LIVE MAP (ABOVE) ... SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0744 AM CDT Wed Jun 28 2023
Valid 281300Z - 291200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
THROUGH LATE EVENING FOR PARTS OF THE UPPER MS VALLEY AND THE
CENTRAL HIGH PLAINS...
...SUMMARY...
Large hail, isolated damaging winds and a tornado or two will be
possible this afternoon/evening across northwest Wisconsin/eastern
Minnesota and across the Nebraska Panhandle and vicinity.
...Upper MS Valley this afternoon through late evening...
Around the northern periphery of the midlevel high over TX, a
shortwave trough (enhanced some by prior convection) will progress
eastward over MN/WI through this evening. An associated/weak
surface cold front will likewise move eastward across MN, while
low-level moistening occurs from the southwest during the day
beneath a lingering plume of steep midlevel lapse rates. MLCAPE
will increase to 2500-3000 J/kg with sufficiently long/curved
hodographs for a supercell threat later this afternoon/evening from
eastern MN into northwestern WI, along and just ahead of the front.
Large hail will be the main threat, though isolated wind damage and
a tornado or two will also be possible.
...Central High Plains this afternoon into tonight...
A surface cold front is moving slowly southward across northeast
CO/northwest KS/southwest NE this morning. Low-level flow will veer
to easterly during the afternoon, with boundary-layer dewpoints from
the mid 50s to lower 60s F in the upslope regime. Subtle speed
maxima aloft and surface heating in cloud breaks should allow
weakening of convective inhibition by mid-late afternoon, when at
least isolated thunderstorm development will be possible from
southeast WY into the western NE Panhandle, and possibly northeast
CO. Moderate buoyancy and long, relatively straight hodographs will
favor supercells capable of producing isolated very large hail,
along with some potential for strong-severe outflow gusts and a
tornado or two. The persistence of the storms past late evening is
uncertain.
...Northern/central IL and vicinity overnight...
The moist boundary layer (dewpoints mid 70s) across OK will spread
northeastward across MO and southern IA through tonight, beneath
steep midlevel lapse rates of 8-9 C/km. Large CAPE is expected in
this regime, though a warm elevated mixed layer will also tend to
cap the boundary layer through the day. However, warm advection
will increase tonight with corresponding strengthening of a
west-southwesterly LLJ, and the chance for elevated thunderstorm
development will increase overnight from eastern IA into IL. MUCAPE
> 2500 J/kg, steep midlevel lapse rates and effective bulk shear >
50 kt will support the potential for elevated supercells to produce
large hail, while DCAPE > 1000 J/kg suggest some potential for
strong gusts to reach the ground. There is substantial uncertainty
regarding the specific corridor of storm development overnight, so
will maintain MRGL risk for now, but later updates will continue to
monitor the northern/central IL area.
..Thompson/Mosier.. 06/28/2023
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