LIVE MAP (ABOVE) ... SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1255 AM CDT Thu Jun 29 2023
Valid 291200Z - 301200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM PARTS OF
SOUTHERN IOWA AND FAR NORTHEASTERN MISSOURI ACROSS ILLINOIS...TO
SOUTHWESTERN PORTIONS OF INDIANA AND PARTS OF NORTHERN KENTUCKY...
...SUMMARY...
Severe storms producing damaging winds and large hail are possible
across the region from southern Iowa southeastward to Kentucky. A
couple tornadoes may also occur. Large to locally very large hail
and damaging wind gusts are also expected from southeastern
Wyoming/northeastern Colorado eastward into the central Plains, with
a tornado or two possible.
...Synopsis...
A belt of enhanced mid-level flow is forecast to persist from the
central High Plains to the Midwest/Ohio Valley, with the mid-level
height gradient between the southern U.S. ridge and central Canada
trough. This enhanced flow will support a roughly coincident zone
of severe-weather risk through the period.
At the surface, a baroclinic zone extending from the Upper
Mississippi Valley vicinity to the central Plains, and then into the
central High Plains region, will make little progress through the
period. Elsewhere, high pressure will largely prevail.
...Southern Iowa across the Illinois/Indiana/Kentucky vicinity...
Thunderstorms will likely be ongoing at the start of the period,
roughly in the eastern Nebraska/southwestern Iowa vicinity. Other
storms will likely be evolving across parts of the
Illinois/southwestern Indiana vicinity early in the period as well.
At this time, it appears that the Missouri Valley-area storms will
further organize and move eastward through the morning and into the
afternoon, posing risk for strong/damaging winds. This risk will be
aided by likely-to-be fast-moving storms, given increasingly strong
deep-layer westerlies progged to be spreading across this area.
Meanwhile, as this convection moves eastward, a more complex
evolution of storms is expected across the Midwest/lower Ohio Valley
area. Various CAM runs show differing convective evolutions, but
overall, likelihood for multiple rounds of southeastward-moving
storm clusters exists, as the aforementioned strong deep-layer flow
field spreads eastward/southeastward with time. The result will be
the potential for fairly widespread severe-caliber wind gusts, along
with large hail and potential for a couple of tornadoes, with these
severe events accumulating from multiple rounds of strong/severe
storms continuing throughout much if not all of the period.
...Central High Plains/central Plains...
Northeast of a surface baroclinic zone backed into the central High
Plains region, the upslope flow regime across southeastern Wyoming
and into eastern Colorado will continue today. Once again, diurnal
heating of a moist boundary layer to the cool side of the front will
yield moderate destabilization, with around 2000 J/kg mixed-layer
CAPE expected by mid afternoon. This will support development of
isolated storms, similar to the previous couple of days, and
initially near the Laramie Range.
As storms increase gradually in coverage with time, deep-layer shear
(augmented by 40-plus kt west-southwesterlies at mid levels) will
result in an expanding risk for very large hail and locally damaging
wind gusts, along with potential for a tornado or two. With time
organized/supercell storms may congeal/grow upscale into the
evening, and move eastward across the Nebraska/northern Kansas
vicinity. As such, risk for damaging winds, and some hail, may
continue/spread eastward through much of the overnight period.
..Goss.. 06/29/2023
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