830
ACUS01 KWNS 171959
SWODY1
SPC AC 171957

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0257 PM CDT Mon Jun 17 2024

Valid 172000Z - 181200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE NORTHERN
PLAINS SOUTHWESTWARD TO THE CENTRAL HIGH PLAINS...AND EASTWARD TO
WISCONSIN...

...SUMMARY...
Scattered strong to severe storms potential persists across parts of
the Upper Mississippi Valley, and over the central High Plains and
northern Plains late this afternoon through tonight. Severe/damaging
winds and large hail appear possible.

...Discussion...
Ongoing convective evolution this afternoon remains largely in line
with expectations, as laid out in prior outlooks.  Generally minor
line adjustments are all that appears necessary at this time, the
most notable of which across the Wisconsin vicinity.  Here, SLGT
risk for hail/wind has been expanded southward in this update, to
reflect severe risk evolving near the convective outflow that now
arcs northeast to southwest across central Wisconsin, near where
storms continue to initiate.

Elsewhere, only minor changes to outlook areas appear necessary at
this time.

..Goss.. 06/17/2024

.PREV DISCUSSION... /ISSUED 1130 AM CDT Mon Jun 17 2024/

...Upper Mississippi Valley/Upper Great Lakes...
A loosely organized thunderstorm cluster is ongoing late this
morning across northern WI into the U.P. of MI. With steep mid-level
lapse rates present per the 12Z sounding from GRB, along with
sufficient deep-layer shear to support organized updrafts, at least
an isolated severe hail/wind risk should continue through the
afternoon across this region along and east of a front. In the wake
of this activity, large-scale ascent appears nebulous/weak across
much of the upper MS Valley. Still, modest forcing associated with
low-level warm advection through the day may be enough for
additional convection to develop this afternoon along the southward
extent of the front across this region.

The best chance for this to occur appears to be across parts of
northern IA/southern MN and perhaps western WI along and near the
surface front, which may try to lift slowly northward through this
afternoon/evening. If surface-based thunderstorms can develop across
this area, they would pose some threat for severe hail and damaging
winds given moderate forecast instability and sufficient deep-layer
shear to support updraft organization. However, this scenario
remains low confidence, as earlier convection has shunted the
surface front well into IA this morning. This boundary is forecast
to lift northward as a warm front tonight ahead of an
mid/upper-level wave approaching from the northern/central Plains,
and mainly a hail threat could persist across parts of MN and
vicinity through early Tuesday morning with elevated supercells that
may develop in a strengthening low-level warm advection regime.

...Northern/Central Plains...
A pronounced upper trough/low over the Northwest will move eastward
through the period over the northern/central Rockies and adjacent
High Plains. Related surface lee cyclogenesis is expected to further
occur through this evening over the central High Plains, focused on
the northeast CO, southeast WY, and NE Panhandle vicinity. Multiple
rounds and zones of severe thunderstorm potential still appear
possible across much of the northern/central Plains this afternoon
through tonight.

Intense thunderstorm development may occur near the surface triple
point in southwest NE and vicinity this afternoon, although the
later timing of large-scale ascent associated with the upper trough
casts some doubt on surface-based thunderstorm initiation. The
presence of steep mid-level lapse rates and rich low-level moisture
should aid in the development of moderate to strong instability as
daytime heating occurs and as the warm front attempts to lift slowly
northward across the central Plains. Deep-layer shear will be strong
enough for supercells with associated large hail threat. Isolated
very large hail may also occur. Some upscale growth/clustering along
and near the front appears possible with time this evening, and a
greater threat for severe/damaging winds may eventually be realized.
Effective SRH is also forecast to quickly increase late this
afternoon into the evening as a southerly low-level jet rapidly
strengthens over the northern/central Plains. If any supercell can
persist in this time frame, it would pose a threat for a tornado.

A somewhat separate area of supercell potential is also evident
across northeast WY/southeast MT, where modest low-level moisture
return and upslope flow to the Bighorns may promote convective
initiation later today as the upper trough continues eastward.
Isolated to scattered large hail appears to be the main threat with
this convection, if it develops and assuming sufficient instability
can materialize. Otherwise, mainly elevated thunderstorms will
likely develop and persist late this evening and overnight across a
broader portion of the northern Plains. Large hail should be the
main threat, although severe/damaging winds may occur with any
convection that can remain near/south of the northward-lifting warm
front.

...Southern High Plains...
Isolated to widely scattered thunderstorms may occur with southward
extent along the length of the dryline/lee trough this afternoon
across the southern High Plains. Deep-layer shear should remain
fairly modest (generally 20-30 kt). Still, any convection that can
develop late this afternoon may pose an isolated threat for severe
wind gusts and hail through early evening given a moderately to
strongly unstable airmass.

...Lower Great Lakes/Upper Ohio River Valley...
A remnant convective cluster/MCV over southern Ontario should
broadly influence additional thunderstorm development to its east
this afternoon across the lower Great Lakes and upper OH Valley
regions. Instability is forecast to gradually increase with
continued daytime heating and low-level moisture streaming
northward. Deep-layer shear should remain generally weak (25 kt or
less). Still, steepening low-level lapse rates and a
moist/moderately unstable airmass could allow for some stronger
pulse-type/occasionally clustering thunderstorms capable of
producing localized wind damage this afternoon and early evening.

$$