Areas affected...Northeast IA...Southern WI...Northern
Concerning...Severe Thunderstorm Watch 429...
Valid 220423Z - 220530Z
The severe weather threat for Severe Thunderstorm Watch 429
SUMMARY...Strong thunderstorms will continue across northern and
eastern portions of WW429 through the early morning hours. A local
extension may be needed for the next few hours.
DISCUSSION...Low-level warm advection appears to be partly
responsible for recent increase in convection across northeast IA
into northwest IL. Latest observational data and short-range models
suggest LLJ is focused atop a pronounced outflow boundary that
should move little over the next several hours. LLJ is expected to
strengthen and veer toward northern IL and this should maintain a
corridor of strong convection much of the night. While isolated
large hail could be noted with this activity, unless it becomes
clear that a damaging squall line or bow echo will evolve from this
convection a new WW will not be issued; however, WW429 may be
extended locally for the next few hours. Heavy rain may be the
greatest risk through sunrise.