|Mesoscale Discussion 1390|
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Mesoscale Discussion 1390
NWS Storm Prediction Center Norman OK
1123 PM CDT Fri Jul 21 2017
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.
...Please see www.spc.noaa.gov for graphic product...
LAT...LON 42839367 42368620 40628620 41109367 42839367
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