MD 1807 CONCERNING SEVERE POTENTIAL…WATCH UNLIKELY FOR NORTHERN IL
Mesoscale Discussion 1807
NWS Storm Prediction Center Norman OK
0334 PM CDT Tue Sep 20 2022
Areas affected...Northern IL
Concerning...Severe potential...Watch unlikely
Valid 202034Z - 202230Z
Probability of Watch Issuance...5 percent
SUMMARY...Isolated strong to severe thunderstorms are possible
across northern IL this afternoon.
DISCUSSION...Elevated thunderstorms continue to gradually shift
southward across southern WI, with several instances of hail
reported this afternoon. Downstream air mass across northern IL is
warm and moist, with most observations across the region reporting
temperatures in the low 90s and dewpoints in the low 70s. These
low-level conditions are occurring beneath relatively steep
mid-level lapse rates and cool temperatures aloft, resulting in
strong buoyancy. Recent mesoanalysis estimates MLCAPE around 2500
J/kg for most of the region. Even so, warm low- to mid-level
temperatures continue to preclude surface-based storms, with the
ongoing activity likely still elevated. Continued heating downstream
may erode this low-level stability, allowing for the ongoing storms
to become more surface-based over time. However, even if this
downstream destabilization is realized, dry-air entrainment will
remain a deterrent for updraft duration and maturity. Additionally,
the lack of cumulus development across this region currently
suggests that the air mass remains hostile for robust storm
development.
Expectation is for the ongoing thunderstorms to continue eastward
this afternoon, with a multicellular/clustered storm mode favored. A
few instances of hail and/or damaging gusts are possible,
particularly if an updraft can persist and mature.
..Mosier/Grams.. 09/20/2022
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...LOT...MKX...DVN...
LAT...LON 42089005 42359006 42528946 42418830 42128798 41498834
41568944 41848987 42089005
