Mesoscale Discussion 1974
NWS Storm Prediction Center Norman OK
1103 PM CDT Thu Aug 13 2026

Areas affected...eastern Iowa...northern/central Illinois...and
central Indiana

Concerning...Severe potential...Watch possible 

Valid 140403Z - 140600Z

Probability of Watch Issuance...40 percent

SUMMARY...Occasional stronger storms may produce small hail and
gusty winds overnight.

DISCUSSION...Thunderstorm activity is increasing within the warm
advection regime across portions of eastern Iowa into northern
Illinois/Indiana. This activity is ongoing north of a surface front
extending from the central Plains across southern Illinois into
southern Illinois/northern Kentucky. The air mass near the ongoing
convection is only marginally unstable located on the northern
fringes of more moderate to strong instability further south across
southern Illinois into portions of southern Indiana/northern
Kentucky. Forecast soundings suggest the presence of a fairly strong
cap at the base of the EML across much of the region of greater
buoyancy, which will likely inhibit surface based convection. 

Generally boundary parallel flow will likely produce training storms
overnight, with little organized severe potential. Later into the
overnight/early morning, the low-level jet will increase into
Illinois/Indiana. Should a cluster be able to develop and drop
southward, there could be some damaging wind potential into the
morning. A few instances of gusty winds and small hail will be
possible with stronger cores. For now, confidence in a more
organized severe risk remains low but trends will be monitored
overnight.

..Thornton/Hart.. 08/14/2026

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

ATTN...WFO...ILN...LMK...IWX...IND...LOT...ILX...LSX...DVN...

LAT...LON   41788993 41859141 41379201 40489155 40219102 39588904
            38778560 38678459 39108416 39748424 40288456 41248686
            41638908 41788993 

MOST PROBABLE PEAK WIND GUST...UP TO 60 MPH
MOST PROBABLE PEAK HAIL SIZE...UP TO 1.25 IN

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0800 PM CDT Thu Aug 13 2026

Valid 140100Z - 141200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM PARTS OF
NORTH-CENTRAL ILLINOIS INTO SOUTHWEST OHIO...

...SUMMARY...
Thunderstorms with severe wind gusts and hail will be possible
tonight from parts of north-central Illinois into southwest Ohio.
Severe gusts and hail will be possible in parts of the central
Plains. A few severe gusts may also occur in parts of the
Intermountain West.

...Mid Mississippi and Ohio Valleys/Southern Great Lakes...
The latest water vapor imagery shows a mid-level anticyclonic flow
pattern over the central U.S., with west-northwesterly flow located
over the eastern U.S. At the surface, a quasi-stationary front is
analyzed from northeast Missouri to northern Kentucky. Surface
dewpoints along and to the south of the front are in the 70s and low
80s F, which is contributing a west-northwest to east-southeast axis
of strong instability. The RAP has MLCAPE along this axis in the
3000 to 5000 J/kg range. To the north of the instability axis,
short-term model forecasts move a subtle shortwave trough
east-southeastward through the Midwest tonight. Large-scale ascent
associated with the trough coupled with increasing low-level flow
will likely result in the development of a line of strong storms.
This is forecast to take place late this evening, with the line
moving southeastward from north-central Illinois across central
Indiana and into southwest Ohio. Severe wind gusts will be possible
with this line segment.

...Central Plains...
Southwesterly mid-level flow is currently in place over much of the
southwestern and central U.S. An embedded mid-level shortwave trough
appears to be moving into the central High Plains. Ahead of this
feature, the RAP has an axis of moderate instability located from
northern and western Kansas into northeastern Colorado, along which
MLCAPE is estimated in the 1500 to 2500 J/kg range. Scattered
thunderstorms were ongoing near the instability axis early this
evening in eastern Colorado with another cluster in central Kansas.
Increasing low-level flow from this evening into the overnight
period will likely sustain convective development. Hail and isolated
severe wind gusts will be possible with the stronger cells.

...Intermountain West...
On water vapor imagery, multiple shortwave troughs appear to be
moving through the Intermountain West. Ahead of these features,
scattered thunderstorms are ongoing across much of Nevada and Utah.
The RAP is currently analyzing an axis of instability from southeast
Nevada into north-central Utah along which MLCAPE is estimated to be
in the 750 to 1000 J/kg range. Near the instability axis, the RAP
also has low to mid-level lapse rates in the 7.5 to 8.5 C/km range.
This thermodynamic environment should support an isolated potential
for severe wind gusts this evening.

..Broyles.. 08/14/2026