No watches are valid as of Thu Mar 26 20:03:01 UTC 2026.MD 0291 CONCERNING SEVERE POTENTIAL...WATCH LIKELY FOR PORTIONS OF ILLINOIS...NORTHERN INDIANA...INTO SOUTHERN LOWER MICHIGAN AND NORTHWEST OHIO
Mesoscale Discussion 0291
NWS Storm Prediction Center Norman OK
0248 PM CDT Thu Mar 26 2026
Areas affected...Portions of Illinois...northern Indiana...into
southern lower Michigan and northwest Ohio
Concerning...Severe potential...Watch likely
Valid 261948Z - 262145Z
Probability of Watch Issuance...80 percent
SUMMARY...Thunderstorm development appears likely over the next
couple of hours along a surface cold front and various lake breeze
boundaries. Ample buoyancy and vertical shear for supercells and
line segments will support an increasing severe risk for all
hazards. A WW is likely.
DISCUSSION...As of 1945 UTC, visible imagery showed a deepening
cumulus field across portions of northern IL into northern IN, Lower
MI and northwestern OH. Mid-level ascent from a shortwave trough and
strong flow aloft north of a subtropical ridge has begun to erode
remnant inhibition from west to east. Amid strong diurnal heating,
dewpoints in the upper 50s to low 60s F are supporting 500-1500 J/kg
of MLCAPE. Continued destabilization is likely over the next couple
of hours, with a favorable cape/shear parameter space for supercells
and line segments. Hail, some very large, is likely with
supercellular elements, given steep mid-level lapse rates > 8 C/km.
A fairly quick transition to more linear structures appears likely
given the frontal forcing. This would favor a risk for
severe/damaging gusts as well.
The tornado threat, especially to the west, remains more uncertain.
Stronger heating/mixing has resulted in nearly 30 degree
temperature/dewpoint spreads over parts of IL, with veered low-level
flow. Still, elongated hodographs will favor supercells along the
frontal zone with hail and damaging gusts likely. The tornado threat
appears highest where low 60s F surface dewpoints hold, and stronger
low-level hodograph curvature is present. Primarily across IN/OH,
closer to the front.
Storms may develop across multiple areas of the surface front and
lake breeze this afternoon into this evening before rapidly
increasing in coverage. Given the expected increase in severe
potential a WW is likely needed this afternoon.
..Lyons/Smith.. 03/26/2026
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...ILN...DTX...IWX...GRR...IND...LOT...ILX...LSX...
DVN...
LAT...LON 42148522 42108469 41668423 41218419 40118451 39658502
39608510 38858825 38999023 39439082 39889086 40629010
41298926 41638787 41768688 42088590 42148522
MOST PROBABLE PEAK TORNADO INTENSITY...100-130 MPH
MOST PROBABLE PEAK WIND GUST...65-80 MPH
MOST PROBABLE PEAK HAIL SIZE...2.00-3.50 IN
SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1108 AM CDT Thu Mar 26 2026
Valid 261630Z - 271200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE MIDWEST/OHIO VALLEY...
...SUMMARY...
Scattered severe thunderstorms are expected this afternoon and
evening across parts of the Midwest and Ohio Valley. Large to very
large hail, a few tornadoes, and severe/damaging winds all appear
likely.
...Mid Mississippi Valley into the Midwest/Ohio Valley...
Water-vapor imagery late this morning shows a flattened upper ridge
centered over the south-central U.S. with strong westerly
mid/upper-level flow across the Midwest/Great Lakes. A mid-level
shortwave trough over the northern Rockies will move quickly
east-southeast into the Upper Midwest and act to suppress mid-level
heights across the Midwest/Great Lakes through tonight. Surface
analysis this morning showed a weak low over eastern IA with a
west-east oriented frontal zone extending east across the southern
Great Lakes. If a weak surface reflection is maintained and
develops east across the southern Great Lakes through this evening,
it may notably influence severe potential within a focused corridor
late this afternoon through this evening. The aforementioned front
will gradually push south and serve as the primary impetus for storm
development.
Beneath a capping inversion, moistening will continue with surface
dewpoints rising into the 56-62 deg F range from the mid MS Valley
east into western PA. Upwards of 500-1500 J/kg MLCAPE is likely by
mid afternoon south of the front. A belt of strong, westerly 50-65
kt 700-mb flow is forecast to move from IA and expand spatially
across the warm sector through early evening. This increase in flow
will act to elongate hodographs despite mainly veered southwesterly
surface flow. Recent convection-allowing model guidance varies
considerably on the depiction of cellular versus mostly linear
clusters evolving in the first few hours of the convective life
cycle. Time-lagged HRRR would imply a more spatially and
numerically extensive supercell hail and tornado risk than most of
the 12z HREF HRW members showing less risk of these hazards. The
tornado risk could focus with potential supercells near a weak low
and where surface flow would locally back to southerly. However,
confidence is muted regarding this specific scenario.
Regardless, current expectations are for thunderstorms to quickly
develop along the length of the front from central IL eastward into
IN, southern Lower MI, and northern OH by 19-22Z as diurnal heating
erodes lingering convective inhibition. A mix of supercells and
organized linear clusters will evolve with large to very large hail
possible. A fairly quick transition to more linear structures
appears likely given the frontal forcing, with an increasing threat
for scattered to numerous severe/damaging winds as one or more
clusters spreads east-southeastward across much of the OH Valley
into western/central PA through the late afternoon and evening.
Given the forecast strength of the low to mid-level flow, isolated
gusts of 75+ mph may occur. There is a threat for a few tornadoes
as well with both supercells and embedded mesocirculations within
the linear clusters.
Farther west across the mid MS Valley (MO into eastern KS), there is
lower confidence in warm sector thunderstorm development this
afternoon and evening due to the presence of a stronger cap.
However, elevated convection may occur along/behind the cold front
this evening, with strong deep-layer shear and sufficient MUCAPE
conditionally supporting supercells with mainly a threat for large
hail.
..Smith/Hart.. 03/26/2026
SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0300 PM CDT Thu Mar 26 2026
Valid 262000Z - 271200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM CENTRAL
ILLINOIS EASTWARD INTO INDIANA...OHIO...AND EXTREME WESTERN
PENNSYLVANIA...
...SUMMARY...
Scattered severe thunderstorms are expected late this afternoon and
evening across parts of the Midwest and Ohio Valley. Large to very
large hail, a few tornadoes, and damaging winds will all be
possible.
...From northern MO across IL, IN, OH and into western PA...
The air mass continues to heat and destabilize this afternoon ahead
of a cold front, which extends from southern Lower MI westward
toward the MO/IA border at 20Z. The air mass remains capped for
surface-based parcels, but clouds will continue to develop along the
boundary with eventual severe storm development along and behind
much of the front. Stronger heating / larger temp-dew spreads
suggest a lesser tornado risk for western areas, while farther east
conditions appear a bit more favorable with more low-level SRH /
with lake breeze effects. GPS water vapor sensors also show higher
values of PWAT over southern IN and KY which will lift northeastward
across IN/OH/PA later today.
In all areas, steep lapse rates aloft and strong deep-layer shear
beneath northwest flow aloft will support supercells producing
damaging hail. This may occur in both elevated cells north of the
undercutting front, and ahead of it.
For more information see mesoscale discussion #0291.
..Jewell.. 03/26/2026
.PREV DISCUSSION... /ISSUED 1108 AM CDT Thu Mar 26 2026/
...Mid Mississippi Valley into the Midwest/Ohio Valley...
Water-vapor imagery late this morning shows a flattened upper ridge
centered over the south-central U.S. with strong westerly
mid/upper-level flow across the Midwest/Great Lakes. A mid-level
shortwave trough over the northern Rockies will move quickly
east-southeast into the Upper Midwest and act to suppress mid-level
heights across the Midwest/Great Lakes through tonight. Surface
analysis this morning showed a weak low over eastern IA with a
west-east oriented frontal zone extending east across the southern
Great Lakes. If a weak surface reflection is maintained and
develops east across the southern Great Lakes through this evening,
it may notably influence severe potential within a focused corridor
late this afternoon through this evening. The aforementioned front
will gradually push south and serve as the primary impetus for storm
development.
Beneath a capping inversion, moistening will continue with surface
dewpoints rising into the 56-62 deg F range from the mid MS Valley
east into western PA. Upwards of 500-1500 J/kg MLCAPE is likely by
mid afternoon south of the front. A belt of strong, westerly 50-65
kt 700-mb flow is forecast to move from IA and expand spatially
across the warm sector through early evening. This increase in flow
will act to elongate hodographs despite mainly veered southwesterly
surface flow. Recent convection-allowing model guidance varies
considerably on the depiction of cellular versus mostly linear
clusters evolving in the first few hours of the convective life
cycle. Time-lagged HRRR would imply a more spatially and
numerically extensive supercell hail and tornado risk than most of
the 12z HREF HRW members showing less risk of these hazards. The
tornado risk could focus with potential supercells near a weak low
and where surface flow would locally back to southerly. However,
confidence is muted regarding this specific scenario.
Regardless, current expectations are for thunderstorms to quickly
develop along the length of the front from central IL eastward into
IN, southern Lower MI, and northern OH by 19-22Z as diurnal heating
erodes lingering convective inhibition. A mix of supercells and
organized linear clusters will evolve with large to very large hail
possible. A fairly quick transition to more linear structures
appears likely given the frontal forcing, with an increasing threat
for scattered to numerous severe/damaging winds as one or more
clusters spreads east-southeastward across much of the OH Valley
into western/central PA through the late afternoon and evening.
Given the forecast strength of the low to mid-level flow, isolated
gusts of 75+ mph may occur. There is a threat for a few tornadoes
as well with both supercells and embedded mesocirculations within
the linear clusters.
Farther west across the mid MS Valley (MO into eastern KS), there is
lower confidence in warm sector thunderstorm development this
afternoon and evening due to the presence of a stronger cap.
However, elevated convection may occur along/behind the cold front
this evening, with strong deep-layer shear and sufficient MUCAPE
conditionally supporting supercells with mainly a threat for large
hail.
SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1126 AM CDT Thu Mar 26 2026
Valid 271200Z - 281200Z
...NO SEVERE THUNDERSTORM AREAS FORECAST...
...SUMMARY...
Isolated thunderstorms are expected from the Ohio Valley into the
Carolinas Friday morning into the afternoon, but severe thunderstorm
potential appears limited.
...Synopsis...
An upper trough will pivot across the eastern U.S. on Friday.
Stronger deep-layer west/southwesterly flow will remain focused
across portions of the Midwest/Great Lakes into the Northeast.
Meanwhile, at the surface a cold front extending from the
Mid-Atlantic to the southern Plains will develop south/southeast
through the period, moving offshore by early Saturday. Ahead of the
front, modest boundary-layer moisture (upper 50s to low 60s F
dewpoints) will be in place across the VA Piedmont into the
Carolinas. Steep midlevel lapse rates around 6.5-7 C/km are expected
across the region, and will aid in weak destabilization near the
front. NAM and RAP forecast soundings maintain capping across VA
before the front moves through around midday. Further south across
portions of NC, stronger heating may allow for sufficient mixing and
erosion of weak midlevel capping. A couple of surface-based
thunderstorms could develop near the front and produce gusty winds.
However, overall severe potential is expected to be limited by weak
instability and mostly anafrontal convective processes.
Further west, isolated thunderstorms will be ongoing Friday morning
near/just behind the cold front into the Ohio Valley. This activity
should diminish with time and southward extent through the day.
..Leitman.. 03/26/2026
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