MD 0638 CONCERNING SEVERE POTENTIAL...WATCH POSSIBLE FOR PORTIONS OF THE MIDWEST AND SOUTHERN GREAT LAKES


Mesoscale Discussion 0638
NWS Storm Prediction Center Norman OK
0342 PM CDT Mon May 04 2026

Areas affected...portions of the Midwest and southern Great Lakes

Concerning...Severe potential...Watch possible 

Valid 042042Z - 042245Z

Probability of Watch Issuance...40 percent

SUMMARY...Widely scattered to scattered thunderstorm development is
expected late this afternoon, with potential for severe/damaging
wind gusts and large hail. Watch issuance is possible for a portion
of the discussion area.

DISCUSSION...Prevailing southwesterly flow has yielded modest
moisture return across portions of the Midwest into the southern
Great Lakes region, with dewpoints climbing into the 40s/low-50s.
While a surface cold front remains displaced to the northwest,
expectation is for widely scattered to scattered strong to severe
thunderstorms to develop within the warm conveyor this afternoon as
convective temperatures are reached and remaining inhibition is
removed. A 700-mb speed max associated with an approaching shortwave
trough will help to promote 30-40 kts of effective bulk shear across
the region, with MLCAPE forecast in the 500-1250 J/kg range. This
will be sufficient to support storm organization into
multicells/clusters and perhaps transient supercell structures;
although, the lack stronger flow aloft and limited hodograph
elongation is likely to limit supercell intensity/persistence.

Dry mid-level air and well-mixed boundary layers (as sampled by
regional ACARS profiles and the 18z DVN observed sounding) will
support a risk for severe/damaging wind gusts. Large hail will also
be possible given modestly steep mid-level lapse rates (>7 C/km per
latest mesoanalysis). While a strengthening of 850 mb flow and some
accompanying increase in low-level hodograph curvature is expected
this evening (especially across northern Indiana and northwest Ohio
within the 21-00z time frame), the tornado threat remains uncertain
owing to the expectation for boundary layer moisture quality to
remain more limited across the region. 

Thus, given the potential for these hazards, a Severe Thunderstorm
Watch is possible for a portion of the discussion area, particularly
from northeastern Illinois into northwestern Ohio where the
potential coverage of severe hazards appears greater.

..Chalmers/Smith.. 05/04/2026

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...CLE...ILN...DTX...IWX...GRR...IND...LOT...ILX...
MKX...DVN...

LAT...LON   40518958 40679037 41009087 41529106 42019081 42459004
            42658882 42808808 42928668 42858577 42578475 42178393
            41858341 41368312 40998314 40728341 40518462 40438591
            40448725 40458834 40478912 40518958 

MOST PROBABLE PEAK TORNADO INTENSITY...UP TO 90 MPH
MOST PROBABLE PEAK WIND GUST...55-70 MPH
MOST PROBABLE PEAK HAIL SIZE...1.00-1.75 IN

SPC 2000Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0233 PM CDT Mon May 04 2026

Valid 042000Z - 051200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
THE MIDWEST INTO THE OHIO VALLEY...

...SUMMARY...
Scattered severe thunderstorms capable of large hail and damaging
wind gusts are possible across portions of the Midwest this
afternoon into tonight.  A conditional threat for severe storms with
large to very large hail extends into portions of the
central/southern Plains.

...20Z Update...
The previous forecast remains largely on track. Only minor changes
were made to the thunder and severe probabilities to reflect the
latest trends in observations and high resolution model guidance.

..Squitieri.. 05/04/2026

.PREV DISCUSSION... /ISSUED 1130 AM CDT Mon May 04 2026/

...IL into the southern Great Lakes...
A mid-level vorticity maximum over the lower MO Valley is forecast
to move east across IL through the late afternoon and into IN-OH
tonight.  An associated speed maximum at 700 mb will intensify and
overspread IL (40-50 kt) east into the southern Great Lakes while a
pronounced strengthening of 850-mb flow (50 kt) occurs during the
21-03z period.  Cold mid-level temperatures (-18 deg C at 500 mb)
will act to offset initially meager moisture.  Model guidance varies
considerably regarding moisture quality with ample spread amongst
different model cores/PBL schemes.  However, it seems a narrow
corridor of lower to mid 50s surface dewpoints will extend
east-northeast from the lower MO Valley into the southern Great
Lakes by mid to late afternoon.  Forecast soundings show weak to
moderate buoyancy (500-1250 J/kg MLCAPE).  Morning model guidance
shows widely scattered to scattered storms developing within the
warm conveyor during peak heating as convective inhibition erodes. 
Have expanded the Slight Risk farther east into this region to
account for a hail/wind risk with the stronger storms.  Uncertainty
remains regarding quality of boundary-layer moisture across the
northern third of IN into northwest OH where hodographs become
enlarged later this afternoon into the early evening.  Will
re-evaluate the tornado risk for the 20 UTC outlook if in fact
moisture quality seems sufficient for a focused, short-duration
tornado risk across the aforementioned corridor. 

...Eastern KS into the Mid MS Valley...
Thunderstorm development is anticipated during the afternoon along a
cold forecast to extend through southern WI and
eastern/southern IA. Thunderstorms along the front will initially be
displaced north of the better shear and buoyancy, so somewhat
transient updraft structures and/or frontal undercutting will likely
limit storm severity. Even so, high cloud bases and a deeply mixed
boundary layer could result in a few strong gusts.  Later in the
evening, more storm development appears likely on the front as it
moves into eastern KS and northern/central MO. Here, stronger shear
and buoyancy should support more robust updrafts and a relatively
higher probability for severe storms. Large to very large hail is
the primary risk.  

...Central Kansas into Oklahoma and northern Texas...
A dryline will extend from central KS south-southwestward into
northwest TX by mid afternoon as a surface low evolves near the TX
Panhandle/OK/KS border region.  Strong diurnal heating will likely
erode most convective inhibition by the early evening, while steep
lapse rates contribute to moderate buoyancy along the dryline.
Isolated thunderstorms are possible on the dryline from central KS
into northwest TX during the 22-02 UTC period.  Veering and
strengthening flow with height beneath 100-kt westerly 200-mb flow
will support supercells.  Isolated large to very large hail will be
the primary risk with the stronger storms, although severe gusts are
also possible.

SPC 1930Z Day 3 Outlook

Day 3 Convective Outlook  
NWS Storm Prediction Center Norman OK
0212 PM CDT Mon May 04 2026

Valid 061200Z - 071200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM EASTERN TEXAS
INTO ALABAMA...

...SUMMARY...
Scattered strong to severe thunderstorms are expected Wednesday
afternoon and evening across portions of Texas into the lower
Mississippi and Tennessee Valleys. Damaging winds, large hail, and a
couple of tornadoes will be possible.

...Synopsis...
A large positive-tilt upper trough will extend from upper Great
Lakes into the Southwest, with a broad zone of strong mid to high
levels southwesterlies extending from the southern Plains across the
lower to middle MS and TN Valleys. Gradual cooling aloft will occur
through the period as this upper trough proceeds gradually east. At
the surface, a cold front will extend from the upper OH Valley into
central TX during the day, and this front will surge south overnight
into the southeastern states and southern TX.

...Eastern TX into the TN Valley...
A very moist air mass will exist ahead of the cold front, with 70s F
dewpoints from TX into AL. Early day storms are likely in the warm
advection regime over parts of KY and TN, aided by southwest 850 mb
winds around 40 kt. This may temporarily stabilize these northern
areas before destabilization occurs later in the day. The strongest
heating will occur from TX into MS/AL, with MUCAPE up to 3000 J/kg.

The greatest risk area will extend from the Sabine River into MS and
northern AL late in the day, perhaps near 00Z, and into the early
evening, as storms finally break the capping inversion after a full
days heating. Deep-layer shear will be oriented mostly parallel to
the front, and low-level winds will be a bit veered with marginal
SRH values. Still, supercells may develop owing to strong effective
shear, with steep lapse rates aloft supporting hail. Damaging winds
may become an issue as storms possibly merge with bowing structures.

For northern areas from TN into KY, the risk will depend on air mass
recovery in the wake of any early day activity. Conditionally,
low-level shear may be stronger in this region, with an isolated
tornado or hail risk.

..Jewell.. 05/04/2026

SPC Day 2 Fire Weather Outlook

Day 2 Fire Weather Outlook  
NWS Storm Prediction Center Norman OK
0156 PM CDT Mon May 04 2026

Valid 051200Z - 061200Z

...NO CRITICAL AREAS...

The forecast remains on track, see the previous discussion for more
information.

..Elizalde-Garcia.. 05/04/2026

.PREV DISCUSSION... /ISSUED 0137 AM CDT Mon May 04 2026/

...Synopsis...
Flow aloft will increase over much of the southern US Tuesday as the
southern stream upper low merges with the second trough over the
northern and central US. As the upper-level troughs deepen, a
surface low over OK will move southward ahead of a surging cold
front over the Plains, while gusty winds are expected over parts of
the eastern US.

...West TX...
The cold front is expected to stall across the TX Panhandle Tuesday,
pushing dry and breezy conditions farther south into Central/West
Texas. South of the front, westerly winds of 10-20 mph are expected
along with RH below 25%. This could support some localized
fire-weather concerns. However, recent plentiful rainfall has
tempered marginal fuels such that widespread fire-weather conditions
appear unlikely. Additional precipitation and cooler temperatures
north of the front should limit fire-weather potential over the
central US.

...Mid Atlantic...
As the upper trough over the central US consolidates, another day of
gusty southerly winds is likely over parts of the Mid Atlantic. Warm
daytime temperatures and minimal moisture ahead of a cold front
could support localized fire-weather conditions over parts of the
Carolinas and VA. However, fuels remain limited and any fire-weather
conditions should be short lived, precluding highlights.

...Please see www.spc.noaa.gov/fire for graphic product...

SPC 1730Z Day 2 Outlook

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1241 PM CDT Mon May 04 2026

Valid 051200Z - 061200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS CENTERED OVER
ARKANSAS AND EXTENDING FROM NORTHEAST TEXAS INTO WESTERN
TENNESSEE...

...SUMMARY...
Scattered strong to severe storms are possible Tuesday afternoon and
evening from northeast Texas into western Tennessee, with the main
threat centered over Arkansas. Some storms may produce large hail,
damaging gusts or a couple tornadoes. Additional strong storms are
possible across parts of the Northeast.

...Synopsis...
A weakening upper low will move from Ontario into Quebec with a
leading speed max moving quickly out of the Great Lakes region.
Behind this system, high pressure will move southward into the
northern Rockies and Plains. The associated cold front will move
across the lower Great Lakes during the day, extending southwestward
across the Ozarks and into eastern OK where a surface low is
forecast.

Meanwhile, a positive-tilt upper trough will exist over the
southwestern states, with moderate to strong west/southwest flow
aloft expanding across the southern Plains to the Lower MS Valley.
Minimal height rises are forecast across this region, with the warm
advection regime aiding northward transport of low-level moisture
toward the Ozarks.

...Northeast TX into western TN...
A low pressure trough is forecast to develop generally from northern
TX into eastern OK and western AR during the afternoon, with the
main synoptic boundary slowing over northern AR. Models indicate
early day storms are likely over southeast MO, northeast AR and into
western KY and TN, dissipating by midday. This activity may
reinforce the effective frontal position into AR, where air mass
recovery will occur. 

By late afternoon, scattered supercells are expected to form near
the surface trough from AR into northeast TX. Given robust moisture
with upper 60s F dewpoints, 60+ kt deep layer shear and effective
SRH maximized over AR, tornadoes will also be possible. The
combination of a capping inversion over much of the area, forced
cells timed with peak heating, and a potential downstream
outflow/enhanced zone of SRH, a strong tornado is conditionally
possible.

...NY into ME...
Strong heating ahead of the cold front and a plume of 50s F
dewpoints will lead to 500-1000 J/kg MUCAPE during the day, beneath
midlevel southwesterlies over 50 kt. Storms are forecast to develop
after 18Z from western into northern NY, with storms moving rapidly
northeastward across VT/NH and into ME. Forecast soundings indicate
40-50 kt deep-layer mean winds, which in combination with a mixed
boundary layer should support cells as well as bowing structures
capable of damaging gusts. The strongest cells may contain hail as
well. A brief tornado cannot be ruled out given 150-200+ m2/s2
effective SRH depicted across northern areas, though veering
low-level flow and/or deepening mixed layers may mitigate that
potential somewhat.

..Jewell.. 05/04/2026

SPC Day 1 Fire Weather Outlook

Day 1 Fire Weather Outlook  
NWS Storm Prediction Center Norman OK
1140 AM CDT Mon May 04 2026

Valid 041700Z - 051200Z

...Morning Update...
No changes were made to the Elevated risk area. Current satellite
imagery portrays high cloud cover overspreading much of the southern
Plains and portions of the northern Plains into the Upper Midwest.
Increasing cloud cover throughout the day is expected to deter
deeper mixing, maintaining marginal RH across the uppermost High
Plains. However, RH is still anticipated to remain elevated to near
critical this afternoon across portions of the TX Panhandle into
western OK where current surface observations depict 15-30 percent
values steadily decreasing. 

Presently, a cold front is progressing across northern NE with
trailing northerly sustained winds of 20-25 mph and gusts up to 35
mph. Model soundings depict a dry sub-cloud layer and elevated
instability ahead of the approaching cold front, enhancing the
possibility for scattered showers and isolated thunderstorms across
southern NE, western KS and eastern CO. Recent rainfall, a slight
transition to green up, and expected precipitation overnight may
alleviate broader fire concerns should any ignitions occur. However,
areas where fuels remain dry, a west-northerly wind shift with
sustained 15-20 mph winds through the overnight hours could
temporarily exacerbate fire weather conditions before appreciable
rainfall arrives. 

See the previous discussion for more information.

..Elizalde-Garcia.. 05/04/2026

.PREV DISCUSSION... /ISSUED 0136 AM CDT Mon May 04 2026/

...Synopsis...
A cut off low over the Southwest is expected to move eastward as it
merges with a strengthening subtropical jet stream south of a second
upper trough over the northern US and southern Canada. Enhanced
westerly flow aloft will move out of the southern Rockies and over
the Plains deepening a lee cyclone. This will promote dry and breezy
conditions over parts of the southern Plains with elevated
fire-weather conditions likely.

...Southern Plains...
Beneath the southern stream upper low, a lee cyclone will deepen
over the southern High Plains this afternoon. Trailing the low, a
developing dryline will serve as the eastern terminus of dry
westerly flow across parts of eastern NM and the TX/OK Panhandles.
Warm temperatures with westerly winds of 15-25 mph and 15-20 percent
RH will overlap a confined region of dry fuels across TX/OK. This
should support several hours of elevated to locally critical
fire-weather conditions. Some uncertainty remains on the exact
dryline positioning later this afternoon. Isolated convection is
also possible suggesting some precipitation may occur on the eastern
edge of the Elevated probabilities.

...Northern Plains/Midwest...
Gusty post-frontal winds are likely today across the northern Plains
and upper Midwest. However, cooler surface temperatures and cloud
cover will likely keep RH minimums above 35%. Still, some pockets of
drier air could support brief localized fire-weather concerns in
pockets of supportive fuels given stronger northwest wind gusts of
20-30 mph.

...Mid Atlantic...
Gusty southerly winds and a drier than normal air mass are likely to
develop this afternoon over parts of the Mid Atlantic and Piedmont.
A strengthening pressure gradient ahead of the deepening upper low
over southern Canada could support gusts of 10-15 mph. While RH will
be below 40%, area fuels remains rather limited owing to recent
precipitation. This should preclude broader fire-weather concerns,
though some localized risk remains possible.

...Please see www.spc.noaa.gov/fire for graphic product...

SPC 1630Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1130 AM CDT Mon May 04 2026

Valid 041630Z - 051200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE LOWER
MISSOURI VALLEY INTO THE SOUTHERN GREAT LAKES...

...SUMMARY...
Scattered severe thunderstorms capable of large hail and damaging
wind gusts are possible across portions of the Midwest this
afternoon into tonight.  A conditional threat for severe storms with
large to very large hail extends into portions of the
central/southern Plains.

...IL into the southern Great Lakes...
A mid-level vorticity maximum over the lower MO Valley is forecast
to move east across IL through the late afternoon and into IN-OH
tonight.  An associated speed maximum at 700 mb will intensify and
overspread IL (40-50 kt) east into the southern Great Lakes while a
pronounced strengthening of 850-mb flow (50 kt) occurs during the
21-03z period.  Cold mid-level temperatures (-18 deg C at 500 mb)
will act to offset initially meager moisture.  Model guidance varies
considerably regarding moisture quality with ample spread amongst
different model cores/PBL schemes.  However, it seems a narrow
corridor of lower to mid 50s surface dewpoints will extend
east-northeast from the lower MO Valley into the southern Great
Lakes by mid to late afternoon.  Forecast soundings show weak to
moderate buoyancy (500-1250 J/kg MLCAPE).  Morning model guidance
shows widely scattered to scattered storms developing within the
warm conveyor during peak heating as convective inhibition erodes. 
Have expanded the Slight Risk farther east into this region to
account for a hail/wind risk with the stronger storms.  Uncertainty
remains regarding quality of boundary-layer moisture across the
northern third of IN into northwest OH where hodographs become
enlarged later this afternoon into the early evening.  Will
re-evaluate the tornado risk for the 20 UTC outlook if in fact
moisture quality seems sufficient for a focused, short-duration
tornado risk across the aforementioned corridor. 

...Eastern KS into the Mid MS Valley...
Thunderstorm development is anticipated during the afternoon along a
cold forecast to extend through southern WI and
eastern/southern IA. Thunderstorms along the front will initially be
displaced north of the better shear and buoyancy, so somewhat
transient updraft structures and/or frontal undercutting will likely
limit storm severity. Even so, high cloud bases and a deeply mixed
boundary layer could result in a few strong gusts.  Later in the
evening, more storm development appears likely on the front as it
moves into eastern KS and northern/central MO. Here, stronger shear
and buoyancy should support more robust updrafts and a relatively
higher probability for severe storms. Large to very large hail is
the primary risk.  

...Central Kansas into Oklahoma and northern Texas...
A dryline will extend from central KS south-southwestward into
northwest TX by mid afternoon as a surface low evolves near the TX
Panhandle/OK/KS border region.  Strong diurnal heating will likely
erode most convective inhibition by the early evening, while steep
lapse rates contribute to moderate buoyancy along the dryline.
Isolated thunderstorms are possible on the dryline from central KS
into northwest TX during the 22-02 UTC period.  Veering and
strengthening flow with height beneath 100-kt westerly 200-mb flow
will support supercells.  Isolated large to very large hail will be
the primary risk with the stronger storms, although severe gusts are
also possible.

..Smith/Chalmers.. 05/04/2026