Mesoscale Discussion 2037
NWS Storm Prediction Center Norman OK
0246 PM CDT Thu Aug 24 2023
Areas affected…Southeast WI…Northeast IL
Concerning…Severe potential…Watch unlikely
Valid 241946Z – 242145Z
Probability of Watch Issuance…20 percent
SUMMARY…Isolated strong to severe thunderstorm development is
possible across southeast WI and northeast IL this afternoon.
DISCUSSION…Recent surface analysis places a low near UNU in
southeast WI, just ahead of a weak front moving
southward/southeastward through southern WI. This front is
demarcated better by the wind field, which shows a shift to more
westerly/northwesterly winds, than temperature field, which shows
little discontinuity. The air mass across the region is very warm
and moist, with numerous observations reporting mid/upper 90s
temperatures amid upper 70s and low 80s dewpoints. This warm and
moist airmass sits beneath relatively steep mid-level lapse rates,
contributing to strong to extreme buoyancy. Recent mesoanalysis
estimates MLCAPE over 4000 J/kg across much of northern IL and
southern WI. Cumulus has been increasing in the vicinity of this
low, and it appears that convective initiation could take place
within the next hour or two.
Even if storms do initiate, updrafts will be battling significant
dry-air entrainment. ECAPE values from forecast soundings are close
to 1500-1700 J/kg, a reduction of more than half versus MLCAPE. This
suggests many updrafts may not survive to maturity, somewhat
limiting the overall severe potential. That being said, any updrafts
that can mature could become robust enough to produce significant
water loading, with an attendant threat for strong downbursts.
Highest probability for thunderstorm development currently appears
to be across southeast WI, to the south of the low but west of the
lake breeze. Convective inhibition is higher south into northern IL,
but a conditional risk for strong/severe storms exists here as well.
Given the general uncertainties regarding development, and likely
limited coverage, a watch is not anticipated. Convective trends will
still be monitored closely.
…Please see www.spc.noaa.gov for graphic product…
LAT…LON 42688945 43468877 43638817 43468800 42818797 41828780