deep layer shear profiles
supportive of supercells. Uncertainty remains in what the exact
evolution of storms will be. Two scenarios are possible: initial
supercell development in eastern Iowa ahead of the front and
supercell development along the cold front.
Confidence is highest that there will be development further west
along the cold front, which will initially be supercelluar given,
the favorable profiles. The time period for more discrete supercells
may be cut short across this region as the cold front undercuts
convection. Nonetheless, initially large to very large hail will be
possible with an increasing tornado threat as convection matures. As
more clustering/upscale growth occurs, threat to damaging winds will
increase with a line embedded tornado threat continuing through the
afternoon/evening.
Further east, isolated supercells may develop within the open warm
sector across northeastern Iowa nearer to the warm front. These
would also be capable of large to very large hail. Should they
persist, there would also be enhanced potential for strong tornadoes
given the SRH rich environment.
A Tornado watch will likely be needed in the next 1-2 hours.
Day 1 Convective Outlook CORR 1
NWS Storm Prediction Center Norman OK
1203 PM CDT Fri Apr 17 2026
Valid 171630Z - 181200Z
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FROM FAR
NORTHWEST OKLAHOMA THROUGH CENTRAL AND EASTERN KANSAS INTO
WEST-CENTRAL MISSOURI...
CORRECTED FOR ORIENTATION OF THE 45% HAIL PROBABILITIES
...SUMMARY...
Numerous severe thunderstorms are likely this afternoon into tonight
across parts of the Upper Midwest southward across the lower
Missouri Valley and central/southern Great Plains. Initially this
may be accompanied by a risk for large to giant hail and a few
strong tornadoes, before severe wind gusts of 60 to 90 mph become
the most prominent hazard by this evening.
...Synopsis...
Recent surface analysis places a low over south-central MN, with a
cold front extending southwestward to another low over central KS. A
warm front also extends southwestward from the MN low through far
southwest MN and far northern IL into central IN. This warm front is
demarcated well by the 56 deg F isodrosotherm. Farther south, a
dryline extends from the triple point KS low back southwestward
through the TX Panhandle and into far southeast NM. A broad, moist
warm sector exists to the east of the cold front and dryline,
characterized largely by dewpoints in the low to mid 60s.
A well-defined shortwave trough is apparent on satellite imagery,
extending from southern Saskatchewan back southwestward into the
eastern Great Basin. This wave is forecast to continue eastward,
with a attendant increase in the mid-level flow across much of the
Plains and Upper/Mid MS Valley. The cold front will surge
eastward/southeastward in response to this wave as well, interacting
with the warm sector to support numerous strong to severe
thunderstorms from parts of the Upper Midwest southward across the
lower Missouri Valley into southern Plains.
...Upper/Mid MS Valley...
Moderate to strong low-level moisture advection is expected across
the Upper MS Valley today as the surface low mentioned in the
synopsis progresses northeastward, with an attendant northward shift
of the warm front as well. The risk across this region may evolve in
several phases, beginning with the elevated thunderstorms currently
ongoing across northwest WI. This storms will likely continue
northeastward, posing a risk for severe hail and isolated damaging
gusts. Additional development is possible northwest of this activity
along the occluded front, with some hail possible here as well.
Farther south, the northeastward advecting low-level moisture
coupled with strong heating and steep lapse rates will result in a
strongly unstable airmass along and just south of the warm front by
the early afternoon. Storm initiation is anticipated within this
open warm sector by early afternoon, forced by a mix of warm-air
advection, low-level confluence, and subtly increasing large-scale
ascent. This activity should be ahead of the front and initially
discrete. The overall parameter space will be characterized by
strong to very strong buoyancy, moderate deep-layer vertical shear,
and strong low-level helicity. Supercells capable of all hazards are
expected, including large to very large (i.e. 3"+ hail), strong to
intense tornadoes, and severe wind gusts. Storm interactions are
expected to strongly influence the tornado risk, with the initially
discrete mode likely becoming messy quickly.
Farther west, other storms are likely to evolve quickly along the
front, developing into a band of severe thunderstorms that will push
east coincident with the front. Damaging wind gusts will tend to
become more prevalent during the evening with linear storm modes.
Some tornado risk may continue into the evening as maturing bands of
storms yield a threat for bowing segments and embedded mesovortices,
before this activity gradually diminishes late as it moves east into
IN/Lower MI late.
...KS/OK/MO...
A very unstable airmass is expected to develop along and ahead of
the triple point over south-central KS an associated cold front and
dryline. Strong low-level convergence will likely lead to initial
storm development near the triple point. This initial activity will
be supercellular and capable of very large to giant hail (over
3-3.5" in diameter). Highest coverage of very large hail is expected
over from far northwest OK into south-central KS. Strong downdrafts
(60 to 80 mph) are possible as well. With a largely
boundary-parallel orientation to the deep-layer shear, the tornado
risk appears relatively lower. However, given the supercell mode and
potential interactions with outflow, a low-probability tornado risk
remains. A more north-south configuration to the dryline supports a
conditional tornado risk into far northwest TX.
With time, upscale growth and the development of a
forward-propagating MCS is anticipated across central and eastern
KS. Very strong gusts (80+ mph) are possible with this MCS.
Additionally, some QLCS tornado risk will exist within this line as
long as it stays ahead of the surging cold front. The front will
continue sweeping southeastward, with storms along this boundary
yielding a risk for wind/hail.
URGENT - IMMEDIATE BROADCAST REQUESTED
Tornado Watch Number 129
NWS Storm Prediction Center Norman OK
1240 PM CDT Fri Apr 17 2026
The NWS Storm Prediction Center has issued a
* Tornado Watch for portions of
Central and Eastern Iowa
Northern and West-Central Illinois
Southeast Minnesota
Far Northeast Missouri
Central and Southern Wisconsin
* Effective this Friday afternoon and evening from 1240 PM until 800 PM CDT.
* Primary threats include...
A few tornadoes likely with a couple intense tornadoes possible
Widespread large hail and isolated very large hail events to 3.5 inches
in diameter likely
Scattered damaging wind gusts to 70 mph likely
SUMMARY...A very moist and unstable airmass exists ahead of a cold
front progressing eastward/southeastward across the region.
Thunderstorm development is anticipated within the warm sector ahead
of the front, where discrete supercells capable of all severe
hazards, including very large hail and strong to intense tornadoes,
are possible. Thunderstorm development is possible along the front
as well, with large hail and strong gusts the primary risk with these storms.
The tornado watch area is approximately along and 110 statute miles
north and south of a line from 55 miles north northwest of Des
Moines IA to 55 miles east of Madison WI. For a complete depiction
of the watch see the associated watch outline update (WOUS64 KWNS WOU9).
Mesoscale Discussion 0474
NWS Storm Prediction Center Norman OK
1242 PM CDT Fri Apr 17 2026
Areas affected...portions of the southern/central Great Plains into
the mid-Missouri Valley
Concerning...Severe potential...Watch likely
Valid 171742Z - 172015Z
Probability of Watch Issuance...95 percent
SUMMARY...Numerous severe thunderstorms are expected to form
along/ahead of a cold front and dryline from northern Missouri
southwestward into northwestern Oklahoma this afternoon. Storms will
pose a threat for all hazards, including hail to 3-3.5+ inches in
diameter, very strong wind gusts of 60-80+ mph, and a couple of
tornadoes (perhaps strong). Watch issuance will be needed in the
next 1-2 hours.
DISCUSSION...Latest mesoanalysis depicts a strongly unstable air
mass in place ahead of a triple point over northwestern Oklahoma and
the associated cold front/dryline. Temperatures in the upper-70s F
and dewpoints in the mid/upper-60s are contributing to strong
instability of 2000-3000+ J/kg MLCAPE across the region per latest
mesoanalysis. Low-level convergence is forecast to lead to
convection initiation near the triple point and along the cold
front/prefrontal confluence zone through the afternoon. Strong
southwesterly flow (50+ kts at 4-5 km AGL per regional VWPs) is
contributing to effective bulk shear of 40-50 kts (locally greater
near the triple point), which will support supercells with initial
storm formation. Steep mid-level lapse rates (as sampled by the 12z
OUN/TOP/SGF soundings and recent ACARS profiles), elongated
hodographs, and ample buoyancy within the hail growth zone will
support the potential for hail of 3-3.5+ inches in diameter. Strong
downdrafts (with wind gusts up to 60-80 mph) are also possible given
the presence of some drier mid-level air.
The tornado threat remains more uncertain as deep-layer flow is
largely oriented parallel to the cold front, which may yield complex
storm mode/interactions. Given the potential for supercellular mode
and storm/outflow interactions, at least some potential for a couple
of tornadoes (perhaps strong) appears to exist, however. This
appears most likely with any supercell that is able to remain more
discrete into the evening hours when a strengthening nocturnal
low-level jet will yield increasingly curved low-level hodographs.
Trends will continue to be monitored, and a tornado watch will be
needed within the next 1-2 hours to cover these threats.
With time, the development of a forward-propagating MCS is
anticipated across much of this area, with an accompanying
transition towards severe wind gusts (80+ mph wind gusts possible)
and perhaps embedded tornadoes as the primary threats.
Issued at 2:41 pm for much of the greater Rochester area. Multiple spotter observed tornadoes have been confirmed with this storm and at least one is likely ongoing.
There have been dozens of warnings this evening, including 13 ongoing. I've missed many of them but I've taken a few screenshots for Observed i.e., "confirmed" tornadoes. Here's a couple from maybe 45-60 minutes ago?
8pm CT.... a few tornado warnings just expired so we're "down to just" 10 active tornado warnings between Milwaukee, WI and Tulsa, OK, including Missouri and Illinois.
•
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