LIVE MAP (ABOVE) ... SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1249 AM CDT Fri Aug 11 2023
Valid 111200Z - 121200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE MID AND
UPPER MISSISSIPPI AND LOWER MISSOURI VALLEYS...
...SUMMARY...
Severe thunderstorms capable of large hail, damaging gusts, and
perhaps a tornado or two are possible across portions of the Mid and
Upper Mississippi Valley and Lower Missouri Valley areas today.
...Synopsis...
A shortwave trough across the northern Plains will intensify as it
moves into the Upper Midwest today. Across the southern Plains,
ridging aloft will modestly increase. At the surface, a low will
move through the Upper Midwest along with its parent trough. An MCV
is expected to move through Iowa into northern Illinois/southern
Wisconsin early in the period. An outflow boundary from this
activity will lie roughly east-west near the Missouri-Iowa border
into parts of central/northern Illinois. Farther northwest, a cold
front will move south and east through the day. A remnant boundary
will also remain in the Southeast.
...Eastern Iowa...southern Wisconsin...northern/central Illinois...
The most complex portion of the forecast will be the evolution of
the MCV. The character of the convection associated with this
feature remains rather loosely organized Thursday night. By this
morning, additional boundary-layer stabilization is likely to weaken
this activity further as it reaches the Mississippi River. Some
reintensification can occur as the boundary layer tries to warm this
morning/early afternoon, but cloud cover moving downstream of the
MCV does not lend much confidence in this scenario. A secondary
possibility is that storms could from along the outflow during the
afternoon. This activity would be more likely to impact parts of
central Illinois. However, convergence along this boundary appears
weak and deep-layer ascent is also minimal. Should one of these
scenarios play out, damaging winds and perhaps a brief tornado would
be possible. A categorical Slight will be maintained this outlook
despite the described uncertainties.
...Mid-Missouri/Mid-Mississippi Valleys...
Strong buoyancy is expected to develop south of the outflow
boundary. Northwesterly flow aloft will contribute to 40-50 kts of
effective shear across this boundary. This environment will support
supercells capable of large hail and strong to severe wind gusts.
The main uncertainty with this activity will be the overall coverage
of storms during the afternoon due to weak forcing for ascent.
Capping appears evident on forecast soundings during the afternoon.
By late afternoon/early evening, the front will approach the region
along with an increase in the low-level jet. Storm initiation will
become more likely into the evening due to these factors. While
storms could be slightly elevated by that point, large hail and
perhaps more isolated wind damage would remain threats.
...Minnesota/Wisconsin...
Lingering moisture and strong heating behind the cold front will
promote convective development along with the passage of the
shortwave trough. Moderate northwest flow at mid levels will
increase effective shear to 40-45 kts by the afternoon. With cold
temperatures aloft and long hodographs, widely scattered to
scattered storms will be capable of large hail and wind damage.
...Southeast...
Though shear will not be overly strong, a very moist airmass and
modestly steep mid-level lapse rates will promote MLCAPE on the
order of 3000-4000 J/kg. Wind damage from downbursts will be the
primary risk. A corridor or two of more organized wind damage
potential could develop as cold pools congeal, but predictability on
where this will occur is low.
..Wendt/Lyons.. 08/11/2023
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