ACUS02 KWNS 210602
SWODY2
SPC AC 210600

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
0100 AM CDT Sat Jun 21 2025

Valid 221200Z - 231200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE UPPER
MIDWEST INTO CENTRAL NE...

...SUMMARY...
Severe thunderstorms are possible on Sunday from parts of the
central and northern Plains into the upper Midwest. Significant hail
and wind are possible across parts of eastern North Dakota and
northern Minnesota, along with some tornado potential.

...Synopsis...
A mid/upper-level low initially over ID is forecast to move
northeastward as a shortwave trough Sunday, reaching parts of the
northern Great Plains and Canadian Prairies by Sunday night. As this
occurs, a surface low initially over parts of NE/SD will move toward
northwest MN, as a trailing cold front moves across parts of the
central/northern Plains and Upper Midwest.

Farther east, a mid/upper-level shortwave trough and associated
surface low and weak cold front will move across parts of New
England. Guidance continues to vary regarding the timing and
intensity of this system. In the wake of this shortwave trough, an
upper ridge will amplify into parts of the Northeast.

...Great Plains into the Upper Midwest/Great Lakes...
Strong to extreme instability will again develop from the
central/northern Plains into the Upper Midwest and Great Lakes,
along/ahead of the front. Stronger deep-layer flow and ascent will
tend to lag behind the front, though sufficient vertical shear for
organized storms will be in place along the front.

The most favorable environment is expected near the track of the
primary surface low from eastern ND into northern MN, where 40-50 kt
of midlevel flow will overlap strong to extreme instability.
Supercell development will be possible near the low track and in the
vicinity of a warm front extending east-northeast from the low, with
some clustering and upscale growth possible with time. With
large-scale ascent tending to lag behind the front, coverage of
storms into early evening is uncertain, but any supercells could
pose a threat of all severe hazards, including tornado and very
large hail potential. Any organized upscale growth would result in
an increasing damaging-wind threat (including conditional potential
for gusts near/above 75 mph) as storms spread east-northeastward
into the evening.

More isolated severe storms will also be possible within the
post-frontal regime across the northern High Plains, where moderate
MUCAPE and sufficient deep-layer shear could support isolated
supercells or small clusters capable of severe hail and wind.

Farther south into the central Plains, both instability and
deep-layer shear will be somewhat weaker, due to warmer temperatures
aloft and weaker flow. However, strong heating near and east of a
developing secondary low across the central High Plains could result
in scattered storm development near the front by evening. Relatively
unidirectional southwesterly flow could result in a few stronger
northeastward-moving cells/clusters capable of damaging wind and
isolated hail.

Scattered storms will also be possible within a weakly capped
environment into parts of the southern High Plains. While deep-layer
flow/shear will weaker in this area, moderate buoyancy and steep
low-level lapse rates could support isolated severe gusts with the
strongest storms.

...Parts of the Northeast/New England...
Isolated strong storms may be ongoing Sunday morning across parts of
the Northeast/New England, within a low-level warm advection regime.
Confidence is low in the details, due to model variance regarding
the strength and timing of the shortwave trough and surface low that
will move through the region. Increasing instability and sufficient
deep-layer shear will conditionally support organized convection
through the day.

At this time, the most likely scenario is for an isolated severe
threat to persist through parts of the morning, before diminishing
during the afternoon as the upper ridge builds into the region.
However, with strong to extreme buoyancy expected to develop during
the afternoon, the area will need to be closely monitored for
diurnal redevelopment along any remnant surface boundaries.

..Dean.. 06/21/2025

$$
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