Chicago area, along with much of north and central Illinois and far northwest Indiana, likely to be under a severe thunderstorm watch later this afternoon
Chicago area, along with much of north and central Illinois and far northwest Indiana, likely to be under a severe thunderstorm watch later this afternoon
Mesoscale Discussion 0974
NWS Storm Prediction Center Norman OK
1223 PM CDT Sun Jul 01 2018
Areas affected...Northern and Central Illinois and Far Northwest
Indiana.
Concerning...Severe potential...Watch likely
Valid 011723Z - 011900Z
Probability of Watch Issuance...80 percent
SUMMARY...Strong to severe storms are expected this afternoon across
northern and central Illinois. The primary threat from these storms
will be damaging wind gusts.
DISCUSSION...Temperatures have risen into the mid to upper 80s
across much of Illinois with dewpoints in the upper 70s. This has
led to MLCAPE around 2500 J/kg. Additional destabilization is
expected through the afternoon as surface heating continues. Storms
are expected to form along the cold front (currently in eastern Iowa
and Eastern Missouri) and move eastward through the afternoon. Flow
is relatively weak on the ILX 12Z sounding, however, low-level flow
is forecast to increase to 35 to 40 knots by mid-afternoon. This
will lead to a marginal shear environment with effective shear
around 25 to 30 knots with most of this shear focused in the lowest
1 to 2 km. Nearly parallel orientation of the cold front to the
deeper level flow will limit a greater severe weather threat,
however, more robust updrafts could mix down stronger winds, posing
a damaging wind threat through the afternoon. The threat will be
maximized with any bowing segments which can orient more normal to
the low-level flow and accelerate northeastward. A severe
thunderstorm watch is likely in the next hour or two to cover this
severe wind threat.