MIL-OSI USA: SPC Jun 16, 2024 1630 UTC Day 1 Convective Outlook

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Source: US National Oceanic and Atmospheric Administration

SPC AC 161630

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1130 AM CDT Sun Jun 16 2024

Valid 161630Z – 171200Z

…THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE NORTHERN/CENTRAL PLAINS INTO THE UPPER MISSISSIPPI VALLEY AND
MIDWEST…

…SUMMARY…
Scattered severe storms appear possible across parts of the upper
Mississippi Valley late this afternoon, with additional storms
likely tonight across the north-central Plains to upper Mississippi
Valley. Large hail and damaging winds are the primary risks. A small
bowing complex, with mainly a severe/damaging wind threat, may also
develop across parts of northern Illinois and vicinity this
afternoon.

…Northern/Central Plains to the Upper Midwest/Upper Mississippi
Valley…
A strong upper trough/low will continue advancing east-northeastward
across the northern Plains and Canadian Prairie provinces today.
While the primary surface low is expected to remain in central
Canada, a weak secondary low should develop generally eastward
across MN through this evening in tandem with a cold front. Warm
mid-level temperatures associated with a cap should tend to inhibit
robust convective development for at least a few more hours into the
early afternoon. But, most guidance now does show thunderstorm
initiation occurring along the front in northern MN by 20-22Z. There
are still concerns/uncertainty with how many intense thunderstorms
will be able to form given fairly prevalent cloudiness that should
temper daytime heating to some extent. Still, strong deep-layer
shear and steepening mid-level lapse rates atop a gradually
destabilizing low-level airmass should support a threat for
supercells and large hail. Some guidance suggests a fairly quick
progression to a MCS, which seems reasonable given the linear
forcing of the cold front. If this occurs, then a severe/damaging
wind threat may persist through the evening into parts of northern
WI and the U.P. of MI. Enough low-level shear is also forecast to
support low-level updraft rotation and a tornado or two across this
region.

A separate area of intense thunderstorm development is possible late
this afternoon and early evening along the trailing portion of the
cold front in NE/northwest KS and vicinity. If convection can
initiate along this boundary, strong instability and modest
deep-layer shear would support a threat for mainly multicells posing
a risk for severe winds given the well mixed boundary layer
forecast. Some hail could also occur with marginal supercell
structures. The Slight Risk has been expanded southward across the
central Plains to account for this scenario. Otherwise, scattered to
numerous elevated thunderstorms are still expected to develop this
evening and overnight generally north of the front from eastern WY
into NE/SD and southern MN. A strengthening low-level jet in this
time frame across these regions and ample deep-layer shear/MUCAPE
will easily support supercells and a hail threat with initial
development. But, convective mode may quickly become messy, with one
or more bows/clusters possible as thunderstorms move eastward across
the upper MS Valley overnight. Even though this activity should tend
to remain elevated, an isolated severe/damaging wind threat may
persist given the strong MUCAPE forecast.

…Northern Illinois/Southern Wisconsin…
A well defined MCV remains evident on visible satellite and radar
imagery late this morning over northeast MO and southern IA. This
feature should continue to track northeastward this afternoon and
evening in the modest southwesterly mid-level flow regime across the
mid MS Valley/Midwest. Ample daytime heating of a moist low-level
airmass should support around 1500-2500 J/kg of MLCAPE by mid
afternoon across northern IL and vicinity. Ascent associated with
the MCV and its associated mid-level vorticity maximum will likely
encourage the development of isolated to widely scattered
thunderstorms by 20-22Z. Modest but sufficient deep-layer shear for
updraft organization is indicated in various RAP forecast soundings
across this region. Scattered severe/damaging winds, along with
isolated hail, could occur with a small bowing complex that may
develop and move east-northeastward across the Chicago metro area
late this afternoon and early evening. Enough low-level shear is
also forecast to support a low chance for a tornado or two. Given
recent guidance and observational trends, a small Slight Risk has
been added across northern IL/southern WI to account for this
scenario.

…Southern High Plains…
Isolated/widely spaced thunderstorms should form once again this
afternoon along the length of a surface lee trough/dryline extending
southward across the southern High Plains. Although deep-layer shear
is forecast to remain weak, moderate instability and a well-mixed
boundary layer should support an isolated threat for severe
downdraft winds. Occasional hail may also occur with the more robust
cores before convection weakens after sunset.

..Gleason/Bentley.. 06/16/2024

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