SPC 1200Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1248 AM CDT Thu Oct 22 2020

Valid 221200Z - 231200Z


A few strong to severe storms capable of producing mainly hail and
strong wind gusts, will be possible Thursday from the eastern Iowa
vicinity into extreme southwest Wisconsin.

...Eastern Iowa into extreme southwest Wisconsin...

An upper trough will amplify over the northern Plains and upper
Midwest today. A warm front currently extends from southern KS
through southern MO and IL. This feature will move northward during
the day and should extend from a weak surface low in east-central IA
to near the IL/WI border by late afternoon. This front will likely
move into southern WI during the early evening. Concurrently, a cold
front extending southwest from the surface low will surge southeast
through the central and southern Plains and middle MS Valley regions
this afternoon and evening. 

A moist warm sector with dewpoints in the low 60s F will advect
northward into the Midwest region in wake of the warm front. A few
cloud breaks may occur, and MLCAPE from 1000-1500 J/kg is possible
just ahead of the cold front. Stronger deep-layer forcing associated
with the upper trough will remain in post-frontal region, but storms
will likely initiate along and just behind the front as it advances
southeast during the day. Vertical wind profiles in vicinity of the
cold front will be favorable for storm organization with 45 kt
effective bulk shear and sizeable low-level hodographs, especially
near triple point region as the weak surface low develops northeast.
However, with upper flow remaining nearly parallel to the initiating
boundary, tendency should be for storms to be undercut shortly after
initiation. Nevertheless, activity developing along the cold front
might become organized and capable of producing a few instances of
large hail and damaging wind. While a brief tornado or cannot be
ruled out, overall tornado threat should remain limited by tendency
for storms to be forced behind the cold front.  

...West Texas...

A compact southern-stream shortwave trough evident on satellite
imagery over AZ is embedded within weak flow aloft and will reach
west TX by late afternoon, where it will interact with an evolving
dryline. A few storms are expected to develop along this boundary by
late afternoon across western TX where the atmosphere is expected to
become moderately unstable. Though vertical shear should remain
modest, steep lapse rates, inverted-V boundary layers and 1000-1500
j/kg MLCAPE will support some threat for a few locally strong wind
gusts and hail, before activity weakens as it moves farther east
into a stabilizing boundary layer by mid evening.

..Dial/Lyons.. 10/22/2020

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