612
ACUS01 KWNS 281942
SWODY1
SPC AC 281941

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0241 PM CDT Fri Jun 28 2024

Valid 282000Z - 291200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE CENTRAL
PLAINS TO THE MIDDLE MISSISSIPPI VALLEY...

...SUMMARY...
Large hail, damaging winds, and a couple of tornadoes may occur from
parts of the central Plains into the mid/upper Mississippi Valley
through tonight.

...20z Update...

Only minor adjustments have been made to the 10 percent general
thunderstorm line for the 20z update. Severe probabilities remain
unchanged from the prior outlook. Isolated strong to severe storms
still appear possible from the central High Plains into parts of
IA/MO from late afternoon into tonight. For more details, refer to
previous outlook discussion below, and any forthcoming mesoscale
convective discussions.

..Leitman.. 06/28/2024

.PREV DISCUSSION... /ISSUED 1130 AM CDT Fri Jun 28 2024/

...Synopsis...
An upper low over the northern Rockies/High Plains will progress
eastward today to the Upper Midwest. At the surface, an occluded low
is forecast to meander slowly eastward over northern MN through this
evening, while a secondary low consolidates over central KS. An
occluded/cold front extending from the northern MN low will develop
slowly southeastward across the central Plains and mid MO Valley
this afternoon. This boundary will likely serve as a focus for
strong/severe convection later today.

...Central Plains into the Mid Mississippi Valley...
Better forcing for ascent associated with the upper trough/low
should generally remain displaced to the north of the central Plains
and mid MO Valley through much of the day. Also, the lingering
effect of morning clouds/precipitation will be to slow diurnal
destabilization to some extent. Still, low-level convergence along
the cold front and glancing large-scale ascent will probably be
sufficient for convective initiation through 20-00Z across parts of
IA into eastern NE, and northeast KS into northern MO. Even modest
daytime heating of the moist low-level airmass ahead of the front
will support a narrow corridor of moderate to locally strong
instability. Strengthening westerly winds through mid/upper levels
will foster strong deep-layer shear and updraft organization.

Initial development along the cold front from eastern NE into
central IA may be supercellular, with an associated threat for large
hail. Upscale growth into clusters and short line segments with a
greater severe/damaging wind threat seems probable with time this
evening. The eastern extent of the severe risk across the mid MS
Valley will be modulated by the narrow zone of stronger instability,
and convection should gradually weaken as it continues eastward late
this evening and overnight. The tornado threat across these areas
today appears less clear. While a modest southwesterly low-level jet
will aid in sufficient low-level shear for updraft rotation, it
remains unclear whether multiple supercells will be able to persist
into the early evening hours. Still, some threat for a couple
tornadoes remains apparent, mainly near/northeast of the surface low
in northeast KS and vicinity where low-level shear should be locally
maximized.

A separate area of high-based convective development should occur
this afternoon across the central High Plains, along/north of the
cold front in a weak low-level upslope flow regime. This activity
will move generally east-southeastward through the evening through a
very well-mixed boundary layer, with generally weak to moderate
instability present. Although low-level winds should remain modest,
gradually increasing westerly flow at mid/upper levels should
support sufficient deep-layer shear for convective organization.
Severe/damaging winds appear to be the main threat as one or more
small clusters continue east-southeastward across western/central
NE/KS late this afternoon and evening. Isolated gusts of 75+ mph may
occur if convection can become well organized into a small bowing
cluster. Some large hail also appears possible, particularly with
any initial supercells.

...Northern Plains into the Upper Mississippi Valley...
Isolated to scattered thunderstorms should develop along an occluded
front extending into parts of ND as the upper trough/low moves
eastward over the northern Plains today. While instability appears
fairly modest, occasional hail and strong/gusty winds may occur with
the more robust convection given the presence of sufficient
deep-layer shear.

$$