SPC 1730Z Day 2 Outlook

Day 2 Outlook Image

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
0101 PM CDT Wed Oct 21 2020

Valid 221200Z - 231200Z


A few strong to locally severe storms, capable of producing marginal
hail and perhaps a strong wind gust or two, will be possible
Thursday from the eastern Iowa vicinity south-southwestward to
eastern Kansas, western Missouri, and the northeastern Oklahoma

A short-wave upper trough digging southeastward across the
Intermountain West is expected to gradually turn eastward Day 2,
reaching the mid Missouri and upper Mississippi Valleys through the
second half of the period.  

As the upper system advances, a surface wave over the western Kansas
area -- along a pre-existing baroclinic zone extending from the
central High Plains to southern New England -- will develop
northeastward to the eastern Iowa area by early evening, and then to
the northern Lower Michigan vicinity by Friday morning.  In the wake
of the progressing low, the cold front will surge southward, and
should extend from Lake Michigan to northern and western Texas by
the end of the period.

...Eastern Iowa and vicinity to the northeastern Oklahoma area...
Early-day convection is expected across northern portions of the
outlook area, but will gradually shift northeastward with time. 
This should permit some clearing -- and diurnal heating -- ahead of
the evolving surface cold front and associated/digging upper system.
 Despite this heating, and low-level moistening/warm advection,
capping will likely remain firm through the day, with the stronger
ascent associated with the upper trough remaining to the cool side
of the front.

Eventually, near-frontal convective development may finally occur
over the eastern Iowa vicinity by early evening as capping weakens. 
However, any surface-based storms will likely become quickly
undercut by the front, while more widespread convective development
is expected to the cool side of the boundary.

Initial storms forming over the eastern Iowa area will evolve in an
environment sufficient for sustained/rotating updrafts.  As such, a
very limited risk for surface-based severe weather -- including
gusty winds and possibly a brief tornado -- may exist for a couple
of hours during the early evening.  Afterwards however, any
lingering severe risk would likely be in the form of marginal hail. 
As primarily anafrontal convection develops southward overnight,
some marginal hail risk may persist through the end of the period.

..Goss.. 10/21/2020

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